A Microstrip Coupled Cylindrical Dielectric Resonator as a Displacement Sensor

This paper presents the numerical and experimental investigations on the use of a cylindrical dielectric resonator (DR) as a displacement sensor in the millimetre range, for the first time. The sensor principle is based on the sensitivity of the coupling between a resonator and a transmission line, which is a simple microstrip line in the present context, to positional changes (displacement) of the resonator. Corresponding change in the input reflection coefficient of the microstrip line can be used to quantify the displacement. It is demonstrated numerically that the sensitivity and the linearity of the displacement sensing are highly dependent on the dielectric constant of the DR, a feature that is absent in other resonator-based sensors. Experimental results for an available DR sample of dielectric constant 24, diameter 19.43 mm and height 7.3 mm, operating in the HEM11 delta mode with a resonant frequency of 3.41 GHz are presented to validate the simulations. Analysis of the results shows that in the measurement range of 1-8 mm, the above arrangement gives a sensitivity of 2.01 dB/mm. Such displacement sensors may find application in strain or pressure measurement, as well as in diagnosing alignment or positional errors.