Piezoelectric materials are widely used in practical applications to genera
te and to detect stress waves. From this point of view, the coupling factor
k is the most useful parameter, in fact it is able to fully characterize t
his energy conversion. Many different k factors are defined in the literatu
re: the k(ij), or the so-called material coupling factor (k(mat)), defined
in static conditions; the effective coupling factor k(eff) defined in dynam
ic conditions; and the coupling factor defined by Berlincourt et al., valid
in static and dynamic conditions. In this work, according to the I. E. E.
E. Standards on Piezoelectricity, we define the k factor as the ratio betwe
en the energy converted from electric to mechanic form (or vice versa) and
the total energy involved in a transformation cycle and we demonstrate that
this definition can be applied both in static and dynamic cases. We also s
how that the effective coupling factor k(eff) has indeed this precise physi
cal meaning and that the Ic factor defined by Berlincourt, computed at the
antiresonance frequency of the piezoelement, has the same value as the k(ef
f) A simple unified treatment of the Ic factor is given in the work.