A Microfluidic, Reversibly Stretchable, Large-Area Wireless Strain Sensor

This article describes the implementation and characterization of a new self-contained large-area wireless strain sensor, operating around 1.5 GHz, based on the concept of multi-layer microfluidic stretchable radiofrequency electronics (mu FSRFEs). Compared to existing solutions, the presented integrated strain sensor is capable of remotely detecting repeated high tensile dynamic strains of up to 15% over very large surfaces or movable parts, and gets rid of all hardwiring to external storage or data processing equipment. Unlike conventional electronic devices, the major part of the sensor is a mechanically reconfigurable and reversibly deformable patch antenna, which consists of two layers of liquid metal alloy filled microfluidic channels in a silicone elastomer. A simplified radiofrequency (RF) transmitter composed of miniaturized rigid active integrated circuits (ICs) associated with discrete passive components was assembled on a flexible printed circuit board (FPCB) and then heterogeneously integrated to the antenna. The elastic patch antenna can withstand repeated mechanical stretches while still maintaining its electrical function to some extent, and return to its original state after removal of the stress. Additionally, its electrical characteristics at frequency of operation are highly sensitive to mechanical strains. Consequently, not only is this antenna a radiator for transmitting and receiving RF signals like any other conventional antennas, but also acts as a reversible large-area strain sensor in the integrated device. Good electrical performance of the standalone antenna and the RF transmitter sub-module was respectively verified by experiments. Furthermore, a personal computer (PC)-assisted RF receiver for receiving and processing the measured data was also designed, implemented, and evaluated. In the real-life demonstration, the integrated strain sensor successfully monitored periodically repeated human body motion, and wirelessly transmitted the measured data to the custom-designed receiver at a distance of 5m in real-time.