Terahertz radiation is non-ionising making it an ideal technology for security scanning of the general public. Scanning devices operating at these sub-millimetre wavelengths can quickly and non-invasively image through clothing, to identify concealed weapons, explosives, drugs and other contraband items. Assessing safety risks associated with terahertz radiation to both device operators and the scanned public requires accurate measurements of the devices power. Techniques are needed to calibrate important performance parameters, such as frequency, amplitude and power against SI definitions.
The EMRP project Microwave and terahertz metrology for homeland security (THz) developed robust calibration methods and a validated modelling approach that has shown that terahertz radiation is safe for use in security surveillance.
- Established improved methods for calibrating the three most common terahertz spectrometer types to SI units.
- Developed a range of complementary reference materials for reliably verifying and comparing microwave and THz spectrometer performance.
- Provided uncertainty analyses for the absorption and reflection coefficients measured in terahertz spectrometers enabling these to be assessed for the first time. This provides the necessary measurement accuracy to enable results from different spectrometers to be reliably compared.
- Validated a modelling approach for the propagation of electromagnetic waves through skin layers and so estimating the amount of heating in human skin from microwave and THz radiation.
This project has made fundamental contributions to improving the accuracy and reliability of microwave and THz calibrations with robust links to SI units. By validating a new pyro-electric terahertz detector transfer standard and an introducing an alternative calibration route based on a table-top sized room-temperature radiometer there are now increased calibration methods available for terahertz users. The projects measurement and calibration methods will enable more effective design and testing of high-performance security devices, and will also ensure that the devices can be used safely.
Compliance with the European “Physical Agents Directive” exposure limits for personnel working with high-frequency radiation can now be demonstrated by using project developed techniques and models. These provide a route for manufacturers to prove that terahertz devices are safe for both operators and the public and will assist in the introduction of new terahertz technologies.