CSRR Metamaterial Microwave Sensor for Measuring Dielectric Constants of Solids and Liquids

The current challenges faced by microwave planar sensors include their low sensitivity, limited detection range, and difficulties in operating small devices. This study proposes a metamaterial microwave sensor based on complementary split ring resonator (CSRR) for determining the dielectric constants of liquid and solid materials. The novelty of the proposed sensor lies in the use of curved slots in the CSRR structure to achieve higher electric field concentration and to store a large amount of energy, the determination of the measurement area based on its electric field distribution, and the design of microfluidic channels to further improve the sensitivity to the resonance frequency change. The sensor operates at 2.45 GHz and has dimensions of $40\times 30\times 0.6\,\,\text {mm}^{3}$ . Since the dielectric constant of the contacting object affects the microwave sensor's resonant frequency, the displacement of the sensor's resonant frequency is measured using various items. The resonant frequency of the sensor adjusts when materials with varying dielectric constants are introduced into the measurement region. By measuring the frequency point of the measured material at the maximum return loss of the resonator, empirical equations with different coefficients are established to derive the dielectric constants of solids and liquids. The sensitivity and resolution were 4.12% and 102 MHz in solid and 0.78% and 8.4 MHz in liquid. The sensors were tested using five substrate materials commonly used in microwave circuits and different concentrations of ethanol solutions as samples. These findings validate the potential application of the sensor as a cost-effective alternative to expensive commercial sensors for dielectric characterization. The results demonstrate that the sensor possesses high sensitivity, high measurement accuracy, low cost, and ease of fabrication, making it an excellent alternative to expensive commercial sensors for dielectric characterization. This confirms the promising application of the sensor in the field of dielectric constant measurement.