Passive Wireless Frequency Doubling Antenna Sensor for Strain and Crack Sensing

This paper presents the design, simulation, and validation experiments of a passive (battery-free) wireless frequency doubling antenna sensor for strain and crack sensing. Since the length of a patch antenna governs the antenna's resonance frequency, a patch antenna bonded to a structural surface can be used to measure mechanical strain or crack propagation by interrogating resonance frequency shift due to antenna length change. In comparison with previous approaches such as radio frequency identification, the frequency doubling scheme is proposed as a new signal modulation approach for the antenna sensor. The proposed approach can easily distinguish backscattered passive sensor signal (at the doubled frequency 2 f) from environmental electromagnetic reflections (at original reader interrogation frequency f). To accurately estimate the performance of the frequency doubling antenna sensor, a multi-physics coupled simulation framework is proposed to aid the sensor design while considering both the mechanical and electromagnetic behaviors. Two commercial software packages, COMSOL and Advanced Design System (ADS), are combined to leverage the features from each other. The simulated performance of the frequency doubling antenna sensor is further validated by experiments. The results show that the sensor is capable of detecting small strain changes and the growth of a small crack.