共振腔受軸向負載下結構彈塑性變形之調整高頻電磁場共振頻率之研究

Resonance Frequency Shift of Electromagnetic Field of the Resonance-Frequency Cavity as Being Elastoplastic Structure Deformed by Axial Loading

林子淵(Lin, Tzu Yuan)

指導教授 ： 葉孟考

國立清華大學/工學院/動力機械工程學系/碩士(2016年)

摘要

本文分析共振腔體受到軸向負載後，對其結構變形與內部共振頻率變化進行探討。先對圓柱形腔體模擬，比較其結果與理論解，及各材料常數對共振頻率的影響，確認分析結果可行後再將流程用至共振基頻約為1.5 GHz的腔體模型，並得到調整共振頻率範圍之軸向負載。文中使用有限單元軟體ANSYS進行結構及電磁場跨領域分析，由於分析所需之基頻共振模態為TM010軸對稱形式，使用四分之一模型並配合適當邊界條件，以及給予材料和內部電磁場材料參數，即可求解出高頻電磁場共振頻率。分析過程為模擬共振腔體調頻步驟，用軸向位移使結構發生彈塑性變形，即可對內部共振頻率產生調整的作用；由數值結果得知圓柱形腔體與1.5 GHz腔體受到拉伸位移，高頻共振頻率皆升高。1.5 GHz腔體調整共振頻率分析中討論厚度及各種負載條件下與高頻共振頻率的相關性，並與實驗結果比較。由結果確定主導高頻共振頻率變化的腔體半徑變化量增大時，其飄移量更敏感。

關鍵字

共振腔體 ； 共振頻率 ； 彈塑性結構變形

並列摘要

The structure deformation and resonance frequency variation of a cavity under cyclic axial loading were not only computed in this study by the finite element software ANSYS but also tested with a copper cavity. The resonance frequency of TM010 mode was chosen to study the effects of structure deformation. Two types of thin-shell cavities were investigated: the circular cylindrical cavity and the bell-shape cavity of 1.5 GHz. A process to link the computations on structure deformation and electromagnetic fields was established, while proper boundary conditions and material properties were assigned in corresponding steps to obtain the accurate results. Elastoplasticity of dynamic hardening model was assigned for the structure computation, thus the actual frequency-tuning process is successfully simulated. Effects of the elastoplastic material properties, various thickness and loading condition on the resonance frequency are thus able to be studied. The computed results of the 1.5 GHz cavity were compared with the experiment results.

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