Time Domain Reflectometry Technique Research Articles

Time-domain reflectometry using arbitrary incident waveforms

A novel time-domain reflectometry technique is developed for detecting the physical structures of transmission lines by using arbitrary waveforms. By discretizing both incident and reflected waves, we formulate the reflection coefficient of a nonuniform transmission line as a polynomial ratio in the Z-transform, wherein the numerator and denominator represent the reflected and incident waves, respectively. A reconstruction scheme is derived to obtain the characteristic impedance profile of a transmission line. Some examples are presented to illustrate the validity of this new technique.

A rainout shelter design for intercepting different amounts of rainfall.

Field manipulative experiments represent a straightforward way to explore temporal relationships between annual precipitation and productivity. Water exclusion usually involves the use of rainout shelters, which are in general formed by a complete roof that intercepts 100% of the rainfall and require complicated mechanisms to move the shelter into place. The rainout-shelter design described here is a fixed-location shelter with a roof consisting of bands of transparent acrylic that blocks different amounts of rainfall while minimally affecting other environmental variables. We constructed thirty 3.76-m2 shelters in an arid steppe near Río Mayo, Argentina (at 45°41'S, 70°16'W), to impose 30%, 55%, and 80% of rainfall interception. We tested the effectiveness of the design by collecting all the intercepted water in storage tanks and we evaluated changes in soil water content with the time domain reflectometry technique. We also measured soil water content in regular grids to assess the magnitude of the edge effect. We analysed the microclimate impact of the shelters by measuring photosynthetically active radiation and air and soil temperature inside and outside shelters. We did not detect significant differences between the observed and the expected rainfall interception for the 30% and 55% interception treatments but the 80% shelters intercepted 71% of incoming rainfall, which was significantly (P<0.05) lower than the expected value. Soil water content was significantly (P<0.05) higher in the control plots than in the plots with rainout shelter at all dates, except in January (summer). Radiation was not affected by the 30% interception treatment, but the roof with the largest number of acrylics bands (80% interception treatment) reduced incident radiation throughout the day by 10%. Air and soil temperatures were lower under than outside the shelters during the period of highest radiation but the opposite occurred with low radiation but with smaller differences. The two characteristics of the shelter, fixed design and low cost, allow for proper replication in space, which is required in ecological field experiments.

Time domain reflectrometry: Calibration techniques for accurate measurement of the dielectric properties of various materials

In this work, an extensive theoretical and experimental analysis has been carried out on the main factors that affect the accurate evaluation of dielectric properties using time domain reflectometry (TDR). Dielectric constant measurements have been performed under different experimental conditions for various types of materials having a wide range of permittivity values. Interpretation of the results on the basis of the transmission-line theory emphasizes the importance of a suitable calibration procedure that takes into account several critical aspects, some of which seem to have been disregarded or underestimated in the literature. Qualitative and quantitative information is given on the kind of corrections needed in order to significantly improve the reliability of the TDR technique for permittivity measurements.

Predicting the Dielectric Constant–Water Content Relationship Using Artificial Neural Networks

Accurate measurements of soil water content (θ) are important in various applications in hydrology and soil science. The time domain reflectometry (TDR) technique has been widely used for θ measurements during the last two decades. The TDR utilizes the apparent dielectric constant (Ka) for estimations of θ. The Ka–θ relationship has been described using both empirical and physical models. Universal calibration equations that fit a wide range of different soil types have been developed. However, to achieve high accuracy, a soil‐specific calibration needs to be conducted. In the present study, we use an artificial neural network (ANN) to predict the Ka–θ relationship using soil physical parameters for ten different soil types. The parameters that give the most significant reduction in the root mean square error (RMSE) are bulk density, clay content, and organic matter content. The Ka–θ relationship for each soil type is predicted using the other nine for calibration. It is shown that ANN predictions are as good as a soil specific calibration with comparable coefficient of determination and RMSE. Thus, by using ANN, highly accurate data can be obtained without need for elaborate soil specific calibration experiments.

In situ measurement of particle deposition and its removal in microfiltration by ultrasonic time-domain reflectometry

An ultrasonic time-domain reflectometry (UTDR) technique was used for the non-invasive, in situ visualization of particle deposition and its removal during crossflow microfiltration with a nylon membrane. The study was carried out with 0.5 g/l kaolin (average particle size 2 μm). Ultrasonic response signals were obtained upon particle deposition and subsequent cake layer formation on the membrane surface. A cake layer echo appeared in the time domain. The UTDR technique was also used to quantify the thickness of a fouling layer on the membrane surface. Moreover, UTDR was applied to monitor membrane cleaning and evaluate the effectiveness of various cleaning methods. Flux measurements and SEM analyses corroborated the UTDR results. Overall, the results confirmed the effectiveness of the UTDR technique for visualizing particle deposition on and removal from membrane surfaces.

Dielectric study of pharmacologically important drugs in ethanol at different temperatures using time domain technique

The dielectric relaxation study of pharmacologically important drugs in ethanol has been carried out at various temperatures and concentrations in the frequency range of 10 MHz to 10 GHz using Time Domain Reflectometry (TDR) technique. Dielectric properties i.e. dielectric constant and relaxation time were obtained from the complex permittivity spectra using nonlinear least squares fit method. From the values of relaxation time, thermodynamic parameters were determined. The results obtained are used to interpret the nature and kinds of solute-solvent interactions.

Soil-water behaviour of sandy soils under semi-arid conditions in the Duero Basin (Spain)

This paper examines the soil-water behaviour of sandy soils representative of a broad area in the Duero river basin (Spain), with semi-arid bioclimatic characteristics. Soil-moisture measurements of the first 25 cm of soil profile were taken using time domain reflectometry (TDR) methodology. The infiltration process was studied by means of field experiments combining rainfall simulations and TDR techniques. Finally, a set of hydrodynamic variables was calculated in the laboratory (i.e. available soil-water content, soil-water-retention curves and hydraulic conductivity). The average available soil-water content is 0·07 cm3 cm−3, in accordance with the predominance of the sandy textural fraction (≅85%). The rainfall simulation experiments show that infiltration prevails over overland flow, with a steady-state infiltration rate higher than rainfall application (40mmh−1) in most cases; a low water-retention capacity was also observed. The evolution of soil-moisture over time indicates a close dependence on intra-annual rainfall variability due to the low water-retention capacity of sandy soils. With a maximum water-storage capacity of around 0·18 cm3 cm−3, the soils studied show high sensitivity to dry spells and may remain with <50% of the available soil-water content for several months during the year.

Soil-water behaviour of sandy soils under semi-arid conditions in the Duero Basin (Spain)

This paper examines the soil-water behaviour of sandy soils representative of a broad area in the Duero river basin (Spain), with semi-arid bioclimatic characteristics. Soil-moisture measurements of the first 25 cm of soil profile were taken using time domain reflectometry (TDR) methodology. The infiltration process was studied by means of field experiments combining rainfall simulations and TDR techniques. Finally, a set of hydrodynamic variables was calculated in the laboratory (i.e. available soil-water content, soil-water-retention curves and hydraulic conductivity). The average available soil-water content is 0·07 cm 3 cm −3, in accordance with the predominance of the sandy textural fraction (≅85%). The rainfall simulation experiments show that infiltration prevails over overland flow, with a steady-state infiltration rate higher than rainfall application (40mmh −1) in most cases; a low water-retention capacity was also observed. The evolution of soil-moisture over time indicates a close dependence on intra-annual rainfall variability due to the low water-retention capacity of sandy soils. With a maximum water-storage capacity of around 0·18 cm 3 cm −3, the soils studied show high sensitivity to dry spells and may remain with <50% of the available soil-water content for several months during the year.

Mapping the volumetric soil water content of a California vineyard using high-frequency GPR ground wave data

Water distribution in the top 1 m of the earth's surface soil layer often controls the success of agricultural crops. In this near-surface zone, large spatial and temporal variations in soil water content are associated with soil heterogeneities, topography, land cover, evapotranspiration, and precipitation. Conventional techniques of measuring soil water content for agricultural purposes—e.g., time domain reflectometry (TDR), neutron probe, or gravimetric techniques, are intrusive and provide information at a point scale only, which is often inadequate for capturing the variations in soil water content with sufficient resolution. Both passive and active remote sensing methods have also been investigated as a tool to provide soil water content in the top 0–5 cm of the subsurface over large spatial areas and in a rapid manner. However, it is still a challenge to obtain information about soil water content from remote sensing data in the presence of a mature crop cover. At the spatial and temporal scales ne...

Evaluation of Discontinuities in Microstrip Transmission Lines by Picosecond Time Domain Reflectometry Technique

The narrow and wide trace discontinuities in microstrip transmission lines are designed and fabricated on glass-epoxy board by standard printing circuit board (PCB) technology. These discontinuities are characterized by evaluating their characteristic impedance (Z0), excess inductance (ΔL), excess capacitance (ΔC), and peak percent reflection (pmax), by single ended time domain reflectometry (TDR) technique at room temperature. It is observed that narrow trace discontinuities lead to increase in values of characteristic impedance and inductance while wide trace discontinuities lead to decrease in characteristic Impedance and capacitance. The experimental values of various parameters like characteristic impedance, Z0 excess inductance, ΔL, excess capacitance, ΔC, and maximum peak reflection, pmax, are found to be in good agreement with their corresponding theoretical values.

Dielectric properties for the binary mixture of dimethylsuphoxide and dimethylacetamide with 2-nitrotoluene at microwave frequencies

The dielectric properties of various organic solvents and binary solvent mixtures at different temperatures over the frequency range of 10 MHz–20 GHz, are investigated using the time domain reflectometry technique, at various temperatures from 15 to 45 °C. These solvent mixtures—dimethylacetamide–2-nitrotoluene and dimethylsulphoxide–2-nitrotoluene as well as pure solvents display a Debye type dispersion. Their frequency-dependent dielectric properties can be summarized by the three parameters in the Debye equation: a static permittivity, permittivity at high frequency and a dielectric relaxation time constant. The free energy of activation for dipolar relaxation process and the Kirkwood correlation factor were determined using these fitting parameters, for these solvent systems at various temperatures. By using these dielectric parameters, the excess permittivity and excess inverse relaxation time is obtained. The static permittivity increases with increase in volume percentage of 2-nitrotoluene in dimethylacetamide as well as dimethylsulphoxide whereas the relaxation time decreases for both the systems.

Novel in-service supervisory scheme for the amplified WDM link with modified optical time domain reflectometry

We propose a novel optical supervisory system for the wavelength division multiplexing (WDM) transmission link including in-line erbium-doped fiber amplifiers (EDFA). By employing a newly proposed EDFA structure supporting bi-directional transmission at pre-determined wavelength and modified optical time domain reflectometry technique, it was possible to accurately monitor the status of transmission fiber link under in-service condition. A proof of the concept experiment with 8 channel, 320 km WDM transmission in-service state has been successfully carried out giving a clear loss/gain/reflection profile of the link with negligible BER power penalty less than 0.3 dB.

Non-invasive visualization of the fouling of microfiltration membranes by ultrasonic time-domain reflectometry

An ultrasonic time-domain reflectometry (UTDR) technique has been applied to the non-invasive study of fouling in microfiltration (MF) membrane modules operating at 100 kPa. The experimental results show a good correspondence between the UTDR signal response from the membranes and the development of a fouling layer on the membrane surface. The ultrasonic technique could effectively detect fouling-layer initiation and growth on the membrane in real-time. For experiments conducted at different axial velocities, ranging from 1.83 to 23.0 cm/s ( Re from 65.4 to 811), a sequential mode fouling layer growth was observed. The UTDR technique was capable of distinguishing individual modes of growth. The data also suggest the formation of a second echo in the time domain at 100 kPa operating pressure. Therefore, the UTDR technique was used to quantify the thickness of a fouling layer. The non-invasive UTDR visualization of the fouling on the membrane surface was supported by “post-mortem” SEM analysis of the membrane surface. The UTDR technique can be more suitable for non-invasive visualization of the fouling in MF system.

Note of clarification about: Field and laboratory calibration and test of TDR and capacitance techniques for indirect measurement of soil water content, by P.N.J. Lane and D.H. Mackenzie, Vol. 39, pp. 1371-1386

Time domain reflectometry (TDR) and a frequency domain sensor, the Didcot Capacitance Probe, were tested in the field and laboratory. The results from an undisturbed large core TDR laboratory test found the Topp equation returned a close correspondence to thermogravimetrically derived water content, although there was a slight underestimation. Coefficients of determination and efficiency were &gt;0.98 and 0.92, respectively, for individual cores, and 0.98 and 0.97 for the whole data set. The field exercise revealed the Topp equation to be superior to the laboratory derived equation and other published empirical equations, suggesting the Topp equation to be adequate. A field test of the capacitance probe found poor correspondence between measured and predicted observations of profile point soil water content. Although 81% of the variance was explained by the calibration regression, there was a poor fit to the 1:1 line (E = 0.34), and a non-significant relationship between measured and predicted soil water content for the A horizon. The instrument design proved problematic for use as a determiner of point profile soil water content, and the recommended calibration procedure was impossible in the study site soils.

Dielectric relaxation study of chloro group with associative liquids. II. 1,2-dichloroethane with methanol, ethanol, and 1-propanol

Frequency spectra of the complex permittivity for 1,2-dichloroethane–alcohol binary mixtures have been determined over the frequency range 10 MHz to 20 GHz at 15, 25, 35, and 45°C, using the time-domain reflectometry (TDR) technique, for 11 compositions of each 1,2 dichloroethane–alcohol system. The alcohols used in the study were methanol, ethanol, and 1-propanol. The relaxation in these systems can be described by a single relaxation time using the Debye model. The static dielectric constant, relaxation time, the corresponding excess dielectric properties, Kirkwood correlation factor, and Bruggeman factor of the mixtures have been determined. The static dielectric constants for the mixtures have been fitted with the modified Bruggeman model.

Temperature dependent dielectric relaxation study of ethyl acetate — Alcohol mixtures using time domain technique

The dielectric relaxation studies of Ethyl Acetate in Methanol, Ethanol and Propan-1-ol have been carried out using a Time domain Reflectometry (TDR) technique in the frequency range 10 MHz to 20 GHz, at different concentrations and temperature range from 15 to 45°C. The dielectric parameters, the Kirkwood correlation factor, the excess dielectric properties have also been determined. The excess permittivity is found to be negative for all the systems. The excess inverse relaxation is negative except near methanol rich region. The Bruggeman model for the nonlinear case has been fitted to the dielectric data for mixtures.

Novel in-service supervisory system using OTDR for long-haul WDM transmission link including cascaded in-line EDFAs

We propose and demonstrate a novel optical supervisory system for long-haul wavelength-division-muitiplexing (WDM) transmission link including cascaded erbium-doped fiber amplifiers (EDFAs). By employing a modified optical time domain reflectometry technique with a wavelength selective bidirectional EDFA, it was possible to monitor the status of the WDM transmission link and EDFA at in-service states with negligible power penalty. Proof of the concept with a 2.5 Gb/s/spl times/eight-channel WDM transmission system [single-mode fiber, 320 km] shows clear trace of the transmission line loss/gain/reflection map with minimal signal power penalty of 0.3 dB.

Applicability of multiple length TDR probes to measure water distributions in an Andisol under different tillage systems in Japan

Time domain reflectometry (TDR) has become increasingly popular worldwide for measuring soil moisture. The objective of this study was to show if the TDR technique with multiple length probes could be used to evaluate the distributions of water content in root zones under both minimum and conventional tillage conditions. TDR calibrations for an Andisol (Hydric Pachic Melanudands) with three different bulk densities were tested, and field measurements were conducted. A single as well as three separate calibration functions were examined for the measured data with three different bulk densities. The water contents measured by TDR and gravimetric sampling were compared to each other. Even though the single calibration function tended to overestimate at a moisture range larger than 0.50 m 3 m −3, the standard deviation (S.D.) of the difference between the TDR and gravimetric values was ±0.035 m 3 m −3. This value was only ±0.002 m 3 m −3 larger than the S.D. obtained using the separate calibration functions. We found the single calibration function to be accurate enough for describing the relationship between volumetric water content and apparent dielectric constant for this specific soil with different bulk densities. The TDR measurements with multiple length probes were conducted intermittently under both minimum and conventional tillage in a field over time. The TDR technique easily determined water distributions, and characterized the soil moisture regime resulting from different tillage systems. The TDR measurement with multiple length probes can provide useful information on the relationship between crop yield and soil environment and for improving soil water management under various conditions.

Efficacy and safety of an irrigated-tip catheter for the ablation of accessory pathways resistant to conventional radiofrequency ablation

Surface moisture was measured at selected sites in the Lago Maggiore (Italy) target area before and during Mesoscale Alpine Programme (MAP) Special Observing Period (SOP). Additional soil moisture measurements were performed contemporaneously with remotely sensed microwave measurements carried out by another MAP team. The soil moisture conditions influence the runoff produced during heavy precipitation events but long records of soil moisture measurements, like that presented here, are difficult to obtain. This data set, available at MAP Data Center, may be useful to improve real time flood forecasting and Numerical Weather Prediction models. The Osservatorio Geofisico (University of Modena and Reggio Emilia) team collected volumetric water content measurements by the Time Domain Reflectometry (TDR) technique. The TDR system was equipped with a multiplexer so that 14 buriable probes, installed at different depths, were automatically scanned at four hour time intervals and the daily soil moisture profiles were recorded. The data have been collected from the end of March 1999 up to the end of MAP-SOP (November 15, 1999). During this period, the first 70 cm of soil were monitored; the minimum of the soil moisture was 17.7 %; the maximum of the soil moisture was 56.0 %. The data allow also investigation of the soil behaviour after heavy precipitation events (e.g. the one happened during the MAP Intensive Observation Period (IOP) 02) depending on its moisture condition before the precipitation. Finally, from the soil water content profile, the cumulative evaporation is computed on the basis of a mass balance, when drainage is supposed to be ceased and no horizontal flux is present.

Measurement of soil water content and electrical conductivity by time domain reflectometry: a review

Non-destructive measurement of soil water content and electrical conductivity has been desired for many years. Recent development of time domain reflectometry (TDR) enables us to simultaneously obtain soil water content and electrical conductivity using a single probe with a minimal disturbance of soil. Research on water and solute transport in porous media using TDR has flourished in the last few years. In this review article, an overview of theoretical background for measuring water content and electrical conductivity is presented as well as characteristics of different types of probes. Limitations of applying TDR techniques to measuring soil water content and salinity are also addressed. The review is designed to equip other scientists and engineers with background information so that the development of TDR for studies on water and chemical movement can continue.