$\mathrm{x}(\mathrm{t})$	Acquired signal
${\mathrm{x}}_{\mathrm{j}}(\mathrm{t})$	jth IMF of the signal $\mathrm{x}(\mathrm{t})$
T	total duration of the signal
N	the total number of data points
C	Covariance matrix
E	Residual error matrix
${\mathrm{C}}_{{\mathrm{x}(\mathrm{t})\mathrm{x}}_{\mathrm{j}}(\mathrm{t})}$	covariance between ${\mathrm{x}(\mathrm{t}) \mathrm{and} \mathrm{x}}_{\mathrm{j}}(\mathrm{t})$
${\mathsf{\sigma }}_{\mathrm{x}(\mathrm{t})}$	standard deviation of x(t)
${\mathsf{\sigma }}_{{\mathrm{x}}_{\mathrm{j}}(\mathrm{t})}$	standard deviation of xj(t)
$\mathrm{X}$	Response matrix
$\overline{\mathrm{X}}$	Zero mean response matrix
XIMF	Matrix consisting of IMFs corresponding to response matrix
LiNbO3	Lithium Niobate
${\mathsf{\theta }}_{\mathrm{ref}}$	Principal angle corresponding to reference case
${\mathsf{\theta }}_{{\mathrm{d}}_{\mathrm{i}}}$	Principal angle corresponding to damage-i case