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 DynamicRibbon

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

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 samplePower Spectral Density (PSD)

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

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

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

16. Example Geophone examples 1-second samplePower Spectral Density (PSD)

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

18. 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.

19. 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)

20. 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.

21. Example PIRs from Visionic Ltd.

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

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

24. 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

25. 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

26. 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

27. 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.

28. Thank you! Questions?