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.

StressTMechanically free
FieldEElectrical short circuit
DisplacementDElectrical open circuit
StrainSMechanically clamped

Curie Temperature
The crystal structure of a material changes at the Curie temperature, Tc, 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
ASurface area (m2)
cStiffness coefficient (N/m2)
CCapacitance (F)
dPiezoelectric charge coefficient (C/N)
DDiameter (m)
f1, f2-3dB points from the resonance frequency fr
faAnti-resonance frequency (Hz)
frResonance frequency (HZ)
gPiezoelectric voltage coefficient (Vm/N)
kCoupling factor
KRelative dielectric constant
LLength (m)
NFrequency constant (Hz*m)
QMechanical Q factor
sElastic compliance (m2/N)
TThickness (m)
TcCurie temperature (oC)
WWidth (m)
YYoung¹s modulus (N/m2)
ZmMinimum impedance at fr (ohm)
tan δDissipation factor
εoPermittivity of free space (8.854x10-12F/m)
εTPermittivity (F/M)
νSonic velocity (m/s)
ρDensity (kg/m3)
σEPoisson's ratio