壓電超音波元件聲阻匹配層之材料設計與性能分析

Abstract

在高能聚焦超音波的領域，鋯鈦酸鉛被應用成為一種新穎的聲阻匹配層。此層鋯鈦酸鉛匹配層可將原本超音波探頭之寬頻率分佈過濾成某些特定頻率之峰值，且沒有降低該頻率峰值相對於原始探頭強度之強度。這個現象可歸納為鋯鈦酸鉛之壓電性質與機械性質，並且，在本論文裡設計一系列之實驗，藉由改變鋯鈦酸鉛匹配層之壓電性質，例如有無極化與表面電荷特性，來更深一步探討鋯鈦酸鉛匹配層之性質。 傳統之聲阻匹配層，例如陶瓷高分子複合材料，也在本篇論文裡探討。利用三種不同的陶瓷粉末混合環氧樹脂形成聲阻匹配層，並且探討三種陶瓷高分子複合材料之超音波匹配性質。在這三種陶瓷高分子複合材料內，氧化鋯粉末混合環氧樹脂之複合材料的超音波能量衰減係數與聲阻匹配值為最適當之選擇數值。因此，將氧化鋯環氧樹脂之複合材料應用於一個實驗室自製的高能聚焦超音波探頭上，藉由實驗去探討其聲阻匹配效果。此實驗藉由水診器量測並分析探頭之聲波強度分佈，且藉由豬肉之活體實驗印證此聲阻匹配層之效能。 最後，在本論文裡還探討結構孔洞陶瓷材料與孔洞陶瓷填充環氧樹脂之複合材料的性質，利用其低超音波能量衰減係數與可調式聲波聲阻值，是一個有潛力應用於匹配超音波探頭與水或是人體組織之材料。

A novel active matching layer made of lead zirconate titanate (PZT) plate has been developed as an “impedance matching layer” for high-intensity focused ultrasound (HIFU) applications. The PZT matching layer redistributes the frequency spectrum of an original broadband ultrasonic probe, and acts as a frequency filter without reducing the wave amplitude. These behaviors are contributed to electromechanical and mechanical properties at the PZT matching layer, and are investigated in this study by a series of experiments on PZT matching plates with different electromechanical properties and polarization and surface charge conditions. Traditional passive matching layers, such as ceramic-polymer composites, are also studied. Three different ceramic-epoxy composite are developed and their impedance properties studied. Among the three, the zirconium oxide-epoxy composite exhibits a tolerable attenuation level and an optimum impedance value. It is then integrated on to a home-made HIFU transducer to test its effectiveness. The beam profile of the matched HIFU transducer is characterized by a hydrophone, and an in-vivo experiment is carried out to gauge its performance. In this study, structure materials such as porous ceramics and porous ceramic-epoxy composites are also proposed as candidate materials for impedance matching for water and human tissues due to their low attenuations and impedances.