Non-invasive Microwave Planar Rotation Sensors Based On Inductive And Capacitive Coupling

The demand for high precision non-contact angular displacement sensors operating in a wide range of applications and operating conditions has led researchers to develop new techniques and designs for the realization of miniaturized,highly sensitive,low cost,environmentally robust,non-contact sensors.The purpose of this thesis is to realize sensitive,low cost,compact,rotational displacement/velocity sensors based on resonance frequency modulation and amplitude modulation while employing the same design.The proposed devices basically consist of a planar microstrip fed ring resonator coupled to a suspended rotating linear resonator.The two distinct responses were able to be realized using the same design by exploiting the dielectric materials used;where for the resonance frequency shift sensor a low dielectric permittivity substrate and a slightly higher permittivity substrate were used for the rotating and stationary parts respectively;while for the amplitude modulation sensor the same dielectric material with a low permittivity was used for both the stationary and rotating parts.The effect of using different dielectric materials(in the frequency modulated case)is that resonance is seen to occur on the ring resonator which is shifted accordingly when a metallic suspended linear resonator is in close proximity through inductive coupling between the two structures which is highly dependent on the angle of rotation.While in the latter case the use of a low permittivity substrate material for both structures enhances the fringing capacitances which allows for energy to be coupled to the suspended linear resonator consequently resulting in its resonance which depends on its electrical length with respect to the guided wavelength.In other words change in angular position of the linear resonator results in change in its electrical length hence the amount of coupling depends on its angular position.Furthermore by changing the ring resonator shape into an oval geometry so as to increase the current path and by carefully tapering it in order to compensate for the non-uniformity of electromagnetic fields along the ring resonator;a highly sensitive amplitude modulated based angular displacement/velocity sensor capable of measuring angles of up to 5° while exhibiting good linearity over a dynamic range spanning from 0° to 90° was realized.Moreover,the proposed sensors offer high design flexibility with regard to their applicability in different operating environments while ensuring low manufacturing costs.