Table 1.

Comparison of piezoelectric materials.

Materials	ZnO [24,25,26,27,28]	AlN [24,25,26,28,29]	PZT [26,28,30]	β-PVDF [28,31,32,33,34,35]
$\mathrm{Density}(g/c{m}^3$)	5.61	3.26	7.55	1.78
$\mathrm{Acoustic}\mathrm{velocity}(m/s$)	6340	11,350	3603	2200
$\mathrm{Young}\prime \mathrm{s}\mathrm{Modulus}(GPa$)	210	320	1200	3
$\mathrm{Acoustic}\mathrm{Impedance}({10}^6 kg/m^{2}s)$	36.2	37	27.2	2.7
$\mathrm{Effective}\mathrm{coupling}\mathrm{coefficient}.k_{eff}^2$(%)	7.8	6.0	20.25	14
$\mathrm{Piezoelectric}\mathrm{coefficient}{d}_{33} \left(pC/N\right)$	12	4.5	289–380	−24 to 34
$\mathrm{Coefficient}\mathrm{of}\mathrm{thermal}\mathrm{Expansion}(CTE, {10}^{-6}$)	4	5.2	1.75	42–75