Recent Advances in Broad-Band VHF and UHF Transmission Line Methods for Moisture Content and Dielectric Constant Measurement

Chudobiak, W.J.; Syrett, Barry; Hafez, H.M.

doi:10.1109/tim.1979.4314833

Cited by 17 publications

(6 citation statements)

References 4 publications

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“…In the 1970s broadband VHF and UHF transmission line methods were developed for characte.rizing materials based on their dielectric and magnetic properties [Bussey, 1967 [Chudobiak et al, 1979b]. The relationships between the complex permittivities and permeabilities and the dimensions of the transmission, the characteristic impedance, and the velocity of propagation for all the above discussed geometries are presented by Chudobiak et al [1979a, b].…”

Section: Introductionmentioning

confidence: 99%

Comparison of Time Domain Reflectometry Performance Factors for Several Dielectric Geometries: Theory and Experiments

Maheshwarla¹,

Venkatasubramanian²,

Boehm³

1995

Water Resources Research

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We propose three nontraditional dielectric geometries and present an experimental and theoretical analysis and comparison of time domain reflectomerry (TDR) performances for them. The traditional geometry (the probes inserted in material of essentially infinite extent) is compared to three nontraditional geometries where the probes are affixed outside of a core sample, inside of a bore, or flat on the surface of a semi-infinite solid. Our derivation relates the velocity of electromagnetic wave propagation to the complex permittivities and permeabilities of the media and the geometry for the three nontraditional configurations. Experimental results for air, styrofoam, dry sand, wet sand of varying water content, nylon, dry wood, and ferromagnetic steel are obtained for the three proposed configurations and are in fair agreement with the literature within the experimental uncertainties. Through experiments and theoretical analysis, the TDR performance is found to be the same within the experimental uncertainties for the three nontraditional geometries. The proposed geometries yield slightly lower sensitivities compared to the traditional geometry. Advantages and disadvantages of the geometries compared to the traditional geometry are also discussed.

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Section: Introductionmentioning

confidence: 99%

Comparison of Time Domain Reflectometry Performance Factors for Several Dielectric Geometries: Theory and Experiments

Maheshwarla¹,

Venkatasubramanian²,

Boehm³

1995

Water Resources Research

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“…The design of TDR probes has been described in the literature by several researchers (e.g., Chudobiak et al, 1979; Dalton and van Genuchten, 1986; Heimovaara, 1993; Ferré et al, 1998). The different concepts vary in terms of dimensions, spacing, shape, and diameter of the probe wires (plates or rods).…”

Section: Theorymentioning

confidence: 99%

A New Coaxial Time Domain Reflectometry Probe for Water Content Measurement in Forest Floor Litter

Canone

Previati

Ferraris

et al. 2009

Vadose Zone Journal

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M the evolution of soil water storage for either water resource management or fl ood risk prevention requires knowledge of the soil water content profi les during infi ltration and evaporation.Forests are present in many sensitive areas such as most mountain areas of Europe. Forest fl oor soils are generally covered by forest litter layers of variable thickness. Th e role of forest litter should therefore be accounted for in forest hydrologic models, as indicated by Ogée and Brunet (2001), who reported the lack of moisture measurements as a limitation for validating modeling approaches.Th e relevance of forest litter water content in the hydrologic behavior of forest land becomes even more crucial when taking into account its eff ect on the water repellency of litter material. In fact, recent studies have shown a relationship between wetting properties and the water content of forest litter, suggesting water content threshold values below which the organic material becomes hydrophobic (e.g., Greiff enhagen et al., 2005).Time domain refl ectometry is a much used method for the measurement of water content, as it is noninvasive and does not require sample collection for time-consuming laboratory measurements; however, the TDR technique has shown limitations for its use in loose material such as forest litter. In these materials, it is diffi cult to establish and maintain good contact between the probe and the surrounding material.Th e aim of this work was to develop a TDR probe that can be used for loose materials while ensuring optimum working conditions in terms of ease of insertion into the porous medium, contact with the surrounding porous medium, and homogeneity and confi nement of electrical energy storage. Theory Probe DesignTh e design of TDR probes has been described in the literature by several researchers (e.g., Chudobiak et al., 1979;Dalton and van Genuchten, 1986;Heimovaara, 1993;Ferré et al., 1998). Th e diff erent concepts vary in terms of dimensions, spacing, shape, and diameter of the probe wires (plates or rods). As a result, they diff er with respect to their infl uence on bulk soil electrical conductivity (EC) interference, sampling volume, and the spatial distribution of the electrical energy. Th e aim of probe design is usually to fi nd a good compromise between mitigation of the EC eff ect (i.e., short rods) that causes attenuation of the TDR waveform, and the length and spacing of the probe wires to A : EC, electrical conductivity; MAE, mean absolute error; TDR, time domain refl ectometry.O R Knowledge of water content is important for water resources management and risk preven on. For areas covered with forest, the presence of decomposed or undecomposed forest li er poses a real problem for the monitoring of volumetric water content. Tradi onal methods such as me domain refl ectometry (TDR) are diffi cult to apply, as the inconsistence of the porous material o en leads to density modifi ca ons close to the probe wires. The aim of this work was to develop a TDR probe that can be used for loo...

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“…Figures 22a through 22d compare the more commonly used TDR probes constructed with rods, whereas Fig. 22e and 22f show cross sections for parallel plate geometries that have been proposed by a number of authors (Chudobiak et al, 1979; Robinson and Friedman, 2000; Inoue et al, 2001).…”

Section: Probe Design Construction and Calibrationmentioning

confidence: 99%

“…The diagrams illustrate that more of the energy is closer to the conductor using rods than using plates. Chudobiak et al (1979) first suggested the use of TDR probes with a plate geometry. More recently plates acting as blades have been proposed for both static (Robinson and Friedman 2000) and mobile (Inoue et al, 2001) TDR measurements.…”

Section: Probe Design Construction and Calibrationmentioning

confidence: 99%

A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry

Robinson

Jones

Wraith

et al. 2003

Vadose Zone Journal

718

119

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Substantial advances in the measurement of water content and bulk soil electrical conductivity (EC) using time domain reflectometry (TDR) have been made in the last two decades. The key to TDR's success is its ability to accurately measure the permittivity of a material and the fact that there is a good relationship between the permittivity of a material and its water content. A further advantage is the ability to estimate water content and measure bulk soil EC simultaneously using TDR. The aim of this review is to summarize and examine advances that have been made in terms of measuring permittivity and bulk EC. The review examines issues such as the effective frequency of the TDR measurement and waveform analysis in dispersive dielectrics. The growing importance of both waveform simulation and inverse analysis of waveforms is highlighted. Such methods hold great potential for obtaining far more information from TDR waveform analysis. Probe design is considered in some detail and practical guidance is given for probe construction. The importance of TDR measurement sampling volume is considered and the relative energy storage density is modeled for a range of probe designs. Tables are provided that compare some of the different aspects of commercial TDR equipment, and the units are discussed in terms of their performance and their advantages and disadvantages. It is hoped that the review will provide an informative guide to the more technical aspects of permittivity and EC measurement using TDR for the novice and expert alike.

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Recent Advances in Broad-Band VHF and UHF Transmission Line Methods for Moisture Content and Dielectric Constant Measurement

Cited by 17 publications

References 4 publications

Comparison of Time Domain Reflectometry Performance Factors for Several Dielectric Geometries: Theory and Experiments

Comparison of Time Domain Reflectometry Performance Factors for Several Dielectric Geometries: Theory and Experiments

A New Coaxial Time Domain Reflectometry Probe for Water Content Measurement in Forest Floor Litter

A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry

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