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Please use this identifier to cite or link to this item: http://hdl.handle.net/2031/6243

Title: Investigation of high-frequency performance of micro vacuum dielectric capacitors
Other Titles: Wei xing zhen kong jie zhi dian rong gao pin xing neng de yan jiu
微型真空介質電容高頻性能的研究
Authors: Wong, Oi Ying (0)
Department: Department of Electronic Engineering
Degree: Master of Philosophy
Issue Date: 2009
Publisher: City University of Hong Kong
Subjects: Vacuum capacitors.
Notes: CityU Call Number: TK6565.C65 W66 2009
ix, 69 leaves : ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2009.
Includes bibliographical references (leaves [65]-67)
Type: thesis
Abstract: The use of gigahertz electromagnetic spectrum for wireless communications results in some stringent requirements on the capacitors. The dielectric losses of the capacitors constructed with commonly used dielectric materials increase significantly at high frequency. Theoretically, the capacitors using vacuum as dielectric should have low dielectric loss and can achieve stable characteristics over a wide frequency range in high frequency operations. However, vacuum capacitors were used in low frequency and high power applications instead of high frequency applications. This is because of the limitation posed by the bulky structure of the vacuum capacitors found in the market. To overcome this problem, a new manufacturing method for making micro vacuum dielectric capacitor (VDC) was proposed recently. It allows vacuum or other gaseous to be used as the dielectric for high-frequency ready capacitors. The structure consists of two parallel-plate electrodes supported by periphery sealant at the boundary. Due to the vacuum dielectric inside and the simple structure, the capacitors are expected to have excellent high-frequency characteristics. However, the effect of the sealant on the capacitor properties has not been investigated. In this work, a model is derived to characterize the capacitance and frequency-dependent loss tangent of the VDCs. It has shown that the capacitance of the VDCs depends on r, which is the ratio of the width of boundary sealant layer to the capacitor side length. We have shown by both analytical study and experimental measurement that the smaller the r, the smaller the dissipation factor of the VDCs. An equivalent circuit is further developed which can be used as an analytical tool to compute the high-frequency loss tangent of VDCs. It was found that the dielectric loss of the capacitor at high frequency mainly arises from the dielectric loss of the periphery sealant. Smaller value of the width of boundary sealant layer to the capacitor side length ratio will give smaller loss tangent. Meanwhile, the resonant frequency of the VDCs also depends on the sealant. Empirical studies of the resonant frequency of the VDCs have been shown to match well with that derived from the proposed model. Based on the developed analytic model, VDC with a required performance and a given value of capacitance can be designed through the analytical derivation. Finally, the thesis is concluded with a presentation of some structures to further improve the VDC characteristics.
Online Catalog Link: http://lib.cityu.edu.hk/record=b3947855
Appears in Collections:EE - Master of Philosophy

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