A Sustainable and Low-Waste Temperature Sensor Based on 3D Liquid Metal and Carbon/Polymer-Loaded Lossy Transmission Lines

We present a simple, low-waste RF temperature sensor based on liquid metal and a polydimethylsiloxane-carbon fiber (PDMS-CF) composite in a variable-attenuation coplanar waveguide (CPW) architecture. The sensor consists of a 3D-printed and liquid metal-filled CPW, and a PDMS-CF sensing element on the signal line. The PDMS-CF sensing element measures 10 mm × 3mm and is loaded on the CPW's signal line. The PDMS-CF element acts as a lossy transmission line, and the resulting transmission coefficient has an average sensitivity of 0.21 dB/°C at 50 MHz This sensitivity is greater than most of amplitude-based temperature sensor. The liquid metal and the PLA used for 3D printing are recyclable and biodegradable, respectively, with the PDMS-CF sensing element fully re-usable; the proposed RF sensor shows how chipless antenna-based sensors can be realized sustainably.