壓電換能器與低頻管路換能器之有限元素分析與模擬

Abstract

本文運用有限元素分析，探討壓電換能器的機械、電學以及聲學特性。機械與電學特性主要討論壓電圓盤在不同的直徑厚度比(D/T ratio)下對於共振頻率以及機電耦合係數(Electromechanical coupling coefficient)的影響，此外本文也討論加入了不同阻尼的背膠層(Backing layer)，對於結構振動以及機械品質因子(Mechanical quality factor)的影響。聲學特性方面，本文利用圓形活塞的指向性函數，分別在不同頻率的驅動下，探討其指向性(Directivity)的差異以及產生的旁辦(Side lobe)，並且利用有限元素模擬，透過壓電圓盤振動時產生的法線加速度，將此自由度傳遞於流體介質，所以在流體空間中將會產生聲壓分佈。最後本文嘗試設計與模擬一種應用在水下流速量測的換能器，稱之為低頻管路換能器(Low Frequency Organ Pipe Projector)，此種換能器的聲源端可以由壓電陶瓷的徑向振動，轉化為金屬板的彎曲運動，放大金屬板垂直方向的振動位移，造成較大的出力，並且以理想活塞聲源探討頻率與管長的關係，將所設計的聲源端以及推算的最佳管長合併計算，討論理想與非理想活塞聲源產生的聲壓分佈。

This study use finite element analysis to discuss mechanical、electrical and acoustical characteristics of the piezoelectric transducer. Mechanical and electrical characteristics are concerning the influence of electromechanical coupling coefficient and resonance frequency under different D/T ratio. It is also concerning the influence of vibration behavior and mechanical quality factor when adding different backing layers. In acoustical characteristics, this study use the circular piston directivity function to discuss the differences of directivity and side lobe generated under different excitation frequency. It also use finite element simulation to verify the result. When piezoelectric disk vibrating, it will produce the normal acceleration on the disk surface. This degree of freedom to pass on the fluid medium, it will produce sound pressure distribution in the fluid space. Finally, this study tries to design and simulate an underwater flow measurement transducer, which called Low Frequency Organ Pipe Projector. Transducer sound source can be generated by the radial vibration of piezoelectric ceramic transfer into the metal plate bending motion. It can enlarge vertical displacement of the metal plate to generate greater sound output. However, the frequency generated by the transducer has relationship with tube length. This study tries to determine optimal tube length and discuss the differences of sound pressure which generated by ideal sound source and non- ideal sound source.