壓電陶瓷材料於3C產品之應用

Abstract

本論文對於壓電陶瓷材料提出三項不同應用，分別為壓電平面喇叭之最佳化設計、時間反轉法於觸控面板之應用及能量擷取器之最佳化設計。在第一項應用中，壓電平面喇叭之設計採用兩片式壓電陶瓷平板來驅動振膜，最佳化設計之過程在於決定壓電陶瓷平板之最佳貼合位置。以能量法為基礎之有限元素模型用以建構電、機械及聲學負載之耦合系統。在最佳演算法上，模擬退火法用於取得最佳化設計以期降低共振基頻及提高聲壓輸出。實驗方法用以證實數學模型之正確性，實驗結果與數值模擬比較驗證了數值預測之可信度。從數值演算結果可以得知，相較於未最實施最佳化之設計，以最佳化演算法所求得之最佳設計有效地降低了共振基頻與改善整體效能。 結合了觸控定位及力回饋系統為本論文探討及研究的第二項應用。在平板上任意兩點之理論脈衝響應可藉由彎曲波於平板中傳遞之模型推導得知。在此一基礎下，時間反轉法可同時運用於觸控定位及力回饋。處理多頻率於迴響空間之強韌性為時間反轉法之主要優點，此一優點正符合彎曲波於平板中傳遞之實際物理狀態。本應用中，感測器使用壓電陶瓷平板及動圈式馬達兩種型式，同時動圈式馬達亦作為力回饋之致動器。實驗結果證明了本法在平板上之觸控定位效能，以及脈衝力可藉由時間反轉法有效地回饋至原觸控點。就現今多媒體需求而言，結合了觸控定位及力回饋系統將可有效的增強界面之即時互動性。 能量擷取器之最佳化設計為探討的最後一項裝置，移動質量引致振動能量且藉由壓電效應所轉化的電能為本論文之研究方向。在數學模型中，以伯努力由拉樑為基礎之機電耦合有限元素模型將用以估算能量擷取器所產生之電能。對於產生電能之相關影響參數如移動物體與樑的質量比、樑長度、移動質量速度及阻抗負載均有詳盡的探討。如數值模擬與實驗結果，數值模型成功的預測了機電耦合系統在固定阻抗負載下之動態行為。在設計階段，導入非線性共軛梯度法以尋求最佳化設計，期使能量擷取器之輸出能量最大化。數值結果顯示最佳化設計與負載、移動物體速度與移動物體質量有著高度的關連性。此外，較大的能量輸出亦可藉由增加樑長或增加移動物體質量的方式來達成。

The thesis focuses on three applications of piezoelectric ceramic materials: optimization of the piezoelectric panel speakers, touch panel application based on time-reversal approach and optimized design of the energy harvester. The first application deals with the optimized design of the piezoelectric panel speaker, two piezoelectric ceramic plates serve to excite the diaphragm is adopted in the panel speaker design. In light of an optimization procedure, the optimal position on the diaphragm to mount the piezoelectric ceramic plates is determined. In the system modeling stage, a finite element model (FEM) is established using the energy method, where the electrical system, mechanical system and acoustic loading of the transducer are considered as a coupled system. The simulated annealing (SA) algorithm is exploited to attain a design that enables low fundamental resonance frequency and high acoustic output. Experiments are conducted to verify the numerical model. The experimental results are in good agreement with the numerical prediction, in which the performance of the optimized configuration is found to be significantly improved over the non-optimal design. In the second application, a combined impact localization and haptic feedback system presented for the touch panel application is presented in the thesis. Theoretical impulse responses are derived based on propagation of bending waves in a thin elastic plate. On the basis of the impulse responses, the time reversal technique is exploited to localize the impact location as well as to generate haptic feedback. The chief advantage of the time reversal technique lies in its robustness of tackling broadband sources in a reverberant environment. Piezoelectric ceramic plates and voice-coil motors are used as sensors for localization, whereas only voice-coil motors are used as the actuator for haptic feedback. Experimental results demonstrated that the proposed system is effective in impact localization for a thin panel, while haptic feedback that is also implemented using time reversal principle can generate an impulse at the previously touched position. The combined impact localization and haptic feedback system effectively enhances the sensation of interaction in real time fashion. Energy harvester is the last device studied in the thesis. The thesis presents a piezoelectric energy harvester by which the vibration energy induced by a moving mass is converted to electrical energy through the piezoelectric effect. An electromechanically coupled FEM based on the Euler-Bernoulli beam theory is employed to estimate the electrical energy that can be generated by the energy harvester. The effects of mass ratio, beam length, travel time and load resistance on the energy output are examined. As indicated by the simulation and experiment results, it is observed that the numerical model can successfully predict the dynamics of the couple system based on the selected electrical load resistance. In the design stage, the nonlinear conjugate gradient (CG) algorithm is applied for calculation to maximize the energy throughput from the energy harvester. Results have shown that the harvested energy depends heavily upon the optimal choice of load resistance and travel time of the moving mass. In addition, the longer beam or the higher mass ratio, the higher energy throughput can be achieved.