面剪切水平偏振導波壓電纖維複材換能器

Abstract

壓電纖維複材為三明治結構，芯材由數根壓電纖維埋入環氧樹脂組成，不容易產生面剪切致動。本文提出新方法，開發垂直壓電纖維極化，平行纖維電場驅動之壓電纖維複材，作為面剪切水平偏振導波換能器，簡稱TH-PFC。數值模擬與實驗驗證其具有優異的致動及感測特性，數值模型的幾何參數是以金相顯微鏡觀測獲得，透過數值模擬分析找出垂直壓電纖維軸向極化所需之適當電壓，並具體實現。本研究設計、製作波長4.48mm之TH-PFC，黏貼於厚度1 mm之鋁板，做為水平偏振導波換能器，有效地激發及感測鋁板的水平偏振TH0、TH1板波，具有良好的訊號品質。數值及實驗驗證顯示該換能器能以兩種共振頻率激發TH0模態板波，單側指叉電極驅動TH-PFC生成的TH1板波響應振幅較雙側驅動強，雙側指叉電極驅動生成TH0板波響應振幅較單側驅動強。 數值模擬TH-PFC貼於鋁板之輻射聲場，發現換能器能在鋁板上激發水平偏振橫波與蘭姆波。換能器正前方生成的TH0板波響應較大，還會產生較小的側瓣，響應較小的A0、S0板波分別發生在10o、22o方位。TH-PFC黏貼於鋁板進行衰減試驗，實驗顯示共振頻率0.42MHz激發鋁板TH0板波的衰減係數最小，僅3.3 Np/m，非頻散TH0板波擁有長距離檢測的應用潛力。

Piezoelectric fiber composites (PFC) are in the sandwiched configuration. The core material is made of parallel piezoelectric fibers embedded in epoxy resin; face shear deformation is of difficulty to induce therein. This thesis presents a novel face shear PFC device to generate transverse horizontal plate waves by applying an alternating electric field along the piezoelectric fibers which were transversely poled. Such piezoelectric fiber composites are abbreviated as TH-PFC. The sensing and actuating performances of TH-PFC were verified through numerical and experimental investigation. Dimensions of the PFC device measured by metallographic examination are used in the thereafter numerical analysis. An appropriate working condition for transverse poling is found by numerical study based on the strain monitoring data during axial poling along the fibers. The single ply TH-PFC transducers of 4.48 mm wavelengths are designed and manufactured in the laboratory, and can effectively excite and sense both TH0 and TH1 modes in one mm thick aluminum plates. The transverse horizontal plate wave signals are in high quality. The TH0 modes can be generated by the transducers at two separate resonant frequencies. Single-side excitation induces the TH1 mode with a stronger response than double-side excitation. For TH0 mode, larger responses are usually actuated by double-side excitation. The radiation field launched by a TH-PFC attached to the aluminum plate was examined numerically. It is found that the transducer can excite both TH waves and Lamb waves. High response TH0 modes are induced in front of the transducers; side lobes cannot be ignored. Smaller A0 and S0 modes can be yielded at the orientations of 10o、22o. Attenuation measurement has been conducted, and it reveals that the TH0 mode excited at 0.42 MHz has a low attenuation coefficient of 3.3 Np/m. The non-dispersive TH0 modes have been shown to have a good potential for long distance inspection.