Time Domain Reflectometry Method Research Articles

Temperature dependent dielectric relaxation study of triol-water mixtures using picosecond time domain technique

Picosecond time domain reflectometry method has been used in the frequency range of 10 MHz to 20 MHz to determine dielectric properties of aqueous solutions of triol in temperature range of 15 to 35 °C. The excess permittivity, Kirkwood correlation factor and Bruggeman factor of triol-water system have also been determined. A hydrogen bonded theory is applied to compute correlation terms for the mixtures. A hydrogen bonded model gives good qualitative account of the dielectric constant for triol-water mixture.

Low-Power STDR CMOS Sensor for Locating Faults in Aging Aircraft Wiring

A CMOS sensor used to locate intermittent faults on live aircraft wires is presented. A novel architecture was developed to implement the Sequence Time Domain Reflectometry method on a 0.5-mum integrated circuit. The sensor locates short or open circuits on active wires with an accuracy of +/-1 ft when running at a clock speed of 100 MHz. A novel algorithm is proposed that utilizes the shape of the correlation peak to account for sub-bit delay, thus increasing the accuracy of fault location. The power consumed by the microchip is 39.9 mW

Simultaneous measurement of dielectric properties and levels of liquids using a TDR method

Several monitoring methods, in the recent years, involved microwave/radio frequency (RF) reflectometry techniques, particularly in remote sensing, environmental and industrial application fields. The main advantages using reflectometry are due to its relevant performance characteristics, in terms of high flexibility, high sensitivity and large application conditions. Furthermore, the time domain reflectometry (TDR) presents some attractive advantages, related to the possible determination of the spatial location and nature of various objects, in real-time and with a non-destructive approach. This makes the TDR technique an appealing candidate for a variety of environmental and industrial applications. Although TDR instruments are commonly used today, particularly for the above mentioned purposes, the state of the art is rather lacking in liquid monitoring applications. In this paper we demonstrate that a suitable combination of TDR detecting functionalities, in terms of spatial localization, dielectric properties estimation and coaxial probe performance characteristics, leads to an enhanced quantitative and qualitative monitoring method. Really, in one shot, the analysis of TDR data allows the measurement of liquid levels, the determination of multiple interfaces in layered media, as well as the evaluation of dielectric properties, such as dielectric permittivity or electrical conductivity. Moreover, some applications to real cases are proposed, referred to petrol–chemical mixtures or water-based liquids, thus validating the approach on a wide range of materials.

A Time-domain Reflectometry Method for Automated Measurement of Crack Propagation in Composites during Mode I DCB Testing

This article describes a new technique for automated measurement of crack initiation, growth, and propagation in composite materials during mode I double cantilever beam (DCB) testing. The proposed method uses time-domain reflectometry (TDR) to detect changes in geometry and electromagnetic properties (dielectric or magnetic) along a transmission line that can be embedded in or bonded to the surface of the specimen. Two types of transmission line TDR sensors are evaluated (IM7 carbon fiber and ARACON) during DCB tests. A P-SPICE transmission-line simulation model is used to verify the baseline signal response for the DCB sensor and the sensitivity for crack detection, with good agreement. Comparison with standard visual methods in DCB testing showed excellent correlation in crack location, crack propagation (LC), and the interlaminar fracture toughness (GIC) values. The TDR sensor design and model-based parametric studies are carried out to determine optimal sensor geometry and configuration. The results demonstrate that the TDR-based method can measure crack propagation parameters at high resolution and accuracy, in an automated manner using low-cost sensors.

Electrical Characterization of FCBGA Package Based on Measurement Approach for High-speed SOC Applications

With high-speed computers and wireless communications system become more popular in the electronic market, these communication-oriented products require high packaging densities, clock rates and higher switching speeds over Gb/s. A multilayer flip-chip Ball grid array (FCBGA) package used for applications running at more than 1 Gb/s has been characterized in this work. Electrical characterization of the package becomes essential beyond 1 GHz considering that the interconnections on the package behave not only just as interconnections but also as transmission lines. In this paper, we present the measurement and simulation results for interconnection of an FCBGA package using the time domain reflectometry (TDR) method. Simulation and measurement results are compared to establish a proper equivalent circuit model of the FCBGA interconnections. The parasitics of the power network can be measured through TDR, vector network analyzer (VNA) and impedance analyzer (IA). The complete models generated in this work are targeted for high-speed system-on-chip (SOC) devices that have a wide range of uses across commercial electronic applications.

Measuring optical fiber length by use of a short-pulse optical fiber ring laser in a self-injection seeding scheme

A method for measuring the length of an optical fiber by use of an optical fiber ring laser pulse source is proposed and demonstrated. The key element of the optical fiber ring laser is a gain-switched Fabry-Perot laser diode operated in a self-injection seeding scheme. This method is especially suitable for measuring a medium or long fiber, and a resolution of 0.1 m is experimentally achieved. The measurement is implemented by accurately determining the pulse frequency that can maximize the output power of the fiber ring laser. The measurement results depend only on the refractive index of the fiber corresponding to this single wavelength, instead of the group index of the fiber, which represents a great advantage over both optical time-domain reflectometry and optical low-coherence reflectometry methods.

The influence of time domain reflectometry rod induced flow disruption on measured water content during steady state unit gradient flow

Intrusive measurement techniques require placing a sensor within the sample, possibly changing the conditions under which the measurement is collected and thereby affecting the quality of the measurement. In this study we consider time domain reflectometry (TDR), which is an intrusive water content measurement method. TDR rods are impermeable, and thus water is forced to flow around the rods. In an unsaturated medium this changes the water content distribution in the vicinity of the rods, with the water content increased at the tops of the rods and decreased at the bottoms of the rods. TDR has nonuniform spatial sensitivity, with much higher sensitivity immediately adjacent to rods, in the regions that experience the greatest change in water content due to this flow disruption. Furthermore, the spatial sensitivity of TDR depends on the water content distribution within the sample volume. This raises the possibility that flow disruptions caused by TDR rods may affect the TDR‐measured water content. In this study we are specifically interested in the effects of flow disruption due to TDR rods. Therefore we consider steady state unit gradient unsaturated flow in a homogeneous medium to eliminate spatial heterogeneity of water content due to soil heterogeneity and transient flow conditions. For common TDR probe designs in the wide range of soils examined, flow disruption gives rise to a water content measurement error that is less than 0.005 cm3 cm−3. This is smaller than the reported accuracy of the TDR method of 0.02 cm3 cm−3. As a result, we conclude that it is appropriate to ignore flow disruption caused by commonly used TDR probes when assessing sources of TDR measurement error.

Determination of Moisture Diffusivity using the Time Domain Reflectometry (TDR) Method

The time domain reflectometry (TDR) method is commonly used for the measurement of moisture content in soil science. In this study, the method is employed for the measurement of moisture profiles in building materials. The practical applications of the method are presented on an example of water penetration into cellular concrete (aerated autoclaved concrete) samples. The measured results are then used for the determination of moisture diffusivity as a function of moisture content.

Experimental determination of bulk dielectric properties and porosity of porous asphalt and soils using GPR and a cyclic moisture variation technique

This paper describes a new method for determining porosities in two porous construction and geologic materials (asphalt and soil) by using ground-penetrating radar (GPR) over a wide range of controlled degrees of water saturation [Formula: see text]. We call this method a cyclic moisture variation technique (CMVT). Freshwater is used as an enhancer or a tracer to allow GPR to easily detect and differentiate amounts of water or other moisture in these materials. The CMVT is based on measuring the changes of real permittivity [Formula: see text] and [Formula: see text] in the test materials as they transition from partially saturated states to a fully saturated state via cycles of water permeation and dewatering. This method does not disturb the test materials, as do the methods associated with traditional laboratory testing on cored samples. It also tests a large mass of in situ material, compared with the small mass tested by the conventional or electromagnetic coaxial transmission line (EMCTL) method (also known as a dielectric cell) and the time-domain reflectometry (TDR) method. Porosity values of asphalt [Formula: see text] and of soils [Formula: see text] were determined by fitting the data into the complex refractive index model (CRIM). Dielectric hysteresis of both soils and asphalt also is observable during the tests and shows that the pathways of water-ingress and water-egress processes are not identical in the plot of [Formula: see text] versus degrees of water saturation [Formula: see text].

Comparing Ambient Temperature Effects on Heat Pulse and Time Domain Reflectometry Soil Water Content Measurements

Time domain reflectometry (TDR) and the heat pulse method are both used to measure soil water content. Changes in ambient temperature have been shown to affect TDR measurements, but less is known about the behavior of heat pulse sensors in response to changes in temperature. This study directly measured and compared the temperature sensitivity of the TDR and heat pulse methods. Both methods were used to estimate water content in silt loam and sand at two fixed water contents across a wide temperature range. An increase in temperature led to an increase in measured water content in most cases. Across the 40°C temperature range, changes in measured water content were generally 0.04 m3 m−3 or less for both methods. Weighted linear regression showed that in these soils the heat pulse method exhibited greater temperature sensitivity than the TDR method, although the differences were not statistically significant. A previously proposed correction for the temperature sensitivity of the TDR method produced mixed results. The temperature sensitivity of the heat pulse method was attributed to the changes in the density and specific heat of water and specific heat of soil with respect to temperature. When the changes in these parameters were accounted for, the temperature sensitivity was eliminated in three out of four cases.

Dielectric Relaxation of Propan-1-ol with Chlorobenzene, 1,2-Dichloroethane, and Dimethylene Chloride at (288, 298, 308, and 318) K Using Time-Domain Reflectometry Technique

The values of complex permittivity of molecules containing chlorine with propan-1-ol binary mixtures have been determined over the frequency range of (0.1 to 20) GHz, at temperatures of (288, 298, 308, and 318) K, using the time-domain reflectometry (TDR) method for 11 molalities of each molecule containing chlorine with propan-1-ol system. The dielectric relaxation in these systems can be described by a single relaxation time using the Havriliak and Negami model. The static dielectric constant (ε0) and relaxation time (τ) have been obtained by fitting experimental data with the Havriliak−Negami equation.

Three-dimensional numerical modeling of a four-pin probe for soil water content

Soil probes with 4-pin configuration have been widely used in frequency domain (FD) and time domain reflectometry methods for determining soil water content. The techniques of FD sensors largely rely on the port impedance of the probe. This study provided a 3-dimensional numerical model to represent the electric behaviours of the 4-pin probe, which is valuable for analysing the effect of the soil dielectric constant, geometry, and the operating frequency on the port impedance of the probe. The model was performed with high frequency structure simulator software based on Maxwell’s equations and finite element method. A typical 3-dimensional electromagnetic distribution of the 4-pin probe was presented. The model was validated with 3 experiments under the aid of a network analyser. First, the experiment was performed using a series of fluids of known relative dielectric constants, then numerical simulations were carried out and confirmed by soil sample test with varying frequencies and the probe lengths. The effects of these parameters on FD methods are discussed based on the 4-pin probes. The 3-dimensional numerical model appears to be a meaningful tool to investigate more deeply a 4-pin probe in FD method.

Time domain reflectometry for water content and density of soils: study of soil-dependent calibration constants

The paper studies the soil-dependent calibration constants used for determining water content and density of soil using time domain reflectometry (TDR), specifically, to establish the typical soil calibration values and study the extent of the uncertainty in calibration factors on measurement accuracy. The TDR method described here makes use of a calibration equation normalized by soil dry density, which involves two soil-dependent constants, a and b. Both a and b have physical significance, with the value of a related to the apparent dielectric constant of the dry density – normalized dry soil solids and the value of b related to the apparent dielectric constant of the pore fluid. From theoretical predictions, typical values of a are around 1.0, and typical values of b are around 9. Practically, the constants a and b are obtained through calibration tests performed in conjunction with standard compaction tests. Experimental study shows that calibration constants fall within the ranges from theoretical predictions. Tests on five soil mixtures provided average values of a = 0.945 and b = 8.76, while 11 clean sands resulted in average values of a = 1.0 and b = 8.5. The study also shows that there are no significant effects of compaction energy on the measured values of a and b. Sensitivity analyses indicate that variations in a and b both cause variations in TDR-determined water content and density, but the variations are typically within acceptable limits for engineering application purpose. Results from TDR tests on simulated field experiments are consistent with the sensitivity analyses.Key words: time domain reflectometry, TDR, calibration constants, water content, dry density, sensitivity.

A dripper-TDR method for in situ determination of hydraulic conductivity and chemical transport properties of surface soils

Field determined hydraulic and chemical transport properties can be useful for the protection of groundwater resources from land-applied chemicals. Most field methods to determine flow and transport parameters are either time or energy consuming and/or they provide a single measurement for a given time period. In this study, we present a dripper-TDR field method that allows measurement of hydraulic conductivity and chemical transport parameters at multiple field locations within a short time period. Specifically, the dripper-TDR determines saturated hydraulic conductivity ( K s), macroscopic capillary length ( λ c), immobile water fraction ( θ im/ θ), mass exchange coefficient ( α) and dispersion coefficient ( D m). Multiple dripper lines were positioned over five crop rows in a field. Background and step solutions were applied through drippers to determine surface hydraulic conductivity parameters at 44 locations and surface transport properties at 38 locations. The hydraulic conductivity parameters ( K s, λ c) were determined by application of three discharge rates from the drippers and measurements of the resultant steady-state flux densities at the soil surface beneath each dripper. Time domain reflectometry (TDR) was used to measure the bulk electrical conductivity of the soil during steady infiltration of a salt solution. Breakthrough curves (BTCs) for all sites were determined from the TDR measurements. The K s and λ c values were found to be lognormally distributed with average values of 31.4 cm h −1 and 6.0 cm, respectively. BTC analysis produced chemical properties, θ im/ θ, α, and D m with average values of 0.23, 0.0036 h −1, and 1220 cm 2 h −1, respectively. The estimated values of the flow and transport parameters were found to be within the ranges of values reported by previous studies conducted at nearby field locations. The dripper TDR method is a rapid and useful technique for in situ measurements of hydraulic conductivity and solute transport properties. The measurements reported in this study give clear evidence to the occurrence of non-equilibrium water and chemical movement in surface soil. The method allows for quantification of non-equilibrium model parameters and preferential flow. Quantifying the parameters is a necessary step toward determining the influences of surface properties on infiltration, runoff, and vadose zone transport.

Free water content and monitoring of healing processes of skin burns studied by microwave dielectric spectroscopy in vivo

We have investigated the dielectric properties of human skin in vivo at frequencies up to 10 GHz using a time-domain reflectometry method with open-ended coaxial probes. Since γ-dispersion results from the reorientation of free water molecules, the free water content of skin is quantitatively determined by dielectric measurements. The free water content of finger skin increased by about 10% after soaking in 37 °C water for 30 min, and it systematically decreased again through the drying process, as expected. Thus this analytical method has been applied to the study of skin burns. The free water content of burned human cheek skin due to hydrofluoric acid was significantly lower than that of normal skin, and the burned skin recovered through the healing process. In the case of a human hand skin burn due to heat, although the free water content was almost the same as that of normal skin at the beginning, it decreased during the healing process for the first 10 days, then began to increase. Although the number of test subjects was one for each experiment, it was shown that free water content is a good indicator for evaluating skin health and can be well monitored by dielectric spectroscopy.

CHARACTERIZING PREFERENTIAL FLOW OF NITRATE AND PHOSPHATE IN SOIL USING TIME DOMAIN REFLECTOMETRY

Significant quantities of agricultural chemicals can be transported rapidly through preferential flow pathways in soil. Time domain reflectometry (TDR) has been used to characterize solute transport in soil. However, previous TDR studies have not fully addressed the preferential flow of reactive solutes. A TDR method was tested for its ability to measure the preferential flow of nitrate and phosphate in soil. Saturated miscible displacement experiments were conducted using three undisturbed soil cores and a tracer solution containing chloride, phosphate, and nitrate. An inverse curve fitting method (CXTFIT) was used to estimate mobile-immobile model (MIM) parameters using the TDR and observed effluent data. The parameters fitted to the time-varying TDR-determined relative resident concentration were similar to the estimates from measured effluent chloride breakthrough curves (BTCs). Predicted BTCs were obtained from the parameters fitted to the TDR data. The predicted BTCs were comparable to the measured effluent nitrate BTCs, with a root mean square error (RMSE) of 0.0054. The peak times were 0.18, 0.16, and 0.12 pore volumes for the predicted BTCs and 0.26, 0.19, and 0.21 for the effluent nitrate BTCs. Phosphate BTCs differed distinctly from chloride and nitrate BTCs in our study; thus, the TDR method did not work for phosphate. However, the vertical TDR probe technique proved to be a practical method for a first approximation of nitrate preferential flow in soil.

鉄筋コンクリート補強された歴史的煉瓦造建造物に生じる白華現象のメカニズム : 煉瓦中の含水量が白華現象に及ぼす影響

It is indicated that the reinforcement with concrete causes efflorescence and decay of brick because of alkali salts in cement. This paper explains the mechanism of efflorescence on historical brick masonry buildings reinforced with concrete. First, accelerated test method was developed so as to reproduce efflorescence on brick masonry wall reinforced with concrete. Second, we investigated relation between water content and rate of evaporation. It is considered that water did not move in a liquid condition in the brick below the water content of 4〜5Vol%. Finally, model wall specimen similar to actual historical brick masonry wall was made and accelerated test was carried out. And water content of each brick was continuously measured by TDR(Time Domain Reflectometry) method during the test. It is concluded that efflorescence did not occur 4〜5Vol% water content below because movable water in liquid phase was not present in the brick.

Spatially characterizing apparent electrical conductivity and water content of surface soils with time domain reflectometry

Unlike other measurement methods discussed in this special issue, time domain reflectometry (TDR) has the ability to measure both water content ( θ) and apparent electrical conductivity (EC a) of soils. From simultaneous knowledge of θ and EC a, the soil solution electrical conductivity (EC s) and even the concentration of specific ionic constituents such as NO 3–nitrogen may be estimated through soil-specific calibration. This paper provides an introduction, some theoretical background, and a practical review of the TDR method for spatially characterizing θ, EC a, and related attributes in soils. Time domain reflectometry measurement principles for determining θ, EC a, and EC s, along with suggestions for inferring matric potential from dielectric measurements, are addressed. We discuss point, handheld, and vehicle-based measurement methods. Applications of TDR to spatially characterize θ in a hilly agricultural field using TDR and gravimetric methods, and to monitor θ and nitrate concentrations at three depths under peppermint production, are presented. A pickup-mounted TDR measured θ at 100 m × 100 m grid spacing in two wheat fields in north-central Montana. Soil θ, as well as NO 3–N, grain yield, and grain protein increased from upper to lower slopes. Soil θ early in the growing seasons appeared critical to final yields in this rainfed system. An array of fixed TDR probes was monitored over two growing seasons under peppermint in northwest Montana, to estimate θ, EC s, and NO 3–N every 6 h at 12 field locations. Although the field soils appeared uniform, measured spatial patterns of θ, EC s, and NO 3–N were highly space- and time-variant. These results indicate that TDR is a potentially useful tool for precision agriculture, and that fixed TDR arrays could serve as real-time monitoring systems for water and fertilizer salts in soil profiles. The primary limitation of the TDR method for spatially characterizing θ and EC at soil management scales using fixed arrays is the cable length limitation of about 20–30 m. Mobile platforms are of high interest, and prototype designs have been reported in the literature. Truly ‘on-the-fly’ TDR measurements for large-scale applications may be feasible in the near future.

Obtaining the Spatial Distribution of Water Content along a TDR Probe Using the SCEM‐UA Bayesian Inverse Modeling Scheme

Time domain reflectometry (TDR) has become one of the standard methods for the measurement of the temporal and spatial distribution of water saturation in soils. Current waveform analysis methodology gives a measurement of the average water content along the length of the TDR probe. Close inspection of TDR waveforms shows that heterogeneity in water content along the probe can be seen in the TDR waveform. We present a comprehensive approach to TDR waveform analysis that gives a quantitative estimate of the dielectric permittivity profile along the length of the probe and, therefore, the distribution of water content. The approach is based on the combination of a multisection scatter function model for the TDR measurement system with the shuffled complex evolution Metropolis algorithm (SCEM‐UA). This combined approach allows for the estimation of the 40 parameters in the transmission line model using a series of simple calibration measurements. The proof of concept is given with measurements in a layered system consisting of air and water. Finally, TDR waveforms from layered soil samples were analyzed to estimate the distribution of the water content along the length of the probe. Results show that the proposed method provides much more reproducible results than obtained with the traditional travel time method. Because the proposed method can be fully automated, it increases the applicability of the TDR method, especially in applications where detailed (real‐time) data are required on heterogeneous infiltration.

Obtaining the Spatial Distribution of Water Content along a TDR Probe Using the SCEM-UA Bayesian Inverse Modeling Scheme

Time domain reflectometry (TDR) has become one of the standard methods for the measurement of the temporal and spatial distribution of water saturation in soils. Current waveform analysis methodology gives a measurement of the average water content along the length of the TDR probe. Close inspection of TDR waveforms shows that heterogeneity in water content along the probe can be seen in the TDR waveform. We present a comprehensive approach to TDR waveform analysis that gives a quantitative estimate of the dielectric permittivity profile along the length of the probe and, therefore, the distribution of water content. The approach is based on the combination of a multisection scatter function model for the TDR measurement system with the shuffled complex evolution Metropolis algorithm (SCEM-UA). This combined approach allows for the estimation of the 40 parameters in the transmission line model using a series of simple calibration measurements. The proof of concept is given with measurements in a layered system consisting of air and water. Finally, TDR waveforms from layered soil samples were analyzed to estimate the distribution of the water content along the length of the probe. Results show that the proposed method provides much more reproducible results than obtained with the traditional travel time method. Because the proposed method can be fully automated, it increases the applicability of the TDR method, especially in applications where detailed (real-time) data are required on heterogeneous infiltration.