A wireless passive RCS-based temperature sensor using liquid metal and microfluidics technologies

A novel wireless and passive temperature sensor that utilizes microfluidic and liquid metal technologies for the temperature-dependent modification of the sensor´s radar echo is introduced. Liquid metal is used to dynamically alter the number of antenna elements activated along a linear array configuration with respect to temperature. In this way, the sensed temperature value can be accurately quantified by the change in radar cross section (RCS) of the device. Simulation and measurements of the backscattered power of the temperature-reconfigurable array were performed to verify the concept and benchmark the sensitivity and temperature range of the sensor. This study is based on the number of elements activated by the short-circuiting of their gap through the temperature-expansion of liquid metal inside a bridging microfluidic channel. For the first time the remote measurement of temperature based on the RCS variability of a microfluidics-realized sensor is presented. It features an RCS range of 9 dBsm at 29.5 GHz corresponding to a tunable temperature range of at least 20°K and a resolution of 1.8 dBsm per element activated resulting in a temperature resolution around 4°K. It has to be noted that numerous major challenges encountered in the feeding and encapsulation of liquid metal inside microfluidic channels were addressed and preliminary guidelines for a novel generation of wireless sensors based on liquid metal and microfluidic technologies have been established for the first time.