Compact substrate integrated waveguide sensor for liquids permittivity measurement

A compact substrate integrated waveguide (SIW) liquids permittivity sensor structure that utilizes half-mode (HM) and slow-wave (SW) techniques for the miniaturization of SIW sensor is presented in this paper. First, HM miniaturization technique is applied to SIW resonator cavity. Sensor width is reduced by 50% in comparison to the conventional resonator. Due to the complexity of the relationship between the complex permittivity of the substrate and liquids under test, artificial neural network tool is used as a simple and fast method to determine liquids’ complex permittivity through the measured resonant frequency and unloaded quality factor. The sensor is fabricated, and good agreement with simulations is observed according to the obtained experimental results. In the second step, SW and HM techniques are applied to the SIW sensor. The application of the HM and SW techniques indicate that an increase in sensor miniaturization while obtaining a better quality factor could be achieved. Furthermore, HM-SW-SIW is not fabricated, and we are satisfied with simulation results since we have fabricated other components. Moreover, good correspondence between the measurement and simulation results is obtained. Finally, a comparison between the structures presented in this paper and those published previously is made, demonstrating that a minimum of 25% miniaturization is achieved while maintaining acceptable characteristics.