板底薄层的超声谐振检测分析

Analysis of the ultrasonic resonance test for a plate with a thin layer

理论上研究了带有薄层的板的超声谐振频率随薄层的厚度或物性改变而发生变化的规律,研究结果表明,在0≤ω<c2/d2 arctan(Z1/Z2)范围内,板的半波谐振频率因薄层厚度的增加向低频飘移;在一阶近似条件下,飘移量的大小正比于薄层和板的单位面积质量之比。在此基础上,提出了利用板的谐振频率飘移量进行板底薄层厚度检测的方法,并对6.24 mm厚铝板下不同厚度(54-324 μm)的薄层进行了厚度检测,实验得到的厚度相对误差在6％以下。实验结果进一步证实了该规律是正确的,以及基于该规律的板底薄层检测方法是可行的。

The resonance frequencies of a plate with a thin layer are studied in the paper, their shift phenomenon due to the variations of the thickness or other acoustical properties of the thin layer is observed. In the range 0≤ω<c2/d2 arctan(Z1/Z2), the half-wavelength resonance frequencies of the plate shift down due to the existence of the thin layer. Specially, the frequency-shift is linearly with the mass ratio of the thin layer to the plate in the first approximation. An ultrasonic technique is proposed for the measurement of the thin layer thickness based on the theory, and the thickness of the polymer layer (54-324 μm) beneath an aluminum substrate (6.24 mm thick) is measured by it, the measured relative errors of the thin layer thickness are less than 6%, which confirms the correctness of the theory, and furthermore, the validity of the technique based on it.