Design of a High Sensitivity Microwave Sensor for Liquid Dielectric Constant Measurement

In order to improve the sensitivity of liquid dielectric constant measurements, a liquid dielectric constant sensor based on a cubic container structure is proposed for the first time. The cubic container, which consists of a dielectric substrate with a split resonant ring (SRR) and microstrip lines, can enhance the electric field intensity in the measuring area. High sensitivity can be obtained from measuring the dielectric constant with the characteristics of the structure resonate. The research results show that the resonant frequency of the sensor is shifted from 7.69 GHz to 5.70 GHz, with about a 2 GHz frequency offset, when the dielectric constant of the sample varied from 1 to 10. A resonance frequency offset of 200 MHz for the per unit dielectric constant is achieved, which is excellent regarding performance. The permittivity of oil with a different metal content is measured by using the relation between the fitted permittivity and the resonant frequency. The relative error is less than 1.5% and the sensitivity of measuring is up to 3.45%.