Li Ji, Piwakowski Bogdan
Nuclear Power Institute of China, 610213 Chengdu, China; IEMN TPIA UMR CNRS 8520, Ecole Centrale de Lille, BP 48, 59651 Villeneuve d'Ascq Cedex, France.
IEMN TPIA UMR CNRS 8520, Ecole Centrale de Lille, BP 48, 59651 Villeneuve d'Ascq Cedex, France.
Ultrasonics. 2019 Apr;94:242-263. doi: 10.1016/j.ultras.2018.09.003. Epub 2018 Sep 11.
This paper presents a time-domain model for the prediction of acoustic field in an air-coupled, non-contact, ultrasonic surface wave scanner, which includes an air-coupled Emitter, the Propagation space, and an air-coupled Receiver (EPR). The computation is divided into three steps, with each step being modeled in the time domain by its spatio-temporal transfer function. The latter are then used in turn, to find the pulse response of the overall system. The model takes the finite size of the aperture receiver, the attenuation in both air and the tested solid sample, as well as the electric response of the emitter-receiver set h into account. The attenuation is characterized by a causal time-domain Green's function, allowing wideband attenuation of a lossy medium, obeying the power law αω=αω,0⩽η⩽2, to be used. The model is implemented numerically using a Discrete Representation approach. It is then validated quantitatively by comparing the predicted acoustic field with experiment. The prediction error for three typical field features, the system's impulse response, the on-axis field distribution, and the directivity pattern, is globally smaller than 3%. In order to obtain this high level of accuracy in the model, the parameters characterizing the solid sample used during the experiment were measured experimentally, with a specifically developed experimental setup. Overall, the proposed model is approximately 100 times faster than 3D FEM with an equivalent spatio-temporal resolution. In parallel, a simplified model is proposed, which neglects the attenuation in air and assumes the emitter inclination angle to be perfectly adjusted. This approach makes it possible to further shorten the computational time by a factor of about ten, whilst maintaining good accuracy. Thanks to its computational efficiency, the proposed model can be used to formulate various recommendations concerning the scanner settings, in particular the inclination angles of the emitter and receiver, and their distance from the sample.
本文提出了一种用于预测空气耦合、非接触式超声表面波扫描仪中声场的时域模型，该模型包括空气耦合发射器、传播空间和空气耦合接收器（EPR）。计算分为三个步骤，每个步骤通过其时空传递函数在时域中进行建模。然后依次使用这些函数来求解整个系统的脉冲响应。该模型考虑了孔径接收器的有限尺寸、空气和被测固体样品中的衰减以及发射器 - 接收器组合的电响应h。衰减由因果时域格林函数表征，允许使用服从幂律αω = αω,0⩽η⩽2的有损介质的宽带衰减。该模型使用离散表示方法进行数值实现。然后通过将预测声场与实验结果进行比较来进行定量验证。对于三个典型的场特征，即系统的脉冲响应、轴上声场分布和方向图，预测误差总体小于3%。为了在模型中获得如此高的精度，使用专门开发的实验装置对实验中使用的固体样品的特征参数进行了实验测量。总体而言，所提出的模型在等效时空分辨率下比三维有限元法快约100倍。同时，提出了一种简化模型，该模型忽略了空气中的衰减，并假设发射器倾斜角度已完美调整。这种方法可以将计算时间进一步缩短约十倍，同时保持良好的精度。由于其计算效率，所提出的模型可用于制定关于扫描仪设置的各种建议，特别是发射器和接收器的倾斜角度以及它们与样品的距离。
