Wireless mm-Wave Chipless Pressure Sensor

An innovative passive wireless pressure sensor is proposed. The sensor is based on a millimeter-wave chipless tag operating in the $Ka$ -band that works in combination with a dielectric superstrate. The tag consists of a frequency-selective surface (FSS) printed on an ultrathin support dielectric substrate that separates it from a ground plane. The superstrate is placed on top of the tag and encapsulated to obtain the pressure sensor. Applying pressure on the ground plane causes a shift of the resonance peak due to the change in effective permittivity. The proposed sensor can work with copolar and cross-polar interrogation and it is probed without background subtraction using only amplitude measurements. The interrogation system consists of two commercial horn antennas placed up to a distance of 64 cm from the tag and a vector network analyzer (VNA). The proposed sensor is modeled through an equivalent circuit model (ECM) to explain the working principle, it is analyzed with full-wave simulations, and finally fabricated and carefully characterized. This is, as far as we know, the first chipless pressure sensor with a reading range larger than 5 cm which is not equipped with external antennas.