Download Figure 1.1 Generalized instrumentation system The sensor converts

)1( ‫الكترونيات حيوية و قياسات‬
‫ نعمان النجار‬.‫إعداد د‬
Dr.Eng. Noman AL Najjar
[email protected]
Qualification : - PhD in biomedical engineering
1
Biomedical sensors
Chapter 5: Biomedical sensors
Outline
•Introduction & concepts
•Biomedical sensor using &tech nology
•Measurements biosystem
•Optical Measurements are used in biomedical sensors
•Physical measurements
•Physiological Transducers
•Displacement
–Inductive
–Resistive
–Capacitive
–Ultrasonic
•Air flow
•Temperature
•Chemical measurements
•Chemical sensors
Oxygen Sensors
Transcutaneous pO2
pH electrode
------------ cont.
Slide-2
Chapter 5: Biomedical sensors cont.
Outline -----------------------CO2 Sensors- The carbon dioxide electrode
Transcutaneous carbon dioxide sensor
•Other Physical Sensors
The oximeter catheter system
Cardiac output measured by thermodilution
•Biosensors
– Major applications for biosensors
-Biosensing Principles
Biosensor-Enzymatic biosensors
Biosensor -Immunosensors
Biosensor -SPR biosensors
Biosensor - BIACORE biosensors
Biosensor -Fiber optic based biosensors
Biosensor - Chemical sensors based biosensors
•Optical biomedical sensors-Fiber Optics
•Optical biomedical sensors-Radiation Sources & sensors
•Pressure Sensors
-Silicon Pressure Sensors
-Ultra Low Pressure Sensing
-Capacitive Pressure Sensors
-Other Pressure Sensors
•References
Slide-3
Biomedical sensors
Introduction
• Transducer is a device that converts energy from one form to another
• In sensors, a transducer converts an observed change into a measurable signal
• Integrated with other parts to “read” out the signal (electrically, optically, chemically)
• Some are used in vivo to perform continuous, invasive or non-invasive monitoring of critical
physiological variables
– pressure, flow, concentration of gas
• Some are used in vitro to help clinicians in various diagnostic procedures
– electrolytes, enzymes, metabolites in blood
concept
• in vivo: inside a living body (human or animal)
• ex vivo: outside the living body
• in vitro: in a test tube
• in situ: right in the place where reactions happen (could be in the cells, tissue, test tube ,
etc.)
Biomedical Sensor
Issues in developing a biomedical sensor
 1- Configuration
 2- Supply of power
 3- Individual sensing of variables
 4- Processing of different signals
 5-Interconnection to the other modules in the system
 6- Manufacturing
Biomedical Sensor technology
•Use of microelectronics
 Electronic components are incorporated into sensors for signal processing and conversion
•Use of Optical devices
calorimetry, spectrophotometry principles are used to develop biomedical sensors based on
optoelectronic systems
Slide-5
Biomedical sensor using force sensors
 1- Used to measure force required for grasping at the thumbs and finger tips
 2- Sensor based upon variable capacitance priniciple
 3- Used in spinal cord injury patients
 4- Sensor used as a feedback element in a closed loop control system.
Trends in biomedical sensors
Key technologies for miniaturization of biomedical sensors and realization of biochips:
microfluidics, semiconductor fabrication processes, microelectro mechanical systems (MEMS)
Equally important are: the development of more stable and effective biomolecules used for
recognition; search for new target analytes that are of diagnostic and/or biological significance
Slide-6
Measurements biosystem
What are the Transduers, Sensors, and Actuators?
•Transducer is a device that converts energy from one form to another
• In principle, Transducers are devices that convert signals in one form of energy into signals
in another form of energy.
• Sensors
• Actuator
• Conventional v.s. Intelligent Transducers
Transducer - A device that converts energy of one form to another.
• Sensor - A device that converts a physical parameter to an electric output.
• Actuator - A device that converts an electric signal to a physical output.
Slide-7
Measurements biosystem
8
Measurements biosystem
What are the Transduers, Sensors, and Actuators?
Slide-9
Measurements biosystem
Three types of output signal
1- Self-generating (active) transducers:
– The electrical signal output of
transducer is generated from another
form of input energy.
2- Modulating (passive) transducer:
– The input signal energy of
transducer is used to modulate the
electrical energy flow from the power
supply to the transducer output.
3-Tandem transducers:
– The original input signal energy is
converted to a final output of electrical
energy through two or three effects or
conversions in tandem.
Slide-10
Measurements biosystem
11
Measurements biosystem
Physical Quantities for Measurement
• Displacement measurement
– Resistive sensors: Potentiometers, Strain gages, and Bridge circuit
– Inductive sensors: Self-inductance, Mutual inductance, and Differential transformer
(LVDT)
– Capacitive sensors
– Piezoelectric sensors: Piezoelectric effect
• Temperature measurement
– Thermocouples: Thermoelectric effect (Discovered by Seebeck in 1821), Peltier effect,
Thomson effect,
• Three empirical thermocouples laws: Homogeneous circuits, Intermediate metals,
Successive (Intermediate temperature)
– Thermistors
– Radiation thermometry
– Fiber-optic temperature sensor
Slide-12
Optical Measurements are used in biomedical sensors
Optical Measurement
– Optical systems are widely used in medical diagnosis, especially in clinical-chemistry lab.
– Application example: Blood or tissue sample analysis, oxygen saturation of hemoglobin,
cardiac output.
– Radiation sources: Tungsten lamp, Arc discharges, LEDs, LASERS
Figure :
(a) General block diagram of an
optical instrument.
(b) Highest efficiency is obtained by
using an intense lamp, lenses to
gather and focus the light on the
sample in the cuvette, and a
sensitive detector.
(c) Solidstate lamps and detectors
may simplify the system.
Slide-13
Optical Measurements are used in biomedical sensors
Light sources and detectors
Sources
Detectors
•
Incandescent bulb
• Thermal detector (pyroelectric)
•
Light emitting diode (LED)
• Photodiode
•
Gas and solid state lasers
•
• Phototransistor
Arc lamp
•
Fluorescent source
• Charge-coupled device (CCD)
• Photoconductive cell
• Photomultiplier tube
14
Optical Measurements are used in biomedical sensors
Absorption/Fluorescence
•Different dyes show peaks of different values at different
concentrations when the absorbance or excitation is plotted against
wavelength.
•Phenol Red is a pH sensitive reversible dye whose relative
absorbance (indicated by ratio of green and red light transmitted) is
used to measure pH.
•HPTS is an irreversible fluorescent dye used to measure pH.
•Similarly, there are fluorescent dyes which can be used to measure
O2 and CO2 levels.
Slide-15
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
CLASSIFICATION OF TRANSDUCERS
The transducers can be classified in many ways, such as:
(i) By the process used to convert the signal energy into an electrical signal. For this,
transducers can be categorized as:
Active Transducers—a transducer that converts one form of energy directly into
another. For example: photovoltaic cell in which light energy is converted into
electrical energy
Passive Transducers —a transducer that requires energy to be translate changes
due to the measured. For example: a variable resistance placed in a bridge in
which the voltage at the output of the circuit reflects the physical variable
(ii) By the physical or chemical principles used. For example: variable resistance
devices and optical fiber transducers.( ‫)ادوات المقاوم ِة المتغيّر ِة ناقل الطاقة ذو الليف ضوئي ِة‬
(iii) By application for measuring a specific physiological variable. For example: flow
transducers, pressure transducers, temperature transducers,
Slide-16
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
1-Dsplacement transducers:
1- 1. Linear Variable Differential Transformer (LVDT)
or Inductive Sensors
The primary coil P is excited by an AC current.
The induced potentials at the 2 secondary coils are
canceled due to the opposite polarities.
When the core moves toward one coil, the induced
potential in the coil increases and the
voltage in the other coil decreases
An LVDT is used as a sensitive displacement sensor: for example, in a cardiac assist device or
a basic research project to study displacement produced by a contracting muscle.
Taken from http://www.pages.drexel.edu/~pyo22/mem351-2004/lecture04/pp062-073lvdt.pdf
17
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
1-Dsplacement transducers:
2- 1. Resistive Sensors - Potentiometers
Potentiometer: resistance is proportional to position . If the current through the
resistor is constant, the displacement (linear o angular) will be proportional to
Taken from www.fyslab.hut.fi/kurssit/Tfy-3.441/ luennot/Luento3.pdf
Slide-18
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
1-Dsplacement transducers:
3- 1. Strain gauge
Measures a small change in the length of an object as a
result of an applied force.
Resistance of a conductive materiel with length
/ and cross-sectional area A. p is a constant (resistivity)
The fractional change in length of an object is called
strain
Now consider a metal wire as a strain gauge
For silicon strain gauges, G > 100 (much more sensitive than metal)
Taken from www.fyslab.hut.fi/kurssit/Tfy-3.441/ luennot/Luento3.pdf
Slide-19
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
1-Dsplacement transducers:
3- 1. Strain gauge
The types of Strain Gauge Pressure Transducers:
a).Unbonded Strain Gauges: Most of the pressure transducers for the direct
measurement of blood pressure are of the unbonded wire strain gauge type. The
arrangement consists of strain wires of two frames which may move with respect to
each other.
:‫•مقاييس اإلجها ِد الغير المرطب ِتة‬
.ّ‫مباشر لضغ ِط الدم‬
‫قياس‬
ِ ‫• ِمن هذا النوع هو أغلب ناقلي الطاقة للضغ ِط الذي يقوم ب‬
ِ
.‫تحركا ِن حركة تتعلق ببعضهم البعض‬
‫من‬- ‫• تتركب بالترتيب‬
ِ
ّ ‫أسالك اإلجها ِد ذات اإلطايين التي يمكن ان ي‬
Taken from www.fyslab.hut.fi/kurssit/Tfy-3.441/ luennot/Luento3.pdf
Slide-20
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
1-Dsplacement transducers:
3- 1. Strain gauge

The types of Strain Gauge Pressure Transducers:
b). Bonded Strain Gauges: The bonded strain gauge consists of strain-sensitive gauges
which are firmly bonded with an adhesive to the membrane or diaphragm whose
movement is to be recorded.
•In practice, it is made by taking a length of very thin wire (for example, 0.025 mm dia)
or foil which is formed into a grid pattern (Fig. 3.7 a,b) and bonded to a backing
material.
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
1-Dsplacement transducers:
3- 1. Strain gauge
 The types of Strain Gauge Pressure Transducers:
•C). Silicon Bonded Strain Gauges:
•Lead wire resistance and capacitance change with temperature.
•Compensation for temperature variation in the leads can be provided by using the three
lead method. In this method, two of the leads are in adjacent legs of the bridge which
cancels their resistance changes and does not disturb the bridge balance. The third lead
is in series with the power supply and is, therefore, independent of bridge balance.
Diffused p-type strain gauge
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
1-Dsplacement transducers:
4- 1.Capacitive Sensors
( Electrolytic or ceramic capacitors are most common)
:
change in distance between two parallel plates (an insulating material sandwiched in
the middle) results in a change in capacitance
A: area
d: distance between two conductors
where ε0 is the permittivity of vacuum = 8.85×10-12 F/m
εr is dielectric constant of the insulating material
e.g. An electrolytic capacitor is made
of Aluminum evaporated
on either side of a very thin plastic
film (or electrolyte).
23
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
1-Dsplacement transducers:
5- 1. Piezoelectric Transducers (PZT) - ‫ناقل طاقة ذوإجهاد كهربائي‬
•The piezo-electric effect is a property of natural crystalline substances to develop electric potential along a
crystallographic axis in response to the movement of charge as a result of mechanical deformation
‫•(التأثير الكهربائي االجهادي ذو الخاصية الطبيعية لموا ِد البلّويي ِة ينمي جهد كهربائي على طول محوي المادة البلويية كردّ او استجابة‬
. ).‫لشحن حركي ناتخ عن تشويه ميكانيكي‬
•Thus, piezoelectricity is pressure electricity. On application of pressure, the charge Q developed along a
particular axis is given by
Q = kF coulomb (‫(وحدة قياس كمية كهربا‬
where k is the piezoelectric constant (expressed in Coulombs/Newton, i.e. C/N) and F is the applied force.
•The Piezoelectric Effect ) principle)
The principle of operation is that when an asymmetrical crystal lattice is distorted, causing a relative
displacement of negative and positive charges.
ّ ‫إن مبدأ العملي ِة‬
ّ
.‫هذا يسبّب إزاحة نسبية للشحن السلبة واإلموجبة‬،)‫شوه(يتعرض لضغط خايجي‬
ّ ‫بأن المشب ِّك بلّويي ِ ال متماث ِل ي‬
.‫هذه اإلزاحة تترجم الي إشايات كهربائية لغرض القياس‬
24
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
2-The Scand type -Flow Sensors
Flow : the motion of a fluid
(1) Blood flowmeters :
- ultrasonic (doppler, transit time)
- electromagnetic
(2) Gas flowmeters :
- pneumotachometer
- spirometer
- Wright's respirometer
- rotameter
-ball float meter
Flow rate :
(1) mass flow rate : mass transferred per unit of
time (ex:[kg/sec])
(2) volumetric flow rate : volume of material
transferred per unit of time(ex:[cc/sec])
(3) Total flow or flow volume : integration of flowrate
25
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
2-The Scand type - Air flow
1-1.Fleish pneumotachometer
•This measures the flow rate of gases during breathing. The breath is passed through a short
tube (Fleisch tube) in which there is a fine mesh which presents a small resistance to the flow. -The screen obstruction provides some resistance to the air flow and therefore generates
pressure drop across the screen.
-The resulting pressure drop across the mesh is in proportion to the flow rate.
-The pressure drop is very small (e.g. 2 mmHg) and so the measuring circuit must be of high
quality and produce very little drift with time.
Fleisch tube : It consists of a wide bore tube in which there is a mesh or screen which slightly
restricts the airflow through it.
The resistance to flow presented by the screen produces a differential pressure which is
proportional to the airflow through the device.
Spirometer : These measure the volumes of gases breathed in or out. They are usually
displacement (bell) devices, a bellows, or a small turbine device with gears to drive a pointer
Flow rate ∝ ΔP
Pressure is measured at both
sides of the resistive screen
26
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
2-The Scand type
2-2.Electromagnetic Blood Flowmeter :Faraday's
principle of electromagnetic induction can be applied to any electrical conductor (including
blood) which moves through a magnetic field. This probe applies an alternating magnetic
field (typically at 400 Hz) across the vessel and detects the voltage induced by the flow via
small electrodes (microvolt region) in
contact with the vessel.
where
B = magnetic flux density, T
L = length between electrodes, m
u = instantaneous velocity of blood, m/s
27
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
2-The Scand type
2-2.Electromagnetic Blood Flowmeter :Blood flow
Apply a uniform magnetic field B across blood
vessel
If velocity of blood flow is v, F is force
experienced by charged particles in blood
This force causes movement of charges ⇒
distribution of charges generates an electric
field E
For charged particles, there is a second force
qE, at equilibrium:
28
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
2-The Scand type
3-2.Ultrasonic Blood Flowmeter
(1) transit time methods in which the blood velocity is calculated from the time taken
to cross the vessel oblique to the direction of flow.
(2) The most practical form of ultrasonic blood flowmeter is the continuous wave
doppler system with the doppler-shifted components being fed to a zero-crossing
detector. Forward and reverse flow is represented by the doppler- shifted
components above and below the ultrasonic frequency.
Transit Time
29
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
2-The Scand type
3-2.Ultrasonic Blood Flowmeter
30
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
2-The Scand type -Flow Sensors
31
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
3-The third type -Temperature transducer (Temperature Sensors )
1. Resistance based
a. Resistance Temperature Devices (RTDs)
b. Thermistors
2. Thermoelectric – Thermocouples
3. Radiation Thermometry
4. Fiber Optic Sensor
3-1. Resistance based
a) .RTDs
RTDs are made of materials whose resistance changes in accordance with temperature .
Metals such as platinum, nickel and copper are commonly used.
They exhibit a positive temperature coefficient.
A commercial ThermoWorks RTD probe
Slide-32
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
3-The third type -Temperature transducer (Temperature Sensors )
3-1. Resistance based
b).Thermistors :Thermistor: semiconductor; the resistance is a function of temperature.
Thermistors are made from semiconductor material.
Generally, they have a negative temperature coefficient (NTC), that is NTC thermistors are
most commonly used.
where R0 is the resistance at a reference temperature, T0, and RT is the resistance at
temperature T. β is a material-specific constant. Both
temperatures are expressed in degrees K
Thermistors:
- have high sensitivity (<<1°C)
- range is not as great as thermocouples (-50°C –
100°C), but
suitable for biological/physiological measurements
- need calibration (R vs. temperature curve)
- can also be made very small
Slide-33
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
3-The third type -Temperature transducer (Temperature Sensors )
3-2. Thermoelectric – Thermocouples- : two different metal wires welded together
Seebeck (1821)effect:
- Thermal to electrical
-An electromotive force (emf) exists across the junction and is temperature dependent.
If we use two such junctions, one is at a known temperature and the other is at the sample
Figure -Thermocouple circuits (a) Peltier emf. (b) Law of homogeneous
circuits. (c) Law of intermediate metals. (d) Law of intermediate temperatures
Slide-34
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
3-The third type -Temperature transducer (Temperature Sensors )
3-3. Radiation Thermometry
Governed by Wien’s Displacement Law which says that at the peak of the emitted radiant
flux per unit area per unit wavelength occurs when lamda maxT=2.898x10-3 moK
-Variations of ε with λ is very important in absolute-temperature measurement, but less
important in relative temperature measurement.
– For T = 300 K and λ = 3 μm, a 5% change in ε is equivalent to a temperature change of
approximately 1oC.
– Two types of infrared sensors: Thermal and photon (quantum) detectors.
– Thermal detector has low sensitivity and responds to all wavelengths, whereas photon
(quantum) detector respond only to a limited wavelength band.
– Radiation thermometry - A technique that determines the internal or core body temperature
of the human by measuring the magnitude of infrared radiation emitted from the tympanic
membrane and surrounding ear canal.
Slide-35
Physiological Transducers - )‫ناقل الطاقة الفسيولوجي (كهر وحيوي‬
3-The third type -Temperature transducer (Temperature Sensors )
4-3. Fiber Optic Temperature Sensors
Nortech's fiber-optic temperature sensor probe consists of a gallium arsenide crystal
and a dielectric mirror on one end of an optical fiber and a stainless steel connector
at the other end.
Figure - Details of the fiber/sensor arrangement for the GaAs semiconductor
temperature probe.
Slide-36
Chemical measurements
Important analyses and their normal ranges in blood, which indicate the physiological
status of the body: gas pressure and related parameters, electrolytes, and metabolites
Introductions
• Chemical sensors
– For recognition of presence of specific substances and their concentration
– Sensitive to stimuli produced by various chemical compound or elements
– High selectivity
– Very small output electrical signal : need high quality interface electronic devices
– Gas/liquid phase sensor : ex, O2 in air/ dissolved oxygen
37
Chemical measurements
Blood Gas Measurement
•
Blood pressure : arterial BP, CVP, intracardiac BP, PAP, spinal fluid pressure,
intraventricular brain pressure.
•pressures of oxygen (pO2), carbon dioxide (pCO2) as well as the concentration of hydrogen
ions (pH) are vital in diagnosis.
•Oxygen is measured indirectly as a percentage of Haemoglobin which is combined with
oxygen (sO2).
• pO2 can also provide the above value using the oxyhaemoglobin dissociation curve but is a
poor estimate.
Blood oxygen measurement
Measuring arterial blood gases pO2: in operating room and intensive care unit to monitor
respiratory and circulatory condition of a patient.
Slide-38
Chemical sensors -Oxygen Sensors
1- Oxygen Sensors
• Oxygen content of gases and liquid
– Partial pressure : pressure exerted by one gas in a mixture of gases.
– The dissolving process for gases is an equilibrium.
The solubility of a gas depends directly on the gas pressure.
If the temperature stays constant increasing the pressure will increase the amount of
dissolved gas. – O2(g) <--->O2(aq)
• Sensor methods – Paramagnetic properties of oxygen
– Clark electrode
– Fuel cell, galvanic cell type
Figure - PO2 electrode
(From R. Hicks, J. R. Schenken, and M. A. Steinrauf, Laboratory Instrumentation. Hagerstown, MD: Harper &
Row, 1974. Used with permission of C. A. McWhorter.)
39
Chemical sensors -Oxygen Sensors
1- Oxygen Sensors
1-1.Clark electrode: measures partial pressure of O2.The pO2 electrode produces a current
at a constant polarizing voltage (0.6 V) which is directly proportional to the partial pressure
of oxygen diffusing to the reactive surface of the electrode.
40
Chemical sensors -Oxygen Sensors
1- Oxygen Sensors
2-1. Blood oxygenation - Oxygen saturation
Oxygen saturation (% of oxygenated hemoglobin) can be measured and used to represent
blood oxygenation .
Relationship between arterial blood oxygen saturation and partial pressure of O2
Figure - The oxyhemoglobin dissociation curve, showing the effect of pH and temperature on
the relationship between SO2 and PO2.
41
Chemical sensors -Oxygen Sensors
1- Oxygen Sensors
2-1. Blood oxygenation - Oxygen saturation
Oximetry: (color) measures light absorbance at one wavelength where there is a large difference
between Hb and HbO2 and at another wavelength (or more wavelengths)
Figure - The oxyhemoglobin dissociation curve, showing the effect of pH and temperature on
the relationship between SO2 and PO2.
42
Chemical sensors -Oxygen Sensors
2-1. Blood oxygenation - Oxygen saturation-Pulse Oximetry
The pulse oximeter is a spectrophotometric device that
detects and calculates the differential absorption of
light by oxygenated and reduced hemoglobin to get
sO2. A light source and a photodetector are contained
within an ear or finger probe for easy application.
Two wavelengths of monochromatic light -- red (660 nm) and infrared (940 nm) -- are
used to gauge the presence of oxygenated and reduced hemoglobin in blood. With
each pulse beat the device interprets the ratio of the pulse-added red absorbance to the
pulse-added infrared absorbance. The calculation requires previously determined
calibration curves that relate transcutaneous light absorption to sO2.
Slide-43
Chemical sensors - Oxygen Sensors
2-1. Blood oxygenation - Oxygen saturation-Pulse Oximetry
(a)
(b)
Figure :
(a) Noninvasive patient monitor capable of measuring ECG, noninvasive blood pressure (using
automatic oscillometry), respiration (using impedance pneumography), transmission pulse
oximetry, and temperature.
(b) Disposable transmission So2 sensor in open position. Note the light sources and detector,
which can be placed on each side of the finger.
[From Y. M. Mendelson, "Blood gas measurement, transcutaneous," in J. G. Webster (ed.). Encyclopedia of Medical
Devices and Instrumentation. New York. Wiley, 1988. pp.448-459. Used by permission.]
44
Chemical sensors- Oxygen Sensors
2-1. Blood oxygenation - Oxygen saturation-Pulse Oximetry
Pulse oximetry: use the pulsatile (AC) component to extract oxygen saturation information
and the non-pulsatile (DC) signal as a reference for normalization
Change in
arterial
blood
volume
associated
with
periodic
contractio
n of the
heart
Spectrophotometer
Light Source
D
Light Detector
Cuvette
In the Chemistry Lab
Photoplethysmograph
Light Source
Light Detector
Itrans  Iine -Dca λ
Physiological Measurement
Figure - Pulse oximetry
this was taken from Medical Instrumentation: Application and Design, edited by John G. Webster
45
Chemical sensors - Oxygen Sensors
2-1.Blood oxygenation - Oxygen saturation -Pulse Oximetry
Advantages
 Easy to use
 Frequent calibration unnecessary
 Limitations
 Usually only measured by transillumination
 Limited to tissues that can transmit light
 Highly sensitive to motion
 Venous pulsations can affect results
46
Chemical sensors
2-Transcutaneous pO2
The skin is heated to 43°C to increase local blood flow and enhance diffusion of O2
through the skin. Mostly used on newborn babies in the ICU because their skin is thinner
Figure - Cross-sectional view of a transcutaneous oxygen sensor. Heating promotes
arterialization.
(From A. Huch and R. Huch, "Transcutaneous, noninvasive monitoring of PO2," Hospital Practice, 1976, 6, 43-52. Used
47
by permission.)
Chemical sensors
3-pH electrode:
To measure the acidity or alkalinity of solutions determined by activities of [OH-] and [H+]
• pH electrode : Ag-AgCl metallic electrode immersed‫ مغ َِطس‬in a chloride
buffer with a very thin permeable glass membrane that allows hydrogen ions to
diffuse)‫ (ينتشر‬into the buffer
A potentiometric electrode is designed to measure the potential between the sample and a
buffer solution.
This glass electrode is placed in the blood sample and a potential difference is generated
across the glass, which is proportional to the difference in hydrogen ion concentration
48
Chemical sensors
3-pH electrode:
Figure - pH electrode
(From R. Hicks, J. R. Schenken, and M. A. Steinrauf, Laboratory Instrumentation. Hagerstown, MD: Harper
& Row, 1974. Used with permission of C. A. McWhorter.)
49
Chemical sensors
4-CO2 Sensors- The carbon dioxide electrode :
The carbon dioxide electrode is a modified pH electrode in contact with sodium bicarbonate
solution and separated from the blood specimen by a rubber or Teflon semi-permeable
membrane.
• In liquid solutions : pCO2 with a selective pH electrode
• In air or other gases : absorption of infrared by CO2
Figure - PCO electrode
2
(From R. Hicks, J. R. Schenken, and M. A. Steinrauf, Laboratory Instrumentation. Hagerstown, MD: Harper
& Row, 1974. Used with permission of C. A. McWhorter.)
50
Chemical sensors
5-Transcutaneous carbon dioxide sensor
Figure -Cross-sectional view of a transcutaneous carbon dioxide sensor. Heating the skin promotes arterialization.
(From A. Huch, D. W. Lübbers, and R. Huch, "Patientenuberwachung durch transcutane Pco2 Messung bei
gleiechzeiliger koutrolle der relatiuen Iokalen perfusion," Anaesthetist, 1973, 22, 379. Used by permission.)
51
Other Physical Sensors
1-The oximeter catheter system The oximeter catheter system measures oxygen saturation in vivo, using red 660 nm
and infrared 940 nm light emitting diodes (LEDs) and a photosensor. The red and
infrared LEDs are alternately pulsed in order to use a single photosensor.
Figure
52
Other Physical Sensors
2-Cardiac output measured by thermodilution
To oximetry instrument
CVP injection port
Thermistor
Balloon
Cardiac output
computer connector
Transmitting
fiber-optic
Receiving
fiber-optic
Optical module
Proximal
(CVP) lumen
Distal
(PA) lumen
Balloon inflation
lumen
Sampling and pressure
monitoring lumen
Figure - The catheter used with the Abbott Opticath Oximetry System transmits light to the blood through a
transmitting optical fiber and returns the reflected light through a receiving optical fiber. The catheter is optically
connected to the oximetry processor through the optical module. (From Abbott Critical Care Systems. Used by
permission.)
Slide-53
Other Physical Sensors
2-Cardiac output measured by thermodilution
Catheter with multiple ports
- Inject cold saline into the right atrium
(intravenous catheter)
- Measure temperature at the pulmonary
artery over time
- Conservation of energy: The total heat
content of the injected saline will be
Slide-54
Biosensor
What are biosensors?
• Biosensor: is a sensor using a living component or a product of a
living thing for measurement or indication. Or a biosensor is an
analytical device which converts a biological response into an
electrical signal.
Features of a successful biosensor:
1- Biocatalyst highly specific for the purpose of the analyses,
2-Reaction independent of physical parameters,
3- Response accurate, precise, reproducible and linear,
4-No electrical noise,
5- Biocompatible
6- Cheap, small, portable and capable of being used by operators.
Biosensor
Major applications for biosensors
1-Medical Applications
 Suitable for analyzing blood samples using diagnostic sensors
 monitoring of various medical conditions
 Glucose level monitoring
2-Wireless solutions for human-implanted sensors
3-Military combat operations
 can track the soldier movements
4-Civilian applications
 Temperature change notification
 Pollution detection
 Detecting changes in exhaustive systems of the vehicles
Slide-56
Biosensor
Biosensing Principles
Slide-57
Biosensor
Generally a biosensor consists of two parts
– A biological recognition element (enzyme, antibody, receptor) to provide selectivity to
sense the target of interest (referred to as the analyte)
– A supporting element which also acts as a transducer to convert the biochemical reaction
into “signal” that can be read out
Slide-58
Biosensor
“Receptor” provides selective molecular recognition
•For example: enzymes, antibodies, receptors, nucleic acids, polypeptides, etc.
•Transducer types in biosensors: calorimetric, electrochemical, optical, etc.
Biosensor- 1.Enzymatic biosensors
Enzymes are catalysts for biochemical reactions; large macromolecules consisting mostly
of protein, and usually containing a prosthetic group (metals)
Substrate: the target molecule of an enzymatic reaction
S: substrate; E: enzyme;
ES: enzyme-substrate complex;
P: product
Slide-59
Biosensor- 1.Enzymatic biosensors
•Advantages
– Highly selective
– Enzymes are catalytic, thus improving the sensitivity
– Fairly fast
• Disadvantages
– Expensive: cost of extraction, isolation and purification
– Activity loss when enzymes are immobilized
– Enzymes tend to be deactivated after a relatively short period of time
-In an enzymatic biosensor,
the enzyme is immobilized
as the “receptor”
-Enzymes are specific to
their substrates which can be
the analyte
Example: glucose sensors
Slide-60
Biosensor- 1.Enzymatic biosensors
Enzymatic Approach (Glucose Sensors)
•Makes use of catalytic (enzymatic) oxidation of
glucose.
•The setup contains an enzyme electrode and an
oxygen electrode and the difference in the readings
indicates the glucose level.
•The enzyme electrode has glucose oxidase
immobilized on a membrane or a gel matrix.
Figure :
(a) In the enzyme electrode, when glucose is
present it combines with O2, so less O2 arrives at
the cathode.
(b) In the dual-cathode enzyme electrode, one
electrode senses only O2, and the difference signal
measures glucose independent of O2 fluctuations.
(From S. J. Updike and G. P. Hicks, "The enzyme electrode, a
miniature chemical transducer using immobilized enzyme
activity," Nature, 1967, 214, 986-988. Used by permission.)
Slide-61
Biosensor- 1.Enzymatic biosensors
Affinity Approach -Glucose Sensors
This approach is based on the
immobilized competitive
binding of a particular
metabolite (glucose) and its
associated fluorescent label
with receptor sites specific to
the metabolite (glucose) and
the labeled ligand.
This change in light intensity is
then picked up.
Immobilized Con A
Slide-62
Biosensor-Enzymatic biosensors
Alternatively, the reaction product hydrogen peroxide can also be measured through
reduction of H2O2
Use a Clark-type electrochemical cell similar to the one for measuring O2, but at a
positive bias voltage of 0.65V
Problems:
1. The reduction/oxidation potentials are fairly high ⇒ other materials will interfere
2. The concentration of O2 needs to be kept constant, which is difficult since O2 is
involved in the reactions
Slide-63
Biosensor-Enzymatic biosensors
Electron mediators in enzymatic biosensors
In the membrane:
At the anode:
Oxygen is consumed and later regenerated, therefore it only serves to transfer electron ⇒
can be replaced by a mediator
Example: multi-cycle chemical electrochemical reaction chain for detecting glucose
Slide-64
Biosensor 2-Immunosensors
Immunosensors: based on highly specific antigen-antibody reactions
Antibody: works against the foreign body
Immunoglobin: globular proteins that participate in the immune response
Structure of antibody
The Fc end of an antibody can bind to other immune cells and the binding
activate these immune cells
Slide-65
Biosensor 2-Immunosensors
•Detection of the reaction (binding/association) can be either direct or
indirect (labeled)
Direct detection: the binding of the analyte (antigen) to the “receptor” (antibody)
is detected directly through the presence
of the analyte
However, most are indirect due to lack of signal
from the analyte itself
•Indirect detection: signal is provided by an
exogenous reporter
Slide-66
Biosensor 2-Immunosensors
Indirect detection
• Radioimmunoassay (RIA)
– The labels are radioactive isotopes (for example 131I)
– Highly sensitive and specific but inconvenient and expensive
– Less popular now due to safety issues
• ELISA (Enzyme-Linked Immunosorbent Assay)
– Enzymes are used for labeling and signal is provided by the reaction product
– Simple in terms of procedure and equipment
• Fluorescent immunoassay
– Labeled with fluorescent dyes
Slide-67
Biosensor 2-Immunosensors
Slide-68
Biosensor 3-SPR biosensors
•Direct detection – Surface plasmon resonance.
•A surface plasma wave (SPW) is an electromagnetic wave (due to charge density
oscillation) which propagates along the boundary between a dielectric (e.g. glass)
and a metal.
•A surface plasmon wave can be excited optically: when the propagation
constant β of the incident light and the SPW are equal in magnitude and direction
for the wavelength.
•This corresponds to a certain angle of incident light at a fixed wavelength ⇒ the
reflected light reaches its minimum.
•Binding induced change in propagation
constant of SPW is proportional to
the refractive index change in the
sample ⇒ the angle of incident light also
changes (fig.)
Slide-69
Biosensor 3-SPR biosensors
Different parameters are measured in SPR biosensors to indicate the refractive index change in
the sample (due to binding)
Character of SPR biosensors:
•Direct detection ⇒ no need for labeling
• High sensitivity
• Fast ⇒ real-time monitoring
• Used with sample in liquid ⇒ important for biological samples
• Relatively simple device, which makes multichannel parallel detection easier ⇒high throughput.
SPR commercialization - BIACORE
BIACORE optical system:
light from different angle of
reflection is imaged onto
different position of a
photo-detector array.
The corner-stones of Biacore technology
Slide-70
Biosensor 4- BIACORE biosensors
BIACORE features
• Specificity: different molecules interact with a single partner immobilized on a sensor surface
• Kinetics: rates of complex formation (ka) and dissociation (kb)
• Affinity: the level of binding at equilibrium (KD, KA)
• Concentration: can be determined for purified molecules or for molecules in complex
mixtures such as serum (needs a calibration curve)
• Multiple interactions during complex formation
Multiple flow-cells ⇒ simultaneous detection of reflection intensity
Slide-71
Biosensor - Fiber optic based biosensors
• Fiber optic based biosensors
Optical fibers are flexible and compact which are important features for applications that need
miniaturization such as in vivo measurements
Slide-72
Biosensor - Fiber optic based biosensors
• Optical fiber sensor – examples
• Sensing area along side of an optical fiber
• Sensing area located at distal end surface of an optical fiber
Slide-73
Biosensor - Fiber optic based biosensors
• Optical fiber sensor – examples
• A fiber optic (imaging) bundle is used for detecting multiple analytes simultaneously
- Each latex sphere can specifically binds to one analyte
- The analytes can be fluorescently labeled
- Use of reference channels could increase the reliability of detection (e.g. spheres without
recognition element still bind to some analyte molecules non-specifically, so the measured
fluorescence from the reference spheres is considered “background” and should be subtracted)
Slide-74
Biosensor - Chemical sensors based biosensors
Chemical Sensors (Biosensors)
Biosensors produce an output
(electrical) which is proportional
to the concentration of biological
analyses.
Biosensing Principles
• Electrochemical
– Potentiometric
– Amperometric
– FET based
– Conductometric
• Optical
• Piezoelectric
• Thermal
Slide-75
Biosensor - Chemical sensors based biosensors
Electrochemical Sensors
Potentiometric : These involve the measurement of the emf (potential) of a cell at
zero current. The emf is proportional to the logarithm of the concentration of the
substance being determined.
Amperometric : An increasing (decreasing) potential is applied to the cell until
oxidation (reduction) of the substance to be analyzed occurs and there is a sharp
rise (fall) in the current to give a peak current. The height of the peak current is
directly proportional to the concentration of the electroactive material. If the
appropriate oxidation (reduction) potential is known, one may step the potential
directly to that value and observe the current.
Conductometric. Most reactions involve a change in the composition of the
solution. This will normally result in a change in the electrical conductivity of the
solution, which can be measured electrically.
Slide-76
Optical biomedical sensors-Fiber Optics
1-Fiber Optics or Optical fiber
Typically made of glass SiO2, and consisting of a core and a cladding layer. Transmits light
through the core (total internal reflection).
•Diameter can be very small ~μm ⇒ very flexible. The angle of light rays that go into the fiber
core and can be accepted (transmitted) by the fiber is dependent on the core and cladding
materials.
•Incident angle of light rays going
into a fiber must be less than θ
Sensing Principle
They link changes in light intensity to changes in mass or
concentration, hence, fluorescent or colorimetric molecules
must be present.
Various principles and methods are used :
•Optical fibres, surface
•Plasmon resonance,
•Absorbance,
•Luminescence
Slide-77
Optical biomedical sensors-Fiber Optics
1-Fiber Optics or Optical fiber
A fiber optic cable
Most of the light is trapped in the core, but if the
cladding is temperature sensitive (e.g. due to
expansion), it might allow some light to leak through.
-> hence the amount of light transmitted
would be proportional to temperature
-> since you are measuring small changes in light
level, this sensor is exquisitely sensitive
Slide-78
Optical biomedical sensors-Fiber Optics
1-Fiber Optics
• Geometrical optics
– The f number of lens is the ratio of the focal length to diameter.
• Fiber optics
– Fiber optics are an efficient way of transmitting radiation.
It is based on Snell’s law:
– Critical angle for reflection:
Figure - Fiber optics. The solid line shows refraction of rays that escape through the
wall of the fiber. The dashed line shows total internal reflection within a fiber.
Slide-79
Optical biomedical sensors-Fiber Optics
1-Fiber Optics
Geometrical and Fiber Optics
• Fiber optics
– 50 cm glass fiber: transmission > 60% for wavelength between 400 and 1200 nm.
– 50 cm plastic fiber: transmission > 70% for wavelength between 500 and 850 nm.
– Most applications use flexible bundles of about 400 fibers.
– Noncoherent bundles (light guide) and Coherent bundles
• Liquid Crystals
– For an application of voltage, liquid crystals may change their passive scattering or
absorption of light.
– Low power consumption
• Filters of FO
– Filters are frequently inserted in the optical system to control the distribution of radiant
power or wavelength.
– Reflection filters or absorption filters
– Interference filters
– Diffraction gratings
80
Optical biomedical sensors-Fiber Optics
1-1.A reversible fiber-optic chemical sensor
Figure - A reversible fiber-optic chemical sensor measures light scattered from phenol
red indicator dye to yield pH
[From J. I. Peterson, "Optical sensors," in J. G. Webster (ed.), Encyclopedia of Medical Devices and
Instrumentation. New York: Wiley, 1988, pp. 2121-2133. Used by permission.]
Slide-81
Optical biomedical sensors-Fiber Optics
2-1.A single fiber intravascular blood-gas sensor
Figure - A single fiber intravascular blood-gas sensor excites fluorescent dye at one wavelength and detects emission at a
different wavelength. The following modifications are made to the sensor tip:
pH: Chemistry – pH-sensitive dye bound to hydrophilic matrix.
PCO2: Chemistry – bicarbonate buffer containing pH-sensitive dye with silicone.
PO2: Chemistry – Oxygen-sensitive dye in silicone.
(From J. L Gehrich, D.W. Lübbers, N. Optoz, D. R. Hansmann. W. W. Miler, J. K. Tusa, and M. Yafuso, "Optical
fluorescence and its application to an intravascular blood gas monitoring system," IEEE Trans. Biomed. Eng., 1986, BME33, 117-132. Used by permission.)
Slide-82
Optical biomedical sensors-Fiber Optics
3-1.A fiber-optic oxygen sensor
Figure - In a fiber-optic oxygen sensor, irradiation of dyes causes fluorescence that
decreases with Po2.
[From R. Kocache, "Oxygen analyzers," in J. G. Webster (ed.), Encyclopedia of Medical
Devices and Instrumentation. New York: Wiley, 1988, pp. 2154-2161. Used by permission.]
Slide-83
Optical biomedical sensors-Fiber Optics
4-1.An intravascular blood-gas probe measures pH, PCo2, and Po2
Figure - An intravascular blood-gas probe measures pH, PCo2, and Po2 by means of
single fiber-optic fluorescent sensors.
(From J. L. Gehrich, D. W. Lübbers, N. Opitz, D. R. Hansmann, W. W. Miler, J. K. Tusa, and M.
Yafuso, "Optical fluorescence and its application to an intravascular blood gas monitoring system,"
IEEE Trans. Biomed. Eng., 1986, BME-33, 117-132. Used by permission.)
Slide-84
Optical biomedical sensors-Fiber Optics
5-1.The affinity sensor
Figure - The affinity sensor measures glucose concentration by detecting changes in
fluorescent light intensity caused by competitive binding of a fluorescein-labeled
indicator.
(From J. S. Schultz, S. Manouri, et al., "Affinity sensor: A new technique for developing Implantable
sensors for glucose and other metabolites," Diabetes Care, 1982, 5, 245-253. Used by permission) Slide-85
Optical biomedical sensors-Fiber Optics
5-1.The affinity sensor The optical system for a glucose
Figure - The optical system for a glucose
affinity sensor uses an argon laser and a fiberoptic catheter.
Slide-86
Optical biomedical sensors-Radiation Sources
2-Radiation Sources
1-2.Tungsten lamps
– Incandescent tungsten-wire filament lamps are the most
commonly used sources for radiation.
– Their output varies with temperature and wavelength, as
given by
where C1 = 3.74 x 104 (W.μm4/cm2), C2 = 1.44 x 104 (μm4/K),
T = blackbody temperature )K(, and ε = emissivity, the extent by which a surface deviates from a
blackbody )ε = 1)
-Coiled filaments to increase emissivity and efficiency.
- Ribbon filaments for uniform radiation
- Tungsten-halogen lamps have iodine or bromine to maintain more than 90% of
their initial radiant.
Slide-87
Optical biomedical sensors-Radiation Sources
2- 2.Arc discharges
-– Low-pressure lamp: Fluorescent lamp filled with Argon-Mercury (Ar-Hg) mixture.
Accelerated electron hit the mercury atom and cause the radiation of 250 nm (5 eV) wavelength
which is absorbed by phosphor. Phosphor will emits light of longer visible wavelengths.
- Fluorescent lamp has low radiant so it is not used for optical instrument, but can be turned on
in 20 sec and used for tachistoscope to provide brief stimuli to the eye.
- High pressure lamp: mercury, sodium, xenon lamps are compact and can provide high
radiation per unit area. Used in optical instruments.
3-2.Light-Emitting Diodes (LEDs)
A p-n junction devices that are optimized to radiant output.
-GaAs has a higher band gap and radiate at 900 nm. Switching time 10 nsec.
-GaP LED has a band gap of 2.26 eV and radiate at 700 nm
-GaAsP absorb two photons of 940 nm wavelength and emits one photon of 540 nm
wavelength.
Advantages of LED: compact, rugged, economical, and nearly monochromatic.
Slide-88
Optical biomedical sensors-Radiation Sources
4-2. LASERS
– Laser (Light Amplification by Stimulated Emission of Radiation)
– Laser output is highly monochromatic, collimated, and phase-coherent.
– Solid-state laser (ruby laser (693 nm, 1 mJ), Nd:
YAG laser (1064 nm, 2 W/mm), He-Ne laser (633 nm, -100 mW), CO2 laser (50 -500 W)
-He-Ne lasers operate at 633 nm with 100 mW power.
-Argon laser operates at 515 nm with the highest continuous power level with 1-15 W power.
-CO2 lasers provide 50-500 W of continuous wave output power.
-Ruby laser is a solid state lasers operate in pulsed mode and provide 693 nm with 1-mJ
energy.
The most medical use of the laser is to mend tear in the retina.
Figure - Spectral
characteristics of
sources, (a)
Monochromatic outputs
from common lasers are
shown by dashed lines:
Ar, 515 nm; HeNe, 633
nm; ruby, 693 nm; Nd,
1064 nm
Slide-89
Optical biomedical sensors-Radiation Sensors
Radiation Sensors
Classifications of Radiation Sensors
1-Thermal sensors
Thermal Sensors: absorbs radiation and change the temperature of the sensor.
-Change in output could be due to change in the ambient temperature or source temperature.
-Sensitivity does not change with wavelength
-Slow response
– This type of sensor absorbs radiation and transforms it into heat, thus causing a rise in
temperature in the sensors.
– Thermistors and thermocouple
– Pyroelectric sensor absorbs radiation and converts into heat, thus resulting rise in temperature
that changes the polarization of the crystals.
A current may be produced in proportional to the rate of change of temperature.
Example: Pyroelectric sensor: absorbs radiation and convert it to heat which change the electric
polarization of the crystals
Slide-90
Optical biomedical sensors-Radiation Sensors
Radiation Sensors
Classifications of Radiation Sensors
2-Quantum sensors
Quantum Sensors: absorb energy from individual photons and use it to release electrons
from the sensor material.
– It absorbs energy from individual photons and use it to release electrons from the sensor
material.
-sensitive over a restricted band of wavelength
-Fast response
-Less sensitive to ambient temperature
Example: Eye, Phototube, photodiode, and photographic emulsion.
– Photoemissive sensors, Photoconductive cells, Photojunction sensors, Photovoltaic sensors
Slide-91
Optical biomedical sensors-Radiation Sensors
Radiation Sensors
3-Radiation Thermometry
The higher the temperature of a body the higher is the electromagnetic radiation (EM).
Electromagnetic Radiation Transducers - Convert energy in the form of EM radiation
into an electrical current or potential, or modify an electrical current or potential.
Medical thermometry maps the surface temperature of a body with a sensitivity of a few
tenths of a Kelvin.
Application
•Breast cancer, determining location and extent of arthritic disturbances, measure the depth
of tissue destruction from frostbite and burns, detecting various peripheral circulatory
disorders (venous thrombosis, carotid artery occlusions)
•Measuring the core body temperature of the human by measuring the magnitude of infrared
radiation emitted from the tympanic membrane and surrounding ear canal.
Response time is 0.1 second
Accuracy of 0.1 oC
Slide-92
Optical biomedical sensors-Radiation Sensors
3-Radiation Thermometry
Radiation Thermometer System
Figure - Stationary chopped-beam radiation thermometer
(From Transducers for Biomedical Measurements: Principles and Applications, by R. S. C.
Cobbold. Copyright © 1974, John Wiley and Sons, Inc. Reprinted by permission of John Wiley
and sons. Inc.)
Slide-93
Optical biomedical sensors-Radiation Sensors
3-Radiation Thermometry
Radiation Thermometer System
Sources of EM radiation: Acceleration of charges can arise from thermal energy. Charges
movement cause the radiation of EM waves.
The amount of energy in a photon is inversely related to the wavelength:
E
1

1 eV  1.602 10
19
J
Thermal sources approximate ideal blackbody radiators:
Blackbody radiator: an object which absorbs all incident radiation, and emits the
maximum possible thermal radiation (0.7 m to 1mm).
Slide-94
Optical biomedical sensors-Radiation Sensors
Anther radiation sensors 1-Photoemissive Sensors
a).Phototube: have photocathode coated with alkali metals. A radiation photon with energy
cause electron to jump from cathode to anode. Photon energies below 1 eV are not large enough
to overcome the work functions, so wavelength over 1200nm cannot be detected.
b).Photomultiplier An incoming photon strikes the photocathode and liberates an electron.
This electron is accelerated toward the first dynode, which is 100 V more positive than the
cathode. The impact liberates several electrons by secondary emission. They are accelerated
toward the second dynode, which is 100 V more positive than the first dynode, This electron
multiplication continues until it reaches the anode, where currents of about 1 A flow through
RL. Time response < 10 nsec
Slide-95
‫‪Optical biomedical sensors-Radiation Sensors‬‬
‫‪Anther radiation sensors 1–Photoemissive Sensors‬‬
‫المضاعفات الضوئية ‪:‬‬
‫يتألف من أنبوب مفرغ من اهلواء و حتتوي على جمموعة مصاعد )‪ (14‬و‬
‫مهبط مطلي مبادة حساسة للضوء حيث أهنا تصدر إلكرتوانت عندما‬
‫تسقط عليها فوتوانت الضوء‪ .‬إن فرق ألكامن بني املصعد األول و املهبط‬
‫( ‪ ) 100 v‬و نفسه بني املصعد الثاين و األول ‪.‬‬
‫اإللكرتوانت الصادرة عن املهبط تستقبل من املصعد األول و ابصطدامها‬
‫به فإهنا حترر املزيد من اإللكرتوانت اليت تستقبل ابملصعد التايل و تتكرر‬
‫العملية على عدد املصاعد فتنتج إشارة تتناسب مع الضوء اهلابط على‬
‫املهبط تتميز بتخطيتها و حساسيتها العالية للضوء لذلك جيب أن توضع‬
‫يف ظالم دامس‪.‬‬
‫‪Slide-96‬‬
Optical biomedical sensors-Radiation Sensors
Anther radiation sensors 2- Photoconductive Cells
Photoresistors: a photosensitive crystalline materials such as cadmium
Sulfide (CdS) or lead sulfide (PbS) is deposited on a ceramic
substance.
The resistance decrease of the ceramic material with input radiation.
This is true if photons have enough energy to cause electron to move
from the valence band to the conduction band.
Slide-97
Optical biomedical sensors-Radiation Sensors
Anther radiation sensors- 3. Photojunction Sensors
Photojunction sensors are formed from p-n junctions and are usually made of silicon.
If a photon has enough energy to jump the band gap, hole-electron pairs are produced that
modify the junction characteristics.
Photodiode: With reverse biasing, the reverse
photocurrent increases linearly with an increase in
radiation.
Phototransistor: radiation generate base current which
result in the generation of a large current flow from
collector to emitter.
Response time = 10 microsecond
Figure -Voltage-current characteristics of irradiated silicon p-n junction.
For 0 irradiance, both forward and reverse characteristics are normal. For 1 mW/cm2, open-circuit voltage
is 500 mV and short-circuit current is 8 A.
Slide-98
Optical biomedical sensors-Radiation Sensors
Anther radiation sensors - 4. Photovoltaic Sensors
Photovoltaic sensors is a p-n junction where the voltage increases as the radiation increases.
Figure - Spectral characteristics of detectors,
Detectors. The S4 response is a typical phototube response. The eye has a relatively narrow
response, with colors indicated by VBGYOR. CdS plus a filter has a response that closely
matches that of the eye. Si p-n junctions are widely used. PbS is a sensitive infrared detector.
InSb is useful in far infrared.
Note: These are only relative responses. Peak responses of different detectors differ by 107.
Slide-99
Pressure Sensors - Silicon Pressure Sensors
Silicon Pressure Sensors
• Pressure sensors contain sensing elements that consist of four piezoresistors
buried in the face of a thin, chemically-etched silicon diaphragm.
•A pressure change causes the diaphragm to flex, inducing a stress or strain in the
diaphragm and the buried resistors. The resistor values change in proportion to the
stress applied and produce an electrical output.
Slide-100
Pressure Sensors - Silicon Pressure Sensors
Silicon pressure sensors best used for (Applications ):
1- Medical equipment: respiration, dialysis, infusion pump; data storage, and gas
chromatography equipment; process controls; industrial machinery; pumps; robotics; and offroad applications.
• Costs for extremely accurate sensors can be as low a $50.
• Pressure sensors are used in almost every industry and is widely used
2-Eye Pressure Testing
• Called an oculocerebrovasculometer the eye pressure sensor measures the blood pressure in
your eye to check to see if you have a glaucoma or stroke.
• The procedure is non-invasive and is quick and painless. The technician uses a pen sized
device with the measuring disk on the end and places it against your eyeball.
3- Pressure Monitoring System
• Using the 140 PC pressure sensor an intercranial pressure
monitoring system was designed where a probe is inserted
into the patients skull and a portable pneumatic system
monitors the changes of the system. Air enters and leaves
the probe at a constant rate.
•Any changes in the system caused by leaks or other
obstructions will set off an alarm so the problem can be
Slide-101
addressed.
The following pressure sensors can be found at ww.honeywell.com
Pressure Sensors - Ultra Low Pressure Sensing
• The Ultra Low Pressure Sensing sensor from Honeywell is one of the most precise pressure
sensing elements on the market.
• The ULPS has the ability to dynamically adjust to changes in temperature thereby reducing
the error in the measurements
• The typical applications of the ULPS are used in medical instrumentation, environmental
controls, and portable monitors.
Slide-102
Pressure Sensors - Capacitive Pressure Sensors
Capacitive pressure sensors are made using thin metallic silicon wafers that are spaced
apart and when pressure is applied to the sensor the capacitance changes in the sensor
thereby allowing the measurement of change in pressure.
Capacitive pressure sensors are inherently non-linear, but extensive FEA analysis has
improved the linearity of these types of sensors.
Slide-103
Pressure Sensors - Capacitive Pressure Sensors
Applications
The medical industry has a wide variety of
uses for pressure sensors. The fact that they
are used in the medical industry, drives the
manufacturers to design more robust and
smaller pressure sensors.
Smaller design of the pressure sensors
allows them to be implanted into patients
without the annoyance of noticing that
something is there, such as on your arm or
wrist. These implanted pressure sensors are
a factor in preserving lives.
These data can be found at www.mems-issys.com
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Pressure Sensors - Other Pressure Sensors
Although almost all pressure sensors now used in industry are electronic, mechanical
pressure sensors still exist. The bourdon tube for example is still used in many analog
pressure gages and are extremely cheap and easy to make. Shown below is how the
bourdon tube pressure sensor works.
(e-funda.com)
Slide-105
Pressure Sensors - Other Pressure Sensors
Medical Pressure
Measurement Systems
• Blood pressure : arterial BP, CVP,intracardiac BP, PAP, spinal fluid pressure,
intraventricular brain pressure
• Flow measurement : venturi tube, orifice
• Different range of measurements
• Need to be least invasive, sterile, electrical isolation from ac power mains
Units of Pressure
Slide-106
Pressure Sensors - Other Pressure Sensors
Types of Pressure Sensors
Slide-107
References
• Medical Instrumentation: Application and Design, edited by John G. Webster
• Chemical sensors and biosensors, by Brian R. Eggins
• Sensors in Biomedical Applications: Fundamentals, Technology & Applications,
by Gábor Harsányi – Ch7: Biosensors
• Information about glucose meters
http://www.diabetesmonitor.com/meters.htm#fcnim
• Biomolecular sensors, edited by Electra Gizeli & Christopher R. Lowe
Slide-108