Abstract
Infrared science and technology has been, since the first applications, mainly dedicated to security and surveillance especially in military field, besides specialized techniques in thermal imaging for medical diagnostic and building structures and recently in energy savings and aerospace context. Till recently the security applications were mainly based on thermal imaging as surveillance and warning military systems. In all these applications the advent of room temperature, more reliable due to the coolers avoidance, low cost, and, overall, completely integrable with Silicon technology FPAs, especially designed and tailored for specific applications, smart sensors, has really been impacted with revolutionary and new ideas and system concepts in all the infrared fields, especially for security applications. Lastly, the advent of reliable Infrared Solid State Laser Sources, operating up to the Long Infrared Wavelength Band and the new emerging techniques in Far Infrared Submillimeter Terahertz Bands, has opened wide and new areas for developing new, advanced security systems. A review of all the items with evidence of the weak and the strong points of each item, especially considering possible future developments, will be reported and discussed.
Highlights
The basic laws of IR radiation (Kirchhoff ’s law, StefanBoltzmann’s law, Planck’s law, and Wien’s displacement law) have been developed many years after the discovery of IR radiation
Terroristic events, based on new types of threats and explosives, have pushed towards the developments of new techniques of detection and alarm employing different parts of the electromagnetic spectrum, extending from infrared to terahertz radiation, that is, the e.m. band between infrared and microwave. In these new developments there is a priority to the developing of imaging systems, at least for the know-how originated in infrared technologies, while spectroscopic detection is mostly developed by microwaves techniques
Radiation at terahertz frequencies has unique properties that may be advantageous for security applications; it can penetrate many nonconducting materials, but unlike X-rays is nonionizing, and can allow radar-like imaging in three dimensions thanks to the extremely short pulses used in pulsed terahertz techniques, as well as the simultaneous collection of spectroscopic information like infrared
Summary
As part of e.m. spectrum, was discovered by Sir William Herschel as a form of radiation beyond red light. Work on uncooled infrared detectors has shown an impressive growth since the first developments, allowing the real expectation for a production of low cost, high performance detector arrays which should follow the rules of a real global market, opening a real market for civil applications following the winning rules of silicon microelectronics For these reasons the emerging room temperature detectors in the 1970s by the use of pyroelectric materials [17, 18], which shows the limitations of not being fully monolithic, but the innovative room temperature silicon microbolometers appearing on the IR scene in 1990 [19], seem to be a real breakthrough for future IR sensors.
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