Wireless crack sensing using an RFID-based folded patch antenna

This paper describes the crack sensing performance of a wireless and passive smart-skin sensor designed as a folded patch antenna. When strain/deformation occurs on the patch antenna, the antenna's electrical length changes and its electromagnetic resonance frequency also changes accordingly. An inexpensive off-the-shelf radiofrequency identification (RFID) chip is adopted in the sensor design for signal modulation and collision avoidance. With assistance from the RFID chip, the resonance frequency change can be interrogated and recorded by a wireless reader. The RF interrogation energy from the reader is captured by the patch antenna, and then used to activate the RFID chip that transmits modulated signal back to the reader. Therefore, the interrogation process is wireless and the antenna sensor is battery-free. In this research, crack sensing performance of the antenna sensor is studied and tested by a specially designed crack testing device. Testing results show strong correlation between interrogated resonance frequency and crack opening size.