Time Domain Reflectometry Method Research Articles

Improvement and Metrological Validation of TDR Methods for the Estimation of Static Electrical Conductivity

Accurate measurement of the static electrical conductivity provides a great insight into the characteristics and quality status of various materials. To overcome some limitations of the traditional measurement methods, there has been a growing interest toward the investigation of enhanced techniques for measuring electrical conductivity. In this regard, time-domain reflectometry (TDR) has attracted considerable attention, also due to the possibility of simultaneously monitoring different physical parameters. Although initially introduced for monitoring soil properties, the application of the TDR-based technique might be an interesting and cost-effective means in many other fields. However, the accuracy of traditional TDR-based electrical conductivity measurements is strongly influenced by the preliminary calibration technique. On such basis, in this paper, two innovative approaches for a more straightforward and accurate evaluation of the electrical conductivity are presented. The first method relies on the combination of the TDR measurement with transmission-line modeling (TLM); the second method simply relies on a couple of independent capacitance measurements (ICMs) performed through an LCR meter. As a further goal, the metrological performance of this last method is compared with that of the traditional method, thus validating its applicability. Experimental results and related uncertainty analysis on various samples demonstrate that the proposed alternative method is definitely suitable for a simpler and accurate estimation of the static electrical conductivity, also when dealing with moistened soils.

Dielectric relaxation and hydrogen bond interaction study of diol-water mixtures

Complex dielectric permittivity measurements in the frequency range 10MHz-20GHz have been carried out in diol-water mixtures over the entire concentration range using a time domain reflectometry (TDR) method at 25°C. A hydrogen bonded theory is applied to compute the dielectric constant for the mixtures. It adequately reproduces the experimental values of static dielectric constants for the diol-water mixtures. The dielectric parameters confirm that the intermolecular homogeneous and heterogeneous hydrogen bonding vary significantly with the increase in concentration of the constituents of the diol-water mixtures.

Acoustic properties of gas hydrate–bearing consolidated sediments and experimental testing of elastic velocity models

Although elastic velocities (Vp, Vs) can be used to assess the distribution and concentration of marine gas hydrates in situ and several existing models relate hydrate saturation to acoustic velocity, the accuracy of these models is uncertain because of the difficulty in determining hydrate saturations and velocities of intact hydrate‐bearing sediments. In this paper, the acoustic properties of gas hydrate–bearing consolidated sediments were investigated experimentally. Hydrate saturation (Sh) and acoustic velocities were measured in one system by time domain reflectometry and ultrasonic methods, respectively, during gas hydrate formation and subsequent dissociation in a water‐saturated artificial core. Acoustic velocities change little at low hydrate saturations (0% to ∼10%), whereas they increase rapidly when hydrate saturation is between 10% and 30%. We verified two commonly used models, i.e., the weighted equation (WE) and the Biot‐Gassmann theory modified by Lee (BGTL). In the 0% to 40% hydrate saturation range, the WE model is consistent with the measured Vp data, while a combination of the WE and the Vp/Vs ratio in the BGTL predicts Vs corresponding to the observed data. As hydrate saturation is more than 30%, however, the BGTL is more suitable for predicting both Vp and Vs. This suggests that gas hydrate may be treated as a component within a matrix of consolidated sediments when hydrate saturation exceeds 30%. However, when Sh is less than 30%, the hydrate locates in the pore fluid or partly adheres to the sediment frame.

Laboratory Evaluation of Time-Domain Reflectometry for Bridge Scour Measurement: Comparison with the Ultrasonic Method

Bridge scour is a major factor causing instability of bridges crossing waterways. Excessive scour contributes to their high construction and maintenance costs. Design of innovative scour-monitoring instrumentation is essential to ensure the safety of scour-critical bridges. The ability of real-time surveillance is important since the most severe scour typically happens near the peak flood discharge. A new scour-monitoring instrument based on the Time Domain Reflectometry (TDR) principle has been developed to provide real-time monitoring of scour evolution. A framework based on dielectric mixing model has been developed, which can be easily incorporated into an automatic analysis algorithm. This paper introduces a comparative study of TDR method and ultrasonic method for scour measurements. The results indicate that both TDR and ultrasonic methods can accurately estimate scour depth. TDR method, with the developed analysis algorithm, yields information on the river properties such as the electrical conductivity of river water and the density of sediments. TDR methods are also found less influenced by turbulence and air bubbles, both likely to occur during flood events.

Measurement of Steady‐State Soil Water Flux across a Soil Horizon Interface

Soil horizon interfaces have been shown to be focal points for localized, three‐dimensional redistribution of water and solutes in field soils. Therefore, understanding of the physics of water flow and transport in layered soils requires experimental observations of the magnitude and variability of local soil water flux under a variety of well‐defined boundary conditions. We developed a time domain reflectometry (TDR) method to measure the spatial pattern of steady‐state, local soil water flux density above and below a soil horizon interface under quasi‐steady surface water application and implemented it in laboratory and field experiments. Time series of TDR‐measured bulk soil electrical conductivity and TDR‐measured soil volumetric water content at each location are used to quantify the solute travel time under steady‐state flow conditions, which is then used to quantify steady‐state, local soil water flux density. Results from laboratory and field experiments showed that the proposed methodology yielded local soil water flux density estimates that were, on average, 104% of the applied surface water flux density (i.e., mass recovery = 104%), which is consistent with transient, local soil water flux density estimates from a previous study. For the field experiments, steady‐state, local soil water flux density estimates above and below an A/B horizon interface (measured across the length of a 6.75‐m transect) were negatively correlated to each other. The strength of the negative correlation, however, decreased with increasing surface water application rate, suggesting that the hydrologic response of the soil horizon interface is flux‐dependent. This flux‐dependent correlation between A and B horizon steady‐state soil water flux density is probably attributable to the spatial covariance between A and B horizon soil hydraulic properties.

Microwave dielectric response of binary mixture of N,N-dimethylformamide with propylene glycol using TDR method

Dielectric relaxation study of N,N-dimethylformamide (DMF) has been carried out with propylene glycol (PLG) at different temperatures. Time domain reflectometry (TDR) in reflection mode has been used to measure the reflection coefficient in frequency range of 10 MHz to 20 GHz. The dielectric parameters static dielectric permittivity (ϵ 0) and relaxation time (τ) have been obtained by Fourier transform and least squares fit methods. The experimental results show nonlinear variation in dielectric permittivity and relaxation time with volume fraction of PLG confirm the structural formation due to the intermolecular interaction between N,N-dimethylformamide and PLG. The variation in excess permittivity (ε E), excess inverse relaxation times (1/τ)E, Kirkwood correlation factors (g eff, g f), activation enthalpy (ΔH) and entropy (ΔS) are also calculated to study the binary mixture interaction.

Measurement of Transient Soil Water Flux Across a Soil Horizon Interface

Understanding the physics of water flow and transport in layered soils requires experimental observations of the magnitude and variability of these processes as they occur in the field. In this study, a time domain reflectometry (TDR) method to measure the spatial pattern of transient, local soil water flux above and below a soil horizon interface under quasi‐steady surface water application was developed and implemented in laboratory and field experiments. The method uses vertical TDR probes spanning two or more soil horizons or layers. Time series of soil water storage measured by the TDR probes are used to quantify transient, local soil water flux during infiltration under quasi‐steady surface water application. Results from the laboratory and field experiments showed that transient soil water flux estimates with the presented methodology were, on average, 106% of the applied water flux (i.e., mass recovery = 106%). Furthermore, in field experiments, excellent agreement between two independent measurements of local soil water flux through the A horizon showed that this methodology is robust and sensitive to spatial variations in soil water flux within soil horizons and changes in local soil water flux as the wetting front crosses the interface between two horizons. In the field experiments, transient local soil water flux through the A and B horizons (measured along a 6.75‐m‐long transect) were positively correlated to each other, but the strength of the correlation decreased with increasing surface water application rates. The flux‐dependent covariance between the measured patterns of transient A and B horizon soil water flux indicates that the soil horizon interface is a hydrologically significant component of the soil profile. In‐depth spatial analysis of the measured soil water flux patterns is the subject of a future study.

Structural Behavior of Alcohol−1,4-Dioxane Mixtures through Dielectric Properties Using TDR

The values of complex permittivity for alcohol-1,4-dioxane (DX) mixtures with various concentrations have been determined in the frequency range 10 MHz to 20 GHz using the time domain reflectometry (TDR) method. Numbers of hydrogen bonds between alcohol-alcohol and alcohol-dioxane pairs are estimated from the values of the static dielectric constant by using the Luzar model. The model provides a satisfactory explanation of the experimental results related to the static dielectric constant. The binding energies for alcohol-alcohol (pair 11) and alcohol-DX (pair 12) are estimated to be -13.98 and -16.25 kJ/mol, respectively. The results have also been compared with previous results of the ethyleneglycol-DX system.

Analysis of dielectric mixing models for the moisture assessment of porous building materials

The moisture content in materials has influence on their thermal, acoustic and mechanical properties, what has clear relation to their durability and service life. On this account, there is necessary to monitor liquid moisture content in building materials, and to know its influence on their behavior and performance. This information can find use already in the design of building structures as well in the restoration and reconstruction of existing buildings.In the presented paper, the problem of calibration of high frequency time domain reflectometry (TDR) method for moisture content measurement in porous building materials is studied. In this work there is focused on analysis of dielectric mixing models that can be used for calibration of dielectric moisture measurement methods. Experimentally accessed data were compared with the results of several mixing dielectric models like formulas developed by de Loor, Dobson, Polder and van Santen and Lichtenecker as well as Wiener’s and Hashin-Shtrikman’s bounds, which define a theoretical minimal and maximal value of permittivity for the given moisture content.On the basis of performed experiments and calculations, the suitable mixing models are identified and recommendations for their practical application are formulated.

Microwave Dielectric Study of an Oligomeric Electrolyte Gelator by Time Domain Reflectometry

The dynamics of water molecules in aqueous solutions of an oligomeric electrolyte gelator, poly[pyridinium-1,4-diyliminocarbonyl-1,4-phenylene-methylene chloride] (1-Cl) was characterized by microwave dielectric measurements using the time domain reflectometry method. The dielectric dispersion and absorption curves related to the orientational motion of water molecules were described by the Cole-Cole equation. Discontinuities were observed in the concentration dependence of the dielectric relaxation strength, Deltaepsilonh, as well as in the Cole-Cole parameter, betah. These discontinuities were observed between the samples with concentrations of 6 and 7 g/L 1-Cl/water, which correspond to a change in the transparency. Such a discontinuity corresponds to the observation of the critical concentration of gelation. The interaction between water and 1-Cl molecules was discussed from the tauh-betah diagram. As 1-Cl carries an amide group, it could be expected that 1-Cl may interact hydrophilically with water, but the present result suggests that 1-Cl interact hydrophobically with water.

Monitoring of water and heat transfer in the vadose zone of a carbonate formation: An example of an underground quarry in Gironde, France

This article studies the water and heat transfer in the vadose zone of a carbonate formation during three hydrological cycles (August 2001–May 2004). The application of the time domain reflectometry (TDR) method to determine the volumetric water content of porous rocks has been widely investigated. The study of more than 285 monthly point measurements of the rock water content during three hydrological cycles, distributed throughout an abandoned underground quarry in Gironde, France, shows a permanently undersaturated limestone (between 35% and 50%). Three periods of maximum volumetric water content correspond to the occurrence of three effective rainfall events. The phase lag and amplitude damping of the hydraulic and thermal signals with depth can be modelled and explained by the hydraulic and thermal properties of the porous medium in the unsaturated zone.

Interaction studies on the binary mixture of formamide with 2-butoxyethanol, 2-ethyl-1-hexanol, and isopropanol at 303 K

A molecular interaction study for binary mixture of 2-butoxyethanol, 2-ethyl-1-hexanol, and isopropanol with formamide has been carried out over the frequency range of 10 MHz–20 GHz at 303 K using time domain reflectometry method for 16 concentrations. The bilinear calibration method on least-square method has been used to obtain the static permittivity, relaxation time, and the permittivity at high frequency. The excess permittivity and excess relaxation time have been calculated, which provide information regarding the interaction among the molecules in the mixtures. Short-range interaction and alignment of the dipoles in the mixtures are studied using Kirkwood factors. The dielectric parameters are found to vary with concentration randomly.

Time Domain Reflectometry Studies on a Nematic Liquid Crystal

The complex dielectric permittivity spectra of p-pentyl phenyl-p-propylbenzoate (PPPB) , of a nematic liquid crystal are obtained using Time Domain Reflectometry (TDR) method over a frequency range 10 MHz–10 GHz at various temperatures covering both nematic and isotropic phases. The relaxation behavior at different temperatures was studied through cole–cole arc. The dielectric behavior in nematic (N) phase could be described by the Cole–Davidson model, while isotropic (I) phase is found to obey to a large extent Debye model. Two relaxation times, τ1 and τ2, are obtained for N phase which are the characteristic of Cole–Davidson model. τ1 and τ2 are interpreted as corresponding to different degrees of freedom in different direction in liquid crystalline state. The fact that τ1 and τ2 obtained for the I phase are almost equal favors Debye model. The results are presented over a temperature range, and these results are discussed to understand the phase transition involved. The work included in this article is useful as it provides information about the macroscopic structure of the liquid crystals in general and PPPB in particular. The N phase is the least ordered of liquid crystalline phases, and hence the studies even on an unaligned samples give information that is very close to aligned ones as far as those properties which are due to overall effects like dielectric behavior.

Soil Bulk Electrical Conductivity Measurement using High‐Dielectric Coated Time Domain Reflectometry Probes

Time domain reflectometry (TDR) is a technique that allows simultaneous estimates of apparent permittivity (εa) and hence volumetric water content (θ) and bulk electrical conductivity (σa). Difficulties arise for θ and σa determination, however, when uncoated TDR probes (UP) are used in highly conductive media. This work shows that σa can be estimated in highly conductive media using a TDR probe coated with a high‐dielectric insulator (CP). To this end, the Dalton method for σa estimations was applied to a 10‐cm‐long three‐rod TDR probe insulated with a 0.2‐mm‐thick epoxy‐ceramic composite coating with a relative permittivity, εr, of 32.3. This method was calibrated on different NaCl–water solutions (0–15 dS m−1) and compared with the standard long‐time TDR method for σa estimations using an UP. The method was subsequently used for determining σa in four different soils with different values of θ and σa (0–6 dS m−1) and again compared with the standard TDR procedure. The low error (RMSE = 1.5) for the comparison between the εa measured with the CP and that calculated with the analytical solution for coaxial probes indicates that the CP is accurate enough for εa estimations. For σa values <4 dS m−1, the UP allows determinations of εa and the most accurate estimations of σa using the standard TDR method (R2 = 0.99). For higher σa values, however, estimations of εa were only possible using the CP, where σa was satisfactorily determined (R2 = 0.99) using the Dalton method. To this end, a previous calibration between the real and the apparent bulk electrical conductivity estimated with the CP was required.

Moisture measurements of the chalk rock walls from Kazimierz Dolny with the application of TDR method

The article presents monitoring measurements of the physical parameters and mineralogical-petrographical composition analysis of the chalk rock from the Kazimierz Dolny region. The experiments involve the reflectometric techniques TDR (Time Domain Reflectometry) as a perspective alternative in moisture determinations. The investigation domain was the stone from the Castle of Janowiec by the Vistula river, which walls indicate the progressive corrosion depending on external exposition and age. Other object of investigations was the stone from quarry in Kazimierz Dolny. Porosimetric examinations of the chalk rock from the southern and northern elevation of the castle indicate differences in structure changes of the stones. These differences influence different behaviour of the chalk rock during capillary rise of water and salt solutions. It is connected with the suitable matching of the conservation protection, wall protecting preparations which kind and application depend on porosimetric parameters of the material. The TDR method is applied as a good alternative of water transport measurement in porous building materials and other water parameters characterisig described material.

Measurement of glucose and sucrose concentrations by time-domain reflectometry

The time-domain reflectometry (TDR) technology was applied in this study to measure sugar concentrations below 10%. The influences of temperature and species of sugars were evaluated. The results indicated that the TDR methods could be used for measuring sugar concentrations. The slope of TDR waveforms at a specific range was found to be a function of sugar concentrations and temperature. The differences in TDR waves derived from various sugar species and TDR probes were insignificant. The effects of the concentration and temperature on the slope of the TDR waveforms were established by regression analysis. The accuracy of the TDR method to measure sugar concentrations in new independent samples was within 0.365%. This technique is inexpensive, rapid, in-situ and suitable for online applications.

Time Domain Reflectometry Surface Reflections for Dielectric Constant in Highly Conductive Soils

This paper presents a model-based approach to determine dielectric constants from time domain reflectometry (TDR) measurement in highly conductive soils. It makes use of information contained in the TDR signal from the reflection at the surface of the soil rather than the reflection from the end of the probe. The TDR method is widely used to determine the volumetric water content of soils. Commonly used information from the TDR signals includes the apparent dielectric constant and the electrical conductivity. The apparent dielectric constant is generally measured by analyzing the travel time of electromagnetic waves reflected from the end of the soil probe. In soils with high electrical conductivities, the attenuation of the signal can eliminate the reflection from the end of the probe, which limits the application of TDR to these materials. A simplified frequency-independent dielectric model is utilized to invert the dielectric constant from the reflected signals at the soil surface. Results indicate that the dielectric constant can be determined with reasonable accuracy by the proposed approach for soils with high electrical conductivity, where the conventional travel time analysis fails due to significant signal attenuation.

An evaluation of performance limits in continuous TDR monitoring of permittivity and levels of liquid materials

Time domain reflectometry (TDR) is commonly used for several monitoring applications, particularly in hydrology and soil science for soil water content evaluation. Furthermore, significant advantages of TDR methodology, such as its relevant performance characteristics in terms of high flexibility and high sensitivity, as well as a non-destructive detection approach, render this technique an appealing candidate for a variety of environmental and industrial applications. In a previous paper [A. Cataldo, L. Tarricone, F. Attivissimo, A. Trotta, Simultaneous measurement of dielectric properties and levels of liquids using a TDR method, Measurement, doi:10.1016/j.measurement.2006.11.006] the authors demonstrated that TDR can be successfully used for a simultaneous real-time qualitative and quantitative monitoring of liquids. In this paper, a rigorous metrological characterization of the proposed method is formulated, and the uncertainty contributions are identified. The obtained results, confirm that the system is definitely adequate for simultaneously measuring dielectric constants and levels of liquids, with the associated relative uncertainties of 2% and 3%, respectively, for all the considered liquid samples. This way, challenging perspectives for several monitoring applications are open, especially in the processing of industrial liquids.

A TDR Method for Real-Time Monitoring of Liquids

Time-domain-reflectometry (TDR) measurements, which were originally used to locate and diagnose faults in transmission lines, have been widely applied in geology and soil science for accurate and flexible measurements of soil moisture and water content. Furthermore, the most attractive advantages of TDR rely on the possible determination of the spatial location and nature of various objects, both in real time and with a nondestructive approach. This makes the TDR technique an appealing candidate for a variety of environmental and industrial applications. Although the TDR instruments are commonly used to date, particularly for the aforementioned purposes, the state of the art is rather lacking in liquid-monitoring applications. This paper describes how the suitable combination of TDR detecting functionalities can lead to a simultaneous monitoring of quantitative and qualitative properties of liquid samples. In fact, the proposed TDR method allows, in one shot, the measurement of liquid levels, the determination of multiple interfaces in layered media, and the evaluation of dielectric properties such as dielectric permittivity or electrical conductivity. Some applications to real cases are proposed, which are referred to petrol-chemical mixtures or water-based liquids, thus validating the approach on a wide range of materials.

Accurate Series-Resistance Extraction From Capacitor Using Time Domain Reflectometry

For advanced CMOS technology, series resistance is an important source of error in capacitance-voltage (C-V) measurement. Independent accurate determination of series resistance is generally not possible. Recently, we introduced a new C-V measurement method using time domain reflectometry (TDR). Here, we show that the TDR method also allows series resistance to be determined independently and accurately