Component Recycling in Chipless Devices for Low-Cost, Circular Wireless Temperature Sensors

With the rapid development of smart devices for body area networks and smart packaging, there is a significant demand for low-waste and low-impact electronic systems in industries such as healthcare and transportation. We demonstrate that the dielectric material from capacitors in resistor-inductor-capacitor (RLC) wireless, chipless, resonant temperature sensors can be successfully recovered from flexible PCBs, with pristine sensors re-introduced to the tag’s sensor loading. First, we demonstrate that replacing the dielectric in a parallel plate capacitor with a pristine component, with recycled electrodes and sub-miniature-A (SMA) adaptor, results in only a 3% change in broadband capacitance. An identical substitution of the sensing element in an RLC circuit tuned to resonate at 21.0 MHz, with recycled parallel plates, a resistor, and an inductive PCB coil, results in a change of only 7.6% in the resonant frequency of the tag to 19.4 MHz. This work demonstrates the recyclability of chipless tags for temperature sensing for the first time, offering sustainability gains in smart packaging applications, with the potential to be expanded to other sensing tags for pH, humidity, and chemical analytes, towards chipless product passports.