Temperature Sensor

1. TEMPERATURE
SENSOR : GOLAY
CELL

2. WHAT IS A TEMPERATURE SENSOR ?
A temperature sensor is a device, which senses or convert the surrounding temperature into an
electrical signal, typically, a thermocouple or RTD, that provides for temperature measurement
through an electrical signal.
Reference: https://www.efxkits.co.uk/wp-content/uploads/2017/04/Different-Types-of-Sensors.jpg

3. TYPES OF TEMPERATURE SENSORS:
1. Thermocouples : Thermocouple
2. Thermistors
3. Pneumatic devices : Golay cell.
• https://www.sterlingsensors.co.uk/media/wysiwyg/cms/Picture1.jpg
• http://9727e9d160d99ffc550be91bafb404d116e05b8f50150b1b07c8.r4.cf3.rackcdn.com/UK_Z22_Microtech-Golay-Cell_PI_D.jpg

4. GOLAY CELL
 A Golay Cell is a ”photo-acoustic” device that is sensitive, works at ambient temperatures and
has a broad spectral response.
 Golay Cell is one of the most efficient devices detecting THz radiation.
• Terahertz radiation is considered as the electromagnetic spectrum whose frequency
ranges from 0.1 to 10THz,lying between the microwave and infrared regions.
• THz waves can penetrate many materials and generate images with high spatial
resolution such as THz radar, scattering, security detection, tomography, biology and
medicine.
• Some other features of terahertz radiation are:
 All warm bodies naturally emit THz radiation
 High frequency implies broad bandwidth and very high wireless data transmission
rates
 THz radiation enables imaging through clothing, bandages, and packaging materials.

5. PRINCIPLE OF OPERATION
1. Golay cell consists of a small metal cylindrical closed
by a rigid blackened metal plate.
2. Pneumatic chamber is filled with xenon gas.
3. At one end of cylinder a flexible silvered diaphragm
and at the other end Infra red transmitting window
is present.
4. When infra red radiation is passed through infrared
transmitting window the blackened plate absorbs
the heat. By this heat the xenon gas causes expand.
5. The resulting pressure of gas will cause deformation
of diaphragm. This motion of the diaphragm
detects how much IR radiation falls on metal plate.
6. Light is made to fall on diaphragm which reflects
light on photocell.
Reference :
https://upload.wikimedia.org/wikipedia/commons/5/59/Gol
ay_Cell_Schematic.svg

6. GOLAY DETECTORS IN RECENT TIMES
• According to the principle of thermal expansion, a Golay-Cell detector can work at room
temperature.
• In the long process of signal detection, the energy accumulation in the detector can cause a
dc drift of the detected signal and reduce the accuracy of detector. To avoid the occurrence of
the above circumstances, a chopper is used to make the continuous waves from the THz
source to be cut into alternating signal. Thus the bandwidth is decreased to reduce the noise
and eliminate the 1/f noise(the DC drift of detector).
Reference : https://www.techbriefs.com/images/stories/PTB/2006/BRIEFS/NPO-42724_fig1.png

7. SPECIFICATIONS:
1. Detector Size : 6mm
2. Window Material : HDPE or Diamond
3. Wavelength Range: 7 to 8000 µm
4. Maximum Power : 10 µW
5. Optimum Chopping Frequency : 20 Hz
6. Noise Equivalent Power (NEP) : 1.2 x 10-10 W/(Hz)1/2½
7. Responsivitiy : 150 K @ 20 Hz
8. Power Requirement : V (AC)
9. Operating Temperature Range : 5 to 40ºC
10. Package Size : 126 x 45 x 87 mm
11. Response Time : 30 - 25 msec Fig : Golay cell as a THz detector.
https://en.wikipedia.org/wiki/Golay_cell#/
media/File:Golay_cell.jpg
References : http://www.opt-ron.com/items/tydex-golay-hdpe#tab1

8. TYPES OF WINDOWS IN GOLAY DETECTOR
 Golay detectors can be differentiated on the basis of the material used for the entrance
window of a Golay detector:
I. Golay Detector with HDPE(High-Density Polyethylene) Window:
II. Golay Detector with TPX Window:
• Due to polyethylene window, detectors have wider wavelength range of operation,
spreading down to visible/UV. They can be considered as good substitute to
diamond window model as TPX has higher transmittance in THz than diamond. Also
cheaper than the latter one.
III. Golay Detector with Diamond Window:
• Due to polyethylene window exchange to Diamond , these detectors have wider
operation wavelength range spreading down to visible. It is a bit more expensive
than other detectors.

9.  Advantages:
• The useful wavelength range was very wide(which may be important when measuring a point
source).
• Well characterized THz spectral response .
• Very sensitive (sub nW).
• Has been used as a standard in Astronomy and Extreme IR for years.
 Disadvantages:
• Very fragile (thin membrane).
• Slow response.
• Very sensitive to mechanical vibration.
• Limited dynamic range (10 μW max.)
• Must Include a HDPE or Diamond window for operation.
• One model only (one configuration).
• Expensive (~$12K to $15K).

10. APPLICATIONS:
• Terahertz radiation are absorbed by water or material that contains water—like
human tissue because it is also nonionizing and therefore not harmful (in lower
doses) to humans like x-rays can be.
• Early detection of cancerous growths.
• Non invasive testing in microelectronics.
• Terahertz radiation is attractive for applications such as security scanning of people
and baggage.
• Golay Detector with HDPE window is used in monitoring and control of MIR and THz
radiation.
• Golay Detector with TPX Window is used in monitoring and control UV-NIR and THz
radiation.
• Golay Detector with Diamond Window are usually used when someone needs not
THz and VIS ranges only but MIR also.

11. References:
1. International Journal of Electrical and Electronics, Engineering Research (IJEEER), ISSN 2250-155X Vol. 3 Issue 2 Jun
2013, 115-120 (Trends of golay-cell detector and application of terahertz radiation).
2. De Lucia F C, “Spectroscopy in the terahertz spectral region,” Sensing with Terahertz Radiation, ed. D Mittleman,
(Berlin: Springer), 2003.
3. D. Arnone, C. Ciesla, and M. Pepper, “Terahertz imaging comes into view,” Phys. World. 35-40 (2000).
4. D. D. Arnone et al., “Applications of terahertz (THz) technology to medical imaging,” in Proc. SPIE Terahertz
Spectroscopy.
5. Chévrier J.-B., Baert K., Slater T., “An infrared pneumatic detector made by micromachining technology,” J.
Micromech. Microeng. 5, pp. 193-195, (1995).
6. Yamashita K., Murata A., Okuyama M., “Miniaturized infrared sensor using silicon diaphragm based on Golay cell,”
Sens. Act. A 66, pp. 29-32, (1998).
7. https://en.wikipedia.org/wiki/Golay_cell.
8. http://www.laserfocusworld.com/articles/2010/05/terahertz-detectors.html