Transcript Micro-sensing Modalities in Sensors

Micro-sensing Modalities
Hongtao Du
August 31, 2004
Introduction
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Sensor
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Devices that transform (or transduce) physical
quantities such as sound, pressure or acceleration
(called measurands) into output signals (usually
electrical) that serve as inputs for control systems [1].
Sensors must satisfy a difficult balance between
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Accuracy
Robustness
Manufacturability
Low cost
Small size
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Sensor Network
Smart Sensor Web (SSW)
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SSW exploits the information from commercial
products distributed throughout an area (local TV
cameras and other commercial devices already
transmitting over commercial airwaves and the
Internet), and seed the battlefield by rapidly
deploying military sensors via air drops, robotic
vehicles, pre-positioned assets, soldier
platforms,UAVs, or overhead surveillance [2].
Micro-sensor Node
Sensors can be classified by …
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Working principle
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Electro-magnetic: acoustic sensor, seismic sensor
Conductivity: CCD, temperature sensor
Chemical reaction: biosensor
Application
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Automotive sensors
Powertrain
 Chassis
 Body
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Working Principles of Microphones
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Microphones are used to detect acoustic signals
and produce a voltage or a current proportional to
the sound.
Source
Compression waves (330m/sec)
Microphones
Dynamic
Ribbon
Crystal
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Condenser
Crystal microphone: based on piezoelectric effect of crystal
Condenser microphone: a capacitor with two plates
Directional Patterns
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Omni-directional:
sensitive in all directions
Bi-directional: front and
rear, 90 each
Cardioid: the specific
direction it points to
Acoustic Sensing Phenomenology
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Reflection
Law of reflection: the
angle of incidence
equals the angle of
reflection.
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Refraction
The bending of waves when
they enter a medium where
their speed is different.
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Scattering
Sound waves are scattered
into all directions when they
reach an obstacle.
Doppler Effect
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When the source or the receiver is moving relatively
to each other, the frequency of a wave observed at a
receiver changes.
  vT
f'
v
'
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v
f source
v  vs
f"
v
"

v
f source
v  vs
Example
Microphone used in WINS NG 2.0
sensor platform from Sensoria Co.
1-second sample
Power Spectral Density (PSD)
Geophone /Accelerometer
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Geophone
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Electro-magnetic
Low frequency:
< 100Hz
Accelerometer
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Piezoelectric effect
High frequency
> 100Hz
Structure of geophone
Seismic Waves
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Body wave: travels the earth’s inner layers at a
higher speed and propagates in three dimensions
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Compression (P) waves
Shear (S) waves
Surface wave: moves along the surface of the
ground and propagates in two dimensions
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Surface waves propagate slower than body waves
Love waves
Reyleigh waves
Seismic Sensing Phenomenology
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A: reflection
B: direct path
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C: P-S wave conversion
D: refraction
Example
Geophone examples
1-second sample
Power Spectral Density (PSD)
Magnetic Sensing
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Only detect presence, strength, direction of
magnetic fields
Ferrous object (vehicle, airplane) disturbance in
uniform field
Very useful in navigation control system
Pressure Sensor
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Principle: Piezoelectric effect
Fabrication process
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Batch fabricated and a thousand or more per wafer
Piezoresistive strain-sense elements are implanted in
appropriate areas of an etched silicon diaphragm
The stain-sense elements are electrically connected
into internal circuit, thereby providing a means of
detecting pressure acting on the diaphragm.
Infra-red Sensing
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Infra-red radiation is an electromagnetic wave.
Used in field security, alarm system, remote
control, etc.
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Infra-red motion detectors
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Passive infra-red (PIR)
Active infra-red (AIR)
PIR
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A lens allows the sensor to divide the field of
view into several zones.
For the best performance, the target should move
across the two sensing elements within the sensor
coverage.
Example
PIRs from Visionic Ltd.
AIR
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Two units
 Infra-red photodiode and Infra-red sensitive
phototransistor
 Infra-red reflector
Optical Sensing
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Principle: conductivity
Charge-Coupled Detector
(CCD) Cell
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Electron-Hole Pair (EHP)
Other Sensors
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Thermal sensor
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MicroFLIR
Weight: 70g, volume:12 cubic inches, power:
540 milliwatts.
Sponsored by US Army Night Vision and
Electronics Directorate (NVESD)
Temperature Sensor
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Silicon
Single-Crystal silicon
 Restriction of 150 C
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Important Technology in Sensor Developments
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Micro, Electro-Mechanical Systems (MEMS)
and Micro,Electro-Optical-Mechanical
Systems (MEOMS).
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Economy of batch processing
Miniaturization
Integration of on-chip electronic intelligence
Tendency
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System-on-chip: Integration sensing unit
and processing unit
Low voltage analog/digital circuits
– save power by square
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Sensor die size is shrinking, wafer
diameters is increasing.
– both help to lower the cost of sensor manufacture
Reference
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Norton, H., “Transducer fundamentals”, in Handbook of Transducers,
Englewood Cliffs, NJ:Prentice Hall, 1989.
Paul, J.L., “Smart Sensor Web: Web-based exploitation of sensor
fusion for visualization of the tactical battlefield”, IEEE Aerospace
and Electronic Systems Magazine, Vol.16, No.5, pp.29 - 36, May
2001.
Thank you! 
Questions?