For the acoustic characterization of materials, a method is proposed for interpreting experiments with finite-sized transducers and test samples in terms of the idealized situation in which plane waves are transmitted through an infinite plane-parallel layer. The method uses acoustic holography, which experimentally provides complete knowledge of the wave field by recording pressure waveforms at points on a surface intersected by the acoustic beam. The measured hologram makes it possible to calculate the angular spectrum of the beam to decompose the field into a superposition of plane waves propagating in different directions. Because these waves cancel one another outside the beam, the idealized geometry of an infinite layer can be represented by a sample of finite size if its lateral dimensions exceed the width of the acoustic beam. The proposed method relies on holograms that represent the acoustic beam with and without the test sample in the transmission path. The method is described theoretically, and its capabilities are demonstrated experimentally for silicone rubber samples by measuring their frequency-dependent phase velocities and absorption coefficients in the megahertz frequency range.

中文翻译：

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从超声波束中提取平面波的全息图用于有限尺寸吸收层的声学表征

对于材料的声学特性，根据平面波通过无限平面平行层传输的理想情况，提出了一种用有限尺寸换能器和测试样品解释实验的方法。该方法使用声全息术，它通过记录与声束相交的表面上的点处的压力波形，通过实验提供完整的波场知识。测量的全息图可以计算光束的角谱，从而将场分解为沿不同方向传播的平面波的叠加。由于这些波在声束外相互抵消，如果无限层的横向尺寸超过声束的宽度，则无限层的理想几何形状可以用有限大小的样本来表示。所提出的方法依赖于全息图，这些全息图代表传输路径中带有和不带有测试样本的声束。该方法在理论上进行了描述，并通过测量硅橡胶样品在兆赫频率范围内的频率相关相速度和吸收系数来实验证明其能力。