Correlation of accelerometer and microphone data in the "coin tap test"

In the "coin tap test," an operator taps with a coin-like light tool on the structure to be inspected, feeling the subtle difference of impact force and hearing the resulting sound to discriminate defective regions from normal ones. The test remains largely subjective, and there has been considerable uncertainty about the physical principles behind it. Analyzing and comparing the force measured by an accelerometer in the hammer and the resulting sound recorded with a microphone, this paper seeks an understanding of the fundamental principles underlying the individual measurement techniques. It gives a paradigm for sensor fusion via using the data from one modality to select the optimal time window for signal analysis of another modality.