Local ultrasonic resonance spectroscopy (LURS) is a new approach to material inspection, where the specimen is locally excited by a short mechanical impulse while its local mechanical response is recorded at a position nearby. The local material and geometrical properties can be extracted from the frequency spectrum of the response and visualized by performing a scan over the inspected area. In our experiment, the plate thickness and the reliefs of both plate surfaces (plate curvature) were obtained from thickness resonance and time of arrival analysis without physical contact to the specimen. Ultrasound was generated on the specimen surface by a laser pulse. Local mechanical response of a carbon fiber-reinforced polymer plate with a thickness ranging from 0.6 mm to 4.3 mm was recorded with a broadband optical microphone in through-transmission setup. The precision of this arrangement greatly exceeded the precision of conventional methods limited by the ultrasound wavelength. For thicknesses in the range around 1 mm, standard deviations of up to several µm were achieved. An influence of the through-plate ultrasound velocity on the measured relief of the plate surface nearest to the optical microphone was eliminated by a joint evaluation of thickness resonance and time of arrival. Furthermore, we demonstrated that internal delaminations have an influence on the spectrum of the local mechanical response and can therefore be detected by LURS.

中文翻译：

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通过局部超声共振光谱进行厚度测量

局部超声共振光谱 (LURS) 是一种新的材料检测方法，其中试样由短机械脉冲局部激发，同时在附近位置记录其局部机械响应。可以从响应的频谱中提取局部材料和几何特性，并通过在检查区域上执行扫描来可视化。在我们的实验中，板厚度和两个板表面的起伏（板曲率）是通过厚度共振和到达时间分析获得的，而没有与试样进行物理接触。通过激光脉冲在试样表面产生超声波。厚度范围为 0.6 mm 至 4 的碳纤维增强聚合物板的局部机械响应。3 毫米是在直通传输设置中使用宽带光学麦克风录制的。这种布置的精度大大超过了受超声波波长限制的常规方法的精度。对于大约 1 毫米范围内的厚度，实现了高达几微米的标准偏差。通过对厚度共振和到达时间的联合评估，消除了穿透板超声速度对最靠近光学麦克风的板表面的测量起伏的影响。此外，我们证明了内部分层对局部机械响应的频谱有影响，因此可以通过 LURS 检测到。达到了高达几微米的标准偏差。通过对厚度共振和到达时间的联合评估，消除了穿透板超声速度对最靠近光学麦克风的板表面的测量起伏的影响。此外，我们证明了内部分层对局部机械响应的频谱有影响，因此可以通过 LURS 检测到。达到了高达几微米的标准偏差。通过对厚度共振和到达时间的联合评估，消除了穿透板超声速度对最靠近光学麦克风的板表面的测量起伏的影响。此外，我们证明了内部分层对局部机械响应的频谱有影响，因此可以通过 LURS 检测到。