機械制動壓電極子天線之電磁輻射效應

Abstract

壓電超晶格是一種具有空間中週期性調變壓電係數結構。其內部存在機械波、電磁波，以及機械波與電磁波強烈耦合產生的極子波。這種強烈耦合是藉由與反轉週期匹配的波動形呈均勻電場產生。 根據壓電超晶格的理論，輸入機械能或電磁能都會因為壓電耦合產生電磁輻射。多數研究利用電磁式的輸入來激發壓電超晶格，主要因其振動頻率通常在 MHz 以上，而機械式的激發方式大多是接觸式，容易干擾材料內部的機械場，使得理論分析變得困難。 本研究目標利用非破壞性檢測中使用的脈衝雷射，產生 MHz 等級與壓電超晶格共振的機械波，並在材料內部激發對應頻率的極子波。 為了完整驗證壓電超晶格的理論，本研究利用電磁式激發，並以量測散射參數方式確認輻射頻率，再利用有限元素模擬尋找對應的機械場形與電磁場形。同時，利用模擬不同形式的脈衝雷射等效外力，在材料上產生機械波並觀察其波型。這樣的研究成果可以驗證雷射實驗設置與假設的正確性。

Piezoelectric superlattice is a structure with periodic modulation of the piezoelectric coefficient in space. It contains mechanical waves, electromagnetic waves, and polariton waves generated by the strong coupling between mechanical and electromagnetic waves. This strong coupling is achieved through the generation of a uniform electric field that matches the inversion period. According to the theory of piezoelectric superlattice, both mechanical and electromagnetic energies can generate electromagnetic radiation due to piezoelectric coupling. Most studies use electromagnetic excitation because the vibration frequency is typically above MHz, while mechanical excitation is mostly contact-based, which complicates theoretical analysis by interfering with the internal mechanical field. The objective of this research is to use pulsed lasers commonly used in non-destructive testing to generate mechanical waves resonating at MHz frequencies with the piezoelectric superlattice and excite corresponding polariton waves within the material. To fully validate the theory of piezoelectric superlattice, this study will use electromagnetic excitation and measure the scattering parameters to confirm the radiation frequency. Finite element simulations will be employed to find the corresponding mechanical and electromagnetic field patterns. Additionally, different forms of pulsed lasers will be simulated to generate mechanical waves on the material and observe their waveforms. The results of this research will validate the correctness of the laser experimental setup and assumptions.