Microwave sensor for liquid classification and permittivity estimation of dielectric materials

Abstract

This paper presents a material detection sensor based on SIW technique. Three electric walls of the SIW cavity resonator are made by metallic vias whereas the fourth one is made by λg4 stub. The dielectric substrate under stub is partially removed and by immersing this empty space inside the cup filled with the liquid under test or by inserting the dielectric material inside the sensor, the effective permittivity of the medium under stub will change, shifting the resonant frequency of the cavity resonator. These shifts are taken as an indicator of presence of the liquid or the dielectric material. An analytical model based on mixing rule formula is presented and the obtained result is compared with the simulated one. The comparison indicated that the analytical model is an accurate approximation method of this proposed sensor. In addition, the measurement results showed that the proposed sensor can detect a large dynamic range of permittivity ranging from 1 to 83 and has a high frequency shift (296 MHz). The unique feature of this sensor can be that by changing the volume of the MUT by changing the length of the empty space under stub, the dynamic range and the sensitivity increase greatly.