Laser Self-Mixing Sensor Based on Time–Frequency Spectrum for Material Damping Coefficient Measurement

A new method for measurement of the material damping coefficient based on the laser self-mixing interference (SMI) technique is proposed. The dominant frequency that varies over time is extracted by using the synchro-squeezed wavelet transform to obtain the time–frequency spectrum of a SMI signal. According to the linear relationship between the logarithm of the dominant frequency order and the damping coefficient, the damping coefficient of the material is obtained through linear fitting. The principle and process of the method are elaborated on and its performance is analyzed under different noise interferences and optical feedback factors. In tuning fork measurement, the root mean square error of the measured damping coefficient reaches 0.0133. With adaptive frequency resolution and window length, this method facilitates automated and high-precision damping coefficient measurement in materials.