Infrared radiations are radiations below (infra) visible spectrum. This emergent dual use technology field is fast emerging amongst the most ubiquitous ones. It spans from low-end automatic supermarket door openers to high-end space based detectors used to detect nuclear tests, missiles and intra galactic radiations. At the heart of this technology is the IR detector
Each mobile uses a separate, temporary radio channel to talk to the cell site. The cell site talks to many mobiles at once, using one channel per mobile. Channels use a pair of frequencies for communication. One for transmitting from the cell site, the forward link, and one frequency for the cell site to receive calls from the users, the reverse link.
Communication between mobile units can be either half-duplex or full-duplex. In case of half-duplex, transmit and receive communications between the mobile units are not at the same time, i.e. talking and listening can not be done at the same time. In case of full-duplex communication, transmit and receive communication is at the same time, i.e. one can talk and listen at the same time.
When communications between mobile units are within a cell, and if the same is half-duplex, then it shall require only one pair of frequency. If the same is full-duplex, then requirement of frequency pair shall be two.
When a mobile unit is communicating with a mobile unit outside the cell, then the requirement of frequency pair shall be one per cell for both half-duplex and full-duplex communication. Hence the system resources are utilized more if the mobile units communicate with each other in full-duplex mode.
Infrared (IR) detectors have been called the eyes of the digital battlefield. Military applications in Western countries have spearheaded and dominated the requirements in this field akin to many other emerging fields. In addition to many military applications for IR systems such as target acquisition, search and track, missile seeker guidance, there is a great potential for IR systems in the commercial market. IR systems enhance automobile and aircraft safety, medical diagnosis, and manufacturing quality and control. Industry is looking to expand into the commercial market because the military market is decreasing and concurrently becoming more specialized. Today, only about 20% of the market is commercial. After a decade the commercial market is estimated to grow by over 70% in volume and 40% in value.
The IR detectors evolved initially with theories and subsequently by improvement of materials. During the first half of nineteenth century, efforts were made to improve the speed and accuracy of only known IR detector, the thermometer. In 1829 Nobiloti made the first thermocouple. Melloni utilized this for making a thermopile capable of detecting heat emission from a human at 30 feet. During 1880 s Langly developed a sensitive bolometer that could sense a cow at a quarter of mile. Triad of these three instruments marked the development of IR detectors in nineteenth century. These detectors were sensitive to all infrared wavelengths and operated at room temperature. They had low sensitivity and slow response. Smith discovered photoconductive effect in 1873.
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