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The real-time monitoring of plant water status is an important issue for digital irrigation to increase water productivity. This work focused on a comparison of three biosensors that continuously evaluate plant water status: trunk microtensiometers (MTs), trunk time-domain reflectometry (TDR), and LVDT sensors. During the summer and autumn seasons (DOY 150–300), nectarine trees were subjected to four different consecutive irrigation periods based on the soil Management Allowed Deficit (MAD) concept, namely: MAD10 (light deficit); MAD50 (moderate deficit); MAD100 (severe deficit), and MAD0 (full irrigation). Measurements of stem water potential (Ψstem) and leaf gas exchange were recorded on representative days. A continuous measurement of the plant water status of Ψtrunk, MDS, and Ktrunk revealed the water deficits imposed on the soil. The highest water deficit observed at the end of the MAD100 period (Ψstem = −2.04 MPa and Ɵv = 17%) resulted in a minimum value of Ψtrunk (−1.81 MPa). The maximum value of MDS (408 µm) was observed earlier than that of Ψtrunk, motivated by the low sensitivity of MDS at Ψtrunk < −1.2 MPa and Ψstem < −1.5 MPa due to a decrease in the tissue elasticity of the trunk when severe water deficit conditions are reached. Both Ψtrunk and Ψstem were more dependent on soil water content, while MDS was more responsive to environmental changes. Ktrunk was the weakest indicator for determining plant water status, although when expressed as a daily fraction of depletion (KtrunkFD), it improved, evidencing a process of hysteresis. Ψtrunk showed the highest sensitivity, suggesting the potential use of MTs as a valuable biosensor for monitoring nectarine water status in digital agrosystems. [ABSTRACT FROM AUTHOR]

The purpose of the current study is to investigate the qualitative characterization of nine different pure vegetable oil samples using dielectric spectroscopy which is a vastly resourceful and reasoned technique in the temperature range 0 ℃ to 25 ℃. Time-domain reflectometry technique is applied up to the microwave frequencies of 50 GHz for the first time for qualitative characterization of the selected vegetable oil samples with a special focus on the variances of dielectric properties like dielectric permittivity (ε′), dielectric loss (ε″), relaxation time concerning temperature and other physiochemical properties of the vegetable oil specimens.The experimental methodology involves the use of time-domain reflectometry (TDR) measurements up to the scale of 50 GHz done to analyse the aspects like lower and higher scales of values towards the static dielectric permittivity (εs) and relaxation time (τ) (ps) to further meaningfully compare and correlate this values with the fatty acid profiles of each of the nine vegetable oil samples to reason and draw comparative inferences about the quality aspects of vegetable oils. Microwave TDR studies provide an effective, alternate, simple, rapid, and viable way to exercise quality control and actuate data regarding the quality status of vegetable oils. Variances of dielectric permittivity (ε′) concerning dielectric loss (ε″) are graphically interpreted using the Cole Davidson model. The static dielectric permittivity (εs) was further recertified and measured accurately by using a precision LCR meter. Thermodynamic properties of all the nine vegetable oil samples like enthalpy (ΔH) (kJ/mol) and entropy of activation (ΔS) (J/mol ∙ K) are also calculated to further insight the dependence of dielectric properties of these oil samples concerning temperature.This dielectric spectroscopic study affirms the association of the quality aspects of these nine vegetable oil samples with their dielectric properties by providing meaningful correlations, comparatives and concurrencies of dielectric properties concerning the physiochemical properties which are a part of fatty acid profiles of these samples, which is a novel aspect of this study. The Cole-Cole plot underlines the tendency of realignment of dipoles as per the applied field. The complex permittivity spectra indicate the dwindling nature of molecular alignment including a slow decline to average coinciding values depending on the molecular bonding pattern of vegetable oil samples. The activation energy (ΔH) in (kJ/mol) is calculated for all the samples which are indicative of endothermic nature which experimentally proves that high energy is required for rotation of unsaturated oil sample molecules with low relaxation times.The highlight of the current dielectric spectroscopic study is that it conclusively divides the nine vegetable oil samples into two groups based on the dielectric property of relaxation time. The vegetable oil samples with higher relaxation times were measured in ps [soyabean oil (398.5), groundnut oil (412.5), flaxseed oil (318.4), and castor oil (305.3)] and the oil samples with lower relaxation times [safflower oil (37.91), sunflower oil (30.6), walnut oil (22.4) and sesame oil (38.4)] and correlate this dielectric aspect with the aspect extent of the presence of oleic acid: C18H34O2, linoleic acid: C18H32O2, linolenic acid: C18H30O2 and ricinoleic acid C18H34O3 alongside the percentage of unsaturation present in the fatty acid profile of each sample. Saturated fatty profile of coconut oil (percentage of saturation 82.5) with low relaxation time (41.8) ps and its concurrency concerning the extent of percentage presence of lauric acid C12H24O2 (52 ps) myristic acid: C14H28O2 (21 ps) is also correlated. The current dielectric spectroscopic study further highlights and compares the variances of dielectric permittivity of the nine vegetable oils samples with the percentage of unsaturation /saturation to infer upon the correlation with the fatty acid profile of these oil samples.

This research review article provides a detailed examination of SMA (SubMiniature version A) connectors, which are integral components in high-frequency electronic systems. Through extensive S-parameter and time-domain reflectometry (TDR) measurements conducted on various SMA connector constructions, this study aims to evaluate the performance and impact of SMA connectors on signal integrity. Results reveal insights into the comparative performance of different SMA connector types mounted on PCB land pads, highlighting their strengths and limitations. Additionally, this paper explores the application of reference plane cut-outs for discontinuity impedance compensation, aiming to enhance the frequency response of SMA connectors. By linking measured performance parameters with relative market prices, this study offers valuable insights into the economic viability of different SMA connector types. The best and worst performing SMA connector measurements reveal an S11 < −10 dB bandwidth of more than 8 GHz and 1.5 GHz and a transition impedance of 46.5 Ω and 21 Ω, respectively. Overall, this research contributes to advancing the understanding and selection of SMA connectors for RF applications in telecommunications, aerospace, medical devices, and beyond. [ABSTRACT FROM AUTHOR]

The real-time monitoring of plant water status is an important issue for digital irrigation to increase water productivity. This work focused on a comparison of three biosensors that continuously evaluate plant water status: trunk microtensiometers (MTs), trunk time-domain reflectometry (TDR), and LVDT sensors. During the summer and autumn seasons (DOY 150–300), nectarine trees were subjected to four different consecutive irrigation periods based on the soil Management Allowed Deficit (MAD) concept, namely: MAD10 (light deficit); MAD50 (moderate deficit); MAD100 (severe deficit), and MAD0 (full irrigation). Measurements of stem water potential (Ψstem) and leaf gas exchange were recorded on representative days. A continuous measurement of the plant water status of Ψtrunk, MDS, and Ktrunk revealed the water deficits imposed on the soil. The highest water deficit observed at the end of the MAD100 period (Ψstem = −2.04 MPa and Ɵv = 17%) resulted in a minimum value of Ψtrunk (−1.81 MPa). The maximum value of MDS (408 µm) was observed earlier than that of Ψtrunk, motivated by the low sensitivity of MDS at Ψtrunk < −1.2 MPa and Ψstem < −1.5 MPa due to a decrease in the tissue elasticity of the trunk when severe water deficit conditions are reached. Both Ψtrunk and Ψstem were more dependent on soil water content, while MDS was more responsive to environmental changes. Ktrunk was the weakest indicator for determining plant water status, although when expressed as a daily fraction of depletion (KtrunkFD), it improved, evidencing a process of hysteresis. Ψtrunk showed the highest sensitivity, suggesting the potential use of MTs as a valuable biosensor for monitoring nectarine water status in digital agrosystems.

Undetected leakage of fluid hydrocarbons from pipelines or underground storage tanks into the subsurface environment are environmental and public health hazards. It is evident that there is a need for efficient, effective and accurate technology to detect these leaks rapidly and non-destructively, so as to make the process safe, to make quantitative risk assessment, and to provide effective preventive measures. There are unsurmountable limitations in many existing leak detection techniques. Moreover, early detection of leakage would allow rapid remediation at source to significantly reduce the remediation costs, and more importantly the environmental impact. The results of an experimental investigation for the technical feasibility and practicality of a technique for detection and location of fluid hydrocarbon leaks in underground pipelines and storage tanks based on the principles of time-domain reflectometry (TDR) are presented in this paper. The measurement sensitivity of the technique was evaluated for 3 different types of cables, 2 cable configurations (parallel-wires or coaxial), 2 leaking fluids (tap water or petrol), a single leak or double leaks, and 2 backfill materials (fine sand or gravel) by a series of field-scale model tests. The testing parameters were varied systematically. The experimental results indicate that TDR is a technically feasible technique for the detection of fluid hydrocarbon leaks from pipelines and underground storage tanks when the setup configuration is appropriate. [ABSTRACT FROM AUTHOR]

Time-domain reflectometry (TDR) has been used for the characterization of media; however, the results of TDR tests significantly differ according to the types of solutions. The objective of this study is to suggest a new relationship between TDR output values and bulk electrical conductivity based on a machine learning algorithm for enhancing the reliability of TDR measurement. Various salinities (0%, 1%, 2%, and 3%) and lead concentrations (0, 0.5,1, 2, 5, and 10 mg/L) are applied along with silica sand, classified as SP in USCS, to create media. A laboratory test is performed to measure the TDR waveform at the bottom of the cylindrical cell, and a resistance probe is also installed to obtain the true bulk electrical conductivity in the cell. A deep neural network machine learning algorithm is applied to establish the relationship between the TDR output value and the bulk electrical conductivity at each frequency of 0.1, 0.12, 1, 10, and 100 kHz. The highly important variables are also defined through random forest. This study demonstrates that the TDR can be reliably converted into bulk electrical conductivity when two different solutions are mixed. [ABSTRACT FROM AUTHOR]

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, $500 ~\mu \text{m}$ , and $300 ~\mu \text{m}$ that corresponded to $\lambda $ /30, $\lambda $ /60, and $\lambda $ /100, respectively ($\lambda $ 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 ± $9 ~\mu \text{m}$ 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. [ABSTRACT FROM AUTHOR]

In this paper, a novel method for accurate modeling of microstrip discontinuities based on pulse shaping modulation is presented. The proposed method uses a novel excitation signal to address typical challenges when utilizing conventional TDR using Gaussian pulse excitation. In the first step a Double-Exponential Pulse (DEP) is utilized in a modified TDR system to improve the discontinuity localization precision as it has a sharp rise time. Second, a Linear Frequency Modulated (LFM) signal is used to provide more energy at higher frequencies in contrast with the conventional TDR. Subsequently, a mixed DEP and LFM signals are utilized to combine both advantages: high precision of DEP, and the accuracy of LFM. Simulated results are presented to explore the potential of the proposed method. [ABSTRACT FROM AUTHOR]

Engineers often face the challenge of constructing on soft soils that are associated with low bearing capacity and severe post-constructional settlements. In the subsurface zone, volume-change behavior of saturated soft soil is important in predicting the potential settlements. In this study, laboratory experiments have been conducted to monitor densification and consolidation processes of two soft geomaterials under incremental surcharge loading. During these experiments, densification of the geomaterials have been evaluated through a noninvasive scheme using electromagnetic (EM) methods. For this purpose, a time-domain reflectometry (TDR)-based approach has been accomplished by means of rod probe sensors. Changes of TDR waveforms under several surcharge loadings have been analyzed to establish soil properties, such as dielectric permittivity, volumetric water content, density, and porosity. Translating this laboratory-based nondestructive monitoring scheme to the field would potentially facilitate in management of ground improvement trials prior to, during, and after construction on soft soil deposits. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Time-domain reflectometry (TDR) is an established means of measuring impedance inhomogeneity of a variety of waveguides, providing critical data necessary to characterize and optimize the performance of high-bandwidth computational and communication systems. However, TDR systems with both the high spatial resolution (sub-cm) and voltage resolution (sub- $\mu \text{V}$) required to evaluate high-performance waveguides are physically large and often cost-prohibitive, severely limiting their utility as testing platforms and greatly limiting their use in characterizing and trouble-shooting fielded hardware. Consequently, there exists a growing technical need for an electronically simple, portable, and low-cost TDR technology. The receiver of a TDR system plays a key role in recording reflection waveforms; thus, such a receiver must have high analog bandwidth, high sampling rate, and high-voltage resolution. However, these requirements are difficult to meet using low-cost analog-to-digital converters (ADCs). This article describes a new TDR architecture, namely, jitter-based APC (JAPC), which obviates the need for external components based on an alternative concept, analog-to-probability conversion (APC) that was recently proposed. These results demonstrate that a fully reconfigurable and highly integrated TDR (iTDR) can be implemented on a field-programmable gate array (FPGA) chip without using any external circuit components. Empirical evaluation of the system was conducted using an HDMI cable as the device under test (DUT), and the resulting impedance inhomogeneity pattern (IIP) of the DUT was extracted with spatial and voltage resolutions of 5 cm and $80~ {\mu V}$ , respectively. These results demonstrate the feasibility of using the prototypical JAPC-based iTDR for real-world waveguide characterization applications. [ABSTRACT FROM AUTHOR]

We report on time–frequency analysis (TFA) of dispersion in a 1-D magneto-inductive waveguide (MIW). The short-time Fourier transform (STFT) and Wigner–Ville distribution (WVD) are used to localize the frequency content of the dispersed wave as a function of time and to estimate the group velocity in experiments using a 1-D MIW constructed with planar resonators. Time-domain reflectometry (TDR) measurements are performed after deliberately introducing defects along the waveguide; and the results are analyzed with TFA, demonstrating the potential for using such MIW-TDR configurations as sensors. The WVD-TFA is shown to provide precise time–frequency information, accurate defect localization, and group velocity estimation, confirming the slow wave long-range nature of dispersive MIWs. The adaptability of the MIW-TDR setup and the accuracy of the WVD for localization make the technique a suitable candidate for sensing applications using engineered dispersive media. [ABSTRACT FROM AUTHOR]

Subsurface geophysical investigations have the potential of providing information for the long-term monitoring of geotechnical assets. This research evaluates the suitability of vertically and horizontally orientated, embedded time-domain reflectometry (TDR) measurements for monitoring of near-saturated, fine-grained soils under vertical loading conditions. TDR measurements were carried out regularly during vertical loading and unloading of near- and fully-saturated soil mixtures containing fine sand, kaolinite, and bentonite. The results show that TDR probe orientation, in relation to the load direction, affects the values of TDR measured apparent permittivity (AP) and bulk electrical conductivity (BEC). The relationship between the soil void ratio and AP was found to be clearer when measured in the direction of loading, whereas AP and BEC, measured normal to the load application, appears to reflect changes in pore water pressure. BEC was found to be more variable and less obvious. It is concluded that monitoring relative changes in temporal AP and BEC using embedded TDR sensors can provide unique and valuable information on how a soil responds to loading under near-saturated conditions. [ABSTRACT FROM AUTHOR]

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.

This paper proposes a new method to comprehensively predict the passive intermodulation (PIM) distortion in loose contact coaxial connectors by the time-domain reflectometry (TDR) test. The proposed approach treats the insulating film current and the electrothermal (ET) coupling as PIM sources. An ET coupling model is introduced to analyze the generating process of the PIM caused by the ET coupling in the loose contact coaxial connectors. The simulation and measurement results show good agreement. The proposed method is a cost-effective approach for the evaluation of the PIM distortion, because it uses a common TDR method to replace professional PIM test instruments. The proposed method can also be extended to all the loose metallic contact cases. [ABSTRACT FROM AUTHOR]

Insulated power cables are becoming increasingly popular in today’s developing distribution and transportion 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. [ABSTRACT FROM AUTHOR]

The phenomenon of backscattering in copper cables has been recently observed and initially explicated. It can provide promising techniques to address the problem of loop diagnostic and maintenance. The backscattering is analyzed both in frequency and time domains. To demonstrate the practical use of the phenomenon, we estimate certain properties of the loop using wideband, high-frequency $S_{11}(f)$ measurements performed in the laboratory on real cables. The results corroborate the usefulness and accuracy of the investigated method. [ABSTRACT FROM AUTHOR]

Most dielectric spectroscopy techniques require careful system calibration, tedious measurement, specially designed probes, precise input source, and some even involved complicated inversion models. This paper proposed a rapid, robust, and model-free multiple reflection analysis (MRA) of time-domain reflectometry (TDR) signals to measure the complex dielectric permittivity (CDP) spectrum. The key to MRA approach is to decompose the first top reflection and the subsequent multiple reflections from TDR signal and to compare their spectral ratio (MRA ratio). This ratio was theoretically derived from the transmission line theory and found to be independent of source function and impedance mismatches in the leading sections. Based on this theoretical formulation, the CDP spectrum can be uniquely inverted from the measured MRA ratio through optimization and an iterated initial guess method. Numerical evaluations and experimental verifications had proven that MRA is a reliable algorithm for measuring CDP spectrum covering 10 MHz–1 GHz. Factors influencing the reliable frequency region were discussed and recommendations on enhancing CDP measurement was proposed for highly dispersive materials. The MRA approach enables dielectric spectroscopy to be conveniently conducted in both laboratory and field, without complicated system setup and calibration. [ABSTRACT FROM AUTHOR]

A full-rate parallel pseudo random bit sequence (PRBS)-9 is systematically designed in the IBM 130-nm six-level metalization SiGe BiCMOS process with 2.5/3.3-V dual power supplies for the application of testing high-speed interconnects. The PRBS length and the phase difference between channels are studied using the methods of autocorrelation and cross correlation, respectively. The parallel PRBS streams can be used as stimuli for a serializer, and the autocorrelation method can be applied as a PRBS checker. It can also be used as stimuli for a four-level pulse amplitude modulation-4 signaling format transmitter with the least correlation between the LSB and the MSB by choosing the appropriate channel combinations. Two prototype boards are designed to test the PRBS along with an on-chip type-II third-order charge-pump phase-locked loop. Signal integrity issues are investigated. Finally, the PRBS has been demonstrated at board level with nonreturn-to-zero format operating at more than 10 Gb/s. [ABSTRACT FROM AUTHOR]

The development of the communication networks tends gradually toward exploiting higher frequencies, sometimes even reaching the lowest microwave band (P-band). As the signal bandwidth used for transmission over twisted-pairs increases, as recommended by G.fast and other broadband systems, new phenomenon was observed, namely, backscattering. Motivated by the measurements of copper cables in frequency band up to 400 MHz, we propose a novel backscattering model. It may be productively applied to the problem of loop diagnostics. The methods to accurately and reliable determine the relevant transmission-line parameters are sine qua non condition to appropriately exploit the potential of short-to-medium range access lines. In this paper, a recursive formulation of the frequency-domain response of the backscattering is used for a space–time characterization. To confirm the practical use of the finding, we evaluate the properties of a loop using wideband, high-frequency $S_{11}$ measurements of the real cables. These laboratory results confirm the effectiveness and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

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&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.

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–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.

Time-domain reflectometry (TDR) has been a powerful tool for measuring soil dielectric properties. Initiating from apparent dielectric constant ( K a ) measurement up until apparent and complex dielectric spectroscopies, the embedded information in the TDR signal can be extracted to inspire our understanding of the underlying dielectric behaviors. Multiple full waveform inversion techniques have been developed to extract complex dielectric permittivity (CDP) spectrum, but most of them involved prior knowledge of input function and tedious calibration. This rendered the field dielectric spectroscopy challenging and expensive to conduct. Dual reflection analysis (DRA) is proposed in this study to measure CDP spectrum from 10 MHz to 1 GHz. DRA is a simple, robust, model-free, and source-function free algorithm which requires minimal calibration effort. The theoretical framework of DRA is established and the necessary signal processing procedures are elaborated in this study. Eight materials with different dielectric characteristics are selected to evaluate DRA’s performance, by using both simulated and experimental signals. DRA is capable of measuring non-dispersive materials very well, whereas dispersive materials require the assistance of a long-time-window (LTW) extraction method to further extend the effective bandwidth. The DRA approach is suitable for field applications that can only record a limited amount of data points and in-situ dielectric spectroscopy.

In this paper, a novel planar microwave sensor for nondestructive measurement of strain during testing of printed circuit board (PCBs) is proposed. Planar microstrip patch bridged on both sides with squared split ring resonator is used to measure strain. Measurement of stress of isotropic dielectric materials in their linear elastic region that are uses as PCB substrates is also done using the proposed method. The designed microwave probe works at a frequency of 2.45 GHz. The feasibility of the use of time-domain reflectometry method to monitor strain in materials is presented here. The proposed sensor exhibits a sensitivity of about 333 ps for every 1% change in strain. Finite integration technique and real-time measurements have been done to corroborate the relation derived between the transmit time and the strain experienced by the material. The correlation between the simulated and measured strain is about 99.3%. The proposed sensor can be used for faster and accurate testing of PCB substrates without requiring complex calibrations. [ABSTRACT FROM PUBLISHER]

Dielectric relaxation studies of vegetable oils are important for insights into their hydrogen bonding and intermolecular dynamics. The dielectric relaxation and thermo physical properties of triglycerides present in some vegetable oils have been measured over the frequency range of 10 MHz to 7 GHz in the temperature region 25 to 10 °C using a time-domain reflectometry approach. The frequency and temperature dependence of dielectric constants and dielectric loss factors were determined for coconut, peanut, soya bean, sunflower, palm, and olive oils. The dielectric permittivity spectra for each of the studied vegetable oils are explained using the Debye model with their complex dielectric permittivity analyzed using the Havriliak-Negami equation. The dielectric parameters static permittivity ( ε ), high-frequency limiting static permittivity ( ε ), average relaxation time ( τ ), and thermodynamic parameters such as free energy (∆ F ), enthalpy (∆ H ), and entropy of activation (∆ S ) were also measured. Calculation and analysis of these thermodynamic parameters agrees with the determined dielectric parameters, giving insights into the temperature dependence of the molecular dynamics of these systems. [ABSTRACT FROM AUTHOR]

Vlhkost hlinité černozemní půdy na karbonátovém sprašovém substrátu byla měřena metodou TDR čidly Aqua-Tel-TDR (Automata, Inc., dnes McCrometer CONNECT). Čidla, obalená před osazením pastou z místní zeminy a vody, byla instalována vodorovně do předvrtaných otvorů. Systematická chyba způsobená nedokonale zaplněnými mezerami mezi čidlem a stěnou otvoru byla zmenšena terénní kalibrací. Tytéž mezery umožnily indikovat preferenční proudění v půdních makropórech, díky němuž byla reflektometrická měření citelně vyšší než analogické hodnoty před průsakovou epizodou a někdy i vyšší než pórovitost původní půdy. Je demonstrována jedna typická epizoda. Lze předpokládat, že čidla tohoto typu mohou být použita k semikvantitativnímu odhadu hustoty preferenčního toku, např. za pomoci modelů dvojného nebo vícenásobného pórovitého prostředí nebo teorie rozptylu hybnosti.

The aim of this paper is to clarify some important aspects associated with the possibility to detect degraded compression and bolted joints in power transmission lines using a time-domain reflectometry (TDR)-based remote monitoring. The optimization of a TDR-based remote monitoring method is discussed, studying the effects of the source impedance, source-to-line connection, line characteristic impedance, and scope settings, providing useful guidelines for a future method and instrumentation refinement. The experimental results are presented consisting in the inclusion of lumped resistors of several values along a 130-kV power transmission line. The minimum detectable resistance is discussed based on the present available hardware. The TDR-based method is shown to be able to also identify the main features of the line layout such as phase transpositions and different heights of adjacent towers. This paper represents a preliminary base to keep developing the proposed method, with the aim to overcome the actual limitations (costs, reliability, etc.) in power line monitoring. [ABSTRACT FROM AUTHOR]

This paper introduces models of the time-domain echoes generated by faults in transmission lines excited by test signals, e.g., as in applications of time-domain reflectometry (TDR). Faults considered here include local modifications of the propagation characteristics of a transmission line. It is shown that the responses of faults are strongly dispersive in nature, which implies that the peak of their echo is far from providing an accurate measure of the severity of the fault, as it heavily depends on the frequency content of the test signal as well as on the length of the fault. It is argued that fault detection in transmission lines is an ill-posed problem that requires a priori knowledge on the fault itself. These results are important for applications of TDR methods, particularly for early warning monitoring of potentially critical faults from their onset, since it is shown that echoes from faults tested at relatively low frequencies can lead to underestimate their actual severity. [ABSTRACT FROM PUBLISHER]

Precise measurements of the downward movement of precipitation through the unsaturated zone, as well as return flow of moisture to the atmosphere via evaporation, have always been challenging in regard to in-situ monitoring techniques. This study investigates the profile of volumetric water-content fluctuations within the unsaturated zone through a combination of field techniques, including in-situ measurements of the volumetric porewater content at different depths using specially designed time-domain reflectometry (TDR) probes. The probes are installed through direct-push vibro-coring methods, at significant depths within the unsaturated zone, providing continuous readings of the soil-moisture content throughout the unsaturated column. The measured waveform is analyzed by using the inverse modeling approach resulting in an apparent relative dielectric permittivity profile of the surrounding medium along the TDR probe length. The approach sufficiently analyzes the mechanisms of water fluxes through significant depths within the unsaturated zone, which in turn can be used to quantify groundwater recharge at areas where the unsaturated zone hydrology plays a key role in the recharge of the underlying aquifers (such as arid and hydrologically sensitive areas). The approach was applied at an experimental field site in the Upper Rhine Valley, Germany. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The time-domain reflectometry technique can characterize both the position and the nature of any discontinuity in the circuits, but as far as complex circuits are concerned, the technique faces limitations. In this letter, separation, position extraction, and nature of multiple close discontinuities in ultra wide-band (UWB) Microwave/mm-wave circuits are investigated and improved using a new technique based on Gaussian modulated ultra short pulse and a useful new algorithm. It is shown that this technique can improve the discontinuities separation, by at least 70%. Also, through the simulation and measurement results of a designed complex UWB power divider and analyzing the reflected signal, ability to this technique (by using a new algorithm) in discontinuity analysis, extraction of reflection positions and separation of discontinuities, with an error less than 4%, is verified. Furthermore, designers can analyze the reflection coefficient from individual discontinuities and reflections in complex Microwave/mm-wave circuits to improve the total circuits’ results. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

The performance of high-frequency ground-penetrating radar (GPR) for high-resolution imaging of the near surface can essentially be controlled by the soil electromagnetic (EM) properties. One of these properties influencing sensing depth and image resolution of GPR is the intrinsic attenuation. We investigated the frequency-dependent electrical and dielectric properties of a broad range of soil samples. In order to derive the effective complex dielectric permittivity between 1 MHz and 10 GHz, we applied the coaxial transmission line (CTL) technique. A generalized dielectric response model, consisting of one Debye and one Cole-Cole type relaxation and a constant low-frequency conductivity term was used to analyze the dielectric relaxation behavior. Splitting the spectra into individual loss processes shows that dielectric relaxation mechanisms play a crucial role in most natural soils. Especially for high-frequency applications, attenuation cannot be described by a dielectric constant and dc-conductivity alone. Therefore, a simple conductivity-attenuation relation without dielectric losses can highly overestimate the GPR performance. As an alternative to the CTL technique in the lab, we suggest to use time-domain reflectometry (TDR) for the in Situ assessment of high-frequency electrical properties and deduced prediction of GPR performance. [ABSTRACT FROM PUBLISHER]

The development of a one-port laser-based vector network analyzer (VNA) is described. Measurements are carried out in the time domain using a femtosecond laser for the generation and detection of ultrashort voltage pulses on a coplanar waveguide (CPW). The accurate separation of voltage signals propagating in forward and backward directions, being one of the key tasks of vector network analysis, is achieved by measuring voltage pulses at different positions on the CPW. This separation technique even works in the case of temporally overlapping forward and backward propagating signals. With this laser-based VNA, a frequency spacing of 500 MHz, a measurement bandwidth of approximately 500 GHz, and a dynamic range of more than 40 dB are obtained. As an application example, the laser-based VNA is used to realize an ultra-broadband voltage pulse standard. [ABSTRACT FROM PUBLISHER]

This paper focuses on the synthesis of ultralow-noise signals for the use in a timebase of impulse radar systems. These systems are used in manifold applications and their accuracy is strongly dependent on the spectral purity of the timebase. Current systems use either phase-locked loops (PLLs) or direct digital synthesizers (DDSs). These PLLs comprise an excessive amount of components and recent DDSs still have a low spurious-free dynamic range (SFDR). Therefore, this paper presents two new approaches for the direct synthesis. They are based on frequency dividers with both short division factor sequences and noise-shaping techniques. Ideas for spur avoidance and noise reduction are described to improve the noise behavior in terms of SFDR and phase noise. The presented approaches have been realized in hardware and measurement results are depicted. For the system using frequency dividers with short division factor sequences, the best results are a SFDR better than 117 dB at a signal frequency of 10.7 MHz. The phase noise level is below −140 dBc/Hz at offset frequencies greater than 1 kHz. Regarding the frequency dividers with noise-shaping techniques, no discrete spurious are visible. The phase noise level at offset frequencies greater than 7 kHz is below −150 dBc/Hz. These results are comparable with state-of-the-art PLL concepts and thus confirm the approaches. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

A time-domain transmission measurement technique for extracting the complex propagation constant of a cross-linked polyethylene cable is proposed. For this extraction, a pulse transmitted through the cable is measured in the time domain and analyzed in the frequency domain. The proposed technique does not use an open termination for reflection, and therefore increases the upper frequency of the bandwidth for extraction; by reducing the pulse width, it decreases the measurement error as compared with an existing time-domain reflectometry method. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to improve the management of cables that need much time and work in the measurement environment that has many multichannel cables. Therefore, a monitoring system that inspects faults and connection states of multichannel cables is suggested and designed. The system is based on time-domain reflectometry (TDR) and has two features that distinguish it from the precedent researches. One of them is a hardware interface for the multipair cable, which is a channel distributor designed using a switch. The other is the TDR-signal analysis algorithm based on the database. In other words, the system can check a number of signal wires included in a multichannel cable automatically with one step. In addition, it is able to show results of the signal analysis immediately. The performance of such a system is verified through tests. As a result, it is shown that the monitoring system is fast and reliable and it provides a reasonable analysis result on the TDR signal. [ABSTRACT FROM PUBLISHER]

By a modeling technique of equivalent lumped circuit for high-speed interconnections, an innovative method is proposed to predict the physical intrinsic eye diagram. Such a technique is based on the measured impedance profile results of time-domain reflectometry, which includes the electric characteristics both of the connector itself and testing jigs. The latter's are to be removed to leave the connector's part only for the eye diagram prediction. This method can be verified further by SPICE simulation and measurement in this paper. [ABSTRACT FROM AUTHOR]

Time-domain reflectometry (TDR) is a well-known measurement principle for evaluating frequency-dependent electric and dielectric properties of various materials and substances. Although TDR is a proven method, the high price for TDR measurement equipment and complex laboratory setups is often a limiting factor for cost-sensitive applications or large-scale field experiments, where a large number of TDR meters is required. This paper reports on the development of a new miniaturized low-cost TDR meter capable of sampling a repetitive rectangular waveform, which is used as an excitation signal. The developed sampling circuit is based on a digital delta modulator (DM) and allows for capturing the waveform of a repetitive measurement signal. A 1-MHz signal can be captured with a virtual sampling resolution of 1 ps within a measurement interval of 1 s. The generated pulses have a rise time of 2 ns and can be captured with an amplitude resolution of approximately 10 bit and an accuracy of approximately 8 bit. The developed digital DM architecture is implemented inside a small field programmable gate array and integrated into a miniaturized low-power TDR meter prototype for battery-powered outdoor applications. The captured measurement data are stored on integrated micro-SD card memory and can be read out either via a Universal Serial Bus, an RS-485 bus system, or a wireless interface. The TDR meter is controlled by an integrated microcontroller and a real-time clock and therefore can operate completely independent from any additional control setup. The TDR meter targets applications within the field of geoscience and agricultural monitoring, where large-scale measurement systems are required. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

The measurement of circuit parasitic parameters and the evaluation of equivalent circuit models are both necessary techniques for noise analysis and the circuit design of high-speed power electronics circuits. Recently, time-domain reflectometry (TDR) has emerged as a technique for measuring circuit parameters. This paper proposes a TDR method for measuring the voltage- dependent capacitance of power devices and passive components. This method can be used to measure the capacitance on any dc bias voltage. The Coss value of MOSFETs with VDS = 0-350 V, the anode-cathode capacitance under reverse bias condition on SiC diodes, and voltage-dependent capacitances of ceramic capacitors were measured in experiments. [ABSTRACT FROM AUTHOR]