A novel micro-vibration sensor for activity recognition: Potential and limitations

This paper researches the potential of a novel ball switch as a wearable vibration sensor for activity recognition. The ball switch is available as a commercial, off-the-shelf sensor and is unique among such sensors due to its miniaturized design and the low mass of the ball. We present a detailed analysis of the physical properties of the sensor as well as a recommendation for circuit design, sampling method and a feature generation algorithm for activity recognition. The analysis reveals that it is sensitive to vibrations between 1.5 kHz and 8 kHz, where the acceleration sensor is responsive below 1.6 kHz. Furthermore, the ball switch is substantially cheaper (3x), smaller (2x) and uses less power (50x) than an accelerometer based system, but delivers less information. We also present the results of a case study in activity recognition done in parallel with an acceleration sensor using 5 subjects and 8 different activities. It shows that the ball switch can increase recognition rates when added to an accelerometer-based system, demonstrating that it can sample activity-pertinent information which an accelerometer can not. We conclude that this ball switch can be used to recognize high-frequency activity components and effectively improve recognition rates while representing a very low cost sensor in terms of price, device size and power consumption.