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In this contribution we describe new possibilities regarding TDR measurements, related to the measurement of the electromagnetic characteristics of lossy and possibly magnetic and dispersive materials. The proposed advancement is related to the introduction of a spatial diversity in TDR measurements, achievable by means of extensible probes or alternatively by means of arrays of probes. The spatial diversity can replace the frequency diversity increasing the information achievable at single frequency, so allowing measurements immune from the effects of a possibly unknown dispersion law. Moreover, measuring the reflection coefficient at fixed frequency we can achieve information about both the propagation velocity of the electromagnetic wave along the line and about the intrinsic impedance of the line, which in its turn allows to discriminate between the dielectric permittivity and the magnetic permeability of the material, meant as complex quantities in order to include lossy cases too. There are several possible fields of application and in particular, with regard to the properties of the soil (of interest for archaeological prospecting), the attenuation of the waves in the soil can be estimated (which is important in relation with GPR prospecting), or the water content or in some cases the possible presence of some pollutant.

In this paper, the practical implementation of an innovative time domain reflectometry (TDR)-based system for leak detection in underground water pipes is presented. This system, which had been previously developed and experimented on pilot plants, has now been installed (for the first time) on a large scale, in 10 km of pipes. The present work describes all the practical aspects and technical details (from the design to the functional tests), related to the implementation of the system.

This paper describes the operating and technical details of the practical implementation of an innovative time domain reflectometry (TDR)-system for monitoring rising damp in building structures. The proposed system employs wire-like, passive, diffused sensing elements (SE's) that are embedded, at the time of construction or renovation, inside the walls of the building to be monitored. The SE's remain permanently inside the wall, ready to be interrogated when necessary.

In this work, the feasibility of the adoption of microwave reflectometry (MWR) for diagnosing the status of structures made of composite materials is investigated. In particular, two different "sensing structures", based on microstrip and coplanar configurations, are considered. The analysis focused on carbon fibre-reinforced composite structures, which are extensively used in aircraft industry. It goes without saying that, despite the widespread diffusion of this class of materials in the aircraft industry, there are two crucial requirements for which effective diagnostic methods are far from being adequately implemented. First, it is necessary to detect the possible presence of gaps between structural components after they are assembled. Secondly, there is the need to periodically control (during the service life of the aircraft) the amount of moisture that may have been absorbed by the composite structure. To this purpose, the present work intends to pave the way for future practical implementation of MWR based systems for these diagnostic requirements.

In this paper a metrological assessment on the accuracy provided by a Time Domain Reflectometry (TDR)- based method for the estimation of moisture content of granular materials is proposed. In particular, comparative moisture content measurements are carried out through two different TDR instruments: an inexpensive portable unit and a high-performance unit. The main goals are first to assess a robust procedure for TDR moisture monitoring (in particular for sand-like materials), and second to provide a deep metrological analysis for minimizing and characterizing error contributions. This feature is particularly important when considering the proposed measurement procedures for industrial applications, where both accuracy and low cost must be guaranteed.

In this paper, a low-cost time domain-based approach to antenna characterization is presented. The goal is to prove that time domain-based antenna measurements, after appropriate processing, represent an accurate and more practicable alternative to the universally accepted (yet highly expensive) antenna measurements in anechoic chamber, and provide information just as complete. Measurements on two commercial antennas are carried out in the time domain (in a non-controlled environment) and in the frequency domain (in an anechoic chamber): experimental data obtained from the two approaches are compared in terms of Return Loss. Results show that reliable results can be extracted from time domain data, and that a good insight into the antenna characteristics can be obtained even without using highly expensive facilities.

Recently, an innovative system based on time domain reflectometry (TDR) for the individuation of leaks in underground pipes has been proposed and validated. Starting from the results obtained so far, the present works aims at further investigating the practical applicability of the aforementioned system. In particular, the goal of this work is to assess the system in the detection of two close leaks (i.e. leakages that may occur on the same length of pipe). To this purpose, an experimental setup was arranged: two “leakage conditions” were imposed, and the position of the leaks were considered as unknown and calculated through the dedicated developed algorithm. Results show that, differently from traditional leak detection methods (in which the presence of a leak may “mask” the presence of other leaks), the TDR-based system successfully individuates and correctly localizes the presence of two leaks.

One of the most common applications of time-domain reflectometry (TDR) is the localization of dielectric permittivity variations (DPVs) along cable systems. However, signal attenuation and dispersion phenomena limit the usability of TDR when used on long cable systems. Some TDR measuring instruments offer the possibility of modifying the amplitude and the width of the TDR test pulse signal, along with the gain of the input stage amplifier. Increasing these parameters generally allows to investigate longer distances; nevertheless, increasing the gain may saturate the instrument analog to digital converter (ADC) and increasing the pulse width leads to worse spatial resolution. For this reason, it is customary for the operator to repeat TDR measurements several times, with different settings, and proceed by focusing each time on a different TDR reflectogram; however, this procedure is time-consuming and, eventually, it does not guarantee optimal performance. Starting from these considerations, in this work, a new measurement algorithm for facilitating and making more effective the TDR-based localization of large DPVs on long cable systems is proposed. The algorithm automatically acquires several TDR reflectograms obtained by setting different values of the gain of the input stage amplifier and the values of the pulse width of the test signal. The reflectograms are then automatically processed, in an effort to balance the short-distance resolution and long-distance gain in a single composite reflectogram (CR), which can be conveniently used also by non-skilled operators. The developed algorithm was implemented and validated through experiments on a practical case study to localize DPVs on a 300 m-long cable system.

Most sensing networks rely on punctual/local sensors, thus lacking the ability to spatially resolve the quantity-To-be-monitored (e.g., a temperature profile, a humidity profile, etc.) without relying on the deployment of numerous inline sensors. At the state of the art, most quasi-distributed or distributed sensing technologies rely on the use of optical fiber systems; however, these are generally expensive and this limits their large-scale adoption. On the other hand, recently, elongated sensing elements have been successfully used with time-domain reflectometry (TDR) for implementing diffused monitoring solutions. The advantage of TDR is that this is a relatively low-cost technology, with adequate measurement accuracy and the potential to be customized to suit the specific needs of different application contexts of the 4.0 Era. Starting from these considerations, this paper addresses the design, implementation and experimental validation of a novel generation of elongated sensing element networks (SENs) that can be permanently installed in the systems to be monitored and used for obtaining the diffused profile of the quantity-To-be-monitored. In particular, as case studies, three applications are considered: monitoring irrigation process in agriculture (SEN-A, agriculture); leak detection in underground pipes (SEN-W, water); and monitoring of building structures (SEN-B, building).

Most monuments and historical buildings in the Maltese Islands are made of the local Globigerina Limestone (GL). This type of stone, however, is very delicate and prone to degradation caused by the environmental conditions of the islands. Hence, for the preservation of the Cultural Heritage monuments, it is necessary to promptly assess the health status of these structures and, in particular, their water content (which represents one of the major causes of degradation). Starting from these considerations, in this work, a time domain reflectometry (TDR)-based method for estimating water content of GL is presented. More specifically, the proposed method relies on estimating the water content value of the GL structure from TDR-based dielectric permittivity measurements. To verify the suitability of this system, experimental tests were carried out on a GL sample. In addition to this, also the dielectric characterization of GL was carried out. The results anticipate the strong potential of the proposed method for practical applications in the Cultural Heritage diagnostics.

One of the major goals of Health 4.0 is to offer personalized care to patients, also through real-time, remote monitoring of their biomedical parameters. In this regard, wearable monitoring systems are crucial to deliver continuous appropriate care. For some biomedical parameters, there are a number of well established systems that offer adequate solutions for real-time, continuous patient monitoring. On the other hand, monitoring skin hydration still remains a challenging task. The continuous monitoring of this physiological parameter is extremely important in several contexts, for example for athletes, sick people, workers in hostile environments or for the elderly. State-of-the-art systems, however, exhibit some limitations, especially related with the possibility of continuous, real-time monitoring. Starting from these considerations, in this work, the feasibility of an innovative time-domain reflectometry (TDR)-based wearable, skin hydration sensing system for real-time, continuous monitoring of skin hydration level was investigated. The applicability of the proposed system was demonstrated, first, through experimental tests on reference substances, then, directly on human skin. The obtained results demonstrate the TDR technique and the proposed system holds unexplored potential for the aforementioned purposes.

This work presents a microwave reflectometry-based system for monitoring large concrete structures (during the curing process and also while the structure is in use), through the combined use of punctual and diffused sensing elements. In particular, the adoption of punctual probes on a reference concrete specimen allows the development of an innovative and accurate calibration procedure, useful to obtain the value of the water content on a larger structure made of the same material. Additionally, a wire-like diffused sensing element can be permanently embedded in buildings and used to monitor the structure along the entire length of the sensing element. The adopted diffused sensing element can be used not only to detect dielectric variation during the curing process, but also throughout the service life of the structure. The combined use of punctual and diffused sensing elements represents an important innovation from a procedural point of view, able to provide detailed and quantitative information on the health status of the structure both during and after construction.

It is known that bi-wires can be employed as passive distributed sensing elements (SEs), to accurately locate water infiltrations in soil, concrete materials, and so on, using the standard time-domain reflectometry instrumentation and proper signal processing. This paper examines the possibility of using the same kind of SEs with simpler techniques and cheaper hardware, in order to trigger an alert in the case of water infiltrations. Two techniques are examined: the first measures the SE capacitance, and the second measures the time-of-flight of electromagnetic waves in the SE. The performance of the techniques is comparatively evaluated, in terms of sensitivity to the presence of water and the influence of temperature variations. The capacitance-based technique is found to be more sensitive to the presence of water, but also more prone to the influence of temperature, as long as the temperature variations are of modest entity (below 10 °C). For higher temperature variations, the capacimetric method appears to be advantageous. The results of this paper are useful to practically implement the monitoring of water leaks in a large set of buried pipes, water infiltrations in a large concrete structure, and so on.

A transmission line simulator for applications to TDR measurements and TDR-based sensors is presented. The proposed simulator, fully developed in MATLAB environment, is designed to be a fast, efficient and easily customizable tool, and its performance are compared with commercial simulation software packages. The simulator is intended for measuring arbitrary profiles of primary parameters (R, C, G, L) of a transmission line, by matching simulated TDR waveform with experimental TDR data. In the paper, this use is demonstrated by measuring the parameter profiles of actual coaxial cables. The simulator can be used in any kind of TDR measurement, e.g. leak detection in pipes, distributed moisture measurements in soil, health monitoring in building concrete, etc.

In this paper, the most recent advances in the time-domain reflectometry (TDR)-based system for leak-localization in underground pipes are described in detail. More specifically, a new design of sensing element and the use of a new connection modality are proposed. Thanks to these new features, the practical implementation of the system becomes much quicker and its use more effective. Additionally, the present work also describes all the practical aspects and technical details (from installation to functional tests), related to the practical implementation of the system. Finally, to assess the possibility of further increasing the cost-effectiveness of the TDR-based leak localization system, experimental tests were carried out by comparatively using two TDR instruments, differing in specifications and costs, to identify the position of a leak.

In this work, the validation and the practical implementation of a methodology exploiting a time domain reflectometry (TDR)-system for monitoring rising damp in building structures are described in detail. The proposed system employs wire-like, passive, diffused sensing elements (SEs) that are embedded, at the time of construction or renovation, inside the walls of the building to be monitored. The SEs remain permanently inside the wall, ready to be interrogated when necessary. Experimental and simulation results are reported, which demonstrate the possibility of practical implementation and the associated performance in terms of sensitivity.

In this work, the performance of three time domain reflectometry (TDR) instruments (with different hardware architectures, specifications and costs) is comparatively assessed. The goal is to evaluate the performance of low-cost TDR instrumentation, in view of the development of a completely permanent TDR-based monitoring solution, wherein the costs of the instrument is so low, that it can be left on-site, even unguarded, and controlled remotely. Without losing generality, the applications considered for the comparative experiments are the TDR-based detection of leaks in underground pipes and, more in general, of soil water content variations. For this reason, both laboratory and in-the-field experiments are carried out by comparatively using three TDR instruments, in conjunction with wire-like sensing elements (SEs).

Olive oil production represents a big part of the Mediterranean economy, and as such it must be protected from frauds. For this reason, it is necessary to develop alternative low-cost techniques, applicable on large scale, for checking the quality of the product and for detecting adulteration. On such bases, the present work deals with the possibility of adopting microwave reflectometry for obtaining a 'spectral signature' of vegetable oils. For this purpose, time domain reflectometry (TDR) measurements, in combination with specific data processing, are first used for the dielectric characterization of several oil types. Successively, the acquired data are processed through the principal component analysis (for identifying clusters of oil types that exhibit common features) and through the partial least square analysis (for identifying a predictive model for detecting oil adulteration). Results confirm that the proposed procedure holds considerable potential for quality and anti-adulteration control purposes, especially in view of practical applications. © 2012 Elsevier Ltd. All rights reserved.

In this paper, a time-domain reflectrometry (TDR)- based solution for monitoring moisture content in cement-based samples is presented. The proposed system employs a simple flexible biwire, which acts as a distributed sensing element (SE) (as opposed to traditional, local moisture content sensors). Once embedded, the SE remains permanently inside the cement-based sample and can be used both for monitoring the hydration process of the sample structures (ex-ante monitoring) and, successively, for monitoring possible water infiltration during the service life of the structure (ex-post monitoring). In practical applications, the SE could be employed inside building structures at the time of construction, and it could be used for the aforementioned moisture content monitoring purposes. As a preliminary validation of the practical feasibility of the proposed system, in this paper, two cement-based samples (made of mortar and concrete, respectively) were equipped with a SE, and their water content was monitored through TDR measurements, over a 28-day period (thus mimicking the ex-ante monitoring conditions). Furthermore, to verify the potential of the proposed method also for the ex-post monitoring, the air-dried mortar sample was intentionally subjected to wetting conditions and the resulting rising damp was observed through the proposed TDR-based system.

This paper deals with the shape of the GPR diffraction curve in dependence of the distance of the measurement line from to the air/soil interface. It will be shown that the diffraction curve changes with respect to the case of data gathered at the air-soil interface, and the calculation of the diffraction curve requires the solution of a fourth degree algebraic equation. The solution in closed form of this equation will be presented, and a physical discussion of the effects of the non-null height of the observation line will be provided.

This work aims at assessing the practical applicability of an innovative time domain reflectometry (TDR)-based system for leak localization in underground pipes. For this purpose, two laboratory experiments were carried out. The first experiment (E1) allowed assessing the reliability of the TDR system in presence of two simultaneous leakage-like conditions. The second experiment (E2), which was also carried out in presence of two leaks, allowed assessing the possible effect of the type of soil on the performance of the leak-detection system. Results show that, differently from traditional leak detection methods, the TDR-based system can correctly localize the presence of two simultaneous, closely-spaced leaks and that the type of soil has very little influence on the performance of the system. Finally, in this work, the practical implementation of the system in urban areas is also addressed, thus highlighting the steps to maximize the effectiveness of the system. © 2013 Elsevier Ltd. All rights reserved.

In this work, three different techniques, namely time domain reflectometry (TDR), ground penetrating radar (GPR) and electrical resistivity tomography (ERT) were experimentally tested for water leak detection in underground pipes. Each technique was employed in three experimental conditions (one laboratory or two field experiments), thus covering a limited but significant set of possible practical scenarios. Results show that each of these techniques may represent a useful alternative/addition to the others. Starting from considerations on the obtained experimental results, a thorough analysis on the advantages and drawbacks of the possible adoption of these techniques for leak detection in underground pipes is provided. © 2013 Elsevier Ltd.

In this paper, a time domain reflectometry (TOR)based system for the non-invasive localization of leaks in underground pipes is described and experimentally validated. The proposed system simply relies on TOR measurements performed on a two-wire cable (biwire) that is rolled out on the underground pipe at the time of installation of the pipe (but made accessible from the road surface through an inspection well); the biwire on the pipe acts as a permanent, distributed sensing element and can be connected to the TOR instrument whenever it is necessary to perform a check. Two of the major advantages of the proposed system are that it can be employed with pipes made of any material and that it strongly reduces the inspection time typically required by traditional leak detection methods. To validate the system and to assess its performance, a new pipe was installed and a leak condition was intentionally provoked at a reference position. The TOR system was then used to evaluate the position of the leak as if had been unknown. The results of this experimental test are reported and thoroughly discussed.

In this paper, a time domain reflectometry (TDR)-based solution for detecting water leaks in underground pipes is described and experimentally validated. The proposed method strongly reduces the inspection time that is typically required by traditional leak detection methods. In fact, it can successfully inspect pipes that are hundreds of meters long. In this work, two different configurations of the system are described: one can be used for detecting leaks in 'already-installed' metal pipes; whereas the other is suitable to be employed for detecting leaks in 'newly-installed' pipes made of any material. The performance of both these system configurations was assessed through an extensive, on-site experimental campaign, carried out with the collaboration of one of the largest European water operators, Acquedotto Pugliese S.p.A. (AQP). Representative results, related to both configurations, of three experimental cases (ECs) are reported and commented on. Finally, some practical considerations on the applicability of the system are provided. © IWA Publishing 2013.

In this paper, a time domain reflectometry-based system for locating leaks in underground pipes (made of any material) is presented. The proposed system simply requires that a biwire should be attached to the pipe (all along its length), at the time of installation. Basically, the biwire acts as a permanent sensing element that can be connected to the measurement instrument whenever it is necessary to check for the presence of leaks. It is worth emphasizing that such a simple and low-cost system could tremendously facilitate leak detection not only in water distribution systems but also in wastewater/sewer pipelines. The proposed system was validated through measurements on a newly installed pilot plant, in which a leak was intentionally provoked. © 2012 IOP Publishing Ltd.

In most water distribution systems, a fairly sizable amount of water is lost because of leaks and faults in pipes. For this reason, the individuation of leaks is extremely important for the optimization and rationalization of water resources. However, the techniques and methodologies that are currently used for the individuation of leaks, despite being universally accepted, are extremely time-consuming and require highly-experienced personnel. Additionally, such techniques become unreliable and ineffective when the measurements are not performed in specific operating conditions of the pipe (e.g., high water pressure). On this basis, in this paper, a time domain reflectometry (TDR)-based system for the non-invasive detection of leaks in underground metal pipes is presented. Not only does the adoption of the developed system leads to accurately pinpoint the leak, but it also allows to dramatically reduce the required inspection times. The TDR-based system for leak detection is described in detail (with particular attention to the measurement principle behind the method and to the methodology). Furthermore, a strategy for enhancing the accuracy in pinpointing the leak is addressed. The proposed system is validated through experimental campaign that consisted in carrying out a leak-detection survey through the traditional methods and through the proposed method. © 2001-2012 IEEE.

In this paper, the experimental validation of a time domain re∞ectometry (TDR)-based method for pinpointing water leaks in underground metal pipes is presented. The method relies on sensing the local change in the dielectric characteristics of the medium surrounding the leak point. The experimental validation of the method was carried out through measurements performed on a pilot plant (experimental case P1) and through on-the-fleld measurements performed on two 'already-installed pipes', i.e., already operating and connected to the water distribution system (experimental cases P2 and P3). For the pilot plant, difierent leak conditions were imposed and the corresponding TDR responses were acquired and analyzed. For the on- the-fleld measurements, TDR measurements were performed on pipes for which a leak-detection crew had preliminarily individuated the possible presence of leaks (through traditional leak-detection methods). Finally, in view of the practical implementation of the proposed TDR- based leak-detection system, a data-processing procedure (which gives an automatic evaluation of the position of the leak) is also presented.

In this work, a dielectric permittivity measurement system, to be used for quality control of edible oils, is presented. The proposed system relies both on low-frequency and high-frequency measurements (performed through and LCR meter and through a time-domain reflectometer, respectively), thus allowing a "broadband" investigation of the dielectric behavior of edible oils. The adoption of a single, specifically-designed probe (used for all the measurements), along with the possibility of using portable instrumentation, makes the proposed system an appealing candidate for the realization of a continuous, on-site system for quality monitoring of edible oils. The proposed system was first validated on materials with well-known dielectric characteristics. Successively, it was used to investigate the dielectric behavior of some autochthonous varieties of olive oils and of seed oils. The ultimate goal of this work is to pave the way for the development of an alternative method of analysis that could be able to distinguish among different kinds of oils, to certify oil quality and origin, and to detect the possible presence of adulterants. © 2011 IEEE.

Time domain reflectometry (TDR) is a robust approach for measuring static electrical conductivity of moistened granular materials. Although initially introduced for monitoring soil salinity, its application to granular materials might be an interesting and cost-effective means for monitoring the quality-status of various materials. However, the traditional approach requires tedious and time-consuming preliminary calibration measurements on reference liquids. In this paper, an innovative approach for the direct estimation of the electrical conductivity is presented. In fact, it is demonstrated that the suitable combination of the TDR measurement with a transmission-line modeling of the measurement setup, successfully leads to the avoidance of the preliminary calibration procedure. Investigations carried out on water and on moistened sand samples demonstrate that the performance of the proposed method in estimating the static conductivity is comparable with that achievable through the traditional approach. © 2009 IEEE.

Monitoring soil moisture is a major interest for several practical applications, and this task can be suitably performed through various methods. Although extensive literature deals with the adoptions of standard systems (many of which are commercially available), the state of the art is lacking in a rigorous validation of specific systems, such as those based on the seismic wave propagation (SWP) method. Such methods have attracted a growing interest thanks to the simultaneous combination of reliability, ease of use, low cost and, most importantly, customization possibility. In this regard, in this paper the Authors propose an experimental comparative approach for fully validating a SWP-based system through reference time domain reflectometry (TDR) measurements. To this purpose, reference TDR measurements are performed for different moisture levels, and the corresponding reference propagation velocities are compared with those directly measured through the SWP-based system. This approach provides a comprehensive assessment of the SWP-based method, from both an experimental and a metrological point of view. The ultimate goal is to provide an exhaustive performance characterization of the system, in view of practical implementation for soil moisture evaluation. © 2009 IEEE.

Different approaches and techniques are commonly available for the continuous monitoring of moisture levels and dielectric properties of materials; typically, related applications, are largely used in soil science area. Nevertheless, the state of the art is actually rather lacking in specific sensing methods that combine the low cost and the non-invasive approach of the involved instrumentation. To fill this gap, in this paper the authors study the feasibility of the adoption of the time-domain reflectometry analysis for such purposes, using a patch antenna as sensing element. This way, the extrapolation of the scattering parameters is suitably correlated to the water content levels of the materials under test. Furthermore, the adopted methodology is assessed through full-wave simulations, thus corroborating the experimental measurements. ©2008 IEEE.

Traditionally, antenna characterization measurements are performed in the frequency-domain through a Vector Network Analyzer (VNA) in anechoic chamber. Nevertheless, the expensiveness of this set-up prevents itfrom becoming widespread in laboratories. On such bases, in this paper a time-domain-based approach is comparatively investigated; such a method virtually makes the anechoic chamber unnecessary, thus dramatically reducing the related costs. The proposed approach, based on the evaluation of the scattering parameter (S 11) from Time Domain Reflectometry (TDR) data, has been tested for the characterization of a commercial Radio Frequency Identification (RFID) reader antenna. Data acquired in the time-domain are processed in the frequency-domain through a dedicated algorithm, thus allowing the S11 extrapolation. Furthermore, results are compared to VNA measurements performed in an anechoic chamber. In order to assess the investigated method, from a metrological point of view, the root mean square error between the results is reported as a figure of merit. This way, it is demonstrated that calibrated time-domain measurements represent an alternative, inexpensive and accurate method for characterizing antennas. © 2008 IEEE.

A time domain reflectometry (TDR)-based system for the localization of water leaks has been recently developed by the authors. This system, which employs wire-like sensing elements to be installed along the underground pipes, has proven immune to the limitations that affect the traditional, acoustic leak-detection systems.Starting from the positive results obtained thus far, in this work, an improvement of this TDR-based system is proposed. More specifically, the possibility of employing a low-cost, water-absorbing sponge to be placed around the sensing element for enhancing the accuracy in the localization of the leak is addressed.To this purpose, laboratory experiments were carried out mimicking a water leakage condition, and two sensing elements (one embedded in a sponge and one without sponge) were comparatively used to identify the position of the leak through TDR measurements. Results showed that, thanks to the water retention capability of the sponge (which maintains the leaked water more localized), the sensing element embedded in the sponge leads to a higher accuracy in the evaluation of the position of the leak. Keywords: Leak localization, TDR, Time domain reflectometry, Water leaks, Underground water pipes