In the SI system it has units of kg/m4 (Barron, p. 333) ↑ Responsiveness is the inverse of mechanical resistance (Seely et al., p. 200) ↑ Piezoelectric transducers are frequently modelled as three-port devices, one electrical and two mechanical, because mechanical vibrations are induced on both sides of the crystal (Cheeke, pp. 213-214).