Table 2.

Physical properties of PZT (ceramic), PVDF (polymer), and Piezoflex and Piezel (composite materials).

Property	PZT (PC5)	PVDF	Piezoflex1 #	Piezel *
Density (kg/m${}^3$)	7750	1800	4500	5600
Sonic velocity (m/s)	2830	1400	2100	1687
Acoustic impedance (Mralys)	22	3	10	9.8
Compliance ($\times {10}^{-9}$ m${}^2$/N)	0.02	0.1	13	0.25
Relative permittivity	1800	10	32	70
Tan$\delta$ (at 1 kHz)	0.02	0.05	0.08	0.047
$d_{33}$ (pC/N)	410	30	25	40
$d_{31}$ (pC/N)	−175	−18	−4.6	−24
$g_{33}$ (mV-m/N)	26	340	88	–

Reprinted, with permission, from [11], © 1994 Elsevier. # Piezoflexl PZT embedded in an inactive epoxy resin matrix with a volume distribution of 50–50%. * Piezel is PZT core embedded in a matrix of the PVDF with a volume distribution of 50–50%.