Wireless Modal Testing With Multiple Battery-Free Backscatter Sensors

This paper reports the design, implementation and the result of real-world experiment of wireless modal testing with battery-free backscatter sensors. The battery-free backscatter sensor comprises a custom radio frequency integrated circuit (RFIC), a commodity micro electro-mechanical system (MEMS) accelerometer, and an antenna. Sensor data concurrency demanded in modal testing is realized by allocating a dedicated subcarrier to each backscatter sensor. The orchestration of wireless communications in 920 MHz based on Gen2 protocol and the wireless power supply to the backscatter sensor are performed by a software defined interrogator built on LabVIEW communications and USRP. We developed an over the air (OTA) subcarrier frequency allocation with a sequence of WRITE commands of Gen2 protocol, and its performance was confirmed with the experiments in an indoor radio propagation. The accuracy of the proposed wireless structural modal testing was experimentally verified by comparing with a commercial modal testing system with wired accelerometers. Wireless modal testing were performed both with sine sweep excitation and random excitation. The experiment reveals that wireless modal testing up to 100 Hz can be successfully performed by battery-free wireless sensors. It is also revealed that the selection of subcarrier bitrate is important to secure the bandwidth of the measurement while preserving a sufficient number of subcarrier channels.