Capacitive Sensors Integrated in SIW Structures – A Proof of Concept

The paper presents a circuit technique aimed to integrate interdigital transducer (IDT) based sensors, provided with either coplanar waveguide (CPW) or microstrip ports, into substrate integrated waveguide (SIW) structures for operation as transmission-type sensors. Therefore, two electromagnetically coupled SIW sections are specifically configured to make possible this conversion. In order to demonstrate the validity of the proposed sensing concept, capacitors of different values, and fully compatible with surface-mounting technology, were assembled at the CPW port of the coupled SIW section to simulate various IDT capacitive sensors. Deviation of the maximum rejection frequency from 4.32 GHz to 7.56 GHz was obtained using capacitance values from 4.7 pF down to 0 pF (i.e. open ended CPW).