1. ECE699 – 004 Sensor Device Technology
Chapter 4 Optical Sensors, Radiation Sensors and temperature Sensors
Fall 2018
George Mason University

2. 1. Optical components of Sensors

4. Radiometry
The index of regraction is a ratio of velocity of light in vacuum, c0, to that in a medium, c.

5. transparency

6. Coefficient of reflection ρ
If the light flux enters from air into an object
For an object with a thickness (without absorption)
Transmittance:

8. if with absorption α and transmittance γ

9. Photometry
Lumen
where ω is the solid angle

10. Windows
(due to refraction Fig. 4.4, a passing ray is shifted by a distance L:
a silicon window

12. Fresnel lenses: to gain high quality of ocusing

13. Fiber optics
To achieve total internal reflection

14. Can be used to detect strain

15. Electro-optic modulators

16. 2. Optical sensors 2.1 Introduction The energy of a single photon
The photoelectric effect

17. The conductivity of semiconductor
The band structure

18. Spectral response

19. Compare the characteristics of difference photodetectors:
NEP (noise-equivalent power)
D* (detectivity)
IR cutoff wavelength (λc)
Maximum current
Max reverse voltage
Radiant responsivity
Field of view (FOV)
Junction capacitance (Cj)

20. 2.2 Photodiodes

21. Equivalent circuit of a photodiode

22. Rate of production of electron
(η is the probability of photon hv to produce an e)
The current is
Current to voltage response

23. PN photodiodes

24. The fabrication of a PN photodiodes

25. Connection to an amplifier (photovoltaic mode)

26. Use current-to-voltage converter

28. Photoconductive mode (better linearity)

29. 2.3 Phototransistor

30. Equivalent circuit
Max frequency
gm is the transistor
forward transconductance

31. 2.4 Photoresistors Change in conductance

32. 2.5 Cooled Detectors
- photons with long wavelength
Intrinsic noise > photoconductive signal
Detectors are based on PbS, InAs, PbSe, HgCdTe, Ge
Can be used for many applications: thermal imaging, water content and gas analysis

35. 2. 6 Thermal Detectors – mid/far-infrared spectrum 2. 6
2.6 Thermal Detectors – mid/far-infrared spectrum Golay Cells – for infrared detection

36. 2.6.2 Thermopile sensors Can also be implemented by MEMS

38. 2.6.3 Pyroelectric Sensors Heatvoltage
Thermal motion detector

39. 2.6.4 Bolometers Sensitivity ZT thermal capacity, w is frequency

40. 2.6.5 Active Far-Infrared Sensors
“active“ –surface temperature is maintained at Ts by a circuit (Ts is higher or equal to the highest temp of the targets)

41. 2.7 Gas Flame Detectors A unique feature of the flame: a noticeable portion of its optical spectrum is located in the UV spectral range