Microwave Sensor Loaded With Complementary Curved Ring Resonator (CCRR) for Material Permittivity Detection

In the field of microwave measurement, how to miniaturize devices and improve measurement sensitivity is a major challenge. In this article, a planar microwave sensor loaded with a complementary curved ring resonator (CCRR) is proposed to measure the permittivity of substrate materials. The current forms a magnetic field along the path of the curved ring, which acts on the capacitance between the rings of the curved ring and makes the circuit resonate. At this time, the curved ring structure stores a huge amount of energy. When the substrate materials with different permittivity are loaded into the measurement area of the sensor, the resonant frequency of the sensor will change. By establishing a mathematical model between the permittivity and the resonant frequency and conducting a full-wave electromagnetic simulation, it can be seen that the CCRR combined with the substrate integrated waveguide (SIW) structure can effectively enhance the electric field intensity in the measured region. Compared with the conventional planar microwave resonator. The sensitivity, resolution, and size of the proposed sensor are 3.51%, 133 MHz, and 52 $\times $ 34 $\times $ 0.508 mm3, respectively. After optimizing the structural parameters of the sensor, the actual sensor was manufactured. Four kinds of substrate materials commonly used in microwave circuits are used as samples to test the sensor. The results show that the sensor has the characteristics of high sensitivity, high resolution, and high measurement accuracy, which confirms the promising application of the sensor in the field of permittivity measurement.