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扫描电子显微镜

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扫描电镜应用之:高频电磁波吸波材料  

2010-12-31 08:29:16|  分类: 默认分类 |  标签: |举报 |字号 订阅

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扫描电镜应用之:高频电磁波吸波材料 - 驰奔 - ---DEMA 驰奔---
 

Introduction

Information and communications technology is rapidly developing. Electromagnetic waves with ultra high frequencies (300 MHz¨C3 GHz) and super high frequencies (3¨C30 GHz) are used to transfer a great amount of information at high speeds. In practice, such electromagnetic waves have already been applied to cordless phones (0.8¨C2 GHz), wireless local area network (2.45¨C5.2 GHz), electronic toll collection (5.8 GHz) etc. In the near future, electromagnetic waves with frequencies over 30 GHz or extremely high frequencies will be required for higher speed communications and the spread of intelligent transportation system. However, the electromagnetic waves with extremely high frequencies cause some other serious problems such as the malfunction of electronic equipment, information leakage and the like. A solution to the problems is to develop radar-absorbent materials (RAMs) which can absorb broadband electromagnetic waves.

In general, RAMs are classified into three categories, dielectric, magnetic and conductive RAMs which have different mechanisms to absorb electromagnetic waves [1-6]. Most commercial dielectric and magnetic RAMs are heavy and just cover narrow ranges of frequencies. And the radar absorbency of the dielectric and magnetic RAMs depends on their nature, composition, loading amount and thickness. On the other hand, when conductive RAMs catch electromagnetic waves, current induced from the electromagnetic waves flows on the RAMs, leading to the decrease in the reflection of electromagnetic waves. Recently, we have developed succeeded in a new preparation method of polypyrrole (PPY) nanoparticles-coated non-woven fabrics with high conductivity [7]. In the present study, we investigate the radar absorbency of the conductive non-woven fabrics to clarify the usefulness as a new RAM material.

Experimental

Preparation of a Dopant Solution

BANS and BATS were used as a dopant in the present study because we have found experimentally that they were suitable for forming uniform PPY nanoparticles with high conductivity. 1-Butylamine (143 mL) was slowly added to a 1.57 M (= mol L- 1) 2-naphthalenesulfonic acid aqueous solution while keeping the temperature below 20??C to produce a 1.36 M BANS aqueous solution. To prepare 1.36 M BATS aqueous solution, the same procedure was performed, except that p-toluenesulfonic acid was used in place of 2-naphthalenesulfonic acid.

Preparation of Conductive Non-Woven Fabrics

As an oxidizing agent, ammonium persulfate (APS) was dissolved into distilled water, followed by adding the BANS aqueous solution, BATS aqueous solution, and ethanol for improving wettability of non-woven fabric and then stirring. The resultant solution is called ?°solution A?±. The concentration of ethanol was fixed to 5 M in the present study. The molar ratio of BANS to BATS, [BANS]/[BATS], and that of both dopants to APS, ([BANS]+[BATS])/[APS], were fixed to 1, respectively.

After immersing a non-woven fabric (WO-ME150, Mitsubishi Paper Mills Limited, 50??50 cm) in the solution A for 10 min, the fabric was dehydrated at 0.3 MPa using the nip roll apparatus of ??12 cm and then dried for 10 min at 60??C. A laboratory dish containing 20 mL of pyrrole was placed at the bottom of a closed cubic acrylic box (100??100??100 cm). The pretreated fabric was laid in the box filled with pyrrole vapor. After 10 min, the fabric was removed from the box and dried for 10 min at 100??C. The fabric was washed thoroughly using distilled water and then dried for 10 min at 100??C again.

Before investigating the radar absorbency of conductive non-woven fabrics, they were piled up on an aluminum foil with a thickness of 0.05 mm which prevented any electromagnetic waves from transmitting.
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