A Flexible Microwave Sensor Based on Complementary Spiral Resonator for Material Dielectric Characterization

In this paper, a flexible microwave sensor for material dielectric characterization is presented. The sensor is composed of a two-turn complementary spiral resonator (CSR) in coplanar waveguide (CPW) technology developed on a flexible polyethylene terephthalate (PET) substrate. The sensing principle is based on the measured transmission coefficient of the designed structure, where the resonant frequency and its magnitude are in function of the dielectric properties of loaded materials under test (MUTs). A prototype of the proposed sensor is fabricated and experimentally validated by extracting the dielectric constant and loss tangent of the reference samples loaded above the region of the CSR. Specially, due to the flexibility, the fabricated sensor can be conformally attached to the palm of a dexterous robotic hand to function as robotic electronic skin for material dielectric characterization, more specifically, to obtain dielectric properties of the objects grasped by the dexterous robotic hand. Moreover, the sensing functionality of the sensor structure under different bending levels is validated by calculating the dielectric property of loaded objects with non-planar surfaces.