基于稀疏表示的叶片热障涂层太赫兹检测回波信号定位分离方法

Location and Separation of Terahertz Echo Signal of TBCs Based on Sparse Representation Method

针对带热障涂层叶片样品多层反射、材料色散吸收以及噪声等原因造成太赫兹回波信号定位不准的问题,提出一种基于稀疏表示的时间切片稀疏色散模型,考虑材料色散对太赫兹时域回波信号脉冲展宽的影响,结合太赫兹回波信号的卷积模型,建立对应的太赫兹稀疏色散字典,并通过谱投影梯度凸优化算法重构稀疏的脉冲响应函数,实现复杂回波信号延迟时间的定位。此外,引入方均根误差和稀疏性评价指标,从重构精度和稀疏性两个维度定量衡量提出方法对太赫兹回波的定位效果。理论模拟和热障涂层试验结果表明所提出的方法具有更好的重构精度和稀疏度,回波定位效果优于频域小波解卷积和未考虑色散的稀疏重构方法,更能适应于复杂太赫兹回波信号的精确定位,为太赫兹复杂信号的处理提供了一种新的途径。

In order to solve the problem of inaccurate location of complex terahertz echo signal caused by multi-layer reflection,material dispersion absorption and noise of blade samples with thermal barrier coatings,a time sliced sparse dispersion model based on sparse representation is proposed to locate the complex terahertz echoes.Considering the influence of material dispersion on the pulse spreading of terahertz time domain echo signal,the corresponding terahertz sparse dispersion dictionary is established based on the convolution model of terahertz echo signal.The sparse pulse response function can be reconstructed by spectral projected gradient convex optimization algorithm to locate the delay time of complex echo signal.In addition,the evaluation indicators composed of the root mean square error and sparsity are introduced to quantitatively assess the performance of the proposed method on THz echoes from the two dimensions of reconstruction accuracy and sparsity.Then,theoretical simulation and thermal barrier coating experimental results indicate that the proposed method has better reconstruction accuracy and sparsity,and the echo location performance is better than that of frequency wavelet domain deconvolution and sparse reconstruction method without considering dispersion.It is more suitable for precise localization of complex terahertz echo signal,and provides a new way for the processing of complex terahertz signal.