How Touch Screens works

HIGHER INSTITUITE FOR APPLIED SCIENCES AND TECHNOLOGY
Touch Screen Technologies
Prepared by: Mohammed Al-Shirif
Supervisor: Eng. Mohedeen Awad
Language supervisor: Mrs. Nada Mouhanna
Coordinator: Dr. Nizar Zarka
Date: 28/03/2013 2nd Semester

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TABLE OF CONTENT:
1. ABSTRACT: ......................................................................................................................................................... 5
2. INTRODUCTION: ............................................................................................................................................ 6
3. ADVANTAGES AND DISADVANTAGES OF TOUCH SCREENS: ........................................................................................ 8
4. ANATOMY OF A TOUCHSCREEN: ............................................................................................................................ 8
5. RESISTIVE TOUCH TECHNOLOGIES:......................................................................................................................... 9
5.1 RESISTIVE TOUCH STRUCTURE: ......................................................................................................................... 9
5.2 HOW DOES RESISTIVE TOUCH SCREEN WORK?...................................................................................................... 9
5.3 FOUR-WIRE RESISTIVE TOUCHSCREEN TECHNOLOGY............................................................................................ 10
5.4 FIVE-WIRE RESISTIVE TOUCHSCREEN TECHNOLOGY: ............................................................................................ 11
5.5 FOUR-WIRE VS. FIVE-WIRE RESISTIVE TOUCHSCREEN TECHNOLOGY: ..................................................................... 12
5.6 DIGITAL RESISTIVE TECHNOLOGY:............................................................................................................................ 13
5.7 PROS AND CONS OF RESISTIVE TOUCHSCREEN TECHNOLOGY: ................................................................................. 13
6. CAPACITIVE TOUCH TECHNOLOGIES: .................................................................................................................... 14
6.1 PROJECTED CAPACITIVE TOUCH TECHNOLOGY: ................................................................................................... 14
6.1.1 How does it work? .....................................................................................................................14
6.1.4 Mutual-capacitance vs. Self-Capacitance: ......................................................................................16
6.1.2 Projected capacitive technology advantages:..................................................................................17
6.1.3 Projected capacitive technology drawbacks:...................................................................................17
6.2 SURFACE CAPACITIVE TOUCHSCREEN TECHNOLOGY: ....................................................................................................... 18
6.2.1 How does it work? .....................................................................................................................18
6.2.2 Surface capacitive technology advantages: ....................................................................................18
6.2.3 Surface capacitive technology disadvantages:.................................................................................19
6.3 PROS AND CONS OF CAPACITIVE TOUCH TECHNOLOGY: ......................................................................................... 19
7. SAW TOUCH SCREEN TECHNOLOGY:..................................................................................................................... 20
7.1 HOW DOES IT WORK?......................................................................................................................................... 20
7.2 OPPORTUNITIES AND LIMITATIONS OF SAW TOUCH TECHNOLOGY: ...................................................................................... 21
8. BENDING WAVE TOUCHSCREEN TECHNOLOGY:...................................................................................................... 22
9. INFRARED TOUCH SCREEN TECHNOLOGY: ............................................................................................................. 23
9.1 HOW IT WORKS? .............................................................................................................................................. 23
9.2 LIMITATION AND CONSIDERATION OF INFRARED TOUCHSCREEN: .......................................................................................... 23
10. OPTICAL IMAGING TOUCH TECHNOLOGY: ........................................................................................................... 25
10.1. HOW IT WORKS?......................................................................................................................................... 25
10.2. PROS AND CONS OF CAMERA-BASED TECHNOLOGY: ..................................................................................................... 26
10.3. FUTURE OF CAMERA BASED TOUCHSCREEN TECHNOLOGY: .............................................................................................. 27
11. COMPARISON STUDY: ...................................................................................................................................... 28
11.1. LIGHT TRANSMITTANCE: ................................................................................................................................... 28
11.2 THE DURABILITY: ............................................................................................................................................ 28
11.3 CALIBRATION STABILITY: .................................................................................................................................... 28
11.4 STYLUS FLEXIBILITY: ......................................................................................................................................... 28
11.5 SIZE:.......................................................................................................................................................... 29

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11.6 APPLICATIONS: .............................................................................................................................................. 29
11.7 COST: ........................................................................................................................................................ 29
11.8 TOUCHSCREEN RESOLUTION ......................................................................................................................... 29
12. PRACTICAL GUIDE TO DETERMINE WHICH TYPE IS YOUR TOUCHSCREEN: ................................................................. 30
13. MULTI TOUCH TECHNOLOGY: ............................................................................................................................ 31
13.1. WHY MULTI-TOUCH HAS BECOME SO IMPORTANT?.................................................................................................... 31
13.2. HOW MANY TOUCHES ARE ENOUGH? ................................................................................................................... 31
14. CHEEK CHECK AND Z-AXIS: ................................................................................................................................ 32
15. TOUCH SCREEN OS:.......................................................................................................................................... 32
16. INTERACTION:................................................................................................................................................. 33
17. MARKET TRENDS: ............................................................................................................................................ 34
17.1. THE RECENT HISTORY: ..................................................................................................................................... 34
17.2. MAINSTREAM TECHNOLOGIES: ............................................................................................................................ 34
17.3. 2013 TRENDS: ............................................................................................................................................. 35
17.4. WHAT IS NEXT? ............................................................................................................................................ 37
18. CONCLUSION: ................................................................................................................................................. 38
19. REFERENCES: .................................................................................................................................................. 39

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LIST OF FIGURES:
FIGURE 1:EASE OF USING TOUCH SCREENS .............................................................................................................. 6
FIGURE 2: TOUCH SCREEN TECHNOLOGIES .............................................................................................................. 7
FIGURE 3: STRUCTURE OF THE RESISTIVE TOUCH PANELS............................................................................................... 9
FIGURE 4: WORKING OF RESISTIVE TOUCHSCREENS ..................................................................................................... 9
FIGURE 5: FOUR-WIRE RESISTIVE .......................................................................................................................10
FIGURE 6: WORKING OF 4-WIRE SYSTEMS .............................................................................................................10
FIGURE 7: LIMITATION OF 4-WIRE ......................................................................................................................11
FIGURE 8: FIVE-WIRE RESISTIVE ........................................................................................................................11
FIGURE 9: WORKING OF 5-WIRE TECHNOLOGY........................................................................................................12
FIGURE 10: DIGITAL RESISTIVE TECHNOLOGY ..........................................................................................................13
FIGURE 11: LIFE CYCLE OF THE ISOLATING DOTS ........................................................................................................13
FIGURE 12: CONCEPT OF CPACITIVE TECHNOLOGY.....................................................................................................14
FIGURE 13: PROJECTED CAPACITIVE STRUCTURE.......................................................................................................14
FIGURE 14:WORKING OF PROJECTED CAPACITIVE.....................................................................................................15
FIGURE 15: SENSING METHOD OF PROJECTED CAPACITIVE ...........................................................................................15
FIGURE 16: SELF CAPACITANCE .........................................................................................................................16
FIGURE 17: MUTUAL CAPACITANCE ....................................................................................................................16
FIGURE 18: WORKING OF SURFACE CAPACITIVE.......................................................................................................18
FIGURE 19: SURFACE ACOUSTIC WAVE.................................................................................................................20
FIGURE 20: WORKING OF SAW TOUCH SCREEN .......................................................................................................20
FIGURE 21: CONCEPTUAL DRAWING OF A BENDING-WAVE TOUCH SCREEN ............................................................22
FIGURE 22: WORKING OF INFRARED TOUCH TECHNOLOGY ...........................................................................................23
FIGURE 23: WORKING OF CAMERA-BASED TOUCH TECHNOLOGY .....................................................................................25
FIGURE 24: CAMERA-BASED OVERLAY CAN EASILY CONVERT ANY LCD SCREEN INTO TOUCHSCREEN ...............................................26
FIGURE 25: THE FUTURE OF OPTICAL IMAGING TOUCH TECH. ........................................................................................27
FIGURE 26: IGNORED TOUCH............................................................................................................................32
FIGURE 27: TOUCH SCREEN MODULES DISTRIBUTION .................................................................................................34
FIGURE 28: MARKET SIZE FOR TOUCH MODULES BY DEVICE SIZE IN 2012 .............................................................35
FIGURE 29: GLOBAL TOUCH SCREEN MARKET REVENUES..............................................................................................36

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LIST OF TABLES:
TABLE 1: ADVANTAGES & DISADVANTAGES OF TOUCH SCREENS .......................................................................................8
TABLE 2: DIFFERENCES BETWEEN 4-WIRE AND 5-WIRE............................................................................................... 12
TABLE 3: PROS & CONS OF RESISTIVE TOUCH TECHNOLOGY.......................................................................................... 13
TABLE 4: DIFFERENCES BETWEEN MUTUAL-CAPACITANCE & SELF-CAPACITANCE ................................................................... 16
TABLE 5: PROS & CONS OF SURFACE ACOUSTIC WAVE TECHNOLOGY ............................................................................... 21
TABLE 6: PROS & CONS OF TRADITIONAL INFRARED TOUCH TECHNOLOGY .......................................................................... 24
TABLE 7: A BRIEF COMPARSION BETWEEN DIFFERENT TOUCH TECHNOLOGIES ...................................................................... 30

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1. Abstract:
Touchscreen technology and devices that use that technology have become widely popular over the past few years. Even so, very small amount of people knows that there are different technologies implemented in those devices that they use in everyday life. Through this seminar, we would try to present the different solutions currently available on the market. Simultaneously, we will compare between those solutions, emphasizing on differences between those technologies, and making the differences between them more obvious and understandable. Later, we will give our opinions on market trends in the future, and our vision and conclusion about this topic.
Keywords:
Touchscreen technologies, resistive touchscreen, capacitive, surface acoustic wave, infrared, optical imaging, multi-touch, interaction.

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2. Introduction:
After over two decades virtually been dominated by the use of mice and keyboards, the last few years have been characterized by the rise of alternative input devices, generally designed for improved ergonomics. The touchscreen is the most sophisticated computer access technology to- date, with the fastest growing market demand. Today, virtually all software requires some kind of pointing device. The Touch Screen is a technological advancement on traditional input and pointing devices used to access applications.
A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreens can also sense other passive objects, such as a stylus.
The touchscreen has two main attributes. First, it enables one to interact directly with what is displayed, rather than indirectly with a pointer controlled by a mouse or touchpad. Secondly, it lets one do so without requiring any intermediate device that would need to be held in the hand (other than a stylus, which is optional for most modern touchscreens). [MA10]
With touchscreen technology a computer display can function as both input device and output device. A touch sensitive screen provides a user with a friendlier input interface that doesn’t require extensive computer skills or literacy. Such interface is an easy way to communicate with devices where the user touches the screen to select options presented on the screen.
Mechanical QWERTY keyboards and their associated mice are falling out of favor to be replaced by sleek touch screens. In touch screen systems the user doesn't need to look away from the screen to a keyboard and back again. Entering wrong information is impossible with a touchscreen, only valid options are offered on the screen. There are no loose pieces of hardware to be damaged or lost
Touchscreens are very intuitive; it is natural for people to respond to their environment by touching. Not only adults but also Children can easily interact with this technology (see figure 1). Moreover, this interface can be beneficial to those that have difficulty in using other input devices such as a mouse or keyboard. Touch panels are accessible to people with significant physical disabilities. They are also efficient for Visually Impaired, providing full access to the screen with easy adjustments that adapt to individualized needs.
Touch screens started to be developed in the second half of the 1960s. Early work was done at the IBM, the University of Illinois, and Ottawa Canada. By 1971 a number of different techniques had been disclosed. Touchscreens have subsequently become familiar in everyday life.
Touch screen technology are widely available and in use in many facets of society. Touch screen can be found in use as public information displays, retail and restaurant systems, POS, ATM, computer-based training systems, customer self-service aids, control and automation systems, assistive technology for the disabled, tourism kiosks, GPS systems, phones, tablets, game consoles, and continues to appear in newer technologies. Touch screens have reached into every industry, every product type, every size, and every application at every price point.
Figure 1: Ease of Using touch screens
Figure 1:Ease of using touch screens

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As touchscreen usage increases and new applications emerge, it is important to understand the differences between touchscreen technologies. There are over a dozen touch-screen technologies in use, and no single technology can meet 100% of the requirements for every application. As a result, there has been an accelerated stream of innovations in touchscreen technologies in the last few years. The range of user environments for these applications has created a wide variety of touch technologies, each with unique characteristics contributing to application advantages and disadvantages. The most used touch technologies include projected capacitive, resistive, surface capacitive, surface acoustic wave (SAW), infrared beam (IR) and camera-based. Other technologies include: dispersive signal technology (DST), acoustic pulse recognition, LCD in-cell optical, and force sensing are out of use.
Touch technologies are classified into four main types: resistive, capacitive, acoustic and optical. Each type has its own different specific technologies. See figure (2).
Figure 2: Touch Screen Technologies
Actually, there are 11 categories within the touchscreen market, but projected capacitive screens have taken the majority of the market. Resistive screens held the leading market share for many years, but the higher-quality projected capacitive screens took the lead in 2010
Let's see how the screen of your tablet or smartphone responds to touch and slide of your fingers. What there in between your fingers and mobile screen that is makes it happen?
With just swiping of your fingers you can control the whole functionality of your gadgets. It was IBM, that introduced touch screen in mobiles for the first time in mobile technology's history and since then almost every new Company is manufacturing its devices with this technology. Thanks to brilliant minds behind this technology, Dr. Sam Hurst, Steve Jobs, Helwett & Packard and others.

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3. Advantages and Disadvantages of touch screens:
Advantage
Disadvantage
 Touching a visual display of choices requires little thinking and is a form of direct manipulation that is easy to learn.
 Touch screens are the fastest pointing devices.
 Touch screens have easier hand eye coordination than mice or keyboards.
 Touch screens are durable in public access and in high volume usage.
 There are no loose pieces of hardware to be damaged or lost.
 No extra work space is required as with other pointing devices
 User's hand may obscure the screen.
 Screens need to be installed at a lower position and tilted to reduce arm fatigue.
 Some reduction in image brightness may occur.
 They cost more than alternative devices.
 These devices require massive computing power which leads to slow devices and low battery life
 Touchscreen devices usually has no additional keys and this means when an application crashes, without crashing the OS, you can't get to the main menu as the whole screen becomes unresponsive
Table 1: Advantages & Disadvantages of touch screens
4. Anatomy of a touchscreen:
Knowing what you need is an important first step in designing a touchscreen product. Vendors in the touchscreen supply chain frequently offer different pieces of the puzzle, often times combining several to create a value chain for the end customer. There are four key elements:
1- Front panel or bezel: The front panel or bezel is the outermost skin of the end product. In some products, this bezel will encompass a protective clear overlay to keep weather and moisture out of the system, and to resist scratching and vandalism to the underlying sensor technology.
2- Touch controller: The touch-controller is generally a small microcontroller-based IC that sits between the touch sensor and the embedded system controller. This IC can either be located on a controller board inside the system or it can be located on a flexible printed circuit (FPC) affixed to the glass touch sensor. This touch controller takes information from the touch sensor and translates it into information that the PC or embedded system controller can understand.
3- Touch sensor: A touchscreen "sensor" is a clear glass panel with a touch-responsive surface. This sensor may be placed over an LCD (Like resistive and capacitive systems) or on the frame (in SAW and Infrared touch systems) so that the touch area of the panel covers the viewable area of the video screen. There are many different touch-sensor technologies on the market today, each using a different method to detect touch input. Fundamentally, most technologies use an electrical current running through the panel that, when touched, causes a voltage or signal change. This voltage change is sensed by the touch controller to determine the location of the touch on the screen.
4- System software: This software allows the touchscreen sensor and system controller to work together and tells the product's operating system how to interpret the touch-event information that is sent from the controller.

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5. Resistive Touch Technologies:
Before 2010 Resistive was the dominant type of touch screen technology. It is a low-cost solution found in many touch screens, including hand-held computers, PDAs, consumer electronics and point-of-sale-applications. The resistive screen is popular because of its relatively low price (at smaller screen sizes), and ability to use a range of input objects like fingers, gloves, credit card, and any stylus as the Resistive touchscreens are pressure sensitive. There are two different basic resistive technologies: 4-wire (low cost, short life) is common in mobile devices and 5-wire (higher cost, long life) is common in stationary devices.
5.1 Resistive Touch Structure:
A resistive system consists of a several layers that detect and register the location of the touch. The outermost layer is a durable hard coating to protect the more delicate touch sensors usually made of Polyester .The innermost layer is a rigid Glass Substrate .The exterior face of the glass substrate is coated with a conductive transparent layer. The interior face of the polyester film is also coated with another conductive transparent layer made of Indium Tin Oxide (ITO). Between the glass and the polyester sheet there are thousands of tiny separator dots isolating top and bottom conductive layers from each other .See figure 3.
5.2 How does Resistive Touch Screen Work?
When an object such as a finger, presses down on a point on the panel's outer surface the two conductive layers become connected at that point producing a switch closing in the circuit .See figure 4. The panel then behaves as a pair of voltage dividers with connected outputs. This causes a change in the electrical voltage which is registered as a touch event and sent to the controller for processing. The touch screen controller gets the alternating voltages between the two layers and converts them into the digital X and Y coordinates of the activated area. Once the coordinates are known, a special software driver translates the touch into something that the operating system can understand.
Figure 3: Structure of the Resistive Touch panels
Figure 4: Working of resistive touchscreens

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5.3 Four-Wire Resistive touchscreen technology
All resistive touch screens use essentially the same voltage-driven operating principles. The electrically simplest way to produce a resistive touch screen is to utilize 4-wire technology.
The goal of a 4-wire circuit is to be able to produce two alternating linear voltage gradients in both the X and Y direction. To achieve this two resistive circuits are used, a circuit in X-axis and another one in Y-axis. Each circuit consists of two bus bars and one of the ITO conductive layers .See figure (5). Therefore, Four-Wire technology use two layers to create X- and Y-axis measurements while in 5-Wire method x-circuit and y-circuit are both on the same layer of glass.
The bus bars are in essence broken up, producing a variety of resistor patterns in the perimeter of the screen. These individual elements form adjacent geometric shapes consisting of low resistance material that is screen printed directly onto the ITO substrate.
When a touch occurs. The touch point introduces a pair of voltages for X and Y direction.The X and Y-axis data points are derived using both conductive planes. In the first phase of data collection, the top conductive layer is electrically charged and the bottom conductive layer acts as the feedback sending raw voltage of the touch point to the electronics ,deriving one-half of the full touch coordinate. In the second phase, the bottom layer is electrically charged and the top layer serves to send the voltage information to the electronics, completing the X and Y coordinate signal .See figure(4).
As we see, Four-Wire Technology must use the top film to represent the X or Y-axis depending on the design. It is important that the resistance value remain stable on both axis after initial calibration. frequent flexing of the top layer upon single locations (such as on and off icons) will cause mechanical damage to the conductive cover coating changing its electrical characteristics (resistance) with use .See figure(6).This damage will affect the accuracy of the axis that represented by the cover sheet.[MA10]
Figure 5: Four-Wire Resistive
Figure 6: Working of 4-Wire Systems

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The primary reason for this is the physical properties of the clear conductive coating. ITO is a ceramic and, when coated onto a flexible substrate, is therefore prone to crack if the base substrate is deformed. If the ITO coating is cracked, the properties of the flexible circuit will no longer allow for a linear voltage gradient to be generated and the screen therefore becomes non-linear.
Another drawback of the 4-wire system is the fact that ITO on a flexible substrate is affected with environmental changes, primarily shifts in humidity and temperature because it is never fully oxidized.It will expand and contract with changing conditions, thereby causing changes to the initial resistance values.This change results in what is known in the industry as “drift” to the touch point location, which diminishes the touch screen reliability and results permanent electrical failure of the touch screen. See figure (7).
The benefits of a 4-wire are its widespread usage, which has helped keep the cost low and prompted numerous chip manufacturers to make electronics accessible and economical.
5.4 Five-Wire Resistive touchscreen technology:
Resistive 4-wire touch screens have long been a successful touch screen user interface for hand-held devices. However mainstream industrial businesses such as warehousing, inventory control, retail, hospitality and medical applications have placed new demands on the interface pushing 4-wire resistive technology beyond its physical limit. This has prompted manufacturers to develop new and more rugged resistive touch screens for these harsh environment applications.
Unlike Four-Wire technology that must use two opposing layers to create X- and Y- axis measurements, Five-Wire Technology Utilizes the bottom substrate for both X and Y-axis measurements. The flexible coversheet acts only as a voltage-measuring probe. See figure 8. This means the touch screen continues working properly even with non-uniformity in the cover sheet's conductive coating. The result is an accurate, durable and reliable touch screen that offers drift free operation.
Electrically, the 5-wire operates by applying a voltage to two adjacent corners of the resistor pattern while the two opposing corners are grounded. This generates a semi-linear voltage gradient across the entire surface of the screen in one axis. The top film, which is connected to the 5th wire, is used only as a pick-off layer and, similar to a 4-wire touch screen, the voltage that applies at the point of actuation will apply to the entire top circuit, which corresponds directly to the point of actuation.
Figure 7: Limitation of 4-Wire
Figure 8: Five-Wire Resistive

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To determine the second coordinate, the role of two diagonally opposing corners is reversed. See figure (9).This generates a voltage gradient in a 90o offset direction. Again, the top circuit is used only as a voltage pick-off to take the measurement for the second touch coordinate.
Because the top film is working only as a pick-up layer, it is not required to handle any current. Hence it can tolerate resistance changes without impacting the reliability of the touch points’ accuracy from the base layer. Any cracks or fissures induced due to misuse or prolonged actuations therefore do not affect the screen’s accuracy. It is for this reason the 5-wire is able to withstand temperature, humidity and mechanical stresses. [MA10]
5-wire has been the resistive solution for tough environment applications such as industrial control modules, POS applications and Kiosks for nearly 20 years, but has been limited to diagonal sizes of 6.4'' or larger. This diagonal limitation prevented the technology from consideration in hand-held applications, which are typically 3.9'' in diagonal or smaller.
5.5 Four-Wire vs. Five-Wire Resistive Touchscreen Technology:
Four-Wire Technology
Five-Wire Technology
Durability
1 million-touch life max (film/glass)
35 million finger touches with no performance degradation
Cost
Lower
More expensive
Image Clarity
70%
80%
Design Flexibility
Not available in spherical designs
Advanced design allows flat and spherical designs
Screen Size
All sizes
6.4" or larger
Application
Commercial mobile
stationary applications
Table 2: Differences Between 4-wire and 5-Wire
Figure 9: Working of 5-Wire Technology

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5.6 Digital Resistive Technology:
The previous explained resistive technology is widely called Analog Resistive to distinguish from Digital Resistive. Digital resistive uses the same technology of analog resistive except that it is simply a matrix of analog resistive panels in one screen. This technology has the advantage of Multi-Touch in addition to analog resistive advantages, but it is more expensive. See fig (10).
5.7 Pros and Cons of Resistive touchscreen technology:
Resistive
Advantages
Disadvantages
 Works with finger, gloves, stylus or any non-sharp object so it can be used in hospitals and restaurants.
 Relatively easy to manufacture.
 Lowest-cost touch technology
 Widely available
 Low power consumption
 Resistant to screen contaminants
 Less sensitive to scratches as compared to capacitive screens
 Not durable enough.
 Loss of clarity of image.
 Not recommended for public locations
 Non-zero touch-force.
 Exponential cost to manufacture as screen sizes increase
 Becomes non-responsive at temperature extreme.
 Poor multi-touch capability.
Table 3: Pros & Cons of Resistive touch Technology
Main limitations of technology:
1- Not durable enough: Resistive Touch Screens are durable and resistant to humidity and liquid spills. But they offer limited durability because they are susceptible to vandalism and scratched. The surface can be easily damaged by sharp objects and the isolating dots can also be damaged over time degrading the accuracy of the touches. See figure (11).
2- Poor optical quality: less light transmittance than other touchscreen types. Transmission typically in 80% to 85%.The decrease in light transmission is the result of metallic resistive and conductive coatings
3- Not recommended for public locations: Resistive displays are less effective in public environments due to the degradation in image clarity and the need for periodic recalibration caused by the breakdown of the layers of resistive film, and its susceptibility to scratching.
4- Non-zero touch force(25-50 grams pressure sensitive)
5- No multi-touch: Can’t touch with two fingers on the same square
Best Usage: Restaurants, hospitals, factories, handheld applications (phones)
Figure 10: Digital Resistive Technology
Figure 11: Life cycle of the isolating dots

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6. Capacitive Touch Technologies:
Capacitive touch panels represent the second most widely used sensing method after resistive film touch panels. Recently, capacitive popularity has grown, as it has become one of the leading technologies used in touch screen devices. In 2001, it began appearing in consumer devices, such as MP3-players and smart phones. This increase in attention is likely due to the effectiveness of its design, its use of multi-touch technology, and the popularity of Apple products using this technology: iPod Touch, iPhone and most recently the iPad.
Capacitive touchscreen displays rely on the electrical properties of the human body to detect when and where on a display the user touching. See figure (12). Because of this capacitive displays can be controlled with very light touches of a finger, generally they cannot be used with a mechanical stylus or a gloved hand.
There are two types of capacitive touchscreen generally available, surface and projected, and it’s the latter that you’ll find in Apple's iPhone and iPod. The internal structures differ between the two types. They are both based on the fact that the application of a finger changes the capacitance in a local region enabling the system's electronics to detect a touch and determine its position on the screen. Comparing with resistive, capacitive systems detect changes in electrical fields but don't rely on pressure.
6.1 projected Capacitive Touch Technology:
6.1.1 How does it work?
The design of projected capacitive touch screens is somewhat similar to that of resistive touch screens, in that they both utilize 2 layers of ITO See figure (13). An XY array is formed either by etching a single layer to form a grid pattern of electrodes, or by etching two separate, perpendicular layers of conductive material with parallel lines or tracks to form the grid. This grid projects the electric field through the top layer of glass- hence the name projected capacitive touch screens. See figure (14). Because of this projection, when the user touches the top layer of glass it “changes the measured capacitance values of the electrodes closest to it”. This change in capacitance is due to the slight electric charge contained in the human body.
Figure 12: Concept of Cpacitive technology
Figure 13: Projected Capacitive Structure

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These changes in capacitance are measured and calculated as touch points in a very similar way to resistive touch screens, by using the X and Y components.[MA10]
Actually, there are many ways to build projected capacitive screens. On lens, on cell and in cell designs are the most dominant. Suppliers with the simplest designs tend to be the most successful, since complex screens are more expensive to build. Technical challenges include eliminating noise so that touch gestures can be detected more accurately, reducing power consumption of the displays, handling the issue of sweaty fingers, and the need to make the devices both thin and strong.
A projected capacitive sensor array is designed so that a finger will interact with more than one X sensor and more than one Y sensor at a time . See figure (15).This enables software to accurately determine finger position to a very fine degree through interpolation. For example, if X-sensors 1, 2 and 3 see signals of 3 mV, 10 mV, and 7 mV, the center of the finger is at:
[(1 × 3) + (2 × 10) + (3 × 7)] / (3 + 10 + 7) = 2.2
Figure 15: Sensing Method Of projected Capacitive
Figure 14:Working Of Projected Capacitive

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6.1.4 Mutual-capacitance vs. Self-Capacitance:
There are two approaches to determining finger position with a projected capacitive touchscreen: measuring self-capacitance and measuring mutual capacitance. Touchscreen solutions that measure self- capacitance measure an entire row or column for capacitive change.
Self-capacitance works OK for single-touch systems, but with multi-touch systems there is no way to resolve the positional ambiguity that results from more than one simultaneous touch on different parts of the screen.
For example, if a user touches on the capacitive grid at locations X1, Y1 and X2, Y2, the energized lines simply tell the chip that X1, X2, Y1, Y2 lines have all been touched. It doesn't know the combination thereof. It could be that the chip reports X1, Y2 and X2, Y1 were the touch locations. This problem is known as ghosting. See figure (16).
So, when input is one (or many) touch in self-capacitance system output is only one capacitance value for whole panel. In contrast, in a mutual capacitance system Output is an array of capacitance values for each X-Y intersection.
If two touches are present in a mutual capacitance system, this would be detected as (X1,Y1) and (X2,Y2), whereas in a self-capacitance system it would be detected as (X1,X2,Y1,Y2), leaving two potential combinations of coordinates. The self-capacitance ghosting problem is exponential and becomes impossible to solve as you transition to three or more touches. See figure (17).
A mutual capacitive array is interpreted as a complete touch surface that maintains the ability to resolve multiple touch points within each individual "small" screen. Because the capacitive coupling at each point in the matrix can be measured independently, it means that there is no ambiguity in the reported coordinates for multiple touches. It is then technically possible to have unlimited touch recognition.
Figure 16: Self Capacitance
Figure 17: Mutual Capacitance
Table 4: Differences between Mutual-Capacitance & self-Capacitance

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6.1.2 Projected capacitive technology advantages:
There are several benefits to using projected capacitive technology but the most important are:
1- Capacitive is very durable, because users touch the top of a glass or plastic substrate, while the ITO layers are protected below. This makes projected sensing more accurate and repeatable than other capacitive sensing methods. In addition, projected capacitive touchscreen Functions even if glass is scratched or broken.
2- Projected capacitive touch screens are ''scanned'', meaning most of these screens are made up of a matrix of rows and columns that are "read" one by one to get a reading or count. The result is extremely precise. Scanning also has an advantage of being free of coordinate drift. This is possible because the rows and columns are physically fixed and each measurement is made in small area. Without the issue of coordinate drift, p-cap touch screens do not have to be calibrated by the end-user as long as the touch screen is mounted on the same place on the display.
3- Support multi-touch: Since projected-capacitive panels have multiple sensors, they can detect multiple fingers simultaneously, which is impossible with some other technologies. In fact, projective capacitance has been shown to detect up to ten fingers at the same time. This enables exciting new applications based on multiple finger presses, including multiplayer gaming on handheld electronics or playing a touchscreen piano.
4- If sensitivity is increased, projected capacitive can be operated with gloved fingers.
5- Projected capacitive responds to light touch. No pressure force is needed for detection.
6- High optical transmission: The capacitive system can transmit 90% of the light
7- Extreme long life time because it has no moving parts in operation.
8- Higher resolution than resistive and surface capacitive.
All these features make them ideal for harsh, industrial, or outdoor applications.
6.1.3 Projected capacitive technology drawbacks:
1- Low noise Immunity: Projected capacitive is susceptible to electrical noise due to its detection mechanism. Noise from LCD is especially influential to the sensor. Recently, various methods are developed to improve tolerance for noise.
2- Comparing with resistive, projected capacitive technology is relatively expensive: Projected capacitive requires fine pattering, thus takes high processing cost.
3- will not react to any input device other than a finger or specially designed probe
4- Touch screens larger than 24'' (diagonal) are difficult to build.
These drawbacks can be improved or even be eliminated completely

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6.2 Surface Capacitive Touchscreen Technology:
6.2.1 How does it work?
Surface capacitive is another form of capacitive touch screen technology. The primary difference between surface capacitive and projected capacitive is that surface capacitive uses only one ITO surface. See figure (18).This layer calculates touch points using principles that are very similar to projected capacitive touch screens, in that touch points are observed by changes in capacitance if the ITO layer in the touch screen. However, these touch points are measured in a very different way. The computer measures the change in capacitance from each corner of the ITO layer, and with these 4 separate measurements, the X and Y coordinates of the touch point are calculated. In other words, the touch screen system calculated the position of the touch from relative differences in charge at each corner.
So, only one side of the insulator is coated with a conductive layer. A small voltage is applied to the layer, resulting in a uniform electrostatic field. When a conductor, such as a human finger, touches the uncoated surface, a capacitor is dynamically formed. The sensor's controller can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the panel.
Surface capacitive touch screens tend to be employed for applications that are large size (over 12inch), used by general public, and requiring high-quality looking, high resolution and high durability.
6.2.2 Surface capacitive technology advantages:
1. This type of capacitive touch panel has a simpler structure than a projected capacitive touch panel and for this reason offers lower cost.
2. Life span of more than more than 50 million touches in one location.
3. Surface capacitive technology is suitable for large size monitors.
4. Technology with fastest touch response time
5. Visibility is higher than projected capacitive because structure is only one glass layer. Transmission typically 88% to 92%
6. Withstands contaminants and moving liquids on the screen, and continues to function over entire touch screen area
Figure 18: Working Of Surface Capacitive

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6.2.3 Surface capacitive technology disadvantages:
1. Poor multi-touch: it is structurally difficult to detect contact at two or more points at the same time
2. A gloved finger, pen, stylus, or hard object will not work. As a result, it is inappropriate for use in many applications, including medical and food preparation.
3. Scratches in the coatings can cause dead spots on the screens
4. moderately durable and has limited resolution
5. Prone to false signals from parasitic capacitive coupling.
It is therefore most often used in simple applications such as industrial controls and kiosks.
6.3 Pros and cons of capacitive touch technology:
Capacitive touch screens are very common in many consumer devices. Although there are two different types of capacitive touch screens, their performance is very similar, with the exception that projected capacitive touch screens are a little more accurate than surface capacitive touch screens, but this difference is relatively negligible An important feature of this technology is its use and application of multi-touch gestures. This is because less force is required to maintain a “touch point”, making dragging and zooming items much easier. However, a drawback of this technology is that you can only touch the screen with your finger. This means that stylus and gloves, depending on their thickness, will not work with this technology. Another drawback is the cost of the screen. These screens are more expensive than resistive touch screens. Overall, capacitive touch screens are very effective in their current uses.
Main limitation of technology: Requires human touch, scratches in coatings cause dead spots and Sensitive for electromagnetic interference.

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7. SAW Touch Screen Technology:
Surface Acoustic Wave touchscreen technology is widely used in applications that demand durability and high image quality such as information directories, museum displays, training systems, gaming and vending machines, and more. SAW technology uses an all-glass panel with no films or active layers, giving it a higher clarity and durability than other resistive and capacitive touchscreen types.
7.1 How does it work?
SAW technology uses ultrasonic waves that pass over the touch screen panel. Ultrasonic is a cyclic sound pressure wave with a frequency greater than the upper limit of the human hearing range. When the panel is touched, a portion of the wave is absorbed and attenuated by the finger. This change in the ultrasonic waves registers the position of the touch event and sends this information to the controller for processing. See figure (19).
Actually, the surface wave system consists of pair of two transducers (one receiving and one sending) which are placed along the x and y axes of the glass plate. The other important element of
SAW, Reflectors are also placed on the glass plate to reflect the electrical signal between the two transducers. The touch screen controller sends a 5 MHz electrical signal to the transmitting transducer, which converts the electrical signal into ultrasonic waves. Each wave is spread across the screen by bouncing off reflector arrays along the edges of the screen. These mechanical waves are directed across the opposite side gather and direct the waves to the receiving transducer, which reconverts them into an electrical signal. When the front surface of the touch screen is touched, a portion of the energy of the acoustic wave is absorbed, thus changing the received signal. See figure (20). The signal is then compared to a stored reference signal, the change recognized, and a coordinate calculated. This process happens independently for both the X and Y-axis.
Figure 19: Surface Acoustic Wave
Figure 20: Working of SAW touch screen

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7.2 Opportunities and Limitations of SAW Touch Technology:
Surface acoustic wave (SAW) touch panels were developed mainly to address the drawbacks of low light transmittance in resistive film and capacitive touch panels. SAW touchscreen structure has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system better for displaying detailed graphics (both resistive and capacitive systems have significant degradation in clarity).
Additionally, the surface glass provides better durability and scratch resistance than a capacitive touch panel. Another advantage is that even if the surface does somehow become scratched, the panel remains sensitive to touch. Structurally, this type of panel ensures high stability and long service life, free of changes over time or deviations in position, tested to over 50 million touches at one point. Moreover, SAW touch panels can be deployed to a curved surface.
Weak points include compatibility with only fingers and soft objects (such as gloves) that absorb ultrasound surface elastic waves, something hard like a pen won't work. Because SAW panels can be activated by a very light touch, they may react to substances which can absorb acoustic energy like water drops and small insects on the panel creating reported touch coordinates or false/unintended touch responses. Unsurprisingly, this type of touchscreens can be adversely affected by surface contaminants and water, making it unsuitable for many industrial or commercial applications. Acoustic absorbing contaminants can cause SAW screens to perform with decreased sensitivity or create performance issues with the touchscreen. The biggest challenges are with contaminants near or in the reflector patterns of the touchscreen. The contaminants can cause dead spots on the screen, requiring periodic cleaning of the sensor and sometimes recalibration. So, The SAW type screen may not perform well in extremely dirty or dusty environments.
Surface Acoustic Wave
Advantages
Disadvantages
 Better clarity than Resistive and Capacitive
 Work almost with any stylus
 Very high scratch immunity
 can be deployed to a curved surface
 provides superior resolution
 Must use soft object to enable touch
 Surface contaminants cause dead spots
 Low weather immunity (water and dust)
 Cannot be completely sealed
 require periodic cleaning of sensor
 can be activated inadvertently by dirt
Table 5: Pros & Cons of Surface Acoustic Wave Technology
Best usage: Healthcare, Retail, Point of Sale, Hospitality and banking applications or other high Traffic indoor environments. It is not recommended to use SAW panels in open environments.

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8. Bending Wave Touchscreen Technology:
Bending-wave touch technology is simple in concept (Figure 21). A finger touch on a glass plate generates sound waves that propagate within the glass. These sound waves are detected with “microphones” in the form of piezoelectric transducers bonded to the glass. Resulting signals are digitized by electronics and numerically processed to reconstruct touch positions.
Bending-wave touchscreens and SAW touch screens have much in common. Both are acoustic touch screens that require nothing more than a glass plate in the touch input area. Bending-wave and SAW touch screens share the valued features of high transparency, no-wear mechanism for normal usage, and stable calibration based on the speed of sound.
However, bending-wave touch screens and SAW touch screens are only distant cousins and have some significant differences. For example, bending-wave touch screens are completely unpowered signal sources (much like a receiving radio antenna), while SAW touch screens must be powered to constantly generate waves to illuminate touches. A particularly interesting difference concerns the effect of contaminants on the touch surface. When compared to SAW, bending waves travel inside the glass substrate. Once excited, bending waves are difficult to stop. This is because bending-wave power is distributed throughout the entire thickness of the glass plate, while SAW power is concentrated at the surface. Therefore, bending waves are little affected by contaminants on the touch surface such as water or even the palm of the user’s hand. [KH06]
The above discussion suggests that from a scientific perspective, bending-wave touch technology has much in its favor. Why did bending- wave technology not become a dominant touch technology many years ago? The answer lies in the engineering challenges of the associated signal processing.
While simple in concept, bending-wave signal processing provides challenging complexities in practice. Bending waves are highly dispersive. Bending waves typically reflect many times before damping away. Reflections add complexity to time signal processing.
One approach here is to add specially designed acoustic dampers at the glass perimeter to minimize reflected waves. Another approach is to limit touch-screen designs to very large sizes so that reflections are fewer, weaker, and more delayed in time. In this fashion, time of signal-processing requirements can add design requirements, complicating the sensor’s construction.
Another complication is that actual finger touches are wave sources that are not ideal – they are similar to isolated radar pings. This is clearly the case for a dragging stylus. However, what a human perceives as a quick touch continues for a finite amount of time. This compounds the signal complexity facing time of signal processing.
However, a new approach to bending-wave touch-screen signals processing called acoustic pulse recognition (APR) makes bending-wave signal complexity a benefit rather than a problem. The APR approach may be described as acoustic fingerprinting. When a touch signal is received, no attempt is made to compute an arrival time or otherwise clean up the signal. The signal in all its complexity is simply recorded much like collecting a fingerprint. Each location on the touch-screen surface has its own distinctive fingerprint. Signal complexity is now a friend. APR represents a step forward for bending wave touch-screen technology, one that holds the promise of allowing bending-wave to become a standard technology for touch screens. [KH06]
Figure 21: Conceptual drawing of a bending-wave touch screen

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9. Infrared Touch Screen Technology:
9.1 How it works?
Infrared touch screens are primarily used for large displays, banking machines, and in military applications. Infrared touch screens are based on light-beam interruption technology. Instead of an overlay on the surface, a frame surrounds the display (figure 22). The frame has light sources, or light emitting diodes (LEDs) on one side and light detectors (photo sensor) on the opposite side. The LED and photodiode pairs create an optical grid across the screen. When an object touches the screen, the invisible light beam is interrupted, causing a drop in the signal received by the photo sensor. The measured photo sensor outputs can be used to locate a touch-point coordinate. [I07]
So, Infrared technology relies on the interruption of an infrared light grid in front of the display screen.
9.2 Limitation and consideration of Infrared Touchscreen:
Widespread adoption of infrared touchscreens has been hampered by two factors: the relatively high cost of the technology compared to competing touch technologies and the issue of performance in bright ambient light. This latter problem is a result of background light increasing the noise floor at the optical sensor, sometimes to such a degree that the touchscreen LED light cannot be detected at all, causing a temporary failure of the touch screen. This is most pronounced in direct sunlight conditions where the sun has a very high energy distribution in the infrared region.
In addition, Contaminants can also cause false activation on the screen inside the thick border that is required for the frame. Another major issue with infrared touchscreen is that it is susceptible to early activation before the finger or stylus has actually touched the surface. This Early activation ability can be used to detect Z-axis, as we will see later.
Figure 22: Working of Infrared Touch Technology

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However, certain features of infrared touch remain desirable and represent attributes of the ideal touchscreen, including the option to eliminate the glass or plastic overlay that most other touch technologies require in front of the display. In many cases, this overlay is coated with an electrically conducting transparent material such as ITO, which reduces the optical quality of the display. This advantage of optical touchscreens is extremely important for many device and display vendors since devices are often sold on the perceived quality of the user display experience. [I07]
Another feature of infrared touch which has been long desired is the digital nature of the sensor output when compared to many other touch systems that rely on analog-signal processing to determine a touch position. These competing analog systems normally require continual recalibration, have complex signal-processing demands (which add cost and power consumption), demonstrate reduced accuracy and precision compared to a digital system, and have longer-term system-failure modes due to the operating environment.
Moreover, this technology has multi-touch capability because the beams of light are never fully obstructed by the user’s touch.
Here are the most important pros and cons of Infrared touchscreen:
INFRARED
Advantages
Disadvantages
 Less re-calibration is needed which results in higher accuracy, precision and system durability.
 Excellent clarity, 100% light transmission, doesn’t require a glass or plastic overlay.
 Especially suitable for large-size (over 40 inch) touch screens.
 Can be operated with finger, stylus, etc.
 Less prone to vandalism (scratching etc.)
 Support Multi-touch.
 Expensive to manufacture.
 Issue of performance in bright ambient light (e.g. sunlight)
 Overlay sensitive, touch can be sensed before screen touched
 Pollution in the active areas inside corners of the bezel may influence system function. Cleaning from time to time resolves this issue.
Table 6: Pros & Cons of Traditional Infrared touch Technology
Best usage: Infrared touch screens are often used in manufacturing and medical applications because they can be completely sealed and operated using any number of hard or soft materials. It is also used in outdoor applications and Point-Of-Sale systems which can't rely on a conductor (such as a bare finger) to activate the touchscreen.

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10. Optical Imaging Touch Technology:
Optical imaging touchscreens are a touchscreen revolution. Optical imaging is a relatively new touch screen technology that is very quickly expanding its fan base because of the scalability and versatility it offers. It is especially feasible for large units or devices. This touch screen technology is unlike others in that it can even recognize the size of the object touching the screen. This is because it uses an infrared backlight and image sensors along the screen sides. When an image touches the screen it casts a shadow and two image sensors can triangulate the position of the object that touches the screen as well as on the size of the object based the shadow the object casts.
10.1. How it works?
Optical imaging touchscreen technology is a photonics-based technology that differs from the previous touch technologies in that it uses optical imaging techniques to "see" and record the touch point. Optical imaging is a simple touch screen using cameras (or image sensors) in order to detect and pinpoint touch points (figure 23). Two cameras or more are placed around the edges (mostly the corners) of the screen, Working together to track the movement of any object close to the surface by detecting the interruption of an infrared light beams. The light is emitted by Infrared backlights placed in the camera's field of view on the other sides of the screen. A simple image processing techniques are used to combine the output of the two cameras placed. A touch shows up as a shadow and each pair of cameras can then be triangulated to locate the touch or even measure the size of the touching object.
Figure 23: working of Camera-based touch technology
(a) The basic elements that comprise a camera-based optical touch screen are two cameras, a distributed light source around the periphery, and a controller. (b) When possible, triangulation is accomplished using the sides of touching object, producing four sets of coordinates for each object.
The location of the touch can be calculated using mathematical techniques based on principles of triangulation, as also shown in Fig. The angles A and B between the top of the screen and the touch point are found by analyzing each camera’s output and determining the pixel location of the shadow. The distance W between the cameras is fixed, so the X-Y location of the touch point can be calculated using the tangents of A and B as follows: Y = X*Tan (A) and Y = (W-X)* Tan (B) .
Hence we can find X from the resulting equation, X = W*Tan (B)/ [Tan (A) + Tan (B)] .
Note that this is an intentionally oversimplified explanation; real-world calculations are much more sophisticated, taking into account factors such as lens distortion and sensor skew.

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10.2. Pros and Cons of camera-based technology:
Optical imaging touchscreen technology revolutionizes the way we interface with computer technology. Unlike many touch screen displays, the entire screen, corners included, is sensitive to the touch. This technology uses optical components. No surface coatings are used on the screens - hence images are kept crystal clear. Any method can be used to touch the screen: a finger, a gloved hand or any pointer. Only a light touch is required. Optical imaging technology provides touch sensitivity over the whole screen, including the corners.
By using image sensors at two corners of the screen, Optical imaging Touch “sees” the touching object from two angles. The result is extreme accuracy, with no contact pressure required. In addition, scratches on the touch surface will not affect the touch screen operation. No special coatings and films are needed—there’s nothing to scratch, wear out, or cloud the display image. The screen can be sealed against dirt, dust, and moisture, ideal for heavily used kiosks in public areas.
Camera-based Optical touch is also Multi-touch capable. It accommodates multiple touch points with exceptional precision. You can touch the screen anywhere, with anything like a finger, a pen, a credit card. Even the lightest touch will be registered. Annotations are fast and precise.
In addition, it is easily to mount an overlay touch onto a standard LCD or plasma monitor, converting it into a fully functional, interactive touch screen (figure 24). The overlay uses a robust design to provide touch solutions suitable for high-traffic, public environments. This model connects through a plug- and-play HID-compliant USB interface for power + connectivity. Easily turn any large Plasma or LCD into an interactive touch screen. The system integrator or end user can install it over a monitor, without the need to open the display's enclosure and possibly void warranties. This advantage makes touch ability more dynamic. [I07]
Optical imaging provides a solution without calibration drift. Once the touch screen has been calibrated it does not require any further adjustment. This means virtually zero maintenance costs. Optical touch typically is found in large format displays and enjoys popularity with digital signage applications. Optical touch is the cheapest choice for large format screens.
Optical Imaging
Advantages
Disadvantages
 100% image clarity.
 Cost effective for large displays
 No calibration drifts.
 Operation unaffected by screen scratching.
 Easy to manufacture.
 Can be retrospectively incorporated into existing non-touch screen.
 Can use anything to create the touch.
 Ambient light can affect the systems performance.
 The Profile of the frame is typically high.
 Limited to large sizes.
Table7: Benefits and Drawbacks of Optical Imaging touch
Figure 24: Camera-based overlay can easily convert any LCD screen into touchscreen

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High levels (direct sunlight) of ambient light can affect the systems performance and result in missed touch or unintended touches. Direct sunlight on the camera lens can disrupt the camera's ability to accurately detect touch response. Optical-based technology is also subject to the effects of on-screen contaminants. If the camera view is blocked by an object or contaminant on the touch surface then the screen may not be able to resolve touch points elsewhere on the screen, especially in the vicinity of the obstruction.
10.3. Future of Camera based touchscreen technology:
Optical camera-based touch’s strongest penetration has been in the Windows 7 desktop space. Competitive touch technologies in this space are surface acoustic wave (SAW) and analog multi- touch resistive (AMR). Neither of these technologies currently has more than a few percent market share in the desktop space. Projected capacitive, the newest entry in the desktop space, entered the market in the second half of 2010. Camera-based touch’s applications in the large format space are found in four main applications as follows:
- Interactive information kiosks, such as way finders and directories.
- Digital signage, in both commerce and branding environments.
- Interactive whiteboards in education and training, in both schools and businesses.
- Conference rooms.
The primary competitive touch technology in the large-format space is traditional infrared, although iSuppli forecasts that optical touch’s penetration in large-format applications will be almost double (187%) that of traditional infrared by 2013 (figure 25).
“Camera-based optical touch offers high optical performance, robustness and scalability, and is a very strong candidate for the signage and professional market. In addition, its cost-effective scaling is an advantage against competing technologies such as IR.” [G10]
Figure 25: The Future of Optical Imaging Touch tech.

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11. Comparison study:
Every single one of the different touch technologies has its own strengths and weaknesses and is therefore used in very different applications. In the end of this study you will find that there is no perfect touch technology.
11.1. Light Transmittance:
The resistive system, due to its metallic coated layers, decreases light transmittance and the image is not optimally clear. The capacitive system also reduces the amount of transmitted light, 90% as compared to 75% in resistive, again due to its metallic coated capacitive layer. In the Acoustic and the optical systems the ~100% transmission of light is accomplished due to the lack of metallic layers such as resistive and capacitive systems.
11.2 The durability:
Capacitive and resistive systems are sensitive to scratches which can produce errors. The screen durability of the surface acoustic wave and the optical systems is such that razor blades can be used to remove paint on the display surface.
Environmental elements can also impact the durability of the touch screen computer displays. If the display systems are to be located outside a building, the presence of water can be a critical issue especially in SAW technology.
11.3 Calibration Stability:
In resistive touch screens, due to the deformation and warping of the ITO layer, the screens performance will be changed. This change creates a need to recalibrate the screen. This problem, however, is not found in capacitive touch screens. This is because the ITO layers are less susceptible to damage. Additionally, this is capable “because the system can self-calibrate for environmental changes and is better able to adapt to environmental issues than resistive technology”.
Infrared touch-screen calibration is very stable because the physical location of the LEDs and phototransistors define the geometry of the infrared beams. This difference has a large impact on the use of each of the devices. Since capacitive and infrared devices do not need to be calibrated, they are more accurate than resistive devices after some wear. This difference between capacitive and resistive also increases because the ITO layers in resistive devices deteriorate over time. Capacitive touch screens are, therefore, more accurate and more durable than resistive touch screens.
11.4 Stylus Flexibility:
Another difference between the types of touch screens is the type of input devices allowed. In both resistive and optical systems, you can use nearly any object to create a touch point. The only limitation on resistive systems is that the object needs to be somewhat pointed while. This means that these touch screens allow for the use of fingers or a stylus. Surface acoustic touch panels can be activated by a finger or any soft object like gloves in surface acoustic systems stylus mustn't have hard surface. This is a great benefit over capacitive touch screens, where a user can only use a finger or an object made up of conductive material to create touch points. Capacitive touchscreen is not responsive to stylus, gloves or other object. The flexibility of using a stylus or finger allows for greater accuracy, and also allows the technology to be used in varied ways.

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11.5 Size:
Infrared and optical imaging touch screens are by far the biggest of the touch screen technologies. The size of resistive and capacitive touch screens is relatively similar, due to the similar nature of their technologies. While resistive and capacitive screens have the potential to be large, they do not perform as well as the optical technologies. This is because optical technologies uses sets of infrared LEDs and either cameras or sensors to detect the changes. Having a large capacitive or resistive system would require a large amount of wire throughout the screen; wires of that size would increase the chance for malfunction in detection, as well as wear and tear.
11.6 Applications:
Optical touch screens are best suited to devices like the Microsoft Surface, which require a very large touch screen. Capacitive touch screens are best suited for high end, portable electronic devices, and devices that need to perform consistently in many conditions. This is because of its durability, accuracy, multi-touch support and ease, and its aesthetically pleasing appearance.
Finally, resistive touch screens are best suited for mobile applications, in which conditions will be consistent.
11.7 Cost:
One area where resistive screens win out is on price, since capacitive screens (plus their associated controller chips and other trimmings) usually cost around half as much again as their resistive counterparts. Capacitive touch screens are more expensive than resistive touch screens because the systems of circuitry and measurement are more complex. This isn’t too significant in a high-end smart phone where the margins tend to be pretty large, but it becomes an issue for entry-level devices. SAW are more expensive than resistive and capacitive touch screens. But infrared are the most expensive. In large format touch displays optical imaging is the simplest for manufacture hence it is the cheapest.
11.8 TOUCHSCREEN RESOLUTION
The resolution, or number of touch active points on the touchscreen, affects the level of pointing precision and selection errors. For example, a capacitive screen has a touch resolution of 256 x 256 and an infrared screen has a resolution of 25 x 40 due to limitations on the number of light beams that can be placed around the screens. Therefore, a higher resolution screen provides additional touch points allowing greater pointing precision because the software can average all the points that have been touched and there are less selection errors as touch points are mapped more easily to the targets on the display.

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12. Practical Guide to determine which type is your touchscreen:
When encountering infrared, resistive, surface wave and capacitive touch screens during travel and daily life, the curious technologist can quickly determine the touch-screen type. Simple experiments reveal much about the basic touch-detection mechanisms of mainstream touch technologies.
Infrared: If a light brush with a piece of tissue paper is sufficient to trigger a touch, it is likely an infrared touch screen.
Resistive: If a poke with a toothpick activates a touch screen that is not an infrared touch screen, it is a resistive touch screen. Resistive touch screens are activated by sufficient pressure to close an air gap between a plastic membrane and an underlying substrate such as a glass plate.
SAW: If a touch screen is activated by the eraser end of a pencil, and it is not an infrared or resistive touch screen, it is in all probability a surface-wave touch screen.
Capacitive: If a touch screen cannot be activated by a firm touch with the eraser end of a pencil, it is a capacitive touch screen. 4-WIRE 5-WIRE Projected Surface cap SAW Infrared Camera Type Surface Technique (Electrical) Surface Technique (Electrical) Edge (Acoustic) Edge Technique (Optical) Technology Pressure to switch on Electrostatic field Ultrasonic wave Light interruption Light transmittance 70% 75-88% >88% 88-93% 90 - 92% 92-99% 92-100% Resolution Moderated Moderated High High High Low Moderated SIZE (inch) 1.7" to 24" 10.4" to 24" 2.8" to 10.4 6.4” to 32” 8” to 30” 8" to 150" >12" COST Lowest Moderate LOW Moderate HIGH Highest LOW Life Expectancy >1 million >35 million >100 million >50 million >50 million Very Long term reliability Stylus Flexibility Anything Anything Only Conductive Must be Soft Anything Anything Calibration stability Low Moderate Moderate Low Lowest High Highest Multi-Touch NO NO >10 NO 2 2 5 Overlay needed YES YES YES YES NO NO NO Contamination HIGH Best HIGH High Low Moderate Moderate Scratch Immunity LOW Moderate Moderate LOW HIGH HIGH HIGH Weather Immunity LOW HIGH Moderate Moderate LOWEST HIGHEST HIGH Sunlight Readability Moderate Moderate HIGH HIGH HIGH LOW LOW Measurement Voltage Voltage Capacitance Current Time delay Absence of light Response Time <10 ms <15 ms <15 ms <15 ms 10 ms <20ms 9-22ms Activation Force 10-100 g 10-100 g Forceless Forceless 10-100 g Forceless Forceless Operating temperature -10 to 60°C -10 to +60°C -20 to +70°C -20 to +50°C -30 to +50°C Power Consumption 5V DV 5V DV DC 6V DC 6V 12V DC 5V DV 5V DV Commercial example HTC Diamond -- The iPhone -- Lenevo PC Nexio 42" HP TouchSmart Major advantage Low cost Any stylus Multi-touch -- High clarity Durability Scalability Major Flaw Low visibility High cost Finger only High drift Delicate Ambient light Profile height
Table 7: A brief Comparsion between different touch technologies

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13. Multi Touch Technology:
Touch technology is intuitive—simply touch the screen to get what you want. Multi-touch takes the experience to the next level. Multi-touch allows you to use more than one finger (or any object) to stretch, rotate, or shrink an object, scroll through menus, and efficiently operate any software program. Multi-touch goes beyond the capabilities of any traditional pointing device, allowing you to tap into the potential of this cutting edge technology.
“Multi-touch technology has been around since early research at the University of Toronto in 1982”. The uses of this technology are very vast, allowing for greater human-computer interaction. As multi-touch functionality grows in popularity, more applications become available to take advantage of its capabilities. In addition to applications for PCs and kiosks, multi-touch is especially well-suited for entertainment and multimedia programs. Multi-touch technology also encourages working together especially with Large-format displays which allow people to collaborate more efficiently, and multi-touch makes these systems even more intuitive and natural.
13.1. Why Multi-Touch Has Become So Important?
1. Apple: Apple established multi-touch as a “must-have” for coolness. The result is that people of all ages expect every display they see to be touchable with multiple fingers
2. Gaming: Gaming is a natural for multi-touch.
3. Unintended touches: One of the major values of multi-touch is to allow the system to ignore unintended touches (palm rejection, grip suppression, etc.). As desktop screens become more horizontal (recline) this will become even more important.
4. Multi-user collaboration: When two people want to collaborate on a large screen (e.g. a student and teacher on an interactive “whiteboard” LCD), multi-touch is essential.
13.2. How Many Touches Are Enough?
The industry has multiple answers: Microsoft has settled on 5 touches for Win8; they wanted 10 at first. The p-cap touchscreen suppliers under 30” either say “10” or “as many as possible” (e.g., 3M’s p-cap supports 60+ touches). The large-format touchscreen suppliers say that 40 is enough.
The answer actually depends on the application:
 For a small mobile device, 2-5 (one hand) are enough
 For a single-user app on any device it’s hard to see why more than 10 (two hands) are needed
 For a multi-user app, it depends: For a 55-inch gaming table, 40 (8 hands) is not unreasonable. For a 65-inch interactive “whiteboard” LCD, 20 (4 hands) is probably enough, although an argument can be made for 40
An important feature of capacitive touch screens is their ability to recognize and calculate multiple touch points at one time. This technology is traditionally associated with capacitive touch screens, but is not limited to this technology. It can also be found in optical touch screens and is beginning to appear in resistive touch screens. Currently, multi-touch technology is being used with a purpose similar to the function keys (Control, Alt, Option, Command, etc.) on a standard keyboard. By adopting these functions, the user is able to complete the same tasks as before, but with one hand. With advances in hardware, multi touch will allow multiple users to access the same device simultaneously, like the Microsoft Surface’s capability of 300 plus touches. While the hardware is available to create such devices, software implementation is holding back the growth of multi touch.

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14. Cheek check and Z-axis:
Cheek check:
Most controllers are capable of sending a message indicating when a large number of locations are being touched at the same time. On stand- alone devices, attribute is customarily used to determine the phone is next to the face or the device has been put away in a pocket –signaling that the touches to the screen should be ignored (figure 26).
Z-axis:
Another attribute of some touch screen technologies is that the touch screen does not actually need to be touched to be activated. The touch screen's level of sensitivity can be controlled by electronics. In most cases, the designer will require a physical touch to activate a coordinate. However, the sensitivity can be increased, adding what is sometimes called a Z-axis or Pre-touch, so that the simple placement of a hand near the touch screen can be detected.
15. Touch Screen OS:
While Windows 7 has been a major PC success, the Windows Phone remains a distant runner-up compared to iOS and Android. Windows tablets running 7 have been largely ignored. Windows 8 is Microsoft’s answer to the touchscreen revolution.
During Microsoft’s Windows 8 launch event, the company paraded a variety of flashy new devices in front of us, and almost all of them featured a touchscreen. We’ve known for a while that Microsoft built Windows 8 optimized for touchscreens.
Windows 8 looks really exciting, but users told that extensive use on a non-touch laptop is frustrating because the OS is always encouraging you to touch the screen. This is not only bad news for anyone upgrading an older laptop, but also for people who work more efficiently using the track pad and keyboard.
Basic Screen specification requirements for win8 Touch OS:
- Minimum of 5 simultaneous touches
- Respond to first touch in < 25 ms
- Subsequent touches must be < 15 ms at 100 Hz for all touches
- Pixel-level (< 1 mm) accuracy, including edges and corners
- No jitter when stationary; < 1 mm when moving 10 mm
- Finger separation >= 12 mm horizontal/vertical, 15 mm diagonal
- Pre-touch < 0.5 mm
Figure 26: Ignored Touch

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16. Interaction:
For now, the latest developments in touch screen technology include what is considered as an interactive touch screen—it is perceived that the screen shapes itself allowing a user to click a button. This technology will change the way we consume, learn and interact with each other. Devices that were designed to make our lives easier to control now appear to be controlling us. The proliferation of technology and our reliance on it is now becoming a familiar part of modern life. Many people welcome the intrusion as it brings with it unprecedented levels of social interactions, entertainment and other things that enrich us. But many owners of smartphones and tablets appear to be inextricably attached to their devices and this attachment permeates their entire home life; not even time spent with their nearest-and-dearest can break the eye-to-screen bond. This is a significant social change, this is the touchscreen life.
One definition of sustainability is the improvement of the quality of life by making life more enjoyable and less burdensome. Touch screen technology fits within this definition very well. Touch screen devices make life more enjoyable by creating a fun and intuitive user interface. This is a reason that the iPhone, iPod Touch, and similar devices are so successful. By allowing the user to operate the device in many different ways, the devices are more versatile and create a better interface for many applications. With a better interface, the devices become more enjoyable to use, and allow for other applications of the device. Sustainability also pertains to making life less burdensome.
Touch screens are very sustainable because of the vast amount of applications that can be done on one device. This can be seen very easily in the iPhone and Microsoft Surface. Before the iPhone, many people carried around a cell phone, iPod, and PDA. With the implementation of a versatile touch screen, the iPhone and other touch screen devices are able to do the tasks of all three of these devices. This is because of the adaptability of the interface. The Microsoft Surface is similar to the iPhone because it makes many applications available to the user. Users are able to transfer contact information, calendars, pictures, etc. with just the touch of a finger. The sustainability aspects of both of these devices show the importance of these technologies.
With the proliferation of low-cost, large format displays, many customers are demanding to make these displays interactive. Typically large-format displays range from 32 inches up to 82 inches. Public displays are intended for out-of-home viewing by multiple people. Touchscreen manufacturers have responded to meet this need in different ways. Some have chosen to develop purpose-built technologies specifically designed for large-format displays, while others have scaled up existing technologies to accommodate these larger sizes.

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17. Market Trends:
17.1. The Recent History:
Touchscreens are the hottest thing in user interfaces for everything from phones to laptops to tablet computers such as the iPad. The late 2000s often attribute Apple as responsible for the touchscreen. The company did not invent the touchscreen, but innovated it. The technology became more useful and commercially available to a widespread audience. In 2007, Apple released the most innovated touchscreen technology anyone had yet seen. The iPhone interface is completely touch-based, including the notorious virtual keyboard. Apple's line of iPhones led to other devices like the iPod Touch and the iPad.
After shaking the mobile industry with the iPhone, the late 2000s saw a race among tech competitors to make the best tablet. Apple, Microsoft, Amazon, Samsung, Google and other giants have all made several devices with touchscreen technology.
Sales of laptops are falling, but sales of touchscreen devices, such as tablets and smartphones, are rising. Touch screens have now been widely incorporated into a huge number of everyday devices. They will continue to be a growing area for innovation in electronic systems. Touchscreens have turned into one of the fastest-growing display markets since Apple launched the iPhone in 2007. They’re now appearing on all sorts of devices, and the touchscreen market is growing 10 times faster than the overall display market. Mobile phones are the largest volume market for touchscreen panels; over 40% of mobile phones use touchscreens in 2012, with nearly complete market share within 10 years. [KK11]
17.2. Mainstream technologies:
The current market leading technology is projected capacitive touch (figure 27). Projected capacitive growth has been explosive since being popularized by Apple in 2007, and many tablet PCs manufacturers have adopted it. This technology became the top touch solution in 2010 in terms of revenue. Due to the pressure to reduce cost and materials, conventional add-on type projected capacitive touch is evolving in three directions: sensor- on-cover, on-cell, and in-cell. Today, the biggest market for projected capacitive touch screens is in mobile and smart phones, but tablets are right behind and quickly gaining momentum. [C12]
Resistive technology is widely used in small size (> 10 inch) healthcare and hospitality applications as well as high-volume retail environments. Embedded touch technology is currently the leading emerging touch technology and on-cell technology in particular has the biggest potential for small size consumer electronics, but is also suitable for medium size applications.
Figure 27: Touch screen Modules distribution

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Resistive is shrinking in units and revenue being replaced by projected capacitive in most consumer applications although it is still significant in commercial applications, especially POS and industrial. Surface capacitive has leveled off and will start to shrink. It will be an irrelevant, obsolete technology in 5-10 years.
Infrared (IR) and surface acoustic wave (SAW) touch technologies are mainly relevant for specialized touch devices, such as ATMs and banking and financial applications, as well as eBooks and mobile phones to some extent.
Optical-imaging touchscreen technology can be very cost-effective in large sizes (>10 in.) “By 2013, optical imaging will emerge as the leading single touch-screen technology in the signage and professional display market, accounting for 25.6 percent of worldwide unit shipments. The dominant use for optical imaging touch-screen technology will be in conference rooms.”[G10]
“Capacity in 2010 and 2011 was slightly higher -- 13% -- than demand, but this level of oversupply is healthy, given the rapid pace of growth in the touch industry,” said Jennifer Colegrove, Ph.D., VP, emerging display technologies for NPD DisplaySearch. “However, the glut is expected to more than double in 2012, to 27%, causing touch sensor prices to reduce rapidly. The oversupply will also force touch suppliers to move to larger size applications to utilize capacity, such as notebook and all-in-one PCs, ATM/finance and point of information,” Dr. Colegrove noted.
17.3. 2013 Trends:
The market for touch screens is already large (figure 29). Only a few years ago the true mass consumer market use of touch screens was conditioned by Apple's adoption of projected capacitive touch screen technology for the iPhone in 2007. After this other global players, such as Samsung and LG Electronics, also started to use touch technology for their wide range of products. Today, touch screen interfaces are becoming increasingly common in mobile consumer devices (figure 28). Leading the touch screen technology market are high-end mobile consumer-electronic devices, such as smart phones and tablets.[C12]
In terms of shipments of touch screen panels used in handsets, resistive touch screen shipments are expected to decrease in 2013 due to Nokia, one of the largest users of the technology, using more projected capacitive touch screen technology in its handsets. In December 2012 DIGITIMES Research forecasted that Global touch screen shipments are expected to reach 1.75 billion units in 2013, up 17.2% on year. Among the shipments, approximately 1.28 billion or 73% are estimated to be for handsets (including smartphones), which will be a 14.2% on-year increase. Shipments for touch screens used in tablets meanwhile are expected to reach 233 million units, up 38.2% on year, while touch screens for PCs are expected to reach 26.33 million in 2013, up 251.3% on year. [J12]
Figure 28: Market Size for touch modules by device size in 2012

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The latest market research expects over 800 million smartphones sold (figure 30). PCs are still one of the most successful classes of devices in the ICT sector. Next year could be approximately 390 million new units – including 235,500,000 155,700,000 notebooks and desktop devices - go to the customers. Sales of tablets will increase to nearly 166 million. A significant proportion of flat computer will account for seven-inch devices. E-readers remain a niche product with a certain connotation, According to a recent estimate, the sales in 2013 amounted to around 18 million units, According to iSuppli Research.
The smartphone boom shows no signs of slowing down. IDC’s analysts are predicting 800 million smartphones to be shipped in 2013. The tablet market is expected to keep its momentum too, with 7-inch tablets taking a significant share of the market.
Tablet PC is a fast-growing application for touch screens. Shipments tripled in 2010 and reached 79.6 million in 2011. Growth continues to be strong, with NPD DisplaySearch forecasting more than 130 million touch screens for tablet PCs in 2012, and more than 190 million in 2013. Revenues for touch screens in tablet PCs are expected to grow by more than $3 billion in 2013,While total touch revenues are about 17 billion US$ in 2013(fig 29). NPD DisplaySearch forecasts touch screen penetration on notebook PCs will increase from 2% in 2011 to about 8% in 2013.[S12]
Figure 29: Touch screen shipment forecast in 2013
Figure 29: Global Touch screen market Revenues

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17.4. What is Next?
“There are lots of opportunities in the touchscreen market,” said Jennifer Colegrove, vice president of emerging display technology at Display Search. “The market is doubling this year (2011) and will double again by 2017.” [SP10]
Apart from adding touch functionality to more and more commercial consumer devices, the next big topic and opportunity will be the replacement of indium tin oxide (ITO), especially in projected capacitive and resistive touch technologies; the two mainstream technologies. Today, half of the costs of projected capacitive touch screen modules come from the ITO sensor. The replacement of this widely used ITO sensor electrode material will not only change the game entirely in terms of costs, but also open the gate to bendable, rollable and stretchable electronics with touch functionality.
The touch screen market is expected to triple in 2022 of the next decade [C12]. The next big markets for touch screens are eBooks, (mobile) game consoles, car displays and navigation devices as well as digital cameras for small to medium size displays. Bigger touch screens over 10 inches can be increasingly found in laptops and PC monitors as well as other screens and TVs. “Demand is growing for thinner, light weight, and lower cost touch panels and devices. In addition, we see strong touch screen growth over the next several years in larger display applications” noted Jennifer Colegrove, PhD, Vice President of Emerging Display Technologies at NPD DisplaySearch.
Over the next few years, adoption by all-in-one PCs and automobile monitors are expected to be leading contributors to touch screen market growth [S12]. Touch technologies with high transmittance, low power consumption, multi-touch, or gesture recognition will benefit the most from these applications. NPD DisplaySearch forecasts that sensor on cover will surpass other add- on type projected capacitive touch and become the leading touch technology in 2015 in terms of revenue. In addition, NPD DisplaySearch forecasts strong touch screen growth over the next several years driven by demand in larger display applications.
In ten years from now, projected capacitive touch technology will continue to lead the market as panel costs are decreasing .Due to extremely low cost, resistive touch technology will continue to lead the market in price sensitive applications that need precise touch .The rise of embedded touch technology, currently the leading emerging touch technology, will be conditioned by more and more LCD manufacturers entering the field.
While displays aren’t nearly as attractive as the tablets and smartphones they go into, they’re an interesting market to observe because they show what happens when the entire manufacturing world pursues a hot trend. Sometimes the window for making profits in such a market is only open for a nanosecond. Of course, the market is fraught with risks, as any commodity hardware market is. If there’s a slowdown in demand, or a new technology emerges, the existing suppliers could face a big drop in demand. For example, Makers of resistive screens have moved from 64 to 91 in the past two years, but the size of that market has shrunk.
The future of touch surface is touchscreen video projectors (figure 30). In a restaurant, for e.g., you can place your order using the surface of the table as the touch interface, instead of using a touch screen laptop. The ability to transform any surface in a touchscreen means lower costs, making the technology more cost effective. [MA10]
Figure 30: Touchscreen Projectors

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18. Conclusion:
Through this seminar we have tried to present currently existing and trending solutions for touchscreen technology. As you can see, there are a lot of existing solutions, but none of them is the best. We have shown each of these technologies in less or more details, and also tried to make differences between them understandable and obvious. Hope we have succeeded doing that, and also, succeeded in making awareness of these technologies larger.

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19. References:
[MA10]: Mudit, B.; Anand, B.: Comparative Study of Various Touchscreen Technologies. International Journal of Computer Applications, Vol. 6 – No.8, pp.0975 – 8887, September 2010.
[KK11]: Ken, P.; Keunjong, K.: Touch Panel Overweight Maintain. Hundai Research Industry Analysis, pp.1– 18, Korea, November 24, 2011.
[G10]: Geoff, W.: Touch On the Consumer Desktop and In Large-Format. NextWindow FPD International 2010, pp.1– 41, 2010.
[J12]: Jason Y., DIGITIMES Research, Taipei, Friday 28 December 2012.
[KH06]: Ken, N.; Henry, D.: Information Display. Acoustic Pulse Recognition Enters Touch-Screen Market, pp.22– 25, 12/2006.
[I07]: Ian, M.: Information Display. An Overview of Optical-Touch Technologies, pp.26– 30, 12/2007.
[C12]: Cathleen Thiele: Touchscreen market to reach $14 billion in 2012. http://www.convertingquarterly.com/industry-news/articles/id/4067/touchscreen-market-to-reach-14- billion-in-2012.aspx ,March 23 2012
[SP10]: San J., Paul S.: Touch screen Market Update. Display Research, pp. 1-20, Nov 10, 2010
Questions: MHSH2025@Gmail.com

How Touch Screens works

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