Wireless Passive Flexible Strain Sensor Based on Aluminium Nitride Film

Abstract

Rolling bearings are important components of a mechanical structure; their state directly affects the operation of the whole mechanical system. To accurately and reliably evaluate the damage state of bearings, a wireless passive flexible strain sensor based on an aluminium nitride (AlN) film was proposed in this paper. The sensor was connected to the system using a plane inductor and an interdigital capacitor to form an LC loop, and the AlN film was deposited in the interdigital capacitor part to enhance the sensing performance. The structure of the sensor was optimised using a high-frequency structure simulator (HFSS), and the optimal coupling distance between the sensor and antenna was determined. The test results revealed that the resonant frequency of the sensor increases from 43.7089 to 43.735 MHz in a strain range of 0– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3000 ~\mu \varepsilon $ </tex-math></inline-formula> , and strain resolution is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20 ~\mu \varepsilon $ </tex-math></inline-formula> . Moreover, the wireless strain sensor has a small size and high resolution. The flexible substrate can stick well to the part to be tested and can be applied to the bearing to detect micro-strain. Therefore, this sensor is applicable in fault prevention, condition monitoring, and non-destructive evaluation.