1 / 36

Tutorial 5

Tutorial 5. Derek Wright Wednesday, February 16 th , 2005. Sensors and Image Systems. Physical Principles of Sensors Optical Imaging Systems IR Imaging Arrays Electronic Nose Tactile Sensors and Arrays. Sensor Basics. Sensors are transducers

leo-love
Download Presentation

Tutorial 5

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Tutorial 5 Derek Wright Wednesday, February 16th, 2005

  2. Sensors and Image Systems • Physical Principles of Sensors • Optical Imaging Systems • IR Imaging Arrays • Electronic Nose • Tactile Sensors and Arrays

  3. Sensor Basics • Sensors are transducers • Transducers convert one form of energy to another • Alternator in your car turns mechanical into electrical • Engine converts chemical to thermal to mechanical • Eyes convert light into electrical

  4. Sensor Basics • Sensors either • Directly convert one form to another • Use one form to change (modulate) another • Direct Conversion: • Solar panel: Light  Electricity • Thermocouples: Heat  Electricity • Modulating: • Thermoresistive, Optoresistive: Changing resistance must be have current driven through it to measure

  5. Biological Sensor Arrays - Eyes • The eye is a biological form of a sensor array • It consists of an array of transducers (rods and cones) • The signals are transmitted by neurons along axons

  6. Optical Imaging Systems • Array structures allow multidimensional measurement to occur • Optical Imaging Systems: • Charge Coupled Devices (CCDs) • CMOS Cameras • X-ray Imagers

  7. Charge Coupled Devices • Incident photons cause creation of electron-hole pairs • Electrons move to insulator boundary under bias for storage • Charge is shifted out of a row or column by a shifting potential • Cannot be integrated on the same substrate as accompanying electronic circuits

  8. CCD Operation

  9. CCD Operation

  10. CCD Operation • http://micro.magnet.fsu.edu/primer/java/photomicrography/ccd/shiftregister/index.html • http://www.extremetech.com/article2/0%2C3973%2C15465%2C00.asp

  11. CMOS Cameras • Can be created with standard CMOS processes • Can be integrated with accompanying electronic circuits • An incident photon creates an electron-hole pair in a reverse biased diode • Configured to cause charge to drain off of a capacitor • Photon absorption  capacitor voltage decrease

  12. CCD vs. CMOS Cameras • CCD has a better Fill Factor (FF) • Better image quality and photon capture • Lower noise • CCD only outputs the analog charge • Must be converted to digital by another chip • CMOS has on-chip integration • Results in high-speed and low-power • Reduces flexibility, but decreases cost

  13. X-ray Imagers • Amorphous thin film techniques can produce large-area x-ray detectors • Two types: • Indirect • Direct • On-pixel amplification means fewer x-rays needed to make an image  Safer!

  14. p-i-n Structure Ec h Ev i a-SiC:H n a-SiC:H Al p a-SiC:H ITO

  15. X-ray Imagers • Indirect Method: • A top layer of phosphor turns the x-ray into a visible discharge • Visible photons are then detected by amorphous silicon (a-Si) p-i-n photodiodes

  16. X-ray Imagers • Direct Method: • Amorphous selenium (a-Se) absorbs x-rays • A layer of a-Se with a huge E-field is used • It converts x-rays into electron-hole pairs • E-field separates them into current

  17. IR Imagers • Two detection methods: • Quantum (photon  e-h pairs) • Thermal (photon  temp) • Useful in night vision systems • Police use them in Ontario to find pot grow houses

  18. IR Imagers • Quantum Detection: • Photons have an energy hf = hc/ • If this energy is bigger than the bandgap of a detector material, e-h pairs will be created • IR has lower energies than visible, so the bandgap has to be reduced • Detector bandgaps can be tuned from 0eV up • These detectors must operate at very low temperatures • Restricted to special uses

  19. IR Imagers • Thermal Detection: • IR photons will turn into heat when they hit certain materials • The heat can be detected and imaged • A pyroelectric material will generate a voltage or current proportional to the IR power shining on it

  20. Microcalorimetric Sensors • A heated chamber is kept at a constant temperature • An incoming gas flow is burned • When the gas burns it releases heat energy • The released heat results in less heat from the chamber to keep a constant temperature • Released heat energy can be measure by how much less the chamber needs to heat the gas flow

  21. Microcalorimetric Sensors

  22. Electrochemical Cells • Use a catalyst to convert molecules to be measured into ions • Two modes of operation: • Amperometric: The ions are moved through a catalyst and electrolyte to create a current • Potentiometric: The ions charge a capacitor and appear as a voltage

  23. Electrochemical Cells Amperometric Potentiometric

  24. Acoustic Wave Devices • Tiny free-standing beams are created through micromachining • They have a mechanical resonance frequency () • They are coated in a polymer that adsorbs the specific molecules to be observed • More molecules stick  mass  

  25. Acoustic Wave Devices

  26. Gas-Sensitive FETs • A small channel lets gas pass between the gate and the substrate (channel) • The underside of the gate can be coated with a material to adsorb certain gasses • When the gasses adsorb into the coating, it changes the threshold voltage

  27. Resistive Semiconductor Gas Sensors • O2 can act as a p-type dopant in silicon • It attacks point defects • The number of point defects increases with temperature • The Si must be heated • The more O2 in the silicon, the higher the conductivity

  28. Resistive Touchscreens • Two flexible resistive layers are separated by a grid of spacers • When the two layers are pressed together the resistance can be measured between several points • This determines where the two resistive layers contacted

  29. Resistive Touchscreens

  30. Capacitive Touchscreens • A conductive layer is covered with a dielectric layer • The finger represents the other plate of the capacitor • A kHz signal is transmitted through the conductive plate, the dielectric, and the finger to ground • The current from each corner is measured to determine the touch location

  31. Capacitive Touchscreens

  32. Ultrasound Touchscreens • Ultrasonic sound waves (>40 kHz) are transmitted in both the horizontal and vertical directions • When a finger touches the screen, the waves are damped • Receivers on the other side detect where the sound was damped • Multiple touch locations are possible

  33. Ultrasound Touchscreens

  34. Fingerprint Sensors • An array of tiny capacitive sensors • Works similarly to the capacitive touchscreen • Finger works as one plate of a capacitor • Chip works as the other • Sensors are small enough to determine if a fingerprint ridge is touching it • An image is produced

  35. Fingerprint Sensors

  36. Thank You! • This presentation will be available on the web.

More Related