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Characterization of moisture sensitive materials for resonant microwave sensors
The optimization of a resonant microwave sensor for moisture measurements in concrete buildings and masonry is presented. Design improvements and the choice of adequate sensitive materials are discussed. A sensor is presented, which is capable of detecting moisture in concrete structures. The sensor consists of two circular waveguide sections, one containing a resonant helix, the other one a sensitive material loading the resonator (Fig. 1). The open end of the waveguide allows environmental moisture in the vapor or in the liquid phase to penetrate the sensor. This changes the dielectric constant of the sensitive material which detunes the resonator. The resonance shift is detected by measuring the reflection coefficient via a coaxial cable. Using a helix instead of a conventional microwave resonator leads to a very compact size: at a resonant frequency of 2.5 GHz diameter and length (w/o coax) do not exceed 10 mm and 30 mm, respectively. Measurement errors due to the presence of ions are negligible, whereas the temperature has to be taken into account. For very short response time, ceramics should be used instead of cement stone. The particle size of the ceramic powders has no verifiable impact on the response time. The ceramic materials are free of hysteresis and the sensitivity can be improved by adjusting the initial water content of the Al2O3 powders.
Characterization of moisture sensitive materials for resonant microwave sensors
The optimization of a resonant microwave sensor for moisture measurements in concrete buildings and masonry is presented. Design improvements and the choice of adequate sensitive materials are discussed. A sensor is presented, which is capable of detecting moisture in concrete structures. The sensor consists of two circular waveguide sections, one containing a resonant helix, the other one a sensitive material loading the resonator (Fig. 1). The open end of the waveguide allows environmental moisture in the vapor or in the liquid phase to penetrate the sensor. This changes the dielectric constant of the sensitive material which detunes the resonator. The resonance shift is detected by measuring the reflection coefficient via a coaxial cable. Using a helix instead of a conventional microwave resonator leads to a very compact size: at a resonant frequency of 2.5 GHz diameter and length (w/o coax) do not exceed 10 mm and 30 mm, respectively. Measurement errors due to the presence of ions are negligible, whereas the temperature has to be taken into account. For very short response time, ceramics should be used instead of cement stone. The particle size of the ceramic powders has no verifiable impact on the response time. The ceramic materials are free of hysteresis and the sensitivity can be improved by adjusting the initial water content of the Al2O3 powders.
Characterization of moisture sensitive materials for resonant microwave sensors
Charakterisierung feuchteempfindlicher Werkstoffe für resonante Mikrowellensensoren
Sokoll, T. (author) / Jacob, A.F. (author)
2004
9 Seiten, 13 Bilder, 2 Tabellen, 10 Quellen
Conference paper
Storage medium
English
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