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FREE-SPACE MEASUREMENT SYSTEM TO INCREASE ACCURACY IN CHARACTERIZATION OF MATERIALS IN THE GIGAHERTZ RANGE
The dielectric properties, of materials (their ability to store electric energy in an electric field) are pertinent to many fields of research, including radar component and antenna design, pharmaceutical processing, and determination of moisture contents in foodstuffs and other materials. Future generations of advanced imaging technology (AIT) systems used for screening people for contraband are expected to distinguish threats from benign objects via their dielectric properties. To be of value, the systems require an accurate measurement of these properties.
Researchers at the Transportation Security Laboratory have invented the Measurement System and Methods of Measuring a Reflection Coefficient (MSMMRC) to address challenges with the setup and calibration of an apparatus to perform dielectric measurements. The innovation provides improved reflection data in the gigahertz frequency range, using a free-space measurement technique while also improving measurement dynamic range. These innovations can be incorporated into a commercialized measurement system.
THE TECHNOLOGY
MSMMRC is a simple, one-port (single-sided) free-space measurement technique. A test sample is placed on top of a conductive material (e.g., metal) in the testing region. A transceiver antenna connects to an electromagnetic radiation source and directs the radiation to the sample. A radar absorbing material sits between the transceiver antenna and the measured sample and acts as an aperture. Radiation reflected from the test sample returns to the transceiver through the radar absorbing material aperture. The measured reflection coefficient of the test sample is used in conjunction with the sample thickness to extract the dielectric constant of the material as a function of frequency.
