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 multi-layered 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