Bioinstrumentation: Chapter 2 - Sensors

Front 1

What is a Transducer?

Back 1

A device that converts energy from one form to another.

Front 2

What is a Sensor?

Back 2

Sensor converts a physical parameter to an electric output.

Front 3

What is an Actuator?

Back 3

An actuator converts an electrical signal to a physical output.

Front 4

What is a Thermocouple?

Back 4

A temperature-measuring device consisting of two dissimilar conductors that contact each other at one or more spots.

Front 5

An electromotive force existing across a junction of two different metals is due to what?

Back 5

The sum of two independent effects:
1. emf due solely to the contact of the two unlike metals and junction temperature (Peltier emf)
2. emf due to the temperature gradients along each single conductor (Thomson emf)

Front 6

What is the net Peltier emf roughly proportional to?

Back 6

The difference between the temperatures of the two junctions

Front 7

What is the net Thomson emf proportional to?

Back 7

The difference between the squares of the absolute junction temperatures (T1 and T2)

Front 8

What are the three empirical thermocouple laws?

Back 8

1. Homogenous circuits
2. Intermediate metals
3. Intermediate temperatures

Front 9

What is the first law of thermocouples?

Back 9

Homogenous circuits: in a circuit of one homogeneous metals, one cannot maintain an electric current by application of heat alone.

Front 10

What is the second law of thermocouples?

Back 10

Intermediate Metals: the net emf of a circuit of a number of unlike metals, maintained at the same temperature, is 0.

Front 11

What is the third law of thermocouples?

Back 11

Intermediate Temperatures: emf E1 is generated when two unlike metals have junctions at temperatures T1 and T2.

Front 12

In thermocouples, increased sensitivity may be achieved by connecting what?

Back 12

A number of thermocouples in series all measuring the same temperature and using the same reference junction.

Front 13

What is a Thermopile?

Back 13

An arrangement of multiple-junction thermocouples

Front 14

What are 4 advantages of Thermocouples?

Back 14

1. fast response time
2. small size
3. ease of fabrication
4. long-term stability

Front 15

What are 3 disadvantages of thermocouples?

Back 15

1. small output voltages
2. low sensitivity
3. the need for a reference temperature

Front 16

What are two BME applications of thermocouples?

Back 16

Inserts for catheters and hypodermic needles

Front 17

Direct measurements of displacement are used to determine what? Examples?

Back 17

The change in diameter, volume, and shape of various organs and structures. Like blood vessels and heart valves.

Front 18

Indirect measurements of displacement are used to do what? Examples?

Back 18

Used to quantify movements of liquids like in the heart

Front 19

What are the 4 types of displacement-sensitive measurement methods?

Back 19

1. Resistive
2. Inductive
3. Capacitive
4. Piezoelectric

Front 20

In a conductor, does random movement of electrons generate a current?

Back 20

No!

Front 21

What are the 3 types of Potentiometers?

Back 21

1. Translational
2. Single Turn
3. Multiturn

Front 22

Provided that the potentiometer is not electrically loaded, potentiometers produce what kind of output as a function of displacement?

Back 22

Linear output!

Front 23

In order to minimize dynamic distortion in potentiometers, what components should be low?

Back 23

Frictional and inertial components should be low

Front 24

What are the resistive elements of Potentiometers?

Back 24

Elements composed of wire-wound, carbon-film, metal-film, conducting-plastic or ceramic material that is excited by either DC or AC voltages.

Front 25

When a fine wire is strained within its elastic limit, what happens?

Back 25

The wire's resistance changes due to changes in the diameter, length, and resistivity.

Front 26

In Strain Gages, the gage factor for semiconductor materials is how much times that of the metals?

Back 26

50-70 times

Front 27

For semiconductors, which effect, the dimensional or piezoresistive, is dominant?

Back 27

The piezoresistive effect!

Front 28

For Metals, which effect, the dimensional or piezoresistive, is dominant?

Back 28

The dimensional effect!

Front 29

Strain gages can be classified as either what two things?

Back 29

Unbonded or Bonded

Front 30

What is a Potentiometer?

Back 30

A three-terminal resistor with an adjustable sliding contact.

Front 31

What is a Wheatstone Bridge?

Back 31

It is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component.

Front 32

When the Wheatstone Bridge is balanced, what is passed from node a to node b?

Back 32

Nothing! No current passes.

Front 33

Why are semiconductor strain gages more nonlinear than metal strain gages?

Back 33

Because the piezoresistive effect varies with strain

Front 34

What is one advantage and 2 disadvantages of semiconductor strain gages?

Back 34

Advantage is high gage factor but disadvantages are more temperature sensitive and more nonlinear.

Front 35

In unbonded strain-gage pressure sensors, is the diaphragm directly or indirectly coupled by an armature to an unbonded strain-gage system?

Back 35

It's directly coupled by an armature to the system.

Front 36

In unbonded strain-gage pressure sensors, when pressure increases, the strain gage on which pair is increased and decreased on what other pair?

Back 36

Pair B and C - Increased
Pair A and D - Decreased

Front 37

What are three types of Bonded Strain-Gage Units?

Back 37

1. Resistance-wire type
2. Foil Type
3. Helical-wire type

Front 38

In a bonded strain-gage element, what is one method of temperature compensation?

Back 38

A second strain gage as a dummy element that is also exposed to the temperature variation but NOT the strain.

Front 39

The Wheatstone Bridge circuit is ideal for measuring what?

Back 39

Small changes in resistance

Front 40

If an increase in resistance, deltaR, is done to all resistances, what happens to the bridge?

Back 40

It continues to be a balanced bridge

Front 41

In capacitive sensors, when charged, the plates carry what kind of charges?

Back 41

Equal charges of opposite sign

Front 42

In capacitive sensors, does the sensitivity increase or decrease as the plate separation decreases?

Back 42

Sensitivity increases as plate separation decreases!

Front 43

How do piezoelectric materials generate an electric potential?

Back 43

When mechanically strained!

Front 44

How are Piezoelectric Sensors used?

Back 44

Used to measure physiological displacements and record heart sounds.

Front 45

What is the principle of operation for Piezoelectric Sensors?

Back 45

When an asymmetrical crystal lattice is distorted, a change reorientation takes place causing a relative displacement of - and + charges.

Front 46

In Piezoelectric sensors, how can surface charge be determined?

Back 46

By measuring the difference in voltage between electrodes attached to the surface.

Front 47

TRUE OR FALSE: In piezoelectric sensors, an electric potential can cause physical deformation of the material.

Back 47

TRUE!

Front 48

In physics, the piezoelectric effect can be described as the link between what two things?

Back 48

Electrostatics and mechanics

Front 49

What are the 4 modes of operation of piezoelectric sensors?

Back 49

1. Thickness or longitudinal compression
2. Transversal compression
3. Thickness-shear action
4. Face-shear action

Front 50

The piezoelectric effect only occurs in what kind of materials?

Back 50

ONLY in NON-CONDUCTIVE materials!

Front 51

What is the disadvantage of Piezoelectric Polymeric film Sensors?

Back 51

1. Low mechanical quality
2. Not allowed for resonance applications

Front 52

Optical sensors can be used to measure what 3 things?

Back 52

1. Strain
2. Temperature
3. Pressure

Front 53

What are 2 benefits of Fiber Optics?

Back 53

1. Immune to electrical interference and chemically inert
2. Safely used in hazardous sensing environments like oil refineries, mining, and pharmaceutical manufacturing.

Front 54

What is the general block diagram of an optical instrument?

Back 54

Source --> Filter --> Detector

Front 55

In Optical Measurment, how is the highest efficiency obtained?

Back 55

By using an intense lamp and lenses to gather and focus light on the sample in the cuvette and a sensitive detector.

Front 56

What are 4 Optical Measurement Sources?

Back 56

1. Tungsten Lamps
2. Arc discharges
3. LEDS
4. Lasers

Front 57

What are Arc Discharges?

Back 57

Fluorescent lamp filled with low-pressured Ar-Hg mixture

Front 58

What does Laser stand for?

Back 58

Light Amplification by Stimulated Emission of Radiation

Front 59

What are some commonly used materials for Piezoelectric Sensors?

Back 59

1. Crystals - quartz
2. Ceramics
3. Piezoelectric Polymeric films like Polyvinylidene fluoride (PVDF)

Front 60

What are two advantages of Lasers?

Back 60

1. Sharp focus
2. Concentrated

Front 61

In Fiber Optics, refraction leads to what?

Back 61

Signal loss!

Front 62

What is Snell's Law?

Back 62

n2sin2=n1sin1

Front 63

What do Fiber Optics do?

Back 63

They convert light energy into an electrical signal

Front 64

What are Fiber Optic cables?

Back 64

Glass or plastic fibers surrounded by a layer of cladding, polymer, material

Front 65

What is the Total Internal Reflection?

Back 65

a phenomenon that happens when a propagating wave strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface.

Front 66

What is the Critical Angle?

Back 66

the angle of incidence above which the total internal reflectance occurs.

Front 67

If the refractive index is lower on the other side of the boundary and the incident angle is greater than the critical angle, what happens to the wave?

Back 67

the wave cannot pass through and is entirely reflected.

Front 68

If the Rays entering the end of the fiber are at larger angles than theta4, what happens?

Back 68

The rays are not transmitted down the fiber and they escape through the walls of the fiber.

Front 69

TRUE OR FALSE: In a fiber-optic sensing system, the emitter and the receiver share a single housing.

Back 69

TRUE.

Front 70

The fiber-optic cable that is connected to the amplifier allows the sensor to do what?

Back 70

To reach areas inaccessible to standard photoelectric sensors.

Front 71

In Fiber optic sensing systems, the affective imaging area is how many degrees?

Back 71

60

Front 72

A patient's body temp gives important information about the physiological state of the individual. List 4 examples.

Back 72

1. Drop in big-toe temp = early sign of shock
2. Infections = increase temp.
3. High fevers = increased ventilation, perspiration, blood flow
4. Anesthesia decreases body temperature by depressing thermal regulatory center.

Front 73

Give an example of how environmental changes and artifacts can cause misleading temperature readings.

Back 73

Skin temperature seldom reflects true body-core temp.

Front 74

List the 4 main Thermal Sensor Types.

Back 74

1. Thermocouples
2. Thermistors
3. Radiation sensors
4. Fiber-optic detectors

Front 75

What are Thermistors?

Back 75

Semiconductors made of ceramic materials that are thermal resistors with a high negative temp. coefficient.

Front 76

Does the resistance of thermistors increase or decrease as temperature increases?

Back 76

Resistance of thermistors DECREASES as temperature increases

Front 77

What are 3 advantages of Thermistors?

Back 77

1. Small size
2. Relatively large sensitivity to temp change
3. Excellent long-term stability

Front 78

What are 3 disadvantages of thermistors?

Back 78

1. small output voltage
2. electrodes fall off
3. need to amplify

Front 79

Radiation thermometry is based on what?

Back 79

A known relationship between the surface temperature of an object and its radiant power.

Front 80

What is Medical Thermography?

Back 80

A technique where the temperature distribution of the body is mapped with a sensitive of a few tenths of a kelvin.

Front 81

List 4 uses of Medical Thermography.

Back 81

1. Detection of breast cancer
2. Location and extent of arthritis
3. Depth of tissue destruction of frost bite and burns
4. Detecting peripheral circulatory disorders (emboli!)

Front 82

What are 3 advantages of Radiation Thermometry?

Back 82

1. Non-contact measurements
2. Sensitive
3. Accurate

Front 83

What is a disadvantage of Radiation Thermometry?

Back 83

Requires a calibration target in order to maintain high accuracy

Front 84

What are some sources of Radiation?

Back 84

The sun! The Human body!

Front 85

What is the principle behind Fiber-Optic Temp. Sensors?

Back 85

Some of the optical power traveling through the semiconductor is absorbed by the process of raising valence-band electrons across the forbidden energy gap into the conduction band. Because the forbidden energy gap is a sensitive function of the material's temp, the amount of power absorbed increases with temp.

Front 86

What is an advantage of the Fiber-Optic Temp Sensor?

Back 86

Nonmetallic probe is particularly suited for temp measurement in the strong electromagnetic heating fields.

Front 87

The visible light spectrum is between what wavelengths?

Back 87

400-700 nm

Front 88

In a fiber optic temp sensor, the amount of energy absorbed by the sensor is related to what?

Back 88

Is related to the temperature!

Front 89

Why is the Sky blue?

Back 89

Colors in the red spectrum are absorbed while blues are scattered and thus we see them.

Front 90

What are the 3 main components of a Biosensor?

Back 90

1. Biological recognition element
2. Signal transducer
3. Signal processing system

Front 91

What is a Biosensor?

Back 91

An analytical device comprising of a biological recognition element directly coupled to a signal transducer which together relate the concentration of an analyte to a measurable response.

Front 92

What are Biological Recognition Elements?

Back 92

They include biological receptors such as enzyme, antibodies, etc.

Front 93

What are 2 important aspects of a Biological Recognition Element?

Back 93

1. High specificity of an antibody to recognize the respective target protein
2. High affinity between antibody and the antigen

Front 94

When the biological recognition element is an antibody, the biosensor is categorized as what?

Back 94

An immuno-biosensor!

Front 95

What is an Epitope?

Back 95

It is the part of an antigen that is recognized by the immune system, specifically by antibodies.

Front 96

The Antibody/Antigen system must be what in order to be triggered? Exception?

Back 96

Must be foreign unless it is small enough (below critical mass)

Front 97

What is Fab?

Back 97

Fragment antigen-binding (Fab fragment) is a region on an antibody that binds to antigens

Front 98

What are 3 methods of Biological Immobilization for biosensors?

Back 98

1. Adsorption
2. Microencapsulation
3. Cross-linking

Front 99

What is Absorption?

Back 99

The easiest way to biologically immobilize but the receptor is unstable to changes in the pH, temperature, and ionic strength, which reduce the biological activity

Front 100

What is Microencapsulation?

Back 100

Biomaterial is trapped by an inert membrane.

Front 101

What is the disadvantage of Microencapsulation?

Back 101

It is applicable only to the detection of small analytes that can permeate the membrane.

Front 102

How does Cross-Linking work?

Back 102

It uses bifunctional agents to bind the receptor to solid supports.

Front 103

What is advantageous about Cross-Linking?

Back 103

It is more permanent and avoids problems of protein leaching from the support.

Front 104

What is the most frequently used binding immobilization method?

Back 104

(Strept)Avidin-biotin bridge.

Front 105

In the (strept)Avidin-Biotin bridge, each avidin molecule can react with how many biotin molecules?

Back 105

4

Front 106

What is Kd? What do we want it to be?

Back 106

In crosslinking, it is the dissociation constant. We want it to be small!

Front 107

If the dissociation constant is small, what happens?

Back 107

The reaction is more favorable towards the product C

(A + B ---> C)

Front 108

In a biosensor, a signal transducer is used to do what?

Back 108

Convert the biorecognition event into a measurable signal, such as light intensity!

Front 109

What is the most widely used biosensor type? Why?

Back 109

Optical! Because is cheap, disposable, and there is no electrical interference.

Front 110

What are the 3 types of Biosensors?

Back 110

1. Electrochemical: chemical reaction -> electrical
2. Piezoelectrical: mechanical -> electrical
3. Optical: chemical -> light

Front 111

Why doesn't fluorescence always occur?

Back 111

Because the signal to noise ratio is greater than 3.

Front 112

What is a Fluorophore?

Back 112

A molecule which absorbs energy of a specific wavelength and re-emits energy at a different (but equally specific) wavelength.

Front 113

What is the disadvantage of Fluorophore?

Back 113

Photobleaching!

Front 114

How can photo-bleaching be prevented?

Back 114

By a protective coat but this only slows oxidation and won't stop the root cause.

Front 115

If the frequency is higher, is the wavelength smaller or larger?

Back 115

Smaller!

Front 116

What is a Quantum Dot?

Back 116

A human made nanostructure made from a semiconductor.

Front 117

Why is the Quantum Dot important?

Back 117

It has unique features that include brighter light, less photo-bleaching, and tuneability.

Front 118

What does Quantum Dot Tuneability mean?

Back 118

It means that the excitation wavelength is the same for each QD, but if the QD are different sizes, they'll give off different colors.

Front 119

What are 3 advantages of the Quantum Dot?

Back 119

1. Traditional dyes complicate design and increase cost
2. They're size dependent
3. You only need 1 laser source

Front 120

What do Fluorosphores depend on?

Back 120

Chemical composition!

Front 121

What are the 4 current Biosensor requirements?

Back 121

1. Real-time
2. Compact
3. Multi-plexed
4. Miniaturized

Front 122

How does a Glucose Biosensor work?

Back 122

As soon as enzyme on electrode surface recognize glucose, it catalyzes glucose into gluconic acid and hydrogen peroxide. The electrode recognizes the number of electron transfer due to hydrogen peroxide/oxygen coupling. This electron flow is proportional to the number of glucose molecules present in the blood.