Time Domain Reflectometry Method Research Articles

Application of time domain reflectometry to triaxial shear tests on hydrate-bearing sediments

Various triaxial shearing apparatus are used to quantify mechanical properties of hydrate-bearing sediments which are basically required to the assessment of risks posed by dissociation of natural gas hydrates. However, the key factor, hydrate saturation, has not been well measured during triaxial shearing tests. This study aims to show how a time domain reflectometry (TDR) method nondestructively measures hydrate saturation for triaxial shear tests on hydrate-bearing sands. Hydrate saturation is determined based on the difference of volumetric water contents measured by using a flexible TDR probe with two rods after calibration. The results suggest that values of hydrate saturation acquired by the TDR method are accurate, and the flexible TDR probe can monitor the kinetic process of hydrate formation and avoid any reinforcement effects on triaxial shearing properties of test specimens.

Short failure localization in advanced package using optoelectronic sampling terahertz time domain reflectometry and deconvolution method

Failure localization in advanced packaging is a challenging task. Optoelectronic sampling Terahertz time-domain reflectometry (OES THz TDR) employs ultrafast lasers to generate high-frequency THz pulse. The THz pulse is coupled into advanced package trace using radio frequency probe. When there is an open or short failure in the circuit, TDR signal could be captured. Deconvolution processing method was introduced to remove noise from multiple reflections of the remaining circuit. A short failure model with remaining circuit was studied. After deconvolution, the TDR localization accuracy improves from 573 μm to 12 μm, and the correlation coefficient improved from 99.612 % to 99.955 %. Advanced package sample including substrate, C4 bump, interposer, and micro bump was analyzed. By comparing the TDR waveform of short failure sample and references, the short failure is localized inside of the die. By destroying the failure sample and measuring the current-voltage curve, the short failure location is verified.

Dielectric relaxation and hydrogen bonding interactions study of aqueous D-sorbitol using time domain reflectometry

ABSTRACT Complex permittivity spectra for D-sorbitol-water mixtures in the frequency range 10 MHz to 30 GHz have been determined over the entire concentration range using a time domain reflectometry (TDR) method. The complex permittivity spectra have been fitted to the Cole-Davidson relaxation model. The static dielectric constant and relaxation time were calculated from the complex permittivity spectra using the nonlinear least square fit method. The Kirkwood correlation factors were calculated. The theoretical dielectric constant for the mixtures has been calculated using the hydrogen bonding model suggested by Alenka Luzar.

Application of automatic image analysis to evaluate the anisotropy of autoclaved aerated concrete for moisture transport

Autoclaved aerated concrete (AAC) is an artificial building material commonly applied in energy efficient buildings. Blocks of AAC are characterized by relatively homogenous distribution of pores and their dimensions. However, during manufacturing there occurs irregular pores positioning which may influence water transport processes. This phenomenon is called anisotropy which could be evaluated using standard gravimetric or electric methods of moisture detection. In this article we propose a method of level of anisotropy evaluation using image analysis. During the research a set of AAC samples was prepared and examined using time domain reflectometry (TDR) method for capillary uptake phenomenon and in parallel the cross-sections visual analyses were conducted. Both techniques confirmed the anisotropic features of the tested material.

A Time-Domain Three-Dimensional Numerical Method for Comprehensive Common-Mode Analysis of Electric Circuits in Inhomogeneous Media

This article presents a numerical method to treat comprehensive common-mode (CM) signals in the time domain, which are electromagnetic noise sources in electrical and electronic devices. Electromagnetic potentials are a better choice to quantify the CM signals because we can easily extend the full-wave analysis of a multiconductor system. We start with the Maxwell equations in inhomogeneous media, which include conductors and dielectrics, and express the wave equations of the electromagnetic potentials. We also introduce a numerical method for the wave equations with lumped-parameter circuits by using the leap-frog scheme based on the central difference method. We calculate normal-mode (NM) and CM voltages in differential circuits with discontinuity and nonuniformity and conduct experiments by using the time-domain reflectometry method. The numerical results of the proposed method are compared with results from the finite-difference time-domain method and experiments for validation, observing conversions and reflections of NM and CM at discontinuities and nonuniformity, and show good agreements among these results.

Temperature Dependent Dielectric Relaxation Studies of 2-Nitrotoluene-DMSO mixture using Time Domain Relectometry from 10MHz to 50GHz

The dielectric relaxation properties of 2-Nitrotoluene (2-NT) with DMSO for 11 different concentrations has been studied in the frequency range from 10 MHz to 50 GHz using time domain reflectometry (TDR) method. In this frequency range Dielectric relaxation spectra of 2-NT-DMSO mixtures shows Debye type behavior. The temperature dependent static dielectric constant and relaxation time have been determined from 20oC to 5oC. Effective Kirkwood correlation factor is calculated to determine the effect of strong directional forces such as microwaves on heterogeneous molecules under different temperatures. The excess permittivity and excess inverse excess relaxation time is found to be negative for 2-NT-DMSO system with weak molecular interactions. The activation enthalpy have been calculated to find the energy required to rotate the molecules

In situ estimation of soil hydraulic and hydrodispersive properties by inversion of electromagnetic induction measurements and soil hydrological modeling

Abstract. Soil hydraulic and hydrodispersive properties are necessary for modeling water and solute fluxes in agricultural and environmental systems. Despite the major efforts in developing methods (e.g., laboratory-based, pedotransfer functions), their characterization at applicative scales remains an imperative requirement. Accordingly, this paper proposes a noninvasive in situ method integrating electromagnetic induction (EMI) and hydrological modeling to estimate soil hydraulic and transport properties at the plot scale. To this end, we carried out two sequential water infiltration and solute transport experiments and conducted time-lapse EMI surveys using a CMD Mini-Explorer to examine how well this methodology can be used to (i) monitor water content dynamic after irrigation and to estimate the soil hydraulic van Genuchten–Mualem parameters from the water infiltration experiment as well as (ii) to monitor solute concentration and to estimate solute dispersivity from the solute transport experiment. We then compared the results with those estimated by direct time domain reflectometry (TDR) and tensiometer probe measurements. The EMI significantly underestimated the water content distribution observed by TDR, but the water content evolved similarly over time. This introduced two main effects on soil hydraulic properties obtained by the two methods: (i) similar water retention curve shapes, but underestimated saturated water content from the EMI method, resulting in a scaled water retention curve when compared with the TDR method; the EMI-based water retention curve can be scaled by measuring the actual saturated water content at the end of the experiment with TDR probes or by weighing soil samples; (ii) almost overlapping hydraulic conductivity curves, as expected when considering that the shape of the hydraulic conductivity curve primarily reflects changes in water content over time. Nevertheless, EMI-based estimations of soil hydraulic properties and transport properties were found to be fairly accurate in comparison with those obtained from direct TDR measurements and tensiometer probe measurements.

Intelligent fault diagnosis for power distribution system-comparative studies

Short circuit is one of the most popular types of permanent fault in power distribution system. Thus, fast and accuracy diagnosis of short circuit failure is very important so that the power system works more effectively. In this paper, a newly enhanced support vector machine (SVM) classifier has been investigated to identify ten short-circuit fault types, including single line-to-ground faults (XG, YG, ZG), line-to-line faults (XY, XZ, YZ), double line-to-ground faults (XYG, XZG, YZG) and three-line faults (XYZ). The performance of this enhanced SVM model has been improved by using three different versions of particle swarm optimization (PSO), namely: classical PSO (C-PSO), time varying acceleration coefficients PSO (T-PSO) and constriction factor PSO (K-PSO). Further, utilizing pseudo-random binary sequence (PRBS)-based time domain reflectometry (TDR) method allows to obtain a reliable dataset for SVM classifier. The experimental results performed on a two-branch distribution line show the most optimal variant of PSO for short fault diagnosis.

Research on the Method of Measuring Soil Water Content by Time Domain Reflectometry

Time domain reflectometry (TDR) can calculate the water content by testing the dielectric constant of the rock and soil medium, but the TDR measurement results under time domain conditions are susceptible to the influence of soil conductivity. This article introduces the basic theory of TDR measurement, then uses the transmission scattering matrix to describe the transmission equation, analyzes the dielectric constant in the frequency domain, simulates the TDR waveform with matlab based on the Debye model, and fits the simulated waveform to the measured waveform, and then according to the simulated waveform The matching degree proves the feasibility of calibrating the dielectric constant of the soil. Taking clay as the measurement object, finally fitting a simulation waveform with a higher degree of matching with the measurement waveform, which proves the feasibility of the method and has certain reference value for the study of the TDR method of measuring soil dielectric constant and water content.

Integrating TDR and GPR methods to study the structure of peatland

Abstract. In this study we compared time-domain reflectometry (TDR) data from boreholes and the results of ground-penetrating radar (GPR) along the cross-sections on a peat deposit. The studied mire located on the Zaonezhye Peninsula (Republic of Karelia, Russia); its structure included layers of peat and bedding lake sediments. To perform the measurements we used GPR with antenna unit 150 MHz and TDR system TDR200 with probe. The mire structure was characterized by a medium basin structure (7 m max depth) and sloping mire topographic. Comparison TDR and GPR data yielded similar dielectric constant values for peat layers. The average mistake in dielectric constant values between TDR and GPR observation was 5 units. The conditions for the formation of interfaces on GPR cross-sections were studied by analyzing dielectric constant change across the peat deposit. We found that the depth positions of the GPR interfaces were quite accurately ( 20 cm) coincides with the intervals of the change of peat type. Our results indicate the difficulty of interpreting GPR cross-sections contained multi-reflectors for subsurface with sub-horizontal structure such as peat deposits or lakes bottom sediments.

Research on SSTDR-based online distance measurement method for single-phase faults in cables

In order to accurately locate the non-destructive faults of distribution network cables, an extended spectrum time-domain reflectometry method based on the equivalent distribution parameter model of transmission lines was proposed to detect and locate single-phase grounding short-circuit and single-phase disconnection faults online. Firstly, the extended spectrum and time-domain reflectometry are analyzed theoretically. Then through simulink simulation platform to build single-phase grounding and single-phase disconnection fault model of distribution network simulation, verify the correctness of the theory; Finally, the influence of fault distance, fault resistance and signal-to-noise ratio is analyzed.

A Novel Method for the Accurate Measurement of Soil Infiltration Line by Portable Vector Network Analyzer.

Accurate measurement of soil infiltration lines is very important for agricultural irrigation systems. It can help monitor the irrigation of soil to control irrigation amounts and promote crop growth. The soil infiltration line is a complex dynamic boundary and is difficult to model accurately, leading to estimation deviation. A traditional TDR (time domain reflectometry) method is used in soil infiltration line measurement, but it lacks good applicability and accuracy. In this paper, we proposed a method—VFTT (The vector network analyzer’s frequency domain signals are converted to the time domain)—by the time domain to frequency domain conversion principle to improve the accuracy of soil infiltration line measurement. The experiment results show that the measurement method of soil infiltration line based on VFTT has high accuracy and robustness. After fitting the measured value with the actual one, R2 reaching more than 0.98 can effectively measure the position of the soil infiltration line.

Accurate Single-Ended Measurement of Propagation Delay in Fiber Using Correlation Optical Time Domain Reflectometry

A correlation optical time-domain reflectometry (COTDR) method is presented, which measures the propagation delay with an accuracy of a few picoseconds. This accuracy is achieved using a test signal data rate of 10 Gbit/s and employing cross-correlation and pulse fitting techniques. In this paper we introduce and evaluate the basic signal processing steps, investigate the measurement accuracy, and discuss applications for monitoring link delay and chromatic dispersion of long fiber spans as well as temperature sensing applications.

Study of Water Transfer Dynamics in a Carbonate Vadose Zone from Geophysical Properties

This paper reports a study of water dynamics in a carbonate vadose zone (VZ). This study is performed in the experimental natural site of Saint-Emilion located in an underground quarry (Gironde, France). For this, two geophysical properties are used: the time domain reflectometry method (TDR) which provides the volumetric water content and electrical properties which provides the spatial water distribution. The dephasing and amplitude attenuation of the water content front were measured and modelled. Physical properties of the porous medium (porosity, permeability and effective diffusivity) can explain the water transfer process in VZ. The electrical resistivity tomography (ERT) gives a series of 2D images of water dynamics in VZ. Variations in water content induce changes in the electrical properties of the medium such as electrical resistivity. Using the time-lapse method, it is possible to model the evolution of saturation over time. The reliability of these electrical tools was confirmed by laboratory measurements.

Interference fading suppression in φ-OTDR using space-division multiplexed probes

We propose and experimentally demonstrate a novel interference fading suppression method for phase-sensitive optical time domain reflectometry (φ-OTDR) using space-division multiplexed (SDM) pulse probes in a few-mode fiber. The SDM probes consist of multiple different modes, and three spatial modes (LP01, LP11a, and LP11b) are used in this work for the proof of concept. Firstly, the Rayleigh backscattering light of different modes is experimentally characterized, and it turns out that the waveforms of the φ-OTDR traces for distinct modes are all different and independent. Thanks to the spatial difference of the fading positions for distinct modes, multiple probes from spatially multiplexed modes can be used to suppress the interference fading in φ-OTDR. Then, the performances of the φ-OTDR systems using a single probe and multiple probes are evaluated and compared. Specifically, the statistical analysis shows that the fading probabilities over both the fiber length and the time scale are reduced significantly by using multiple SDM probes, which verifies the significant performance improvement on fading suppression. By introducing the concept of SDM to φ-OTDR, the proposed novel interference fading suppression method avoids the complicated frequency or phase modulation, which has the advantages of simplicity, good effectiveness and high reliability.

Localization of deep voids through geophysical signatures of secondary dewatering features

Discrete deep targets are a significant challenge for most surface-based geophysical techniques, even when considering high property contrasts. In general, surface-based geophysical methods lose lateral and vertical resolution with depth as a result of the limited acquisition geometry and increased signal attenuation. The former can be overcome through use of cross-borehole methods, but lateral localization is still needed for optimal borehole placement. As such, a relatively small, deep void located near the maximum depth of investigation (DOI) is very unlikely to be detected. Yet, secondary features associated with these voids can be exploited for enhanced detection performance. When voids are located below the groundwater table, a significant amount of dewatering and pumping is required to make them a functional passageway. This dewatering not only removes water from the void space but also the surrounding formation, resulting in a much larger, if more diffuse, secondary target: an induced groundwater table gradient. Many geophysical sensing methods are sensitive to subsurface moisture content. We have implemented a 2D joint-petrophysical mixing model (JPM), using inverted electrical resistivity tomography (ERT) and inverted seismic refraction models to sense changes in the groundwater table gradient. Our results are validated using the depth to bedrock, groundwater-surface water information, ground-penetrating radar, and time-domain reflectometry methods. Our initial proof of concept is applied to a shallow area with a significant soil moisture gradient, through different surface soil types and bedrock. The 2D JPM results are used to generate an estimate of air, moisture, and matrix percent fractions in the investigation area, providing a clear delineation of the groundwater surface and associated gradient. This refined hydraulic gradient estimate can then be used to laterally locate a void at or below the DOI of ERT and seismic refraction.

Time and frequency domain reflectometry for the measurement of tree stem water content: A review, evaluation, and future perspectives

Electromagnetic (EM) methods for estimation of water content in porous media (e.g., soil and tree stems) are based on estimates of the media's bulk dielectric permittivity, which is sensitive to water content. Time domain reflectometry (TDR) and frequency domain reflectometry (FDR) are routinely used for rapid, automated and minimally destructive approach for routine measurement of soil water content (θsoil) and stem water content (θstem) in the laboratory and field. Applications and advances of TDR and FDR in soil science have been well-documented, but no attempt has been made to critically review the use of EM methods for measuring θstem. In this paper we review the principles, calibration, sensor configuration, and sensor installation of the TDR and FDR methods for the measurement of θstem. Perspectives are presented on new TDR calibration, the development of new sensors, and technologies for the simultaneous measurement of θstem, sap flow, bulk density/porosity, radial distribution of θstem, and electric conductivity. Also discussed were the effects of tree morphology and wounding on the accuracy of both methods. This review provides information for the novice and expert alike to guide them on the advantages, limitations, development, and application of the EM methods required to improve the reliability and validity of measured values of θstem.

Distributed static and dynamic detection of an acoustic wave in a Brillouin random fiber laser

The interaction of random laser and gain medium is important to understand the noise origin in random fiber lasers. Here, using the optical time domain reflectometry method, the time-resolved distributed acoustic wave generated by a Brillouin random fiber laser (BRFL) is characterized. The dynamic property of the acoustic wave reflects the gain dynamics of the BRFL. The principle is based on the polarization-decoupled stimulated Brillouin scattering (SBS)-enhanced four-wave mixing process, where the probe light experiences maximum reflection when the phase match condition is satisfied. Static measurements present exponentially depleted Brillouin gain along the gain medium in the BRFL, indicating the localized random SBS frequency change in the maximum local gain region, which varies with time to contribute random laser noise as revealed in the dynamic measurement. The SBS-induced birefringence change in the Brillouin gain fiber is approximately 10 − 7 to 10 − 6 . The phase noise of the BRFL is observed directly inside the random laser gain medium for the first time via time and spatially varied acoustic wave intensity. By counting the temporal intensity statistical distribution, optical rogue waves are detected near the lasing threshold of the BRFL. Different temporal intensity statistical distribution at high and low gain positions is found, which is caused by the SBS nonlinear transfer function and localized gain. The distributed characterization methods in the paper provide a new platform to study the interaction of random lasers and gain medium, giving us a new perspective to understand the fundamental physics of the random lasing process and its noise property.

Natural Amplification of Soft Defects Signatures in Cables Using Binary Time Domain Reflectometry

In our digital world, energy and data transmission play a major role and often rely on electrical wires. Some of these wires are used in harsh or aggressive environments and may be subject to defects. Security and preventive maintenance require tools to detect and precisely locate such defects. This paper details the Binary Time Domain Reflectometry (BTDR) method, presented earlier, which does not rely on the use of expensive and complex digital to analog and analog to digital conversion components. We explain the role of additive white noise and of the use of the time derivative for the improvement of its performances. The study focuses on BTDR's natural capacity of magnifying soft defects' peaks on the reflectogram. The method takes advantage of phase opposition to cancel the contribution of the extremities of the line under test and saturate the amplitudes of the remaining peaks. This can only be achieved if these contributions are equal or very close to each other. A balancing device is added at the cable's interface to meet this requirement. This low complexity additional system, made of two controlable digital potentiometers, is driven by the programmable logic digital system at the heart of the reflectometer. Direct magnification of very low amplitude peaks of incipient defects is obtained without any data post-processing. The amplification performance depends on the adjustment accuracy of the potentiometers and the hysteresis level of the comparator used to replace the converters.

Classification of interference-fading tolerant Φ-OTDR signal using optimal peak-seeking and machine learning [Invited

A simple and effective interference-fading tolerant method for phase-sensitive optical time-domain reflectometry (Φ-OTDR) using optimal peak-seeking is proposed. This method can reconstruct the vibration signal with high fidelity under the premise of using only an ordinary single-mode sensing fiber without changing the structure of the traditional Φ-OTDR system. Based on the data after interference suppression, we applied different machine learning models to recognize the invasive events category. The promising results show potential applications of Φ-OTDR equipment and future implementation with machine learning algorithms.