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Micro-sensing Modalities

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].

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Micro-sensing Modalities

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  1. Micro-sensing Modalities Hongtao Du August 31, 2004

  2. 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

  3. 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].

  4. Micro-sensor Node

  5. 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

  6. 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

  7. Crystal microphone: based on piezoelectric effect of crystal • Condenser microphone: a capacitor with two plates Crystal Condenser

  8. Directional Patterns • Omni-directional: sensitive in all directions • Bi-directional: front and rear, 90 each • Cardioid: the specific direction it points to

  9. 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.

  10. Doppler Effect • When the source or the receiver is moving relatively to each other, the frequency of a wave observed at a receiver changes.

  11. Example Microphone used in WINS NG 2.0 sensor platform from Sensoria Co. 1-second sample Power Spectral Density (PSD)

  12. Geophone /Accelerometer • Geophone • Electro-magnetic • Low frequency: < 100Hz • Accelerometer • Piezoelectric effect • High frequency > 100Hz Structure of geophone

  13. 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

  14. Seismic Sensing Phenomenology • A: reflection • B: direct path • C: P-S wave conversion • D: refraction

  15. Example Geophone examples 1-second sample Power Spectral Density (PSD)

  16. Magnetic Sensing • Only detect presence, strength, direction of magnetic fields • Ferrous object (vehicle, airplane) disturbance in uniform field • Very useful in navigation control system

  17. 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.

  18. 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)

  19. 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.

  20. Example PIRs from Visionic Ltd.

  21. AIR • Two units • Infra-red photodiode and Infra-red sensitive phototransistor • Infra-red reflector

  22. Optical Sensing • Principle: conductivity • Charge-Coupled Detector (CCD) Cell • Electron-Hole Pair (EHP)

  23. 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

  24. 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

  25. 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

  26. 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.

  27. Thank you!  Questions?

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