Wireless Pressure Sensor Based on an Additively Manufactured Thermoplastic Polyurethane (TPU) Transducer

This paper presents a wireless pressure sensor where the transducer element is a 3D-printed elastomeric layer of Thermoplastic Polyurethane (TPU). The device consists of a one-port coplanar-waveguide transmission line terminated with an open-ended patch, the TPU (elastic) layer on top of it, and a step impedance resonator situated with one of the patches on top of the CPW patch and the other one on top of the CPW ground plane. When a pression is exerted vertically on the substrate where the SIR is etched, the effective dielectric constant and thickness of the TPU layer changes, and the capacitances between the SIR and the CPW layer are altered. This modifies the phase of the reflection coefficient, the considered output variable. The device is isolated by adding at both sides a rigid layer of 3D-printed polylactic acid (PLA) shielded with aluminum tape, and it is equipped with a pair of patch antennas to retrieve the pressure wirelessly. The dynamic range of the sensor is about 5 kPa, whereas the maximum measured sensitivity, achieved in the limit of small pressure, is 34.72 °/kPa.