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2019 Vol.31, Issue 1 Preview Page
February 2019. pp. 69-77
Abstract
In this study, to evaluate the electromagnetic shielding effect of UHPC/CNT composites by the content of CNTs, electromagnetic shielding effectiveness (SE) test was performed based on MIL-STD-188-125-1 using specimens similar to actual size of exterior material. Then, experimental results were verified by applying Antenna theory of Schelkunoff. As the CNT contents increased, the SE at the same frequencies increased. However, contrary to the theory, the SE in the magnetic field was decreased with increase in frequency regardless of content of CNTs. The reason was due to the electromagnetic coupling effect and proved by using formula. Percolation threshold of CNT used in this experiment was 0.8∼1 wt.% of cement. In this case, the SE was maximized while maintaining the compressive strength and workability at levels similar to reference proportion. The SE when considering the electromagnetic coupling effect in the magnetic field was 18 dB at 10 kHz. And the SE in the plane wave (1 GHz) was about 22 dB. In conclusion, this composite could be used as a shielding material.
이 연구에서는 탄소나노튜브(CNT)로 보강된 초고성능 콘크리트(UHPC) 복합재료의 전자파 차폐재 적용가능성을 평가하기 위해 실제 외장재료 크기로 실험체를 제작하여 MIL-STD-188-125-1에 의거 전자파 차폐시험을 실시하고 쉘쿠노프의 전송선 이론을 적용하여 해석하였다. 실험결과 CNT 혼입량이 증가할수록 동일 주파수에서의 전자파 차폐효과는 증가하였다. 일반적으로 근역장에서의 차폐효과는 주파수가 증가할수록 그 값이 커지지만 UHPC/CNT 복합재료는 오히려 감소하는 결과가 나타났다. 이는 실험체와 차폐실과의 도전율 차로 인해 전자기 커플링이 형성되어 반사손실에 의한 차폐효과가 감소한 것임을 수식을 사용해 증명하였다. 평면파 원역장에서의 차폐효과는 평면파에서의 실험결과를 바탕으로 원역장에서의 흡수손실을 구하는 식을 유도하여 계산한 결과 실험값과 유사한 결과를 얻을 수 있었다. 이 연구에 사용된 CNT의 경우 침투임계점은 시멘트 중량의 0.8~1.0 %였으며 이때 UHPC의 기계적 성질과 워커빌리티를 유지하는 가운데 차폐효과가 극대화 되어 근역장인 10 kHz에서 18 dB, 평면파인 1 GHz에서 22 dB의 차폐효과를 가지는 것으로 나타났다. 따라서 해당 재료는 손실유전체로 간주할 수 있으며 입사파와의 거리와 목표 차폐효과를 고려하여 두께 등을 조절함으로써 차폐재로서 충분히 적용 가능할 것으로 판단된다.
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Information
  • Publisher :Korea Concrete Institute
  • Publisher(Ko) :한국콘크리트학회
  • Journal Title :Journal of the Korea Concrete Institute
  • Journal Title(Ko) :콘크리트학회 논문집
  • Volume : 31
  • No :1
  • Pages :69-77