Compact Complementary Highly Sensitive Microwave Planer Sensor for Reliable Material Dielectric Characterization

Microwave sensors are increasingly vital for scientific research and high-precision industrial applications. This article introduces a compact complementary microwave planar sensor designed to accurately measure the dielectric properties of solid materials. This sensor consists of a maze-shaped split-ring resonator (MSSRR) patch on the top and a modified microstrip transmission line (MTL) on the back to achieve a high sensitivity of 8.84%. The MSSRR configuration facilitates strong electric field confinement to achieve a larger sensing area and allows accurate measurement of complex permittivity in solid materials. The sensor performances are investigated with known material under test (MUT) samples, covering relative permittivity values from 2.2 to 11.2, which can reliably measure low-permittivity material. A mathematical model based on frequency offset predicts the complex permittivity of the materials, and the sensor also shows potential for liquid detection. Therefore, the proposed sensor demonstrates a sensitivity of 1.7 times higher than existing state-of-the-art sensors, with an accuracy of up to 95%. It also features a compact size of $20\times 25$ mm and offers ease of fabrication, positioning it as a promising alternative to commercial sensors for dielectric characterization.