$j$	Complex symbol
$\omega$	Angular frequency (rad·s−1)
$C$	Capacitance symbol (F)
${\epsilon }_{33}^T$	Dielectric constant (F·m−1)
$2l$	Length of the square PZT (mm)
$h$	Thickness of circular PZT (mm)
$k_p$	Coupling coefficient
$d_{31}$	Piezoelectric strain constant (PC·N−1)
$Y_{11}^E$	Young’s modulus (N·m−2)
$\nu$	Poisson ratio
$\kappa$	Wavenumber (m−1)
$c_p$	Phase velocity (m·s−1)
$Y_{nons}$	Damage-non-sensitive component in admittance model (S)
$Y_{sens}$	Damage-sensitive component in admittance model (S)
$Y$	Coupling mechanical admittance (S)
$\rho$	Density (kg·m−3)
$\eta$	Mechanical loss factor
$\delta$	Dielectric loss factor
$Z_{a,eff}$	Effective driving point impedance of PZT under short-circuited condition (N·s/m)
$Z_{s,eff}$	Effective driving point impedance of host structure (N·s/m)
$Z$	Coupling mechanical impedance (Ω)
$x_{str}$	Real part of ESMI signatures
$y_{str}$	Imaginary part of ESMI signatures
SV	Specific value of two RMSD values in adjacent testing states