IEEE Trans Ultrason Ferroelectr Freq Control. 2017 Feb;64(2):441-451. doi: 10.1109/TUFFC.2016.2628100. Epub 2016 Nov 11.
Control over the direction of wave propagation allows an engineer to spatially locate defects. When imaging with longitudinal waves, time delays can be applied to each element of a phased array transducer to steer a beam. Because of the highly dispersive nature of guided waves (GWs), this beamsteering approach is suboptimal. More appropriate time delays can be chosen to direct a GW if the dispersion relation of the material is known. Existing techniques, however, need a priori knowledge of material thickness and acoustic velocity, which change as a function of temperature and strain. The scheme presented here does not require prior knowledge of the dispersion relation or properties of the specimen to direct a GW. Initially, a GW is generated using a single element of an array transducer. The acquired waveforms from the remaining elements are then processed and retransmitted, constructively interfering with the wave as it travels across the spatial influence of the transducer. The scheme intrinsically compensates for the dispersion of the waves, and thus can adapt to changes in material thickness and acoustic velocity. The proposed technique is demonstrated in simulation and experimentally. Dispersion curves from either side of the array are acquired to demonstrate the scheme's ability to direct a GW in an aluminum plate. The results show that unidirectional enhancement is possible without a priori knowledge of the specimen using an arbitrary pitch array transducer. The experimental results show a 34-dB enhancement in one direction compared with the other.
控制波的传播方向可以让工程师实现对缺陷的空间定位。在使用纵波进行成像时，可以向相控阵换能器的每个元件施加时间延迟，以控制波束的方向。然而，由于导波（GWs）的高度色散性质，这种波束控制方法并不理想。如果已知材料的色散关系，则可以选择更合适的时间延迟来引导 GW。然而，现有的技术需要预先了解材料厚度和声速，这些参数会随温度和应变而变化。本文提出的方案不需要事先了解 GW 的色散关系或试件的特性即可引导 GW。首先，使用阵列换能器的单个元件生成 GW。然后，处理和重新传输来自其余元件的采集波形，使波在穿过换能器的空间影响时产生建设性干扰。该方案本质上补偿了波的色散，因此可以适应材料厚度和声速的变化。该方案在仿真和实验中得到了验证。从阵列的两侧获取色散曲线，以证明该方案在铝板中引导 GW 的能力。结果表明，使用任意间距的阵列换能器，无需事先了解试件，即可实现单向增强。实验结果表明，与另一个方向相比，在一个方向上增强了 34dB。
