Wireless strain sensor based on amorphous carbon for human-motion detection

A wireless strain sensor system has been designed for human motion detection. The amorphous carbon strain sensor was fabricated on a flexible substrate and integrated in a wireless module. Amorphous carbon was sputter-deposited on a 125-μm thick polyimide film and the strain gauges were tailored using laser micromachining followed by an encapsulation process to package the sensor in elastic polydimethylsiloxane (PDMS) polymer. The wearable module included an interface circuit that converted sensor analog signals into digital format feeding to a Texas Instruments MSP 430 microprocessor in an eZ430RF2500 module. The signals were sent wirelessly to an eZ430RF2500 reader module connected to a remote computer in which the demodulated sensor data were displayed and recorded continuously. The sensor was calibrated and the entire wireless system was tested by mounting the sensor module across a knee joint during various types of physical exercises. Results demonstrated the feasibility of using our wireless strain sensors to monitor human body motion.