Enhanced-field ultra-compact resonant cavity for wide-range complex permittivity characterization of arbitrary-form materials

This paper proposes a cavity field-enhanced method, which can be used to measure arbitrary-form materials in a wide range of complex permittivity. A wideband impedance transition is designed to excite the TM010 mode in cavity with enhanced electric field. The main advantage of this cavity is only requiring dielectrics fully filled in the cavity without complex pre-processing. Compared with traditional perturbation methods, the cavity avoids the limitation of samples’ shape and location in measuring. Also, its single-port design decreases the demand for test instruments and makes its physical size only about one-eighth of the free-space wavelength. It works in a wide-range permittivity characterization from 1 to 80, covering both low-loss and high-loss materials. Simulation results show that tan δ = 0.15 serves as a boundary between low and high loss regimes, which allows the extraction of separate permittivity models. The system was experimentally validated using foam, distilled water and ethanol. The measured results are consistent with theoretical expectations. The system's practicality and accuracy for compact, wide-range complex permittivity characterization have been validated.