The influence of the surface load exerted by a piezoelectric contact sensor on testing results: I. The displacement field in the solid

The influence of a strong discontinuity wave on its
measurement with a piezoelectric sensor was analysed analytically. The
one-dimensional model of the mechanical contact between the ultrasonic sensor
and the solid medium was developed. The displacement field was calculated with
the d'Alambert's method. The evaluation was made locally at the front of the
distortion. It was found that the relative difference of a displacements between
the free and loaded surfaces ranges from 10% to 72% and the mass M has no
influence on it in the first time interval. It is affected not only by the wave
impedances but also by surfaces of the sensor and sample. After a long period of
time (depending on the mass M) the influence of the surface loading becomes much
smaller. Part I of the paper contains the discussion of the displacement field
in the solid, the electricaltransients generated by the piezoelectic sensor are
given in Part II.