A Battery-Free, Chipless, Highly Sensitive LC Pressure Sensor Tag Using PEDOT: PSS and Melamine Foam

We have designed and developed a compact, contactless, chipless, high frequency wireless passive LC pressure sensor tag capable of measuring pressure from 0 Pa to 60 kPa. The LC pressure sensor tag design consists of a parallel combination of a planar inductor and a pressure sensitive interdigitated capacitor (IDC). The readout or signal detection and signal processing system combines a Colpitts oscillator, different electronic circuits, and a microcontroller-based signal processing unit. Operation of the sensor is based on mutual coupling of the inductor of the LC pressure sensor tag and the oscillation coil of the Colpitts oscillator. The pressure sensitive IDC consists of interdigitated electrodes and a melamine foam containing poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as an elastic pressure sensitive dielectric material. When pressure is applied to the LC pressure sensor tag, the capacitance of the IDC sensing element changes, which changes the resonance frequency. Because the LC pressure tag and the inductor of the oscillator are inductively coupled, the frequency of oscillation of the Colpitts oscillator changes. The LC pressure sensor has a highly sensitive sensing response of 762.65 Hz/kPa and a linear sensing performance over a wide measurement range, with a correlation coefficient ( $\text{R}^{\sf 2}$ ) of 0.997. The LC pressure sensor tag is lightweight, highly sensitive, inexpensive to fabricate, and has good repeatability and stability values in the percentage of 2.8 and 1.1, respectively.