多层介质中隐含层的太赫兹无损检测

Terahertz Nondestructive Detection of the Hidden Layer in Multilayer Medium

在工业应用中,大多数情况下的复合结构介质仅有一面可以被检测,因此需要研究反射模式下检测介质内部参数的太赫兹无损检测方法.推导了反射模式下太赫兹波在三层结构介质中的传输模型,通过遗传算法共同反演估计得到中间分层的厚度,以及它的折射率,从而获得中间隐藏层的具体信息.制备了具有200μm的隐藏分层的三层结构样品,利用太赫兹时域光谱系统对其进行了测量,将理论模型与实测数据进行对比,利用遗传算法估计得到隐藏层的厚度和折射率,将厚度估计值与测厚仪测量结果对比,误差保持在4%以内,折射率估计值与实际值相比,误差范围波动较大,平均误差为6%左右,最后对误差来源进行了分析,为多层复合材料内部缺陷、中间层材料的介电参数估计提供了理论和实验依据.研究表明该系统作为一种无损评价方法可以广泛应用于层状结构的可靠性评价.

In industrial applications,only one side of the composite media can be detected in most cases,so it is necessary to study the terahertz nondestructive testing method to detect the internal parameters of the desired media based on the reflection mode.The transmission model of terahertz waves in the medium of a three-layer structure is derived under the reflection mode.The thickness of the middle layer together and its refractive index are estimated by a genetic algorithm to attain the specific information about the middle hidden layer.At the same time,samples with the three-layer structure consisting of the hidden layer with the thickness of 200μm are prepared and subjected to a terahertz time-domain spectroscopic system.In addition,a theoretical model is designed to compare the achieved measurements. Thereafter,a geneticalgorithm is designed to estimate the thickness of the hidden layer and the respective refractive index toverify the effectiveness of the proposed method. Compared the estimated value of thickness with themeasurement result of the thickness gauge,the error is kept within 4%. Compared with the actual value,the error range of the estimate refractive index fluctuates greatly,the average error is about 6%. Finally,the error sources is analysed,which provides the theoretical and experimental basis for the iternal defects ofthe multilayer composite material and the dielectric parameter of the intermediate layer material. Thepractice shows that the system as a nondestructive evaluation method can be widely used in the reliabilityevaluation of layered structures.