Biophysical measurements midterm

discrete

* sampled version with in a digital computer * easy to process with digital computer and repeatable * convert analog signal to discrete by ADC process may be called a digitized signal * amplitude value only available at sampled instances of time

resistor temperature change is dependent upon and how to solve

*** more it changes the more sensitive it is going to be *** less it changes the less sensitive it is going to be

measuring voltage across LED

- Dont follow Ohms law (non linear) -cannot measure voltage across LED directly with a voltmeter because that will damage the LED you have too: -determine the voltage by KVL measure the voltage of resistors, battery source, i.e. all other elements other than the LED

filter

- is a part of a system that removes unwanted features or components of a signal - allows desired parts of a signal to pass through

Phase Shift Plot

-A graph of phase shift (y-axis) versus frequency (x-axis) -It shows phase shift, or lag, of the output signal from the input signal in response to frequency. -The output reaches a -45 degree lag at the cutoff frequency for a low-pass filter. -The output reaches a +45 degree lead at the cutoff frequency.

Resistor Types

-Metal film: high precision low cost -composite: medium precision good transit immunity -wire wound: higher power handling and higher inductance

analog signals

-continuous in time and amplitude -no gaps so there are infinite points in time, *infinite amplitude values, *cannot be fully represented by a table of numbers *only a graph can really represent them * many physiological systems use analog encoding and most bio transducers generate analog encoding signals

know the types of sensors for various biophysical measurements

-voltage -optical -mechanical -chemical -acoustic - thermal

What are the two components of a sensor?

1. The primary sensing element that senses the biophysical signal. 2. The variable conversion element that converts the sensed signal to and output that a computer can understand

digital signal characteristic

1. less susceptible to nose 2. easy to process 3. easy to store

man instrument system components

1. measurand 2. sensor/transducer 3. signal conditioning 4. output

Steps of ADC

1. sampling 2. Quantization 3. Coding

analog signals characteristics

1. susceptible to noise 2. difficult to process 3. difficult to store

signals types

1D : 1 dependent , 1 independent variable ex function of a single variable like time f(t) 2D: 1 dependent, 2 independent variable(s) to be spatial position (x, y).

Resistor tolerance example

1st step: get tolerance value (x) = tolerance % * resistor value 2nd step: get Tolerance Range min= resistor value - x max= resistor value + x

components of Op Amp

2 input terminals: inverting (-) terminal non-inverting (+) terminal one output terminal +Vcc and -Vcc power sources

LED definition

2 lead semiconductor that emits light when activated

what the principle of operation of LED (How it works?)-

A light-emitting diode is a two-lead semiconductor light source. It is a p-n junction diode that emits light when activated with current/voltage. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor.

signal conditioning

A portion of the Man-instrument system -amplify, filter, match impedance -analog to digital conversion -noise removal -time-domain to frequency domain -measure/monitor

measurand

A portion of the Man-instrument system -physical quantity, property, or condition on person -internal, external, surface, derived -e.g. bio potential, pressure, flow, dimensions, displacement, impedance, temperature, chemical -localized to specific organ or anatomic structure -may require applying some external stimulus to observe or measure

output

A portion of the Man-instrument system -quantified output to be percieved -numeric or graphical displays -auditory displays -calibration signal, control and feedback -data storage, wireless transmission, remote displays

sensor/transducer

A portion of the Man-instrument system -transducer converts one form of energy to another -sensor converts a physical measurand to an electric circuit -components of a sensor or transducer include the primary sensing element and a variable-conversion element (which converts the sensed information so a computer can understand the signal)

signals definition

Any physical quantity that varies as a function of one or more independent variables.

Biosignals Definition:

Any signal that can be continually measured and monitored in living beings

Differential amplifier

But as a standard operational amplifier has two inputs, inverting and no-inverting, we can also connect signals to both of these inputs at the same time producing another common type of operational amplifier circuit called a

amplifier

Electronic device to amplify voltage, current, or power of an electrical signal

What is the difference between a transducer and a sensor?

Every transducer has a sensor but not every sensor is a transducer. Transducers convert one form of energy into another so sensors are a type of transducer. A sensor is a device that detects one form of energy and converts the data to electrical energy ONLY. While a transducer can output electrical, thermal, chemical, etc. The sensor is made up of the sensing element itself while a transducer will have more associated circuitry. A sensor cannot provide any feedback while a transducer can provide feedback to the system.

Definition of precision

How repeatable the measurement is

Unity Gain Differential Amplifier

If all the resistors are all of the same ohmic value, that is: R1 = R2 = R3 = R4 then the circuit will become a _____________ and the voltage gain of the amplifier will be exactly one or unity. Then the output expression would simply be Vout = V2 - V1.

Aliasing

In signal processing , ----- is an effect that causes different signals to become indistinguishable when sampled. It also often refers to the distortion or artifact that results when a signal reconstructed from samples is different from the original continuous signal

Definition of range

Minimum and Maximum values of signal that can be observed.

More Bits =

More Accuracy and Lower Quantization Error

P vs N type for an LED

P type and N type are sides of the LED each of them are a semiconductors P type- positive charged holes/ atoms N type- negative charged electrons -once a voltage is reached inside the LED they will combine at the depletion region and then once there combined, there emitted as a photon (light) the amount of energy released effects the frequency of the light

Cutoff Frequency

The frequency point at which a filter

Definition of Resolution

The smallest change in a signal that can be identified

The digital numbers used are all basically binary; that is, each "bit," or unit of information has one of two possible states.

These states are "off," "false," or "0," and "on," "true," or "1." It is also possible to represent the two logic states by two different levels of current, however this is much less popular than using voltages. There is also no particular reason why the voltages need be referenced to ground in which positive true, or 1, corresponds to a minimum output level of +2.4 V (inputs respond unequivocally to "1" for levels greater than 2.0 V); and false, or 0, corresponds to a maximum output level of +0.4 V (inputs respond unequivocally to "0" for anything less than +0.8 V).

Characteristics of Biosignals

They are Analog Signals DC and range of AC frequencies Small voltages (mV-mV range) Contain Noise (lower signal-to-noise ratio)

why we use ADC and DAC? -and- what is the need of converting the signal back and forth ?

analog signals are converted into digital signals so they can be easily processed and stored

ADC

analog to digital converter

Superposition

analyze sources separately short circuit voltage source open circuit current sources https://www.chegg.com/homework-help/using-superposition-theorem-find-v0-circuit-fig-48answer-6vf-chapter-4-problem-3pp-solution-9780077263195-exc

Passive filters

are made up of passive components such as resistors, capacitors and inductors and have no amplifying elements (transistors, op-amps, etc) so have no signal gain, therefore their output level is always less than the input.

signal characteristics

continuous or discrete type of energy source (e.g. chemical or mechanical)

sensor

converts a physical parameter to an electric output

actuator

converts an electric signal to a physical output

Definition of accuracy

how close a measurement is to the true value. how close a measurement is to a "gold-standard"

impedance vs frequency for inductor

impedance and frequency is directly proportional so when you increase frequency you will increase the impedance

impedance vs frequency for capacitor

impedance and frequency is inversely related when you increase frequency you decrease impedance

AC to DC conversion

in which we use a transformer to decrease high voltages to low voltages and then input the low voltage into a rectifier for converting voltage into current. Quantization is part of the Analog to digital conversion.

by increasing the number of bits

increases the resolution

The ideal amp in terms of impedance (input ans output) and gain in terms of frequency

infinite input impedance and zero output impedance but has infinite gain.

transducer

is a device that converts energy from one form to another

Electrocardiogram (ECG)-what are we exactly measuring?

is a diagnostic tool that is routinely used to assess the electrical and muscular functions of the heart. can measure the rate and rhythm of the heartbeat

Electrooculography (EOG) -what are we exactly measuring?

is an eye movement-dependent recorded between electrodes placed near the eye at the inner outer Canthus

Resolution

is defined in the number of bits, and here the number of bits refer to the number of bits in which quantized signal is going to get encoded so basically this defines the minimum change in the input signal which can be detected by the ADC.

what is the reason we have to do the quantization?

it provides us with levels of numbers that, for an 8 bit converter, go from 000 to 111. This will allow the coder to convert the numbers to a digital value.

Signal-to-noise ratio (SNR)

level of the desired signal to the level of background noise units of decibels (dB) * higher the SNR the noise is very high (bad lots of background noise need to filter out) * lower the SNR the more representative of the signal itself (good not a lot of background noise signal)

Electromyography (EMG) what are we exactly measuring?

muscle response or electrical activity in response to a nerve's stimulation of the muscle. -waveform of any muscle besides the heart (invasive)

what is an example of biosignal ?

oxygen, carbon dioxide, temperature, pH, muscle movement, blood pressure, muscle contractility, sounds

Electroencephalogram (EEG) , what are we exactly measuring?

that records electrical patterns in your brain.

•The actual gain of an op amp circuit is determined by

the feedback network, which is generally constructed from passive devices. This provides great flexibility with a wide variety of design options and the inherent robustness and long-term stability of passive elements.

I would say the lower bits you have

the more distortion and loss of signal you get (which is called aliasing).

the more bits you have

the more the system will be able to provide an output (converted) signal that represents the input (continuous).

Nyquist Sampling Theorem

the sampling rate should be at least 2x the maximum frequency of the input signal so that after the sampling the signal can be reconstructed. - so for a sine wave with a maximum frequency of f max the minimum sampling rate should be equal to 2x fmax and if the sampling rate is less than this aliasing will take place in the reconstructed form.

Active filters

these filters contain amplifying devices (op-amp) to increase signal strength while passive do not contain amplifying devices to strengthen the signal.

The Band Pass Filter

this filter allows signals falling within a certain frequency band setup between two points to pass through while blocking both the lower and higher frequencies either side of this frequency band.

The High Pass Filter

this filter only allows high frequency signals from its cut-off frequency, ƒc point and higher to infinity to pass through while blocking those any lower.

The Low Pass Filter

this filter only allows low frequency signals from 0Hz to its cut-off frequency, ƒc point to pass while blocking those any higher.

Sampling:

this is the first step in the ADC. In this step, the signal X(N) (continuous time, continuous amplitude) gets converted into a sampled signal X[N] (discrete time, continuous amplitude)

Coding:

this is the last step in the ADC process. In this process the digitized signal Xg[N] (discrete time, discrete amplitude) gets coded into a binary code (please check Lecture 7 in which I talked about coding base 10 to base 2 numbers).

Quantization:

this is the second step in the ADC. In this step, the signal X[N] (discrete time, continuous amplitude) gets converted into a digitized signal Xg[N] (discrete time, discrete amplitude).

operational amplifiers- why do we have two inputs?

to act as a filter for noise

The effect of incorrect sampling is to distort the signal and lose information, while the effect of low quantization is

to effectively introduce noise.

what do we use to convert a analog signal into a electrical signal?

transducer

•Design considerations for number of bits

•Accuracy of quantization •Higher Range decreases accuracy •More bits increases accuracy •Noise from quantization •More bits will decrease noise

Op-Amp - Non-Inverting Amplifier

•Allows output to be amplified Rf and R1 resistors control gain

What are MEMS-Based Sensors or Devices?

•MEMS technology has been used to produce electronic components such as resistors, inductors and capacitors •Micro-machined and integrated in very small packages compared to centimeter-size scale. •Range from micrometers up to several millimeters.

Differential Amplifier Configuration

•Open Loop Configuration 𝑂𝑢𝑡𝑝𝑢𝑡 = 𝐴(𝑉+ - 𝑉-)

Unity Gain Op-Amp

•Output = Input •High Input Impedance Output = sin⁡ (wt)

active transducers

•Require a source of energy from the measurement device to obtain a measurement. It converts the given non-electrical energy into electrical energy by itself •Working principle: take power from the external source which changes the physical properties of transducer •Example - Resistive pressure sensor, pulse oximeter

passive transducers

•Senses a physiologic (non-electric) energy source without needing energy from the measurement device and converts it into electrical (voltage or current) energy by itself •Working principle: draw energy from the measurand source •Example - Thermocouple

MEMS devices: advantages

•Small size •High sensitivity •High accuracy •High precision •Low power consumption •Short response times due to small size

Intra and extra cellular environments

•The cells have an inner and outer environments. The inner one is called intracellular environment and the space outside the membrane is called extracellular environment. • •Both of these environments contain some ions. The four main ions are 〖Na〗^+,K^+, and 〖Cl〗^-. The concentration of these ions is different for each environment.

Action Potential

•The excitable cells in the nervous system are responsible for conveying messages across the body. •If these cells are excited above a certain threshold they will generate an action potential which is a change in the transmembrane potential for the cell. •This action potential then spreads to the adjacent cells.

Noise

•Unwanted disturbance within desired electrical signal •Interfere with desired signal •Intermittent or constant interference

3 factors for noise to be present

•noise source (electrical motors-(external), lightening(external), thermal noise- resistors get hot change the values of the resistors (internal), circuit imperfections (internal)) • the coupling mechanism • signal itself has noise (trying to get electrical signal of one muscle and the noise caused by other muscles around it)