# Piezoelectric charge constant d

A property that determines the degree of piezoelectric effect. d is defined somewhat differently depending on the type of effect (direct or inverse).

Effect Symbol Description Applicability Units
Direct dE d at constant electric field E —
dielectric displacement developed per unit of applied stress
Transducers used as receivers; accelerometers Coulomb/N
Inverse dT d at constant stress T —
strain developed per unit of applied electric field
Transducers used as transmitters m/volt

Although dT and dE have different units, their numerical values in the S.I. system are identical (see Berlincourt (3), equation 24a, p. 188). The value depends on the type of piezoelectric material, the time since poling, and local conditions (e.g., the temperature, electric field strength, static stress, etc.). The value also depends on the orientation of the stress-strain or electric field with respect to the poling direction. For transducers d33 (i.e., parallel orientation) is most common although d31 (i.e., perpendicular orientation) is sometimes used.

Also see other piezoelectric properties.