Complex Permittivity Measurements of Liquid Crystals Using Epsilon-Near-Zero Metamaterials

Liquid crystals (LCs) are a kind of anisotropic materials with tunable dielectric properties in the microwave frequency band, which is of great significance for designing reconfigurable microwave devices such as beam-steering antennas, tunable phase shifters, or filters. Accurate characterization of the dielectric properties of LCs is crucial for designing and optimizing reconfigurable microwave components. In this article, a method for characterizing the dielectric properties of LCs is proposed based on epsilon-near-zero (ENZ) metamaterials. The measurement device is first designed using a waveguide-based ENZ structure. When LC-materials under tests (MUTs) are filled into the coupling tunnel, the strong electromagnetic intensity within ENZ metamaterials is fully utilized to sensitively detect the transmission response. In addition, biased circuits and preconditioned alignments are also designed and integrated to extract complex dielectric permittivities of anisotropic materials. Particularly, due to the metallic structure of the measurement device, a temperature control system consisting of a sensor and heating device can effectively and precisely control LC-MUTs’ temperature so that dielectric responses of LC-MUTs under different temperatures can be obtained. On this basis, according to the measured transmission parameters, the perturbation method is used to calculate complex dielectric permittivities of LC-MUTs. A prototype is fabricated and tested to verify the method. Complex dielectric permittivities of two LC-MUTs are extracted at 1.9 GHz, which verifies the effectiveness of the method. Note that the dielectric properties of a powder sample are also investigated using the same device, demonstrating the universality of this method. This work provides an alternative method for accurately measuring the complex permittivity of solid, liquid, and powder dielectric materials.