| Density (kg/m3) | Young’s modulus (N/m2) | Coefficient of friction |
Piezoelectric material | 8000 | 6.7 × 1010 | - |
Ni alloy | 8911 | 1.43 × 1011 | - |
Silicon rubber | 1198 | 4.812 × 106 | 1.3 |