Conventionally, there are several methods used for measuring permittivity. One method that can accurately measure permittivity is the “resonance method,” but in that case, the material to be measured must be placed in a device called a resonator, which requires precision processing of the material, sometimes less than several hundred micrometers thick. Another drawback is that the permittivity can only be measured at several specific frequencies. Since it is necessary to measure the permittivity of various materials during the development stage of a device, if high-precision processing is required for each measurement, the development process will take a long time. On the other hand, the "free-space method," which has fewer of these drawbacks, is also used, but in this case, an approximation has been used to analyze the measurement results, and the error caused by this makes accurate measurement difficult.
“Compared to other measurement methods, the free-space method has fewer restrictions on the shape of the measurement sample, and it is easy to extend the measurement frequency band,” says Sakai. The new analysis method is used with the “free-space method,” which means that with the new method, we can accurately measure permittivity with fewer constraints.
NAOJ and NICT have jointly been conducting research and development for high-precision material property measurement systems at millimeter-wave and terahertz-wave frequencies. The team is aiming for further technological innovation by combining the knowledge gained through the development of astronomical instruments with that gained from developing communication technology.
These research results were presented in Ryo Sakai et al. “Accurate Free-Space Measurement of Complex Permittivity With the Angular Spectrum Method” in the IEEE Transactions on Terahertz Science and Technology on July 3, 2023.