# Definitions & Terminology

## Piezoceramics Definitions and Terminology

**Definitions and Terminology**

In piezoelectric ceramics, material characteristics depend on the direction of the applied field, displacement, stress and strain. Hence superscripts and subscripts indicating the direction are added to the symbols. The direction of polarization is generally designated as the z-axis of an orthogonal crystallographic system. The axes x, y and z are respectively represented as 1, 2 and 3 directions and the shear about these axes are represented as 4, 5 and 6. This is shown schematically on the Symbols and Terminology Chart. The various piezoelectric material constants are generally expressed with subscripts using this notation. In addition to the above, planar modes are sometimes expressed with a subscript 'p'. Superscripts indicate a constant mechanical or electrical boundary condition. The table below gives a general description of the superscripts.

Parameter | Symbol | Condition |
---|---|---|

Stress | T | Mechanically free |

Field | E | Electrical short circuit |

Displacement | D | Electrical open circuit |

Strain | S | Mechanically clamped |

**Curie Temperature**

The crystal structure of a material changes at the Curie temperature, T_{c}, from piezoelectric (non-symmetrical) to a non-piezoelectric (symmetrical) form. This phase change is accompanied by a peak in the dielectric constant and a complete loss of all piezoelectric properties.

Table of Symbols | |
---|---|

A | Surface area (m^{2}) |

c | Stiffness coefficient (N/m^{2)} |

C | Capacitance (F) |

d | Piezoelectric charge coefficient (C/N) |

D | Diameter (m) |

f_{1}, f_{2} | -3dB points from the resonance frequency f_{r} |

f_{a} | Anti-resonance frequency (Hz) |

f_{r} | Resonance frequency (HZ) |

g | Piezoelectric voltage coefficient (Vm/N) |

k | Coupling factor |

K | Relative dielectric constant |

L | Length (m) |

N | Frequency constant (Hz*m) |

Q | Mechanical Q factor |

s | Elastic compliance (m^{2/N)} |

T | Thickness (m) |

T_{c} | Curie temperature (^{o}C) |

W | Width (m) |

Y | Young¹s modulus (N/m^{2}) |

Z_{m} | Minimum impedance at fr (ohm) |

tan δ | Dissipation factor |

ε_{o} | Permittivity of free space (8.854x10^{-12F}/m) |

ε^{T} | Permittivity (F/M) |

ν | Sonic velocity (m/s) |

ρ | Density (kg/m^{3}) |

σ^{E} | Poisson's ratio |