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

已知声表面波的中心频率由IDT及其指状物的形状和间距决定。对于简单的IDT结构，中心波长和频率由连续的正负电极之间的间距确定。因此，通过在垂直于电极的方向上对材料进行应变，将发生可测量的频率调制。其他物理现象如何允许波的调制还有待研究和理解。此外，还应检查各种传感器技术(例如，三相IDT、手指抽出、变化的手指重叠等)。以达到最好的效果。众所周知，通过将电磁波转换为声波，叉指换能器会激发出比它所需要的更多的模式。更具体地说，可以观察到体波，但它们是不受欢迎的，因为它们会造成能量损失。其他模式也将令人兴奋，关键挑战将是将最慢的模式对整体系统精度的影响降至最低。此外，应考虑和检查导波，以评估其对上述刺激的敏感度，以及(由于最有可能的层叠结构)是否可以抑制模式扩展。最后，还应考虑其他传感方案，例如慢波结构。为了实现上述所有的仿真模型，应建立并测试所有模型。

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.