微型週期性結構表面聲波頻溝理論分析與微機電實驗初探

Abstract

本計畫旨在研究聲子晶體之超聲波頻 溝現象，藉由平面波展開法理論分析(plane wave expansion method)結合實驗量測，進 行微型週期性結構表面聲波頻溝現象之研 究。經由彈性振動材料組成之週期性結 構，在適當調整其材料常數後通過之聲波 有頻溝現象存在，此類結構稱為聲子晶體 (Phononic crystals)。聲子結構的應用，可 作為二維表面聲波濾波器，阻止特定角度 與頻率入射的聲子傳遞，達成濾波之效 果。本報告使用平面波展開法來計算二維 聲子晶體之聲波頻溝，可針對指定入射角 度及結構尺寸設計濾波頻率。並進行微米 尺寸之聲子晶體實驗，設計高頻表面聲波 交指叉換能器，進行表面聲波頻溝現象之 研究，實現微米等級之聲子晶體結構，並 驗證表面聲波頻溝現象。

The purpose of the research is to study the characteristics of the acoustic band gaps in the 2D phononic crystals. The phononic crystal is a kind of periodic elastic material structure that exists band gaps, in which the elastic wave propagation of particular frequency is forbidden. The band gaps phenomena are studied using the plane-wave expansion method, which is composed of the Bloch’s theorem and of the reciprocal lattice vector. The IDT (inter-digital transducer) and a micro scale 2D phononic crystal consists of silicon with a square periodic arrangement of cylindrical holes were designed to verify the band gaps of surface acoustic waves. The fabrication process using the MEMS (Micro Electro Mechanical Systems) technique were studied and realized in the research. These results provide useful guidelines for the design of a phononic crystal device as a frequency filter.