An Angular Displacement Sensor With a Curved Two-Metal-Layer CPW Loaded by an EBG Structure

This paper presents a microwave angular displacement sensor that consists of a curved two-metal-layer coplanar waveguide (TML CPW) loaded by an electromagnetic bandgap structure (two semi-cylindrical periodic air-gap structures of dielectrics, allocated at the top and bottom of the curved TML CPW). Rotating one of the dielectrics against the other one, produces a variation in the depth of the stopband at the central frequency. The magnitude change is proportional to the angle of the rotation. The curved TML CPW line with the length of 140 mm is fabricated on a 254 μm thick RO3010 Rogers substrate (ε
_r
= 10.2 and tan δ = 0.0022), which is arched in a semi-cylindrical shape with a radius of 50 mm. The periodic airgap structures, in order to create the electromagnetic bandgap, are manufactured by laser cutting of an optically transparent polycarbonate (ε
_r
= 2.8 and tan δ = 0.01) in semi-cylindrical shapes. The analysis, finite element method simulation, realization, and measurements have been performed for the sensor with 15 unit cells. An average sensitivity and a dynamic range of about 3 dB/deg and 5° degrees, respectively, have been obtained at 10.2 GHz. The fixed operating frequency and the wide bandwidth of the sensor (>1 GHz) will simplify the design and fabrication of the data readout circuit. The impact of the structure curvature on the sensor response is also investigated as an important practical issue.