Applications
There are many real world applications of THz time domain spectroscopy in addition to cutting-edge scientific spectroscopy. These applications lie across a broad range of areas, including industrial, medical, communications and security. Some of these are outlined in the different sections shown below.
Industrial
THz time-domain-spectroscopy can be to evaluate semiconductor wafer properties and as such is becoming a valuable tool in the semiconductor industry. THz imaging also has applications in finding faults in integrated circuits and other semiconductor devices.[Beard02][Buersgens06]
Medical
By applying THz time-domain-spectroscopy to different materials such as cancer tissue and medicines a profile of the characteristics of these different materials can be built up and subsequently used in diagnosis and development/research.
Studies have been made into the feasibility of diagnosing cancer using THz spectroscopy.[Woodward02] Cancer tissue has a different hydration level than normal skin and it has been found that the absorption of THz radiation is sensitive to polar molecules such as water. Therefore cancerous tissue may be distinguished from normal healthy skin by this method.
Communications
THz radiation lies in a band between infrared and microwave radiation. Wireless computer networks currently operate in the microwave spectrum and as such are subject to interference from other nearby microwave sources. Furthermore, this part of the electromagnetic spectrum is becoming increasingly more crowded. THz frequencies could potentially be used for wireless communication over short distances. One of the key advantages of this would be that far greater bandwidths could be achieved; thereby allowing for high-speed connections.
Existing low-bandwidth wireless links could eventually be replaced by THz frequency links which would provide the bandwidth improvements outlined above. Such systems would be of great benefit to rural communities or for the delivery of video content for telemedicine and entertainment purposes.
Research is continuing into the development of waveguides, modulators and mirrors which function in the THz spectrum. Clearly the potential application to high-speed data networks is attracting a great deal of interest.
Security
When imaged in the THz domain; each narcotic and explosive substance has its own characteristics. This allows for the detection of such substances for reasons of security and safety and hence makes THz spectroscopy techniques very valuable.[Baker07][Davies08]
Identification of illegal drugs would become possible without having to undertake detailed examinations of the chemical composition of the material.[Dobroiu07] Even if the illegal substance were disguised by a so called 'confusion materal' it would still possible to identify it owing to the spectral characteristics of the substance in the THz range. THz radiation below 3.0THz can pass through envelopes allowing for identification of such substances without having to physically open the letter/parcel.
Airport security is a key area of research. Currently employed systems of metal detectors and x-ray machines have significant drawbacks. Metal detectors can only alert security staff as to the precense of some metal object about a person; whence upon a body search must be carried out. X-rays are not suitable for scanning humans for reasons of security due to the risks associated with regular exposure to ionizing radiation and liminations as to which substances can be detected.
The answer to the limitations outlined above could lie in the THz range of the electromagnetic spectrum. THz radiation has no known harmful affect on human tissue and can penetrate clothing and various other materials allowing for the detection of illegal substances and weapons. Furthermore the examination procedure itself would be less intrusive; requiring the person to stand in front of a THz imaging camera for a short period of time.
Finally, THz sensing techniques could be used to detect hazardous gases. Current methods which operate in the infrared spectrum are not able to detect gases through concrete walls. However, THz radiation could penetrate such obstacles allowing for improved detection.
© 2007-2009 G. Jotzu, M. Cooper, P. Parkinson and M.B. Johnston
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