A Quarter-Mode Substrate Integrated Waveguide Microwave Sensor Loaded With CCRR for Solid Material Measurement

This article proposes a quarter-mode substrate integrated waveguide (QMSIW) microwave resonance sensor loaded with complementary curved ring resonator (CCRR) structure for solid material measurement. Compared to the substrate integrated waveguide (SIW), QMSIW reduces the volume by 25%. Etching multiple split-ring structures in series in the center area of QMSIW can effectively construct high electric field environments, so it is designed as the sensing area to achieve excellent performance. When the material under test (MUT) is loaded onto the sensor, it slightly perturbs the electric field, thereby changing the transmission zero (TZ) of the sensor. This article further analyzes the equivalent circuit model and fits the frequency–permittivity curve of the sensor. At the same time, the influence of MUT’s thickness and loss tangent on the sensor is studied, and the design is fabricated on a printed circuit board with a size of
$26.5\times 26.5\times0.762$
mm. The test results indicate that the unloaded TZ frequency of the sensor is 3.54 GHz, which is consistent with the simulation results. When loading a small volume MUT of
$10\times 10\times0.762$
mm, the sensor shows an average sensitivity of 6.15% and an average resolution of 225.25 MHz. The error rate is 1.18%. This work provides a solution of measuring permittivity for smaller size MUTs.