Design of a Highly Sensitive Sensor for Measuring Liquid Permittivity with Flexible Substrate

To further improve the sensitivity of liquid dielectric constant measurements, a cylindrical container-type dielectric constant sensor is proposed in this paper. The container of the sensor consists of a substrate integrated waveguide (SIW) loaded with complementary split ring resonators (CSRRs) and a microstrip line. In order to solve the problem that the electric field distribution of the traditional container liquid dielectric constant sensor is only in a single plane, which cannot obtain good resonance characteristics, the sidewall of the sensor container is surrounded by a flexible material loaded with CSRR-SIW. Higher sensitivity can be obtained from measuring dielectric constant with more concentrated electric field distribution. The simulation results show that when the permittivity of the liquid under test (LUT) changes from 1 to 10, the resonance frequency of the sensor changes from 4.50 GHz to 2.94 GHz. The resonance frequency shift with unit dielectric constant greater than 150 MHz is realized. Using the relationship between the fitting permittivity and resonance frequency, the measurement of the known liquid permittivity of the standard sample is carried out. The test results show that the relative error is less than 2%, and the test sensitivity is 3.85%.