유전율법에 따른 다공질 매질의 특성 파악을 위한 실험적 연구

An Experimental study to estimate physical properties of porous media by a permittivity method

  • 발행 : 2003.12.01

초록

지반을 구성하고 있는 매질에 대한 체적함수비 및 포화 정도를 측정하는 것은 지반의 물리적 성질, 강우에 의한 지하수 함량 및 자연 사면 파괴를 이해하는데 매우 중요한 요소 중의 하나이다 이러한 지반의 요소들을 파악하기 위해 전자기파를 이용한 유전율법은 지반의 유전율상수의 특성에 따라 평가되어 지므로 다양한 분야에 적용되고 있다. 본 연구에서는 전자기파의 측정 주파수 범위 1 - 18 GHz를 사용하는 유전율 시스템인 FDR-V (Frequency domain reflectometry with vector network analyzer)를 적용하여 1 GHz와 18 GHz에서의 두 주파수 범위에 대한 표준사 (Standard sand)와 화강풍화토 (Granitic weathered soil)의 밀도, 온도 및 염분농도 의존성에 따른 유전율상수의 반응에 대해 검토하였다. 실험결과에서, 흙의 밀도 의존성은 체적함수비의 증가에 따라 유전율상수도 증가하는 것으로 측정되었으나, 이들의 밀도 의존성은 다소 낮은 것으로 판단된다. 그리고, 1 GHz 실수부 (Real part)에 대한 온도 의존성 실험에서는 온도의 증가에 따라 물과 표준사의 유전율상수는 점진적으로 감소하는 경향을 보이나 에탄올의 유전율상수는 증가하는 것으로 측정되었다. 따라서, 온도 변화에 따른 각 매질의 유전율상수는 측정 온도에 대한 영향을 고려하여야 한다. 염분농도에 따른 유전율상수의 변화는 1 GHz 허수부 (Imaginary part)에서 염분농도의 증가에 따라 유전율상수의 측정치도 함께 증가하는 것으로 나타났다. 이상과 같이, 다양한 조건하에 대한 유전율상수의 의존성들을 기초로 하여 다공질 매질의 특성을 파악하기 위한 FDR-V 시스템의 적용성을 충분히 검토하였다. 결론적으로, 본 연구에서는 1 GHz의 측정 주파수범위 내에서 다공질 매질의 염분오염도를 충분히 정량적으로 측정할 수 있는 것으로 생각된다.

Measurements of volumetric water content and saturation of porous media are very important factors in understanding the physical characteristics of soil, groundwater recharge by rainfall, pollutant movement, and slope failure. To measure such physical parameters, a permittivity method using electromagnetic wave is applied and use is made of the special permittivity response of understand to water and ethanol. In particular, the estimation is required because permittivity is influenced by the nature of the underground environment. In this study, we carried out experiments on the relative dependency of soil density, temperature and salinity of standard sand and granitic weathered soil using FDR-V system (Frequency domain reflectometry with vector network analyzer) within a frequency range of 1 - 18 GHz. The results of the study showed that the dielectric constants of standard sand and granitic weathered soil increased with increased volumetric water content of soil. However, the dependency of soil density was found to be a little low. Changes of dielectric constant with temperature appeared definitely in the real part of 1 GHz. That is, the dielectric constant of real part at 1 GHz of water and standard sand increased with the rise of temperature. However, ethanol showed decreased tendency. The study also showed that dielectric constant increased with increase in salinity at imaginary part of 1 GHz. It could be concluded from this study FDR-V system can adequately measure the physical properties of soil and the degree of salinity concentration of porous media within 1 GHz frequency range using dielectric constant.

키워드

참고문헌

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