micro-sensing modalities
DESCRIPTION
Micro-sensing Modalities. Hongtao Du August 31, 2004. Introduction. Sensor 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]. - PowerPoint PPT PresentationTRANSCRIPT
Micro-sensing Modalities
Hongtao Du
August 31, 2004
Introduction Sensor
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 Accuracy Robustness Manufacturability Low cost Small size
Sensor Network Smart Sensor Web (SSW)
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 … Working principle
Electro-magnetic: acoustic sensor, seismic sensor
Conductivity: CCD, temperature sensor
Chemical reaction: biosensor
Application Automotive sensors
Powertrain Chassis Body
Working Principles of Microphones 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 microphone: based on piezoelectric effect of crystal Condenser microphone: a capacitor with two plates
Crystal Condenser
Directional Patterns Omni-directional:
sensitive in all directions Bi-directional: front and
rear, 90 each Cardioid: the specific
direction it points to
Acoustic Sensing Phenomenology
Scattering
Sound waves are scattered into all directions when they reach an obstacle.
Reflection Law of reflection: the
angle of incidence equals the angle of reflection.
Refraction The bending of waves when
they enter a medium where their speed is different.
Doppler Effect When the source or the receiver is moving relatively
to each other, the frequency of a wave observed at a receiver changes.
sources
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Example
Microphone used in WINS NG 2.0
sensor platform from Sensoria Co.
1-second sample Power Spectral Density (PSD)
Geophone /Accelerometer
Structure of geophone
Geophone Electro-magnetic Low frequency:
< 100Hz
Accelerometer Piezoelectric effect High frequency
> 100Hz
Seismic Waves Body wave: travels the earth’s inner layers at a
higher speed and propagates in three dimensions Compression (P) waves Shear (S) waves
Surface wave: moves along the surface of the ground and propagates in two dimensions Surface waves propagate slower than body waves Love waves Reyleigh waves
Seismic Sensing Phenomenology
A: reflection B: direct path
C: P-S wave conversion D: refraction
Example
Geophone examples
1-second sample Power Spectral Density (PSD)
Magnetic Sensing Only detect presence, strength, direction of
magnetic fields Ferrous object (vehicle, airplane) disturbance in
uniform field Very useful in navigation control system
Pressure Sensor Principle: Piezoelectric effect Fabrication process
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 Infra-red radiation is an electromagnetic wave. Used in field security, alarm system, remote
control, etc. Infra-red motion detectors
Passive infra-red (PIR) Active infra-red (AIR)
PIR 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 Two units
Infra-red photodiode and Infra-red sensitive phototransistor
Infra-red reflector
Optical Sensing
Principle: conductivity Charge-Coupled Detector
(CCD) Cell Electron-Hole Pair (EHP)
Other Sensors
Thermal sensor MicroFLIR Weight: 70g, volume:12 cubic inches, power:
540 milliwatts. Sponsored by US Army Night Vision and
Electronics Directorate (NVESD)
Temperature Sensor Silicon
Single-Crystal silicon Restriction of 150 C
Important Technology in Sensor Developments
Micro, Electro-Mechanical Systems (MEMS) and Micro,Electro-Optical-Mechanical Systems (MEOMS). Economy of batch processing Miniaturization Integration of on-chip electronic intelligence
Tendency System-on-chip: Integration sensing unit
and processing unit Low voltage analog/digital circuits
– save power by square
Sensor die size is shrinking, wafer diameters is increasing.
– both help to lower the cost of sensor manufacture
Reference 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?