Biomedical brain

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BBM322- Biomedical instrumentation II
Chapter 3 Flow and Temperature Sensors
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BBM322- Biomedical instrumentation II
Chapter 3 Flow and Temperature Sensors

• Outline
• Flow sensor
• 1.1. Air flow-spirometer
• 1.2. Blood flow the motion of a fluid
• Blood flowmeters
• 2. Temperature Sensor
• Resistance based on
• a. Resistance Temperature Devices (RTDs)
• b. Thermistors
• 2. Thermoelectric Thermocouples
• 3. Solid State PN Junctions
• 4- Other Temperature Sensors- Fiber Optic,
  Digital Thermal Sensor
• 3. The modern type sensor

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1. Flow Sensors

• Flow the motion of a fluid
• (1) Blood flowmeters
• - ultrasonic (Doppler, transit time)
• - electromagnetic
• (2) Gas flowmeters
• - pneumotachometer
• - spirometer
• - 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
  flow rate

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1. Flow Sensors

• 1.1. Air flow
• Spirometer measure the volumes of gases
  breathed
• in or out.
• Types of spirometer ?
• A. volume-displacement spirometers
• Conventional spirometers provide a direct measure
  
• of respired volume ?from the ?
• Displacement of a bell (water sealed)
• Bellows (wedge bellows)?
• Piston (rolling sealed)?
• Generally, volume spirometers are simple to use,
• accurate, reliable, and ?easy to maintain and
  provide
• a clear and permanent record of the test.
• ?They are, however, less portable than flow
  spirometers ?

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1. Flow Sensors

• Types of spirometer continue
• B. flow-sensing spirometers
• Flow spirometers generally utilize a sensor that
  measures flow as the ?primary signal and
  calculate volumes by electronic (analog) or
  ?numerical (digital) integration of the flow
  signal.
• The most commonly use flow sensors detect and
  measure flow from the ?pressure drop a cross a
  resistance (e.g. Fleisch-pneumotach), cooling of
  ?a heated wire (Hot-wire anemometer), or by
  electronically counting the ?rotation of a
  turbine blade.?
• Fleish pneumotachometer
• The measuring process-by Fleisch-pneumotach
• 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 mesh obstruction provides some resistance to
  the air flow and therefore generates pressure
  drop across the mesh.

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1. Flow Sensors

• Fleish pneumotachometer continue.
• The measuring process-by Fleisch-pneumotach
• The resulting pressure drop across the mesh is in
  proportion to the flow rate.
• The pressure drop is very small (e.g. 2mmHg) and
  so the measuring circuit must be of high quality
  and produce very little drift with time.
• The resistance to flow presented by the screen
  produces a differential pressure which is
  proportional to the airflow through the device.

Flow rate ? ?P Pressure is measured at both sides
of the resistive screen
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1. Flow Sensors

• Spirometer continue..
• Spirometers can be used to measure several
  parameters
• FVC (Forced Vital Capacity)
• The volume of air that can be exhaled after full
• inspiration.
• FEV1 (Forced Expiratory Volume in 1s)
• The maximum volume of air that can be forcibly
• exhaled in the first second during an FVC.
• PEF (Peak Expiratory Flow)
• The maximum flow (or speed) achieved
• during the maximally forced expiration
• initiated at full inspiration.
• Additional parameters such as tidal volume,
  inspiratory reserve volume and total lung
  capacity.

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1. Flow Sensors
Spirometer block diagram of a desktop spirometer.
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• Flow Sensors
• 1.2. Blood flow

• 1.2.1. 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 400Hz) 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)
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1. Flow Sensors
Apply a uniform magnetic field B across blood
vessel If velocity of blood flow is ?, 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
1.2.1. Electromagnetic Blood Flowmeter Blood flow
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1. Flow Sensors
1.2.2.Ultrasonic Blood Flowmeter

• Transit time methods in which the blood velocity
  is calculated from the time taken to cross the
  vessel oblique to the direction of flow.
• 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.

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1. Flow Sensors
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2.The second type -Temperature transducer
(Temperature Sensors )
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2. Temperature Sensors
Temperature Sensor Options- 3 Common Types 1.
Resistance based on a. Resistance Temperature
Devices (RTDs) b. Thermistors 2. Thermoelectric
Thermocouples 3. Solid State PN Junctions Other
Temperature Sensors- Fiber Optic, Digital Thermal
Sensor

• 2.1. Resistance based on
• a) RTDs
• RTDs are made of materials whose resistance
  changes in accordance with temperature .
• Metals such as platinum, nickel and copper are
  commonly used.
• positive temperature coefficients
• .

A commercial Thermo Works RTD probe
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2. Temperature Sensors

• 2.1. Resistance based on
• b).Thermistors (thermally sensitive
  resistor) semiconductor the resistance is a
  function of temperature, where
• Negative Temperature Coefficient (NTC) device
  will decrease its resistance with an increase in
  temperature, most commonly used.
• Thermistors are made from semiconductor material,
  not metals.
• often composite of a ceramic and a metallic oxide
  (Mn, Co, Cu or Fe)
• RT is the resistance at temperature T,
• where
• R0 is the resistance at a reference
  temperature,
• T0 the reference temperature,.
• ß is a material-specific constant.
• Both temperatures are expressed in
  degrees K

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2. Temperature Sensors
2.1. Resistance based on b).Thermistors Most
thermistors have nonlinear curve when plotted
over a wide range but can assume linearity if
within a limited range
Thermistors characteristics - have high
sensitivity (ltlt1C) - range is not as great as
thermocouples (-50C 100C), but, suitable for
biological/physiological measurements - need
calibration (R vs. temperature curve) - can also
be made very small
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2. Temperature Sensors

• 2.2. Thermoelectric Thermocouples
• two different metal wires welded together, where
  2 dissimilar conductor joined together at 1 end.
  
• The work functions of the 2 materials are
  different, thus a potential is generated when
  junction is heated (roughly linear over wide
  range)
• based on the Seebeck effect(1821)
• - Dissimilar metals at diff. temps. ?
  signal
• 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
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2. Temperature Sensors
2.2. Thermoelectric Thermocouples
A thermocouple measuring circuit with a heat
source, cold junction and a measuring instrument
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2.3. Solid State PN Temperature Transducers. BJT
Bipolar Junction Transistor
2. Temperature Sensors

• Transistor invented in 1947 by Bardeen,
  Brattain and Schockley of Bell Labs.
• Transistor rely on the free travel of electrons
  through crystalline solids called semiconductors.
  
• Transistors usually are configured as an
  amplifier or a switch.

B Base C Collector E Emitter IE I B
I C
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2.3. Solid State PN Temperature Transducers. BJT
Bipolar Junction Transistor
2. Temperature Sensors

• Solid State PN Junction Diode the base emitter
  voltage of a transistor is proportional to
  temperature.
• For a differential pair the output voltage is

K Boltzmans Constant 1.38 x10-23J/K T
Temperature in Kelvin IC1 Collector current of
BJT 1 mA IC2 Collector current of BJT 2 mA q
Coulombs charge 1.6 x10 -19 coulombs/electron
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Example of temperature transducer
2. Temperature Sensors
2.3. Solid State PN Temperature Transducers

• Find the output voltage of a temperature
  transducer in the previous slide if IC1 2mA
• IC2 1mA and the temperature is 37 oC

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2. Temperature Sensors
Other Temperature Sensors- Fiber Optic

• 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.
• Sensor operation
• small prism-shaped sample of single-crystal GaAs
  attached to ends of two optical fibers
• light energy absorbed by the GaAs crystal depends
  on temperature
• percentage of received vs. transmitted energy is
  a function of temperature
• Can be made small enough for biological
  implantation

Figure - Details of the fiber/sensor arrangement
for the GaAs semiconductor temperature probe.
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Thermal Sensor
2. Temperature Sensors
Other Temperature Sensors- Digital Thermal Sensor
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Review

1. What are two types of sensors?
2. List 5 categories of error
3. How do we quantify sensors?
4. What is an electrode?
5. What is a transducer?
6. What is a Wheatstone Bridge? How do you derive
   the output voltage
7. Find resistance of a metallic bar for a given
   length and area
8. How does resistance change in tension and in
   compression and how do you calculate resistance

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Review

1. How do you find resistance change in
   piezoresistive device?
2. How do you determine gauge factor?
3. What is the definition of a strain gauge and what
   is difference between bonded and unbonded strain
   gauge?
4. Determine the output potential given a
   transducers sensitivity.
5. What are inductance, capacitance, and temperature
   transducers?
6. How do you calculate the temperature for a solid
   state PN Junction Diode?

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3.The modern type sensor Touch Screen

1. Resistive touchscreen
2. Capacitive touchscreen
3. Infrared touchscreen
4. Surface acoustic wave (SAW) touchscreen
5. Strain gauge touchscreen
6. Optical imaging touchscreen
7. Dispersive signal technology touchscreen

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Resistive touchscreen
3.The modern type sensor Touch Screen

• Structure
• Resistive touch screens consist of a glass or
  acrylic panel that is coated with electrically
  conductive and resistive layers made with indium
  tin oxide (ITO). The thin layers are separated by
  invisible spacers.

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wire resistive touchscreen
3.The modern type sensor Touch Screen
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3.The modern type sensor Touch Screen
Touch Screen
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Capacitive touchscreen (projected)
3.The modern type sensor Touch Screen
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Capacitive touchscreen
3.The modern type sensor Touch Screen
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Touch Screen
3.The modern type sensor Touch Screen
Capacitive Available for multi touch Not
pressure sensitive, only available with
fingers Less accurate
Resistive pressure sensitive, available with
fingers, pens, and so on. More accurate Hard to
support multitouch, such as zoom in and zoom out
in your iphone and ipad
Resistive Capacitive Galaxy Note 7-inch HTC
Flyer
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• References
• John G. Webster, Medical Instrumentation
  Application and Design
• Brian R. Eggins, Chemical sensors and biosensors.
• Gábor Harsányi , Sensors in Biomedical
  Applications Fundamentals, Technology
  Applications.
• http//www.diabetesmonitor.com/meters.htmfcnim
• Electra Gizeli Christopher R. Lowe,
  Biomolecular sensors, edited by
• James A. Smith, Biomedical Sensors,
• Joseph Carr and John Brown, Introduction to
  Biomedical Equipment Technology ,Chapter 6