Modulation techniques of the SAW sensor's echo in accordance with the physical phenomena

我们已经知道，表面声波的中心频率是由IDT及其手指的形状和间距决定的。对于一个简单的IDT结构，中心波长和频率由连续的正负极之间的间距决定。因此，通过在垂直于电极的方向上拉伸材料，将发生可测量的频率调制。其他物理现象如何允许波调制还有待研究和理解。此外，还需要检查各种换能器技术（如三相IDT、手指拔出、手指重叠变化等）以达到最佳效果。众所周知，通过将电磁波转换成声波，IDT激发出比期望更多的模态。更具体地说，可以观察到体波，但它们是不希望的，因为它们会造成能量损失。其他模式也将被激发，关键的挑战将是最小化最慢的模式对整个系统精度的影响。此外，还应考虑和检查导声波，以评估其对上述刺激的敏感性，以及是否可以遏制模式传播（由于最有可能的层压结构）。最后，应考虑其他传感选择，例如慢波结构。为了实现以上所有的仿真模型都需要建立和测试。

It is already known that the centre frequency of the surface acoustic wave is determined by the shape and spacing of the IDT and its fingers. For a simple IDT structure the centre wavelength and thus frequency is determined by the spacing between consecutive positive and negative electrodes. Thus by straining the material in the direction perpendicular to the electrodes, measurable frequency modulation will occur. It is yet to be researched and understood how other physical phenomena allow wave modulation. Moreover, various transducer techniques shall be examined (e.g. 3-phase IDT, finger withdrawal,varying finger overlap etc.) to achieve the best results. It is known that by converting EM wave into acoustic one the IDT excites more modes than it is desired. More specifically bulk waves can be observed, however they are undesired as they contribute to energy loss. Other modes will also be excited and the key challenge will be to minimize the effect of the slowest ones on the overall system accuracy. Moreover, guided acoustic waves shall be considered and examined to evaluate their sensitivity to the aforementioned stimuli, and whether mode spreading (due to most likely laminated structure) can be contained. Finally, other sensing options shall be considered, e.g. slow wave structures. To achieve all of the above simulation models shall be built and tested.