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Transient radar method (TRM) is introduced as a novel non-destructive testing (NDT) technique that is capable of analyzing fully blindly and simultaneously the electromagnetic (EM) properties as well as geometric parameters of deep sub-wavelength thin single layer slabs. This study focuses on the minimum detectable layer thickness by means of TRM, which mainly depends on the experimental setup configuration. In this article, the complex permittivity and thickness of three polyvinyl chloride (PVC) sheets are extracted by means of a differential TRM set-up. The thickness of these PVC sheets was 1 mm, 500 μm, and 300 μm that corresponded to λ /30, λ /60, and λ /100, respectively (λ is the wavelength in free space). The carrier frequency was 10 GHz and the experiments were done in a bistatic radar setup. A differential TRM structure was used in this experiment. Some error sources, such as switch leakage and non-perpendicular illumination as well as systematic errors are considered as well. The experimentally obtained results are as follows: the thickness of these samples were 1033 ± 12, 535 ± 11, and 302 ± 9 μm with 1.18%, 0.94%, and 2.89% relative error, respectively. Additionally, the complex permittivity of these samples was found as (2.73 ± 0.02)-(0.23 ± 0.01)j, (2.70 ± 0.02)-(0.20 ± 0.02)j, and (2.65 ± 0.02)-(0.37 ± 0.01)j, respectively. This novel technique has the potential for deployment in a wide range of applications ranging from the piping, wind energy industry, and automotive to biotechnology, food industry, clinical monitoring, and pharmacy.

The development of an inexpensive instrumental chain based on time-domain reflectometry is presented. The attention paid to the choice of the components allowed purchase costs reduction compared to the instruments available on commerce. The chain is composed by a hand-made 30-mm needle probe, a square wave fast rise time pulses generator on board, and a digital sampling USB oscilloscope with bandwidth of 11 GHz. Stability measurements and sodium chloride, sucrose, and cow milk were conducted to assess device repeatability and evaluate the predictive potential of estimation for some food parameters. The traditional geometrical-mathematical approach was replaced by multivariate investigation of the time-domain signal. Good results in terms of coefficient of determination up to 0.983 were obtained. The results disclosed show how a cheap and easy-to-use instrumental chain can be very promising for attributes determinations of liquid materials, such as foodstuff.

Intermittent faults (IFs), i.e., temporary malfunctions appearing at the random or periodic moments with normal behavior in between, are the measurable symptoms of the degradation of a system. Their frequency and severity increase over time, eventually leading to permanent faults. In order to optimally plan preventive maintenance, it is essential to catch IFs soon enough to repair them before they turn permanent. This paper introduces a new method, called continuous chaos time-domain reflectometry, which enables real-time monitoring of an electrical network and provides the detection and location information of microsecond IFs together with an estimation of their time of appearance and duration.

Insulated power cables are becoming increasingly popular in today's developing distribution and transportation networks. However, due to aging, deterioration, and various operational and environmental stresses, insulation defects may appear and so the cable needs to be monitored in a timely manner to avoid unexpected failures. Many of these defects are responsible for partial discharge (PD) activity. The localization of the sources of these discharges is a highly decisive facet in the condition-based monitoring of power cables. The techniques for the localization of single-PD defects in insulated power cables are well presented in the current bibliography. However, when several simultaneous PD sources are active, the localization of the sources becomes quite complex. This paper develops an efficient technique for the separation and localization of multiple PD sources in a medium voltage cable. The experimental results are obtained with single-end-based measurements using a high-frequency current transformer in a laboratory environment. The data processing based on the spectral characteristics of the signals is carried out by using the power ratios technique in order to determine the presence of different types of PD. Once the signals are separated, the PD sources can be localized with an individualized analysis of each source through time-domain reflectometry. The proposed methodology can be very valuable to improve the location diagnostic capability of the condition-based monitoring solutions, especially for underground cables. This work was supported in part by the Ministry of Economy and Competitiveness of Spain (MINECO), in part by the European Regional Development Fund (ERDF) under Contract DPI2015-66478-C2-1-R (MINECO/FEDER, European Union), and in part by the Academy of Finland under Grant 309412

Time-domain reflectometry (TDR) is considered as a passive monitoring technique which reveals multi-functions, such as water level, bridge scour, landslide, and suspended sediment concentration (SSC), based on a single TDR device via multiplexing and related algorithms. The current platform for revealing TDR analysis and interpreted observations, however, is complex to access, thus a coherent data model and format for TDR heterogeneous data exchange is useful and necessary. To enhance the interoperability of TDR information, this research aims at standardizing the TDR data based on the Open Geospatial Consortium (OGC) Sensor Web Enablement (SWE) standards. To be specific, this study proposes a TDR sensor description model and an observation model based on the Sensor Model Language (SensorML) and Observation and Measurement (O&amp, M) standards. In addition, a middleware was developed to translate existing TDR information to a Sensor Observation Service (SOS) web service. Overall, by standardizing TDR data with the OGC SWE open standards, relevant information for disaster management can be effectively and efficiently integrated in an interoperable manner.

Sequence time-domain reflectometry (STDR) and spread spectrum time-domain reflectometry (SSTDR) detect, locate, and diagnose faults in live (energized) electrical systems. In this paper, we survey the present SSTDR literature for discussions on theory, algorithms used in its analysis, and its more prominent implementations and applications. Our review includes both scientific litera-ture and selected patents. We also discuss future applications of SSTDR.

Surface and underground stretched deformation is one of the most important physical measurement quantities for geological-disaster monitoring. In this study, a parallel helical sensing cable (PHSC) based on the time&ndash, domain reflectometry (TDR) technique is proposed and used to monitor large ground stretched deformation. First, the PHSC structure and manufacturing process are introduced, and then, distributed capacitance, distributed inductance, and characteristic impedance were derived based on the proposed stretched-structure model. Next, the relationship between characteristic impedance and stretched deformation was found, and the principle of distributed deformation measurement based on the TDR technique and PHSC characteristic impedance was analyzed in detail. The function of the stretched deformation and characteristic impedance was obtained by curve fitting based on the theoretically calculated results. A laboratory calibration test was carried out by the designed tensile test platform. The results of multi-point positioning and the amount of stretched deformation are presented by the tensile test platform, multi-point positioning measurement absolute errors were less than 0.01 m, and the amount of stretched deformation measurement absolute errors were less than 3 mm, respectively. The measured results are in good agreement with the theoretically calculated results, which verify the correctness of theoretical derivation and show that a PHSC is very suitable for the distributed measurement of the ground stretched deformation.

Soil moisture content was measured by TDR sensors Aqua-Tel-TDR (Automata, Inc., today McCrometer CONNECT) in a loamy Chernozem on carbonate-rich loess substrate. The sensors, wrapped in slurry made of local soil and water, were installed horizontally into pre-made holes. The bias caused by imperfectly filled gaps between the wall of the hole and the sensor surface was reduced by field calibration. The same gaps made it possible to detect the preferential flow in soil macropores, due to which the reflectometric readings were perceivably higher than analogous readings before percolation events and sometimes higher than the native soil porosity. One typical event is presented. It is envisaged that sensors of this type can be used for semi-quantitative estimation of the preferential flux density, e.g. with the help of dual or multiple porous medium models or the momentum dissipation theory.

This paper explores the use of a microwave-reflectometry- based system for the automatic control and real-time monitoring of the flow and of the liquid level in intravenous (IV) medical infusions. In medical and hospital contexts, other kinds of devices, mainly based on the optical detection and counting of the infusion drops, are used. Nevertheless, the proposed system is aimed at circumventing some typical drawbacks deriving from the adoption of these traditional methods, thus allowing an efficient alternative for automatically monitoring the instantaneous flow of IV medical solutions. To this purpose, the proposed system combines microwave time-domain reflectometry (TDR) measurements with a noninvasive sensing element (i.e., strip electrodes directly attached to the external surface of the infusion bottle). Experimental results confirm that, by using low-cost portable TDR devices, the solution flow process can be controlled with acceptable accuracy. Therefore, the proposed method can be regarded as a promising control tool for in-hospital patient management as well as for telemedicine programs.

Time-domain reflectometry (TDR) based on instruments are commonly used for several monitoring methods, particularly in soil moisture and volumetric water-content evaluation. Furthermore, significant advantages of TDR methodology, mostly related to the possible determination in real-time and to a nondestructive approach of the spatial location and nature of various objects, make this technique an appealing candidate for a variety of environmental and industrial applications. In this paper, we show that the suitable combination of TDR-detecting functionalities can lead to a joint quantitative and qualitative monitoring method for liquid-control purposes, so that, in one shot, the analysis of TDR data allow the measurement of liquid levels, the determination of multiple interfaces in layered media, as well as the evaluation of dielectric properties, thus opening challenging perspectives for several monitoring applications, particularly in fluid-processing-related industry. For such purposes, a detailed analysis of the uncertainty of the proposed measurement method is mandatory; hence, a metrological characterization of the method is carried out, demonstrating that the presented technique is definitely valid for simultaneously measuring levels and dielectric constants of liquids, with uncertainties under 2%. Results obtained for different liquid samples validate the approach on a wide range of dielectric materials and demonstrate the robustness and reliability of the proposed TDR technique.

Time-domain reflectometry (TDR) methods used for measuring the dielectric properties of materials mostly utilize step or needle electrical pulses of constant amplitudes and shapes. Our novel approach enables determining the dielectric relaxation time of a sample using the analysis of the amplitudes of reflected pulses of two widths, in addition to bulk dielectric permittivity and electrical conductivity commonly obtained by the TDR technique. The method was developed for various values of electrical conductivity and relaxation time using numerical simulations of a five-rod probe placed in a material with complex dielectric permittivity described by the Debye model with an added electrical conductivity term. The characterization of amplitudes of two pulses of selected widths was done with regard to the dielectric parameters of simulated materials. The required probe parameters were obtained solely from numerical simulations. Verification was performed for the probe placed in aqueous KCl solutions with 14 different electrical conductivity values. The determined relaxation time remained roughly constant and independent of electrical conductivity. The obtained electrical conductivity agreed with the reference values. Our results indicate that the relaxation time, dielectric permittivity and electrical conductivity of the tested solutions can be simultaneously determined using a simple analysis of the amplitude and reflection time of two needle pulses of different widths.

This paper describes the main features of the time-domain reflectometry (TDR) measurement technique and, in particular, the TDR analysis performed using a proper operating mode of the vector network analyzer (VNA), which is called synthetic TDR. Furthermore, some results of reflection measurement, which aim to characterize the impedance behavior of transverse electromagnetic (TEM) and gigahertz TEM cells by means of a commercial VNA in time-domain mode, are presented

In this paper, a performance analysis, in terms of accuracy, linearity, and repeatability, of three criteria to estimate the time of flight in time-domain reflectometry (TDR) signals is carried out. In a first set of experiments, the three criteria [referred to as maximum derivative (MD), zero derivative, and tangent crossing (TC)] are applied to TDR signals propagating along a set of coaxial cables, with different known lengths and known electrical parameters. In a second set of experiments, the same criteria are applied to biwire cables in air, with different known lengths and unknown electrical parameters. Finally, in the last set of experiments, the criteria are applied in a more complex situation, i.e., on a biwire used as a sensing element for water-level measurement. The results show that, among the tested criteria, TC appears to provide a very good performance in terms of systematic errors and superior performance in terms of repeatability. The popular MD criterion appears to be more prone to random errors due to noise and TDR artifacts. The results of this paper are relevant to many practical applications of TDR, ranging from fault location in cables to media interface sensing.

In this paper, a time-domain reflectometry (TDR) based system for monitoring liquid level inside tanks is presented. The proposed system resorts to a flexible, two-wire probe, which can be attached to the walls of containers and adapted to their shape. The proposed system is particularly useful for industrial applications; in fact, after a preliminary calibration, it can measure automatically and in real time the level of liquids inside containers (even tens of meters tall). The proposed system was tested on metallic and on nonmetallic containers. In the latter case, as the probe is positioned on the outside wall of the container, a totally noninvasive monitoring of liquids is achieved. The obtained results show that the system has considerable potential for being easily and effectively employed in practical, industrial applications. Finally, simulations were carried out, thus providing useful information for optimizing the system performance and for predicting its limitations.

Reflectometry is a powerful technique that can be effectively employed for a number of practical applications; in particular, the high versatility, the real-time response, and the potential for practical implementation have contributed to the success of microwave reflectometry for monitoring purposes. In this regard, this paper provides a survey of the current state of the art of reflectometry-based methods for diagnostics and monitoring applications. After a brief overview of the theoretical principles at the base of this technique, the different approaches of microwave reflectometry (time domain, frequency domain, and combined approaches) are fully discussed; particular attention is given to the strategies for enhancing measurement accuracy. Finally, the major practical applications of reflectometry and related results are discussed, thus evidencing current achievements, limitations, and potential. © 2010 IEEE.

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. © 2006 IEEE.

Time-domain reflectometry (TDR) techniques have become increasingly attractive for soil moisture evaluation thanks to their adaptability, low cost, and measurement accuracy. Many different TDR-based approaches are currently available for deriving moisture content: empirical calibration curve, empirical dielectric models, frequency-dependent dielectric mixing models, etc. Generally, TDR soil moisture measurements resort to multiple-rod probes, which provide good adhesion to the soil and ease of insertion. However, the typical configuration of such probes does not allow performing a short-open-load (SOL) calibration procedure, which is definitely necessary for retrieving accurate dielectric characterization from TDR waveforms. To overcome the impracticability of the traditional SOL calibration, in this paper, an innovative triple-short calibration (TSC) procedure for commercially available three-rod probes is proposed. First, the robustness of the TSC procedure is validated on well-referenced liquids, demonstrating that its application to TDR measurements leads to a substantial enhancement of the final accuracy in the evaluation of the frequency-dependent reflection coefficient. Successively, the TSC procedure is applied to TDR measurements performed on moistened sand samples. In particular, it is demonstrated that the proposed TSC method, applied to traditional TDR measurements in combination with a dielectric mixing model, leads to an accurate and effective moisture evaluation procedure. This goal is reached through an efficient optimization algorithm that minimizes the difference between experimental and theoretical reflection coefficients. Results show that the proposed strategy is a suitable candidate for low-cost, highly accurate, and easy-to-perform moisture content estimation of soils. © 2010 IEEE.

Monitoring soil moisture is a major interest for several practical applications. This task can be suitably performed through various methods; however, at the state of the art, there is not a single method that successfully combines ease of use, low cost, customization, possibility of measuring large volumes, and, most importantly, measurement accuracy. In this regard, seismic wave propagation (SWP)-based methods, which rely on the evaluation of the propagation velocity of a seismic wave vc through the soil sample under investigation, hold considerable potential for practical implementation. On such bases, in this work, first the authors propose an enhanced version of a previously developed SWP-based system for soil moisture measurement. Successively, to provide an exhaustive performance characterization of the system, a specific comparative methodology, based on reference time-domain reflectometry (TDR)-based measurements, is addressed. More specifically, SWP- and TDR-based measurements are simultaneously performed on river sand for increasing levels of water content. The TDR-measured moisture levels are taken as reference values and are used to infer the theoretical propagation velocity values vc,REF. Then, these reference values are suitably compared with those directly measured through the SWP-based system (vc,REF), thus allowing a consistent metrological assessment. The ultimate goal of this work is to validate and characterize the performance of the proposed SWP-based system in view of practical implementation for soil moisture evaluation. © 2006 IEEE.

This paper deals with the testing of instrumentation loops (ILs) in gas turbines during scheduled maintenance. To both guarantee safe operation and save costs on periodical changing of cables, an innovative measurement device that monitors the status of the IL and indicates whether a replacement is necessary, has been developed. The goal of the research described in this paper is twofold: First, the cable network i checked for faults with time domain reflectometry bu comparing the recorded reflectogram with a reference reflectogram. Second, the sensor state is investigated by calculating its impedance through one-port scattering measurements. For this, a de-embedding technique is described to remove the cabling influences. Changes in the reflectogram or the impedance point to aging or a fault and indicate the location of the defect, so that specific actions can be taken to replace the malfunctioning cable or sensor.

In this work, a time domain-based approach for the estimation of the dielectric parameters of liquids is presented. The proposed approach combines traditional time-domain reflectometry measurements with a specific data processing and modeling that leads to the evaluation of the Cole-Cole parameters. The pivotal step of the procedure is the implementation of an accurate transmission line model of the used measurement cell. In this way, the error contributions due to undesired parasitic effects are minimized; hence, the overall accuracy is significantly enhanced. The proposed approach is tested through repeated measurements on well-referenced materials; this also allowed performing the related metrological analysis. Successively, the proposed procedure is applied for the evaluation of the Cole-Cole parameters of vegetable oils. In fact, at the state-of-the-art, only limited data are available for the dielectric characteristics of vegetable oils. In particular, ten different types of vegetable oils are considered. Results show that the proposed approach has strong potential also for possible practical applications in the area of anti-adulteration and quality control.

Time-domain reflectometry (TDR) is a well-established technique for continuous monitoring of the moisture levels and dielectric properties of materials; typically, it is widely used in soil science applications. Despite the high flexibility, elevated accuracy, and the low cost of TDR instrumentation, the state of the art is actually rather lacking in specific applications for the quality monitoring of agro-industrial processes and agro-food products. Therefore, the possibility of real-time control of moisture level plays a crucial role in terms of optimization, quality preservation, and energy saving in several industrial applications. In this regard, the development of suitable models relating the dielectric properties of granular materials to their moisture content is a still an open issue. To fill this gap, in this paper, the authors study the feasibility of adopting the TDR technique for such a purpose. The proposed goal is successfully reached through a comparative analysis among different calibration procedures and through experimental measurements on various granular materials. Finally, the adopted methodology is assessed through a rigorous metrological characterization, thus allowing the evaluation of the associated measurement uncertainty and repeatability.

Antenna-characterization measurements are traditionally performed in the frequency domain (FD) through a vector network analyzer (VNA) in an anechoic chamber. Nevertheless, the high cost of the required setup strongly limits the possibility of using this approach. Starting from these considerations, a time-domain (TD)-based approach for characterizing antennas without using an anechoic chamber is assessed. As a matter of fact, instruments operating in TD are usually less expensive than VNAs; nevertheless, with appropriate data processing, they provide as much information. Particularly, it is demonstrated that the selection of an optimal time windowing is the main factor that guarantees a high accuracy level in the corresponding FD. The proposed approach leads to the accurate evaluation of the reflection scattering parameter S 11 (f) from time-domain reflectometry (TDR) data. The experimental validation is tested on a commercial radio-frequency identification (RFID) reader antenna, and the results are compared with reference VNA measurements performed in an anechoic chamber. The ultimate goal of this paper is to demonstrate that, through calibrated TDR measurements, along with an optimal time windowing, an accurate antenna characterization can be achieved. © 2008 IEEE.

Several techniques for measuring the moisture levels of materials, particularly in the soil science area, are available. Nevertheless, the state of the art is rather lacking in moisture-sensing methods that are both inexpensive and noninvasive. The time-domain reflectometry (TDR)-based method, despite being a well-established low-cost technique for sensing moisture content, is intrinsically invasive due to the configuration of the probes that are commonly used. These considerations motivated the authors to investigate the adoption of simple inexpensive microstrip antennas as sensing elements for TDR-based moisture content measurements. For this purpose, the water content of the monitored material is sensed through the changes in the reflection scattering parameter S 11 (f) of the antenna. In particular, the change in the resonant frequency of the antenna, which is evaluated through an appropriate processing of the TDR waveforms, is correlated with the water content of the material under investigation. The ultimate goal is to assess a sensing method that can be implemented for inexpensive real-time noninvasive monitoring applications. © 2009 IEEE.

Measurement and control of the dielectric parameters of liquids play a major role in industrial quality-control applications. Although several techniques are currently available to this aim, none of them is simultaneously accurate, cost-effective, and reasonably quick. On the other hand, reflectometry has become a very attractive method for monitoring applications, mostly thanks to its accuracy and flexibility. In this paper, a combined method based on time-domain reflectometry (TDR) and frequency-domain (FD) analysis is presented: the aim is to substantially improve the measurement accuracy of the dielectric parameters of liquids. Starting with typical TDR measurements, the associated FD evaluation of the dielectric parameters is considerably enhanced through the combined effect of the following: 1) specific data-processing techniques; 2) the implementation of a calibration procedure; and 3) the final modeling and minimization routine. Furthermore, to definitively assess the proposed combined procedure, results are compared with measurements directly performed in the FD through a vector network analyzer (VNA). The ultimate goal of the work is to pave the way for the adoption of inexpensive and portable TDR devices in practical industrial monitoring applications.

Nos remerciements à IEEE pour l'autorisation de mise à disposition du papier complet. © IEEE Copyright Notice : Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.; International audience; Time-domain reflectometry (TDR) is a valuable technique for the measurement of dielectric properties of soils. The filtering of noisy TDR traces is treated in this paper. The problem of biased estimation occurs when the permittivity of the soil varies with the depth. In practical issues, only the apparent permittivity of the soil along the TDR line is available. Hence, robust optimal filtering has to be developed to provide a robust and reliable estimation. This filtering step is essential for the estimation of the permittivity with the depth.

A preprocessing algorithm is proposed to visualize the time-domain one-port scattering parameter of a subscriber line measured at the Central Office. To overcome the high line attenuation and the mismatch between the line and the measurement instrument, a preprocessing algorithm is developed to obtain numerically the impulse response of the one-port scattering parameter. The algorithm will search for a quasi-optimal base impedance for the scattering parameter; then, it will de-noise and de-alias the impulse response and will provide an estimate for the first meaningful significant reflection

The time-domain reflectometry technique was compared with the temperature measurement method for locating the frozen- unfrozen interface in water and sandy soils. This technique depends on the high-frequency (1-1000 MHz) electrical properties of water that change significantly and abruptly between the liquid and solid phases. Parallel wire transmission lines were inserted into the soil to guide electromagnetic pulses produced by a time-domain reflectometer (TDR). The frozen-unfrozen interface produced reflections measured by the TDR which were in turn used to locate the interface as it moved along the transmission line. In the laboratory it was possible to locate the interface using the TDR to within + or - 0.5 cm and in the field to within + or - 2.4 cm. These errors were equal to those associated with the temperature measurements.