A modified AMC-based antenna sensor for contactless measurement of complex permittivity

Abstract

The paper proposes a modified artificial magnetic conductor (M-AMC)-based antenna sensor for retrieving the complex permittivity of material under test (MUT). The antenna sensor measurement system is composed of a coplanar waveguide (CPW) antenna and a M-AMC structure. The M-AMC structure consists of a 3×3 array, and each unit cell is fabricated by two-layer dielectric substrates. The M-AMC unit cell is evolved from the traditional square unit one, and in each cell, four bent microstrip lines are embedded in the middle plane of M-AMC structure to connect the top square metallic patch through metallic holes. Compared with traditional AMC structure, the added bent microstrip line can increase the current path. Besides, four complementary split-ring resonators (CSRRs) are etched on the top plane of each unit to improve the density of electrical field. A large metallic patch covers the bottom plane of M-AMC. The resonant frequency of M-AMC structure is reduced a lot than the traditional one, which is beneficial to realize miniaturization. In measurement, the antenna is placed on the upper surface of M-AMC structure with an appropriate distance, and the MUT is placed on top plane of M-AMC. The MUTs with different thicknesses and complex permittivity will alter the resonant frequency and quality factor of the antenna sensor. Experiment is carried out to demonstrate the performances of proposed antenna sensor. An average sensitivity of 1.89 % is achieved and the maximum error is less than 3.516 % in extracting the real permittivity. All in all, the proposed antenna sensor has a potential superiority in the scope of material characterization.