Strain Sensing through a Passive Wireless Sensor Array

This paper presents the strain sensing capability of a wireless and batteryless smart-skin sensor array. The sensor design is based on a folded patch antenna. When the patch antenna is under strain/deformation, its resonance frequency varies accordingly. The frequency variation can be easily interrogated and recorded by a wireless reader based on a backscattering mechanism. The patch antenna utilizes an inexpensive off-the-shelf radiofrequency identification (RFID) chip for signal modulation and anti-collision, in order to avoid interference among multiple sensors. Since the RFID chip harvests electromagnetic energy from the interrogation signal emitted by the reader, the patch antenna itself does not require other (internal) power source and, thus, serves as a batteryless and wireless strain sensor. In this preliminary investigation, several prototype folded patch antennas have been designed and manufactured to form a wireless strain sensor array. Tensile testing results of the wireless strain sensor show strong correlation between interrogated resonance frequency and strain experienced by the sensor. Minimum interference is observed among multiple sensors in the same neighborhood, when interrogated individually by a reader.