$\sigma$	is Stress Vector (N/m${}^2$),
x	is Strain Vector (m/m),
E	is Applied Electrical field in (V/m),
$ϵ$	is permittivity in (F/m),
d	is piezoelectric constant (m/V),
S	is Matrix of compliance coefficients (m${}^2$/N),
D	is Electrical displacement (C/m${}^2$),
g	is piezoelectric constant (m${}^2$/C),
$\beta$	is impermittivity component (m/F).