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

The "coin tap test" is one of the oldest methods of nondestructive test (NDT). It requires an operator to tap with a coin-like light tool on each point of the structure to be inspected, feeling the subtle difference of impact force and hearing the resulting sound to discriminate defective objects from normal ones. Although this is the one of the most cost-effective NDT methods for detection of delamination in multilayered materials, the test technology still remains largely subjective, and there has been considerably uncertainty about the physical principles behind it. Through analyzing and comparing the different aspects of the impact in the coin-tap test mainly the force measured by an accelerometer in the hammer and the resulting sound recorded with a microphone-this paper seeks a better understanding of the fundamental principles underlying the individual measurement techniques, and 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.