超薄弹性层超声反射波频域测厚法

Ultrasonic reflection wave frequency-domain method for the thickness measurement of ultra-thin elastic plate

为了克服超声体积波测量方法只适用于测试厚度大于声波波长的弹性层的缺点,提出了频域相对传递函数法测量超薄弹性层的厚度的新方法.在推导超薄弹性层相对反射传递函数的基础上,用相对反射传递函数幅度谱、相位谱和复谱定征超薄弹性的厚度,分析了影响估计准确性的各种因素,研究了相对反射传递函数对厚度的灵敏度函数在误差传递中的意义.实验结果表明:相对传递函数法能够测量厚度为波长百分之一的铝薄层的厚度,相对误差小于2.5%,其中用幅度谱定征得到的结果最准确.这表明相对传递函数法可以有效地测量超薄弹性层的厚度,在实际应用中更加实用,其定征的准确性主要由相对传递函数对厚度灵敏度函数和测量误差共同决定.

A novel ultrasonic longitudinal reflection wave frequency-domain method suitable for measuring the thickness of ultra-thin elastic layer is presented. The relative reflection transfer function of ultra-thin layer was derived. In the least squares-error sense, an inverse algorithm was used to characterize the layer thickness on the basis of amplitude, phase and complex spectrum. Main sources of estimate deviation were analyzed. The sensitivity of the relative reflection transfer function to the layer thickness and its importance in the transfer of errors were discussed. It is observed in the experiment that the method can measure the thickness of an elastic aluminum layer less than one percent of the wavelength within a relative error of 2. 5 %. The result obtained on the basis of the amplitude spectrum is the most accurate. The relative reflection transfer function method can characterize the thickness of ultra-thin elastic layer effectively. The accuracy of this method is mainly dependent on the sensitivity of the relative reflection transfer function to the layer thickness and the measurement error.