空氣耦合超音波換能器開發

Abstract

本論文針對50kHz壓電超音波換能器（Piezoelectric Ultrasonic Transducer, PUT）進行研究，選用PZT壓電圓片作為核心元件，以有限元素模擬、理論方程式與實驗驗證，系統性探討PZT之阻抗頻譜、聲束指向性及軸向聲壓衰減特性。 本研究建立之阻抗頻譜模擬與實驗量測值平均誤差僅1.19%，建立之複合振動模態指向性模型相較活塞振動理論模型更能反映實際聲場分布，軸向聲壓衰減模型與理論衰減曲線擬合R2>0.99，顯示本研究之模型可準確描述聲波在空氣中的衰減行為。 此外，本研究亦對撓曲式超音波換能器(Flexural Ultrasonic Transducer, FUT)進行模擬分析，透過與文獻數據比對，成功驗證FUT模型在阻抗、振動模態與指向性上的準確性。基於此模型，本研究進一步進行FUT外殼尺寸變化參數研究，確定FUT之第一共振頻率主要由其外殼頂板半徑與厚度主導，為頻率設計提供明確的物理依據。 綜上所述，本論文成功整合多項物理特性模擬與驗證方法，為兩種空氣耦合超音波換能器提供精確且系統性的分析與預測架構，可有效縮短開發時程與實驗成本。

This study systematically investigates a 50 kHz piezoelectric ultrasonic transducer (PUT), using a PZT piezoelectric disk as the core element. Through finite element simulation, theoretical modeling, and experimental verification, the impedance spectrum, beam directivity, and axial sound pressure attenuation characteristics are thoroughly analyzed. The simulation and experimental results of impedance spectra show excellent agreement, with an average error of only 1.19%. Additionally, the established compound vibration-mode directivity model demonstrates improved accuracy compared to the traditional piston vibration theory model. The axial sound pressure attenuation model fits exceptionally well with theoretical attenuation curves (R² > 0.99), confirming that the proposed model accurately represents ultrasonic attenuation in air. Furthermore, this research conducts a simulation-based study on flexural ultrasonic transducers (FUT). The accuracy of the FUT model in terms of impedance, vibration modes, and directivity is successfully verified against existing literature. Based on this validated model, a parametric study on FUT housing dimensions is conducted, indicating that the fundamental resonance frequency is primarily governed by the radius and thickness of its top plate, providing clear physical guidelines for frequency-oriented design. In summary, this thesis successfully integrates multiphysics simulation and experimental verification, offering precise and systematic analytical frameworks for both PUT and FUT. These results effectively reduce development time and experimental costs.