sensors and transducers Module 1 n 2

Sensors and Transducers
Introduction

Sensor- A device that receives and responds to a
signal.
Transducer- A device that converts one form of
energy into another.
Actuator- A device that converts an electrical
signal to physical output. Electrical
signal
Physical
parameter
Physical
quantity
Transducer
Electrical
output

Example: sensor and actuator
sensor
actuator

Example : sensor and transducer
• Transduction Element
• The output of the sensing element is passed on to the transduction element.
This element is responsible for converting the non-electrical signal into its
proportional electrical signal.
• There may be cases when the transduction element performs the action of
both transduction and sensing. The best example of such a transducer is a
thermocouple. A thermocouple is used to generate a voltage corresponding
to the heat that is generated at the junction of two dissimilar metals.

Transducers
•A Transducer is a device which converts one
form of energy into another form.
•Alternatively, a Transducer is defined as a
device which provides usable output response
to a specific input measured which may be a
physical quantity.
•A Transducer can also be defined as a device
when actuated by energy in one system
supplies energy in the same form or in
another form to a second system.

Inverse Transducers
• It is defined as the device which converts an electrical
quantity into a non-electrical quantity. It is a precision
actuator which has an electrical input and a low power non-
electrical output.
• Example : piezoelectric crystal
• It converts electrical input to mechanical displacement.

• Significant parameters which dictate the
transducer capability are:
Linearity
Repeatability
Resolution
Reliability

Classification of Transducers
• Transducers may be classified according to their
application, method of energy conversion, nature of
the output signal, and so on.
Transducers
On the basis of
principle used Active/Passive
Primary
/secondary
Analog/Digital
Transducer/
inverse
transducer
Variable- resistance
Variable- inductive
Variable- capacitive
Voltage generating
Voltage divider

Active and Passive Transducers
• Active transducers : These transducers do not need any
external source of power for their operation. Therefore they
are also called as self generating type transducers.
I. The active transducer are self generating devices which
operate under the energy conversion principle.
II. Example: Thermocouples, photovoltaic cell , thermometers
• Piezoelectric Transducer-When an external force is applied on
to a quartz crystal, there will be a change in the voltage
generated across the surface. This change is measured by its
corresponding value of sound or vibration.

• Passive Transducer: These transducers need external source
of power for their operation. So they are not self generating
type transducers.
• These transducers produce the output signal in the
form of variation in electrical parameter like resistance,
capacitance or inductance.
• Examples – A typical example is POT (resistance)
• Thermistor, Potentiometer type transducer, speaker ,
microphone.

Primary and Secondary Transducers
• Some transducers contain the mechanical as well as
electrical device. The mechanical device converts the
physical quantity to be measured into a mechanical
signal. Such mechanical device are called as the
primary transducers, because they deal with the
physical quantity to be measured.
• The electrical device then convert this mechanical
signal into a corresponding electrical signal. Such
electrical device are known as secondary transducers.

Analog and Digital Transducers
• Analog transducers: These transducers convert the input
quantity into an analog output which is a continuous
function of time.
• Thus a strain gauge, an L.V.D.T., a thermocouple or a
thermistor may be called as Analog Transducers as they
give an output which is a continuous function of time.
• Digital Transducers: These transducers convert
the input quantity into an electrical output which
is in the form of pulses and its output is
represented by 0 and 1

Basic requirements of transducer
• Ruggedness
• Linearity
• Repeatablity
• High output signal quality
• High reliabilty and stability
• Good dynamic response
• No residual deformation
• No hysteresis

Transducer Senstivity
• Senstivity: It is defined the ratio of magnitude
of input quantity to the magnitude of output
quantity.
Senstivity = Output / Input

While selecting a transducer element
i) Mechanical suitability in terms of
Physical size, shape and weight
Mounting arrangements
Ruggedness
ii) Electrical suitability in terms of
Senstivity
Frequency response
Ease of signal transmission
iii) Enviornmental suitability in terms of
senstivity to temperature and self
heating effects
Magnetic fields
Vibrations, dust, humidity
supply frequency etc.
iv) Transducer performance in terms of calibration accuracy
v) Desired measurement accuracy and range
vi) Purchase aspects.

Advantages of electrical transducers
• The electrical systems can be controlled with a very small
level of power.
• Electrical signal obtained from electrical transducer can be
easily processed (mainly amplified) and brought to a level
suitable for output device which may be an indicator or
recorder.
• No moving mechanical parts are involved in the electrical
systems. Therefore there is no question of mechanical wear
and tear and no possibility of mechanical failure.
• The electrical output can be easily used, transmitted, and
processed for the purpose of measurement.
• The output can be indicated and recorded remotely from
the sensing element.

Disadvantages of electrical transducers
• The electrical transducer is sometimes less
reliable than mechanical type because of the age.
• Also, the sensing elements and the associated
signal processing circuitry
comparatively expensive .
• the accuracy of measurement and the stability of
the system are improved, but all at the expense
of increased circuit complexity, more space, and
obviously, more cost.

Transducers actuating mechanism

Resistance Transducer
• The resistance of a metal conductor is expressed as :
• The translation and rotational “ potentiometer “ : change in the
value of resistance with change in length : measure rotary
displacement.
• Strain gauges : change with strain : measures displacement ,
force, and pressure.
• Resistivity of material: changes with temperature : measures
temperature

Classification
• Mechanically varied resistance: Potentiometer
• Thermal resistance change: Resistance
thermometer
• Resistivity change: Resistance strain gauges

• Mechanically varied resistance: Potentiometer
– Linear and angular motion potentiometer
– Linear motion Rotary motion
potentiometer

• Potentiometer are used to measure
– Pressure
– force
– Acceleration
– liquid levels

• Advantages
• High output
• Less expensive
• Available in different sizes and ranges
• Simple to operate
• Electrical efficiency is very high
• Rugged construction
• Insensitivity towards vibration and temperature

Disadvantages
• Limited life due to early wear of the sliding
main.
• They require a large force to move their sliding
contacts (wiper) .
• The output tends to be noisy in high speed
operation

Thermal resistance change:
Thermistors and Resistance thermometer

Resistance thermometers (RTD’s)

Resistive strain gauges
• Strain Gauge is a passive transducer that converts a
mechanical elongation or displacement produced due to a
force into its corresponding change in resistance R.
• If a metal piece is subjected to a tensile stress, the metal length
will increase and thus will increase the electrical resistance of
the material. Similarly, if the metal is subjected to compressive
stress, the length will decrease, but the breadth will increase.
This will also change the electrical resistance of the conductor.
If both these stresses are limited within its elastic limit (the
maximum limit beyond which the body fails to regain its
elasticity), the metal conductor can be used to measure the
amount of force given to produce the stress, through its change
in resistance.

• Initially, when there is no application of strain,
the output measurement will be zero. Thus,
the bridge is said to be balanced. With the
application of a stress to the device, the
bridge will become unbalanced and produces
an output voltage that is proportional to the
input stress.

• the circuit will be balanced without the
application of any force. When a downward
force is applied, the length of the strain gauge
increases and thus a change in resistance
occurs. Thus an output is produced in the
bridge corresponding to the strain.

Classification
• Unbonded: as shown in the figure below, an unbounded
strain gauge has a resistance wire stretched between two
frames. The rigid pins of the two frames are insulated. When
the wire is stretched due to an applied force, there occurs a
relative motion between the two frames and thus a strain is
produced, causing a change in resistance value. This change of
resistance value will be equal to the strain input.

• A bonded strain gauge will be either a wire type or a foil type
as shown in the figure below. It is connected to a paper or a
thick plastic film support. The measuring leads are soldered or
welded to the gauge wire. The bonded strain gauge with the
paper backing is connected to the elastic member whose strain
is to be measured.

• Strain Gauge Applications
• 1. Pressure Measurement
• 2. Acceleration Measurement
• 3. Temperature Measurement
•
Advantages
• There is no moving part.
• It is small andinexpensive.
• Disadvantages
• It isnon-linear.
• It needs to be calibrated

Capacitive Transducers
• What is capacitive transducer?
• Capacitive transducers are nothing but the
capacitors with the variable capacitance.
These are mainly used for the measurement
of displacement, pressure etc. It is a Passive
type of Transducer

Principle of Operation:
• The capacitive transducers works on the familiar
capacitance equation of parallel plate capacitor,
• which is given by
• Where C is the capacitance of the capacitor or the
variable capacitance transducer
• ∈0is the absolute permittivity ; 8.85x 10−12
𝐹/𝑚
• ∈ 𝑟 is the relative permittivity
• The product of ∈0 & ∈ 𝑟 is also called as the dielectric
constant of the capacitive transducer.
• A is the area of the plates
• d is the distance between the plates
𝑪 =
∈ 𝑨
𝒅
=
∈ 𝟎∈ 𝒓 𝑨
𝒅

• The capacitive transducer are commonly used
for the measurement of linear displacement,
these transducers use the following effects:
1. Change in the capacitance due to change in
overlapping area of plates.
2. Change in capacitance due to change in
distance between the two plates.

Capacitive transducer: using change in area of plate

Advantages and Disadvantages of
Capacitive Transducers
• Advantages:
• Very little force is required to operate them and hence
they are very useful in small systems.
• They are extremely sensitive.
• They have a good frequency response and can
measure both the static as well as dynamic changes.
• A resolution of 2.5 x 10^-3 mm may be obtained with
these transducers

• Disadvantages:
• The metallic part of the capacitor must be insulated from each
other.
• Their performance is severely affected by dirt and
other contaminants because they change the dielectric constant.
• They are sensitive to temperature variations and there
are possibilities of erratic or distorted signals due to long lead
length.

Piezoelectric transducers
Common piezoelectric materials are
• Rochelle salts
• Ammonium dehydrogen phosphate
• Ceramics
• Quartz

There are main two groups
1. Natural crystals: such as quartz
2. Synthetic crystals: such as Rochelle salt, lithium sulphate
etc.
Desirable properties of piezoelectric materials
1. High stability
2. High output
3. Insensitivity to humidity and temperature
Natural crystals entail following advantages
1. Higher mechanical and thermal stability
2. Ability to withstand higher stress
3. Low leakage
Quartz : most stable output
Rochelle salt : Provides highest output but can be worked
over limited temperature i.e 45°C.

Working of piezoelectric device

• Mechanical deformation generates a charge and
this charge appears across the electrodes.
• The voltage is E= Q/C
• charge𝑄 = 𝑑α 𝐹 𝑐𝑜𝑢𝑙𝑜𝑚𝑏𝑠
where 𝑑= charge sensitivity (it is constant)
F = Force applied in Newtons
• The piezoelectric effect is direction sensitive.
• The magnitude and polarity of the induced
voltage is proportional to the magnitude and
direction of the force.
• Strain experienced by the crystal
e=
𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑜𝑟 𝑠𝑡𝑟𝑒𝑠𝑠
𝑦𝑜𝑢𝑛𝑔𝑠 𝑚𝑜𝑑𝑢𝑙𝑢𝑠

• 𝐸 =
𝑔𝑡𝐹
𝐴
= 𝑔𝑡𝑝
Where 𝑔 = voltage senstivity in
Vm
N
; g =
d
ꜫ0 ꜫ 𝑟
F= force in Newton
A= area of the crystal in 𝑚2
𝑝 = 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 =
𝐹
𝐴
𝑖𝑛 𝑁/ 𝑚2
t= thickness in m

Hall effect Transducer
What is Hall effect???

Working principle of hall effect
transducer

• Consider the hall effect element shown in the figure below.
The current supply through the lead 1 and 2 and the output
is obtained from the strip 3 and 4. The lead 3 and 4 are at
same potential when no field is applied across the strip.
• When the magnetic field is applied to the strip, the output
voltage develops across the output leads 3 and 4. The
develops voltage is directly proportional to the strength of
the material.
• The output voltage is, 𝐸 𝐻 = 𝐾 𝐻 𝐼 𝐵𝑡
• where,
I is the current in ampere and the B is the flux densities in
Wb/m2
• The current and magnetic field strength both can be
measured with the help of the output voltages.

Applications of hall effect transducers
• 1) Measurement of displacement:

• 2) Measurement of Current – The hall effect transducer is
also used for measuring the current without any physical
connection between the conductor circuit and meter.
• The AC or DC is applied across the conductor for developing
the magnetic field. The strength of the magnetic field is
directly proportional to the applied current. The magnetic
field develops the emf across the strips. And this EMF
depends on the strength of the conductor.

Photoelectric Transducers
• Working principle: Conversion of light energy into
electrical energy.
• When light falls on material then following may results:
1. Electrons may flow
2. A voltage maybe generated
3. A resistance change may take place
• When light falls on photosensitive element electric
current is generated that is measured directly or after
amplification.
• PHOTOELECTRIC EFFECT is the ejection of electrons
from a metal or semiconductor surface when
illuminated by light or any radiation of suitable
wavelength.

Types
• PASSIVE TRANSDUCERS
1. Photo emissive
2.Photo conductive
• ACTIVE TRANSDUCER
3.Photo voltaic

• It consists of a cathode and an anode mounted in a vacuum
tube made of glass.
• The cathode consists of a curved metal plate made of
photosensitive material such as oxidised silver .
• The anode is made of nickel or platinum.
•When radiation of frequency above the threshold frequency falls
on the cathode, electrons are emitted and flow to the anode
constituting an electric current.
Advantages:(i) the emission is instantaneous
(ii) the maximum current is proportional to the intensity of
radiation.
(iii)increased sensitivity.
Disadvantages: (i) Generates extremely small current.
(ii) Direct power supply required for photomultiplier.
(iii)More expensive.

• In this cell sensitive material is a
semiconductor which generates voltage
proportional to the light.
• The most commonly used photovoltaic
cells are barrier layer type.
• It consists of a metal electrode on which
a layer of selenium is deposited.
• Barrier layer is formed by coating a thin
layer of gold and serves as a translucent
electrode through which light can
impinge on the layer below.
• Under the influence of light , a negative
charge is developed on the gold
electrode and a positive charge on the
bottom electrode

Module-2
• LOAD CELLS
• Load cells are used to create an electrical signal whose
magnitude is directly proportional to the force being
measured.
• Load cells are elastic device that is used for the
measurement of force through indirect methods i.e
through the secondary transducers.
• Load cells uses an elastic member as a primary
transducer and strain gauge as secondary transducers
• When a combination of strain gauge and elastic
membrane is used for measurement it is called as load
cell.

• While designing load cells using strain gauges the following
factors should be considered:
1. Stiffness of the elastic element.
2. Optimum positioning of gauges on the elements.
3. Provision for compensation of the temperature.
When large loads are measured – high tensile material should be
used.
Whereas, in case of small load – strain application provided by
bending is used.
Types of Load cells
1. Hydraulic Load cells
2. Pneumatic Load cells
3. Strain- Gauge Load cells

Diaphragms • Diaphragms are thin
circular plates broadly
used for the
measurement of both
low and high values of
pressure, force or load.
The principle is based
on deflection.
• In order to improve the
sensitivity, corrugated
diaphragms, are
designed. These are
called capsules. The
materials used for
diaphragms are nickel,
phosphor and stainless
steel.

1. Hydraulic Load cells • Working principle:
• When a force is applied on a
liquid medium contained in a
confined space, the pressure
of the liquid increases.
• This increase in pressure of
the liquid is proportional to
the applied force.
• Hence a measure of the
increase in pressure of the
liquid becomes a measure of
the applied force when
calibrated.

2. Pneumatic load cells • Pneumatic load cells :also
operate on force-balance
principle.
• The force is applied to one
side of a diaphragm of
flexible material and
balanced by pneumatic
pressure on the other side.
• The counteracting pressure
is proportional to the force
and is displayed on a
pressure dial.

3. Strain gauge Load Cells
•

Proximity sensors
• This sensors involves the use of compressed air ,
displacement or proximity of an object being
transformed into a change in air pressure.
• It consists of three ports A,B,C
• Low pressure air is allowed to escape through Port- A
• In the absence of any obstacle / object, this low
pressure air escapes and in doing so, reduces the
pressure in the port B.
• However when an object obstructs the low pressure air
(Port A), there is rise in pressure in output port B.
• This rise in pressure is calibrated to measure the
displacement or to trigger a switch.
• These sensors are used in robotics

Digital Transducers
• The output in digital transducers is discrete
and gives frequency type output or digitally
coded output, binary or of some other type.

Advantages
1. It is possible to obtain accuracy in pulse
count.
2. It becomes easy to use digital computers
along with the transducers,for data
manipulation.
3. It is easy to transmit digital signals without
distortion and external noise.

Types of digital transducers
• Frequency Domain Transducers: out put in
these transducers is in the form of pulses
– Electromagnetic frequency domain transducers
– Opto-electrical frequency domain transducers
– Vibrating string transducers
• Digital Encoders
– Optical type encoder
– Magnetic type encoder

Electromagnetic frequency domain transducers: for the
measurement of speed

Opto-electrical frequency domain
transducers: for linear motion

Vibrating string transducers: for measuring force applied

• 𝑓 =
1
2𝑙
𝑃
𝑎𝜌
• 𝑓 = 𝑁𝑎𝑡𝑢𝑟𝑎𝑙 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦
• 𝑙 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑡𝑟𝑖𝑛𝑔
• 𝑃 = 𝐹𝑜𝑟𝑐𝑒 𝑎𝑝𝑝𝑙𝑖𝑒𝑑
• a = Area of cross − section of the string
• 𝜌= Mass density of the wire

Digital Encoders
• Optical type encoder

Fiber optic sensors (transducers)

Types of fiber optic sensor
configuration
• Extrinsic sensors:

Light sensors
• Photodiode:
• A photodiode is a p-n junction device that consume light energy to
generate electric current.
• It is also referred as photo-sensor, photo detector or light detector.
• Photodiodes are specially designed to operate in reverse condition.
Reverse bias means that the p-side of the photodiode is connected to the
negative terminal of the battery and n-side is connected to the positive
terminal of the battery.
• So they have very high resistance , so when light falls on the junction
then the diode resistance falls and current in the circuit rises rapidly.
• Photodiode is very sensitive to light so when light or photons falls on
the photodiode it easily converts light to electrical energy.

Phototransistors:
• The photo transistor is a
semiconductor light sensor formed
from the basic transistor with the
transparent cover that provides much
better sensitivity than a photodiode.
• It can be seen that the photodiode
symbol shown does not give base
connection, as light is used to enable
the current flow through the
phototransistor.
• When there is no incident light there
is a very small collector-emitter
current.
• When light is incident, a base
current is produced that is directly
proportional to the intensity of light .
This leads to the production of

• Photo resistors:
• It is a light controlled variable resistor.
• The resistance of a photo resistor decreases
with the increase in incident light.

Recent Trends: Smart Pressure Transmitters
• Smart Transmitters are advancement over conventional analog
transmitters.
• They contain microprocessors as an integral unit within the device.
These devices have built-in diagnostic ability, greater accuracy
(due to digital compensation of sensor nonlinearities), and the
ability to communicate digitally with host devices for reporting of
various process parameters.
• The most common class of smart transmitters incorporates the
HART protocol.
• HART, an acronym for Highway Addressable Remote Transducer,
is an industry standard that defines the communications protocol
between smart field devices and a control system that employs
traditional 4-20 mA signal.

shown above in fig A, the smart transmitter consists of the
following basic parts:
(a) Process Sensor
(b) An Analog to Digital Converter(ADC)
(c) A Microprocessor
(d) A Digital to Analog Converter(DAC)

These basic parts can be organized into three basic sections as
shown in fig B:
(a) Input Section
(b) Conversion Section
(c) Output Section

• Input Section:
• The input section comprises the process sensor or
transducer and the Analog to Digital Converter (ADC).
• The sensor measures the process variable of interest (be
it pressure, temperature, flow etc) which is then
converted into a proportional electrical signal.
• The measured electrical signal is then transformed to a
digital count by the Analog to Digital Converter
(ADC).
• This digital count, representative of the process variable
(PV), is then fed into the conversion section which
contains the microprocessor.
• The output of the input section is a digital
representation of the process variable (PV).

• Conversion Section:
• This section contains a microprocessor whose basic
function is a mathematical conversion from the process
variable to the equivalent mA representation of the
process.
• closely connected to the microprocessor is the memory
where the setup , configuration and diagnostic data of
the transmitter are stored.
• Output Section:
• In this section, the calculated mA value representing the
process variable is fed into a Digital to Analog
Converter, where the mA value is converted into the
actual analog 4 – 20mA electrical signal.

Advantages
• Increased Rangeabilty
• Higher accuracy
• Self diagnostic facilities
• Better noise immunity
• Economical , because of the improved overall
performance
• Adjustability of range ,polarity etc.

Selection of sensors
• Variables measured and application
• Dynamic range
• Required resolution and sensitivity
• Required accuracy and precision
• Environmental conditions
• Power available for sensing
• Availability
• Cost
• Size and available space
• Ease of use
• Ease of maintenance
• Required signal processing

RVDT: Rotary Variable Differential
Transformer

Induction Potentiometer
• It consists of a rotar
attached to transmitting
shaft on which the
primary is wound and its
stator is wound with the
secondary winding
• The windings are also
designed that the output
voltage is directly
proportional to the
angular position of the
rotar.

MEMS: micro-electro-mechanical
systems
• MEMS: micro-electro-
mechanical systems:
Combination of mechanical
functions (sensing , moving ,
heating) and electrical
functions on the same chip
using micro fabrication
technology.
• Made up of components
between 1 to 100 micrometers
in size
• And contains Devices generally
range in size from 20
micrometers to a millimeter.

Block Diagram of MEMS
Micro sensors
Micro sensing
element
Signal
transduction
unit
Micro actuator
Micro actuating
element
Power supply
`
Input
signal
Output
signal
MEMS Package

• Input Signal: These signals are received from various sources
/systems such as mechanical, electrical , optical, chemical etc.
They are supplied to MEMS package.
• MEMS Package:
– Microsensors: a sensor is an object whose purpose is to
detect events or changes in its environment, and then
provide a corresponding output.
This category includes: Pressure ,force , temperature ,
humidity etc.
MEMS sensors can be defined as the combination of micro-
sensors and electronic devices integrated on a single chip.
That package is a bit like processors, but it includes all the
mobile parts of the device.

Micro actuator: The micro actuator is the element which
converts electrical signal to physical signal.
Signal transduction unit: Transfer the signal from one part
to the other
• Output Signal: These are the signals interfaced with the
system to be controlled or monitored.
• Applications of MEMS
• In automotives : Heavy use of mems is found in air bag
systems, vehicle security system, inertial brake lights,
rollover detection, automatic door locks etc.
• In microphones:The mems microphone also called as
microphone Chip is widely used in the present day
communication world
• In military : Micro-electro mechanical system (MEMS)
technology help projectiles to reach their targets
accurately.

• In accelerometers: MEMS accelerometers are widely used in
cars for airbag deployment and in consumer electronics
applications such as smart phones, gaming devices for sensing
motion
• In sensors: A sensor is a device which receives and responds
to a signal when touched . A micro sensor reaches a
significantly higher speed and sensitivity compared with
microscopic approaches.
• Inkjet printers and micro scanners also involve the use of
mems.
• Mems is used in Optical switching technology in which,
switching technology and alignment for data communications
is done.
• In medical field.

• Advantages
• Minimize energy and
materials.
• Improved
reproducibility.
• Improved accuracy and
reliability.
• Increased selectivity
and sensitivity.
• Disadvantages
• Micro-components are
costly compared to
macro components.
• Design includes very
much complex
procedures

Manufacturing of MEMS
• The technique employed for the manufacturing of MEMS is
called micro matching or micro manufacturing.
1. Bulk micro matching:
 ETCHING: Etchingis the process of using strong acid to cut
the unprotected parts of a metal surface to create a design in.
 There are two classes
of etching processes:
Wet Etching
Dry Etching.

This technique involves the
selective removal of the
substrate material in order to
realize miniaturized
mechanical components.
A widely used bulk
micromachining technique in
MEMS is chemical wet
etching, which involves
the immersion of a substrate
into a solution of reactive
chemical that will etch
exposed regions of the
substrate at very high rates.

2. SURFACE MICROMACHINING
• MEMS are produced by
depositing sequence of
thin films
• The deposition
technique used is low
pressure chemical vapor
technique.
• Polysilicon is commonly
used material for
depositing a layer

3. LIGA PROCESS
• LIGA is a German acronym
standing for lithography,
galvanoformung (plating)
and abformung (molding).
• Polymethyl methacrylate
(PMMA) is applied as
photoresist to the substrate
by a glue-down process.
• This technique is useful to
produce thick
microstructure having flat
and parallel surfaces
– Deep X-ray lithrography
– Photoresist with desired
pattern
– Electroplating
– Widely used to produce
micro gears and
microturbines

MEMS Accelerometer- Vibration Microsensor
• It is used to know the condition of
rotating machine by vibration
analysis.
• Vibrations are measured by its
frequency and amplitude.
• accelerometers use the piezoelectric
effect - they contain microscopic
crystal structures that get stressed by
accelerative forces, which causes a
voltage to be generated.
• Material used : PZT (lead zirconate
titanate oxide)
• Piezoelectric material is a self
generating device which is ideal for
sensing shocks and vibrations.
• Advantages of using PZT:
Fast response, better stability, high
frequency and high sensitivity.
• Construction: a membrane on silicon
wafer with SO2 layer is fabricated by
bulk micro matching.
• The film of PZT is sandwiched
between platinum electrodes by
deposition technique.
• When the accelerometer is
connected to the vibrating surface,
the PZT film experiences force and
electric charge is developed between
the electrodes
• This charge variation can be
converted into voltage output

Applications
• Analyzing the vibration levels of rotating machines ,
pumps, compressors and turbines.
• These measurements may be useful flux for
controlling the vibrations to check noise and
damage of rotating machine.

MEMS Humidity Microsensors
• Material used: barium titanate
: it undergoes strong changes
in dielectric when exposed to
humid atmosphere.
• Synthetically produced
piezoelectric
• Good mechanical and thermal
stability
• Low leakage and high
frequency response
• When the assembly is exposed
to humidity, the capacitance C
changes due to change in the
value of k. This change in C is
calibrated into voltage using
charge amplifiers.
• 𝐶 =
𝑘 𝜀0 𝐴
𝑑
• 𝑘 = 𝑑𝑖𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
• 𝜀0 = 𝑃𝑒𝑟𝑚𝑖𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓 𝑓𝑟𝑒𝑒 𝑠𝑝𝑎𝑐𝑒
• 𝐴 = 𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝑎𝑟𝑒𝑎
• 𝑑 =
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑡𝑤𝑜 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑑𝑒𝑠 𝑙𝑎𝑦𝑒𝑟

sensors and transducers Module 1 n 2

More Related Content

What's hot (20)

Similar to sensors and transducers Module 1 n 2 (20)

Recently uploaded (20)

sensors and transducers Module 1 n 2