| Summary: | 碩士 === 國立彰化師範大學 === 光電科技研究所 === 104 === Research objective in this paper is about the transport behavior of surface acoustic waves in phononic crystals. We designed a set of interdigital transducers (IDT) separately as transmitting end and receiving end on both sides of substrate to make a research on the effect of giving different IDT parameters with the propagating surface acoustic waves. After that, we added the phononic crystal in-between two sets of IDTs to observe consequences for crystal resonator via transmitting sound wave.
Surface acoustic wave is generated by IDT on the lithium niobate substrate, and the acoustic wave which is produced by IDT propagate on the substrate surface. When we modified the spacing and width of IDT, the resonance frequency would change. The different IDT pairs would make the bandwidth of acoustic wave different. In this experiment, we picked four different widths of IDT to compare their frequency. Then we found the acoustic frequency is smaller than ideal value, but the trend varied as we had expected. We compared the IDT of 400nm in width with different IDT pairs, and we found if we set more pairs, we would get more energy and better quality.
The phononic crystal is a periodic structure. Band gap will be generated as a result of interference by reflected wave and incident wave, and there are only a minority of acoustic frequency can pass the crystal array. We use different materials and set different periodic parameters to achieve filtering function. We designed phononic crystal structure in-between transmitting end of IDT and receiving end of IDT by this appearance. When the phononic crystal added in non-phononic crystal sample , the acoustic wave which are in band gap frequency was filtered as expected. In the sample which was added in phononic crystal resonators, we setting different input power, and the transmitted intensity of the part of frequency will be modified. To change phononic crystal periodic, there is the situation of frequency translation by the fluctuant frequency would be modified according periodic changed.
|
|---|
