A Novel Additively-Manufactured Pressure Transducer for Zero-Power Wireless Sensing

This work presents a pressure transducer consisting of a 3D coupled-line directional coupler, where the distance between lines varies with the applied pressure. In particular, two quarter-wave microstrip lines facing each other are aligned one on top of the other so that part of the signal flowing in one line is coupled to the other line. When pressure is applied, the distance between lines reduces, while coupling increases. That way, different pressure levels are converted into different coupling values. Two parallel-plate waveguides connect the microstrip line on the top layer to the bottom layer, so that all four ports of the directional coupler are realized on the same layer. The circuit is manufactured with stereolithography 3D printing. Selective metallization is performed embossing the desired patterns on the 3D printed dielectric and then applying silver nanoparticle ink to the protruding areas with a brush. A proof-of-concept prototype, working at 3 GHz, was manufactured and tested. The proposed prototype features a change of the transmission coefficient between the input and the coupled ports from -15.6 dB to -12.4 dB for an applied pressure of 278 kPa compared to zero pressure state, thereby proving the working principle of the circuit. The proposed transducer can be used in a harmonic transponder, and the pressure information can be retrieved from the amplitude difference of the signals at the direct and coupled ports. The obtained results open the door to a new class of pressure transducers that are based on additively-manufactured radio-frequency components, and are suitable for passive wireless sensors.