Development of electromagnetic wave absorber with woodceramics

2002 Fiscal Year Final Research Report Summary

• Project/Area Number: 12450286
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Structural/Functional materials
• Research Institution: Himeji Institute of Technology
• Principal Investigator: MIKI Masamichi Himeji Inst. of Techno. Prof., 工学部, 教授 (00047606)
• Co-Investigator(Kenkyū-buntansha): KIKUCHI Takeyuki Himeji Inst. Of Techno. Res. Assoc., 工学部, 助手 (50316048) ; HATAKEYAMA Kenichi Himeji Inst. Of Techno. Assoc. Prof., 工学部, 助教授 (80305680) ; TAKADA un Okayama University Prof., 工学部, 教授 (60093259)
• Project Period (FY): 2000 – 2002
• Keywords: woodceramics / white charcoal / bamboo charcoal / electromagnetic wave absorber / X-ray diffraction / resistivity / permittivity / carbon

Research Abstract

Recently, the utilization of high frequency electromagnetic waves of GHz range has increased with increasing new communication systems such as cellular phone and local area network. As a result, high frequency electromagnetic waves from such new system or machines have frequently affected medical and avionics equipments and induced many dangerous incorrect actions and accidents. Therefore, the fast development of such materials to not only shield but also absorb completely above harmful waves has been needed.
On the other hand, woodceramics (WCS) are new porous carbon materials which are made by carbonizing wood or woody materials such as MDFs (medium-density fiberboards) impregnated with liquid phenolic resin in a vacuum furnace. The impregnated phenolic resin changes into hard glassy carbon during carbonizing process and reinforces the soft charcoal which originated from wood fibers in the MDF. This study has been done in order to develop the superior absorber for such harmful wave by using WCS.
The WCS boards obtained by carbonizing the phenolic resin impregnated MDF at 650-700℃ showed remarkable electromagnetic absorption (about 50 dB) at about 7 GHz. The boards carbonized at 750-800℃ showed the absorption of about 40 dB at the frequency of about IGHz.
The electromagnetic wave absorption characteristics of the WCS made by the new powder method, namely by carbonizing the compacted mixtures of 30 mass% phenolic resin powder and 70 mass% wood powder, were measured by the coaxial cable method using a network-analyzer. The woodceramics made by carbonizing the compacted mixture of 30 mass% phenolic resin powder and 70 mass% wood powder at 650℃ showed the large absorption peak (about 50 dB) at the frequency of about 2 GHz. The addition of SiC powder to the starting mixture shifted the absorption peak of the sintered composite to the higher frequency, for example, 9 GHz for the specimen containing 47 % SiC.
It is possible to make the absorbers suitable for the electromagnetic waves of 1-10 GHz by changing the carbonization temperature in the MDF method or the amount of SiC powder in the powder method.