Biomedical Instrumentation introduction, Bioamplifiers
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This document provides an introduction to medical instrumentation and bioamplifiers. It discusses how medical instrumentation measures and monitors physiological signals in the body using sensors. The key components of a biomedical instrumentation system are described including the measurand, sensor/transducer, signal conditioner, display, and data storage. It then focuses on bioamplifiers, explaining the types (differential, operational, instrumentation, isolation), their characteristics, and how they are used to amplify weak biopotential signals from the body while maintaining signal integrity.
![Action Potential [Depolarization]
• When a section of a cell membrane is excited by the flow of
ionic current or by some form of externally applied energy,
the membrane allows some Na+ and try to reach some
balance of potential inside and outside.
• Same time some K+ goes outside but not rapidly like
sodium.
• As a result, the cell has slightly Positive potential on the
inside Due to the imbalance of the Potassium ions.
• This potential is known as “action potential” and is
approximately +20 mV](https://image.slidesharecdn.com/bioamplifiers-211201062458/85/Biomedical-Instrumentation-introduction-Bioamplifiers-11-320.jpg)
Biomedical Instrumentation introduction, Bioamplifiers
- 1. UEEG002 Medical Instrumentation – Introduction,Bioamplifiers D.Poornima,AP(Sr.Gr)/EEE, Sri Ramakrishna Institute of Technology, Coimbatore.
- 2. Introduction What is Medical Instrumentation?? • Application of biomedical engineering • Focuses on the devices and mechanics used to measure, evaluate, and treat biological systems. • Uses multiple sensors to monitor physiological characteristics of a human or animal. • Helps physicians to diagnose the problem and provide treatment, to measure biological signals and to design a medical instrument. • Originated as a necessity to constantly monitor vital signs of Astronauts during NASA's Mercury, Gemini, and Apollo missions
- 3. Components of Biomedical Instrumentation System • Any medical instrument consists of the following functional basic parts – Measurand – Sensor / Transducer – Signal Conditioner – Display – Data Storage and Data Transmission
- 4. • Measurand – The measurand is the physical quantity,property or condition that instrumentation system measures. Human body acts as the source for measurand, and it generates bio-signals. Example: Blood pressure (Internal) Electrocardiograms (on the body surface) Blood or Biopsy (Emanate from the body) • Sensor / Transducer – Converts one form of energy to another form usually electrical energy. – The transducer produces a usable output depending on the measurand. – The sensor is used to sense the signal from the source. It is used to interface the signal with the human Example: Piezoelectric signal which converts mechanical vibrations into the electrical signal
- 5. • Signal Conditioner – Used to convert the output from the transducer into an electrical value. – The instrument system sends this quantity to the display or recording system. – signal conditioning process includes amplification, filtering, analogue to digital and Digital to analogue conversions. – Signal conditioning improves the sensitivity of instruments. • Display – Provides a visual representation of the measured parameter or quantity. Example: Chart recorder, Cathode Ray oscilloscope (CRO). – Sometimes alarms are used to hear the audio signals. Example: Signals generated in Doppler Ultrasound Scanner used for Fetal Monitoring.
- 6. • Data Storage and Data Transmission – Data storage is used to store the data and can be used for future reference. – Recent days Electronic Health records are utilized in hospitals. – Data transmission is used in Telemetric systems, where data can be transmitted from one location to another remotely.
- 7. Bioelectric Potential • Human body has many subsystems inside it like – Cardiovascular system – Respiratory system – Nervous system – Digestive system • The systems in the human body generate their own monitoring signals when they carry out their functions. • These signals provide useful information about their function. • These signals are bioelectric potentials associated with nerve conduction, brain activity, heartbeat, muscle activity and so on. • Bioelectric potentials are actually ionic voltages produced as a result of electro chemical activity of certain cell. • Transducers are used to convert these ionic potentials in to electrical signals
- 9. • Certain types of cells within the body, such as nerve and muscle cells are encased in a semi permeable membrane. • This membrane permits some substances to pass through while others are kept out. • Surrounding the cells of the body are the body fluids. • These fluids are conductive solutions containing charged atoms know as ions. • The principle ions are sodium (Na+) Potassium (K+) and chloride (Cl-). • The membrane of excitable cells permits entry of Potassium (K+) and chloride(C-) ions but blocks the entry of sodium (Na+) ions.
- 10. Resting Potential • So potential inside the cell is more negative than outside cell. • This membrane potential is called Resting potentials. • This potential is measured from inside the cell with respect to body fluids. • So resting potential of a cell is negative. • This resting potential ranging from -60mv to -100 mv. • Cell in the resting state is called polarized cell.
- 11. Action Potential [Depolarization] • When a section of a cell membrane is excited by the flow of ionic current or by some form of externally applied energy, the membrane allows some Na+ and try to reach some balance of potential inside and outside. • Same time some K+ goes outside but not rapidly like sodium. • As a result, the cell has slightly Positive potential on the inside Due to the imbalance of the Potassium ions. • This potential is known as “action potential” and is approximately +20 mV
- 12. • A cell that has been excited and that displays an action potential is said to be depolarized • The process from resting to action potential is called depolarization. • Action potential is always positive inside.
- 13. Reploarization • The process of the cell coming to depolarised state from polarised state
- 14. Characteristics of Resting and Action Potential
- 15. Bio potential Amplifiers – Very important part of modern medical instrumentation – To amplify biopotentials which are generated in the body at low levels with high source impedance – are required to increase signal strength while maintaining fidelity • Functions of Biopotential Amplifiers – To take a weak bio-potential and increase its amplitude so that it can be processed, recorded or displayed – To amplify voltage, power and current. – Sometimes used to isolate the load from the source current gain only
- 16. • Characteristics of Biopotential Amplifiers – High input impedance – Low output impedance – The biopotential amplifier must be sensitive to important frequency components of the biosignal – Biopotential amplifiers have a gain of 1000 or greater – Most biopotential amplifiers are differential – High common mode rejection ratio.
- 17. Types of Bio Amplifiers 1. Differential Amplifier 2. Operational Amplifier 3. Instrumentation Amplifier 4. Isolation Amplifier
- 18. Differential Amplifier • Type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. • A differential amplifier is an analog circuit with two inputs (V1 and V2) and one output (V0) in which the output is ideally proportional to the difference between the two voltages. • The formula for a simple differential amplifier can be expressed: • V0 is the output voltage • V1 and V2 are the input voltages • Ad is the gain of the amplifier (i.e. the differential amplifier gain)
- 19. • When V1 = V2, V0 is equal to zero, and hence the output voltage is suppressed. • But any difference between inputs V1 and V2 is multiplied by the differential amplifier gain Ad. • It is also known as a difference amplifier – the difference between the input voltages is amplified.
- 20. Operational Amplifier • Op amp is basically a multistage amplifier in which several amplifier stages are interconnected to each other in a very complicated manner. • Its internal circuit consists of many transistors, FETs and resistors. All this occupies a very little space. • It is packed in a small package and is available in the Integrated Circuit (IC)form. • The term Op Amp is used to denote an amplifier which can be configured to perform various operations like amplification, subtraction, differentiation, addition, integration etc
- 21. • Applying two signals, one at the inverting and another at the non- inverting terminal, op-amp will amplify the difference between them • The difference between two input signals is called as the differential input voltage. • The equation below gives the output of an operational amplifier. • VOUT is the voltage at the output terminal of the op-amp. • AOL is the closed-loop gain for the given op-amp and is constant (ideally) • The feedback is negative if the feedback path feeds the part of the signal from the output terminal back to the inverting (-) terminal. • We use negative feedback to the op-amps used as amplifiers
- 22. Chopper Amplifier • This circuit uses a chopping device which converts slowly varying dc to an alternating form with amplitude proportional to the input direct current and phase depends on the polarity of original signal. • The ac voltage is then amplified by an ac amplifier whose output is then rectified back to get an amplified direct current. • Figure shows single ended chopper stabilizer amplifier. • Aim of this circuit is to avoid the dc offset voltage present in the output signal. • For that purpose first convert the dc signal into ac using a chopper
- 24. Components • Low Pass Filter – The low frequency components derived from the input signal by passing it through low pass filter R2C2 and R2 • Chopper – The output of LPF is then chopped using a transistor switch w.r.t a carrier signal from the oscillator. • Demodulator The original signal recovered in demodulator which is again applied to second stage of amplification. • Low Pass Filter – Before given to the amplifier low frequency components again derived using LPF • Second Stage of Amplification (A2) – At the input of A2 an HPF C1R1 is used to derive the high frequency signals. – This is to reduce the dc offset and drift of second amplifier A2.
- 25. Instrumentation Amplifier • Commonly used Bio-potential Amplifier is Differential amplifier. But it has some limitations. • These limitations overcome with the availability of improved version of differential amplifier called Instrumentation Amplifier • High gain and the high input impedance are attained with an instrumentation amplifier.
- 26. • Usually, a 3-amplifier and 7 resistor setup forms the instrumentation amplifier circuit. • The output from the transducer is given as input to the instrumentation amplifier. • Before the signal goes to the next stage, a special amplifier is required with high CMRR, high input impedance and to avoid loading effects. • Two buffer amplifiers A1 and A2 connected to a differential • amplifier A3. • Op-amp A3 with four equal resistors R form a differential • amplifier with gain 1. • Rg = used to set the gain using the formula
- 28. • Advantage of Chopper Amplifier Insensitivity to component changes due to ageing, temperature change, power supply variation, or other environmental factors. Small offset voltage Used to amplify small dc signals of few microvolts.
- 29. Isolation Amplifier • Used for protection against leakage currents • Isolation between input and output • Isolation between different supply voltages and grounds • Three methods used in the design – Transformer Isolation – Optical Isolation – Capacitive Isolation
- 30. • Transformer Isolation – Uses Frequency modulated or a pulse width modulated carrier signal – Uses internal DC-DC converter comprising of a 20kHz oscillator, transformer, rectifier, and filter to supply isolated
- 31. • Optical Isolation – Can also be achieved by optical means – Patient is not connected electrically to hospital line or ground – Separate battery supplies power to the patient circuit – Patient bio signal is converted into a light by a light source – On output side, photo transistor converts light signal again to electrical signal
- 32. • Capacitive Isolation – Uses digital encoding of the input voltage and frequency modulation to send the signal across a differential capacitive barrier – Separate power supply needed on both sides of the barrier