Making Sense Of Mechanical Vibration Period With Sub-millisecond Accuracy Using Backscatter Signals

Abstract

Traditional vibration inspection systems, equipped with separated sensing and communication modules, are either very expensive (<i>e.g.</i>, hundreds of dollars) and/or suffer from occlusion and narrow field of view (<i>e.g.</i>, laser). In this work, we present an RFID-based solution, Tagbeat, to inspect mechanical vibration using COTS RFID tags and readers. Making sense of <i>micro</i> and <i>high-frequency</i> vibration using <i>random</i> and <i>low-frequency</i> readings of tag has been a daunting task, especially challenging for achieving <i>sub-millisecond</i> period accuracy. Our system achieves these three goals by discerning the change pattern of backscatter signal replied from the tag, which is attached on the vibrating surface and displaced by the vibration within a small range. This work introduces three main innovations. First, it shows how one can utilize COTS RFID to sense mechanical vibration and accurately discover its period with a few periods of short and noisy samples. Second, a new digital microscope is designed to amplify the micro-vibration-induced weak signals. Third, Tagbeat introduces compressive reading to inspect high-frequency vibration with relatively low RFID read rate. We implement Tagbeat using a COTS RFID device and evaluate it with a commercial centrifugal machine. Empirical benchmarks with a prototype show that Tagbeat can inspect the vibration period with a mean accuracy of 0.36<i>ms</i> and a relative error rate of 0.03%. We also study three cases to demonstrate how to associate our inspection solution with the specific domain requirements.