Noncontact Measurement of Complex Permittivity of Electrically Small Samples at Microwave Frequencies

Noncontact measurements of material parameters have important applications in various fields. In this paper, we propose a noncontact measurement of complex permittivity for electrically small samples at microwave frequencies. Based on Rayleigh approximation, we propose a noncontact measurement approach that can linearly retrieve complex permittivity from the measured impedance change. Using a subwavelength resonance, far-field radiation can be effectively suppressed, and thus the measurement is not notably influenced by unwanted environmental reflection. With the features of simple calibration and noncontact measurement, our method can be widely used in repeated on-site measurements of complex permittivity for small-sized samples at microwave frequencies.