Zheng Kai, Zhang Hui, Zhang Shu-yi, Fan Li
Laboratory of Modern Acoustics, Institute of Acoustics, Nanjing University, Nanjing 210093, PR China.
Ultrasonics. 2006 Dec 22;44 Suppl 1:e1343-7. doi: 10.1016/j.ultras.2006.05.166. Epub 2006 Jun 9.
Subharmonics are often observed in ultrasonic infrared thermography (UIR) system as samples are excited by ultrasonic transducers, and it is testified that, as the subharmonics appear, the detectability of cracks or defects in the sample is greatly enhanced in the UIR system. A dynamical model to explore the generation mechanism of the subharmonics and simulate the sample motion excited by an ultrasonic transducer in the UIR system is presented in this paper. In the model, the sample is continuously impacted by the transducer as the transducer is pushed to the sample by a constant force, in which the sample is simplified as a damped oscillator and the transducer is simplified as an active oscillator with constant frequency and amplitude. The impact process is also taken into account, in which the acting force is assumed to vary linearly during the impact process. A stable waveform of subharmonics in the sample can be obtained in appropriate conditions.
在超声红外热成像（UIR）系统中，当样品由超声换能器激发时，常常会观察到亚谐波。并且据证实，随着亚谐波的出现，UIR系统中样品裂纹或缺陷的可检测性会大大提高。本文提出了一个动力学模型，用于探究亚谐波的产生机制，并模拟UIR系统中超声换能器激发的样品运动。在该模型中，当换能器在恒定力作用下被推向样品时，样品会持续受到换能器的冲击，其中样品被简化为一个阻尼振荡器，换能器被简化为一个具有恒定频率和振幅的有源振荡器。冲击过程也被考虑在内，其中假设作用力在冲击过程中呈线性变化。在适当条件下，可以获得样品中亚谐波的稳定波形。
