帶孔隙矩形金屬封裝屏蔽效應之研究

Abstract

一般認為金屬封裝(Metallic Enclosure)具有屏蔽、電磁相容的功能。然而許多模擬與量測結果之文獻指出：在一帶有孔隙(Aperture)之金屬封裝中，由於外界的電磁場可透過孔隙與空腔耦合，進而激發空腔的共振，致使封裝內的電路在某些頻率不僅不能得到完善的屏蔽。甚至在空腔中特定位置有著比無屏蔽時更大的場，對於封裝內的電路構成額外的干擾。 在本文中，我們首先說明屏蔽效應的定義、及所研究的電磁問題；其次，我們簡單地介紹有限時域差分(Finite-Difference Time-Domain, FDTD)法的基礎、及電磁模擬軟體CST Microwave Studio的設定。最後，我們應用以上方法，研究、討論各種因素對帶孔隙矩形金屬封裝屏蔽能力的影響。

In general, it is thought that the metallic enclosure has the functions of shielding and EMC. However, many scientific studies on simulations and measurements indicate that at a metallic enclosure with apertures, the circuit inside the enclosure cannot be shielded completely at peculiar frequencies; moreover, there will be a stronger field at certain positions than when there is no shielding, which may probably cause extra interference in the circuit. It is because through the apertures the exterior electromagnetic field will couple with the cavity, and excite resonance in the cavity. In this thesis, we explain the definition of shielding effectiveness and the electromagnetic structure first. Secondly, the basic FDTD method and the CST simulator are introduced. Finally, the effects of various factors upon shielding effectiveness of a rectangular metallic enclosure with apertures are researched by using above methods.