Sensor technologies. Lin Zhong ELEC424, Fall 2010

Transcription

1 Sensor technologies Lin Zhong ELEC424, Fall 2010

2 Elementary functions of computing Processing (a.k.a computing) Storage Communication Sensing: Interface between computers and the world 2

3 Principles of sensing Energy conversion From one form to electrical energy Electrical signal conversion From analog to digital Microcontroller Sensing Conditioner ADC 3

4 Basic energy domains Electrical Thermal E Output E T R Me M Bio Radiation Mechanical Magnetic Input T R Me M Bio X X X X X Bio (chemical) 4

5 Thermal energy sensing Thermal to electrical Thermal to radiation Thermal to mechanical Output E T R Me M Bio Input E T X X X R Me M Bio 5

6 Pyroelectric effect Heat flow to electrical charge Pyr (Fire, Greek) Directional, reversible Cheap and robust Applications Temperature difference/change Causes Radiation (absorption) Mechanical (friction) Passive infrared sensor 6

7 Passive infrared sensor Far-infrared sensor Motion detector 7

8 Thermoelectric effect Thermal to electrical Temperature difference to electrical potential Seebeck and Thompson effects Low accuracy High temperature Applications Thermocouple Steel industry (high-temperature furnace) 8

9 Thermal to electrical (resistance) Temperature changes resistance Thermistor Ceramic, polymer Small, low-cost, limited-range Battery Resistance temperature detector Metals (Platinum) 9

10 Thermal to mechanical Wikipedia 10

11 Contactless temperature sensors Infrared thermometer Temperature Blackbody radiation Expensive, remote measurement Acoustic thermometer Temperature Sound speed 11

12 Mechanical energy sensing Mechanical to electrical Piezoelectric effect Capacitive effect Mechanical to mechanical Doppler effect Wikipedia.org: A source of waves moving to the left. The frequency is higher on the left than on the right. 12

13 Piezoelectric effect Mechanical energy to electrical energy Piezein (Press, Greek) Directional, reversible Cheap and robust (ceramics) Piezoelectric film Poling dipole 13

14 Applications Pressure change Causes of pressure change Acceleration Mechanic vibration wikipedia 14

15 Accelerometer Applications Motion-based interaction Tilt Hard drive Image stabilization (Camcorder) Anti-blurring (Cameras) The success of MEMS technologies Microelectromechanical system (MEMS) Seismic/inertial/proof mass 15

16 Accelerometer implementation (Contd.) Piezoelectric 16

17 Accelerometer implementation (Contd.) Capacitive 17

18 Capacitive effect Proximity sensor: Distance determines capacitance 18

19 Microphone Creative use of microphones 19

20 Real simple touch sensor Set a GPIO pin as output Output HIGH Set the same pin as input Time it how long it becomes LOW Use interrupt + 20

21 Radiation energy sensing Radiation to thermal Radiation to electrical Antenna Photoelectric effect 21

22 Photoelectric effect Photons to electrons Applications Solar cell Photodiode Active pixel sensor wikipedia 22

23 Bio (chemical) sensing Humidity sensing Humidity changes resistance, capacitance Molecule detectors Antigen vs. antibodies 23

24 Nano sensors 24

25 Laser absorption spectroscopy Beer-Lambert s Law of Linear Absorption Absorber Laser Source I 0 I Detector Gas, Liquid or Solid L I ( ν ) = I 0 e - α ( ν ) P a L α(ν) I(ν) ν 25

26 CO 2 sensor built at Rice 0.2W control system power consumption 0.75W peak consumption for our CO 2 sensor Small size (even with USB, radio, pressure sensor) Low cost (~$250 in qty 5 to build boards) Rice Laser Science Group (Prof. Tittel) 26

27 Application of sensors Types of energy Accuracy Cost Interference Contact or contactless Active or passive Operation conditions Humidity, temperature etc. 27

28 Trend of sensor technologies Ubiquity Miniaturization Semiconductor, in particular silicon CMOS compatible From CCD to active pixel sensor (CMOS) MEMS (microelectromechanical system) Reading: Higher integration System-on-chip Digital microphone, TI 28

29 Sensor SoC Analog Device 29

30 Sight: 5Mp camera & VGA front camera Touch: multi-touch screen & proximity sensor Direction: Digital compass & gyroscope Balance & acceleration: 3-axis accelerometer Hearing: Microphone 6 th sense: Wi-Fi, Bluetooth, Cellular, & GPS 30

31 31

32 Opportunities to computer engineers More efficient computing More useful computing Better system support for sense 32

33 Case discussion: Pilot light Thermocouple vs. light detector 33