Non-contact measurement of complex permittivity based on coupled magnetic and electric resonances

In this paper, we introduce the strongly coupled magnetic resonance and the Rayleigh approximation to the non-contact measurement of complex permittivity, and further extend the same principle to radio frequencies by employing a sub-wavelength split-ring resonator excited by a microstrip line. Experimental measurements show that by applying the proposed approach, while the impedance matching and a high quality factor can be simultaneously obtained, the complex permittivity can be linearly retrieved from the measured change of impedance. The measurement setup can be easily calibrated for both solids and liquids, making it suitable for the measurement of complex permittivity of bio-materials.