奈米碳管-鐵氧磁體-碳基鐵粉/矽氧樹脂複合材料之電磁波屏蔽與吸收研究

A study on the electromagnetic shielding and absorption of MWCNT-Ferrite-CIP /Silicone composite

洪銘遠

指導教授 ： 張士欽

國立清華大學/工學院/材料科學工程學系/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00356

摘要

本研究製備奈米碳管-鐵氧磁體-碳基鐵粉/矽氧樹脂複合材料，以網路分析儀量測並計算45 MHz至4.5 GHz頻段電磁波屏蔽與吸收效果。最後由網路分析儀計算出的介電常數與透磁率，模擬出不同材料厚度的反射損失。
電磁波屏蔽效果隨著增加奈米碳管含量至約4 wt%(超過percolation threshold)而顯著提升，原因是奈米碳管在矽氧樹脂基底中形成良好的連結網絡並提升導電率。少於5 %電磁波能量可在45 MHz至4.5 GHz頻段中穿透含有9 wt%奈米碳管的試片。奈米碳管-碳基鐵粉/矽氧樹脂試片通常比起其他試片有更好的吸收效果(在4.5 GHz達到63.61 %)，此良好吸收效果隨著奈米碳管含量增加而擴展至較低的頻段。奈米碳管-鐵氧磁體/矽氧樹脂試片的吸收效果比起單純加成還要好，此額外有益的效果被認為是因為電磁波在奈米碳管間來回反射並增加了被吸收的機率。在某些頻段，奈米碳管-鐵氧磁體-碳基鐵粉/矽氧樹脂試片的吸收效果比只加入鐵氧磁體或碳基鐵粉來的好。
反射損失超過-20 dB很容易在試片厚度3 ~ 10 mm、0.9 GHz ~ > 4.5 GHz頻段的條件下被觀察到。對於含70 wt%碳基鐵粉、5 wt%奈米碳管和厚度5 mm的試片，反射損失於2.28 GHz達到-91.2 dB (99.9999999 %)，小於-20 dB的頻帶達0.96 GHz。除此之外，奈米碳管-鐵氧磁體/矽氧樹脂試片的可應用頻率是所有試片中最高的；奈米碳管-鐵氧磁體-碳基鐵粉/矽氧樹脂試片的-20 dB頻帶是試片中最寬的。

關鍵字

電磁波屏蔽 ； 碳基鐵粉 ； 鐵氧磁體

並列摘要

In this work, MWCNT-ferrite-CIP /silicone composites were fabricated. The electromagnetic shielding and absorption properties were measured by a network analyzer and calculated in 45 MHz ~ 4.5 GHz. The reflection loss was simulated from the obtained complex permeability and permittivity at various sample thicknesses.
Electromagnetic shielding effectiveness was improved significantly with increasing MWCNT content over the percolation threshold of about 4 wt% when high electric conductivity resulted from well inter-connection among MWCNTs in the silicone matrix. Less than 5 % electromagnetic wave energy can be transmitted in 45 MHz ~ 4.5 GHz with the addition of 9 wt% MWCNT content. CIP /MWCNT composites generally show better absorption performances (reach 63.61% at 4.5 GHz) than others. With more MWCNTs, the capability of the high absorption is extended to lower frequency range. Ferrite/ MWCNT composites show better absorption performances than that would expect by simple addition. This surplus beneficial effect is proposed to be a result of that the electromagnetic wave got reflected back and forth by the fillers in the material and thus increased the probability of absorption. In some frequency ranges, the absorption of ferrite/ CIP/ MWCNT/ silicone composites is better than both ferrite only and CIP only composite.
The reflection loss exceeding -20 dB was observed easily in 0.9 GHz ~ > 4.5 GHz with composite thickness from 3 mm to 10 mm. For 70 wt% CIP/ 5 wt% MWCNT/ silicone composite with 5 mm thickness, the reflection loss reached -91.2dB (99.9999999 %) at 2.28 GH and the bandwidth below -20 dB is 0.96 GHz. In addition, the highest useful frequency bands were observed for ferrite/ MWCNT/ silicone composites and the broadest -20dB bandwidth is observed for ferrite/ CIP/ MWCNT/ silicone composites.

並列關鍵字

electromagnetic shielding ； carbonyl iron powder ； ferrite

參考文獻

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