Flexible Chipless RFID Temperature Memory Sensor

This work presents a flexible and chipless radiofrequency identification (RFID) memory sensor for customizable temperature threshold detection wirelessly. The developed memory sensor is built with a polydimethylsiloxane (PDMS) substrate and metal loaded three microchannel based complementary split circular ring resonators. We inject Eutectic Gallium Indium (EGaIn) liquid metal alloy and composite oil composed of a mixture of two common cooking oils - grapeseed and coconut oil - through the channel results in a stretchable, bendable, rollable, and twistable device suitable for monitoring environmental temperature variation. 3D printed molds are used for designing the microchannel based flexible substrate. The geometry of the design has the novelty of having a microchannel inside a flexible substrate that offers food safe sensor. Moreover, the materials inside the channel can store sensing information for lower temperatures, eliminating continuous temperature monitoring. The experimental results of the fabricated prototype confirm the sensor can detect temperature thresholds of 4°C and 8°C up to 52° of bending angle. This paper also verifies the resonator can work as a permanent temperature memory sensor.