AE	Auto encoder
ANN	Artificial Neural Network
BiLSTM	Bidirectional Long Short-Term Memory
CNN	Convolutional Neural Network
DL	Deep learning
FFT	Fast Fourier Transform
IR	Impact resonance
LSTM	Long Short-Term Memory
ML	Machine learning
NDE	Nondestructive evaluation
PC	Principal component
PCA	Principal component analysis
PR	Piston rod
RMS	Root mean square
RNN	Recurrent Neural Network
SOM	Self-Organizing Map
SR	Steering rack
STFT	Short Time Fourier Transform
SVM	Support vector machine
TF	Time-Frequency