The increased threats of criminal or terrorist action in recent years have led to development of many techniques for detection of concealed weapons, contraband, explosives or other objects.
This lecture will be held on Monday 26th March 2012, starting at 17h30 (duration: approximately one hour).
Systems based on electromagnetic waves between 30-100GHz (wavelengths 1cm – 3mm) in the millimeter-wave and 100GHz-10THz (wavelengths 3mm – 30micron) in the terahertz region have particular advantages that:
- Electromagnetic waves propagate through the atmosphere (not very far because of the absorption by air water vapor : of the order of 30m) and can be used for stand-off detection.
- Waves at these frequencies penetrate many common barrier materials enabling concealed objects to be seen.
- Wavelengths are short enough to give adequate spatial resolution for imaging or localization of threat objects.
Above 500GHz many macromolecules, including common explosives, drugs, pharmaceuticals, pathogenic agents like anthrax, have characteristic resonances (called THz-fingerprints; see the absorption spectra of explosives) in their terahertz spectra which may be used to identify them.
There are a lot of biomedical applications because THz radiation is coupled to the vibrational and rotational spectrum of many biomedical compounds. Radiation at these frequencies is non-ionizing and, at modest intensities, safe to use on people.