Impedance Discontinuities Research Articles

Overvoltage phenomenon initiated by breakdown during on-site withstand voltage tests of GIL and GIS: Mechanisms and consequences

An overvoltage was observed in the withstand voltage tests of GIL and GIS projects in China in recent years. The overvoltage may result in insulation damage and secondary breakdown where there is no defect. The analysis shows that the reason for the overvoltage is the wave impedance discontinuity between the pipeline and the overhead line. It results in the superposition of the reflected and refracted waves, and thus the overvoltage is generated. In fact, in addition to the structural change, the branches in the structure can also form wave impedance discontinuities. For example, unlike GIL, there are many branches in GIS that can also cause the overvoltage. The overvoltage is actually a universal phenomenon. The analyses based on an actual GIS structure show that in on-site withstand voltage tests, the overvoltage may exceed the peak value of the rated lighting impulse voltage, and even the insulation limits of GIS. These analyses are verified by simulation and experiment results. This universal phenomenon seriously endangers the safety of GIL and GIS during the withstand voltage test, because of the possible secondary breakdowns. The GIS will even become more vulnerable. Therefore, the on-site test structures or voltages should be revisited.© 2017 Elsevier Inc. All rights reserved.

Optimization design of the cavity tuning and RF input coupler for an 11 MeV superconducting cyclotron

This study addresses the compact design requirements for a 11 MeV superconducting cyclotron utilized in isotope production by proposing a design and optimization scheme for a radio frequency (RF) input coupling system. The system, comprising a coupler loop, transmission lines, and RF window, has been tailored to accommodate the spatial constraints imposed by the super conducting magnet radius, thereby facilitating efficient RF power transfer to the RF cavity and minimizing input power. Structural optimization of the coupler loop and RF window has achieved S11 parameter of -82.23 dB, significantly reducing input power while maintaining high coupling efficiency. A coaxial coupler suitable for lower frequency ranges has been designed, employing a tapered structure for the transmission line to ensure a smooth transition to reduce impedance discontinuity effects and enhance adjustability. The multi-stage design of the RF window has achieved fine impedance matching, significantly lowering the S11 parameter. In response to frequency drift caused by RF loss and temperature increase, the study utilizes perturbation theory to analyze the perturbation effect of coupling components on the resonant frequency, designing an adjustable structure with both coarse and precise tuning capabilities, realizing tuning precision at the kHz/mm level and a tuning range of several MHz. A conjectural formula has been proposed based on the impact of the tuner's structural parameters on the resonant frequency, accurately calculating the equivalent inductance of the tuner and the resonant frequency of the RF cavity post-tuner installation, with the maximum estimation error of the resonant frequency kept within 0.1%, offering significant guidance for engineering design.

Unveiling the Sub-10 GHz Performance of SMA Connectors: A Comparative Analysis

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.

A Study on Fault Localization Method of Three-Terminal Multi-Section Overhead Line–Cable Hybrid Line Using MEEMD Combined with Teager Energy Operator Algorithm

An improved fault localization method combining total aggregate empirical modal decomposition (MEEMD) and Teager energy operator (TEO) is proposed to address the fault localization issue of three-terminal multi-segment overhead line–cable hybrid transmission lines. This method solves the fault localization problem caused by wave impedance discontinuity in hybrid lines. First, the MEEMD algorithm, which improves modal aliasing, and the Teager energy operator, which reflects transient energy changes, are combined for the accurate detection of faulty traveling wave heads. The fault line section determination condition within the fault branch is used to determine the overhead line section or cable section where the fault is located after determining the faulty branch line. This condition is based on the time difference between the initial traveling wave of the fault arriving at each end measurement point and the T-node. Ultimately, the fault distance is determined using the double-ended traveling wave technique. By combining PSCAD and MATLAB for simulation verification, the accuracy of the ranging method is compared and analyzed, and the results show that the method is able to ensure the accuracy of ranging at different fault locations and transition resistances. Additionally, the localization error is basically kept within 30 m, which significantly improves the accuracy of fault localization.

Electromagnetic fields of lightning return stroke to wind turbines with discontinuous impedance model

This study introduces an electric field calculation model for wind turbine return strokes, incorporating impedance discontinuity within the turbine, a feature not considered in traditional tall tower models. The model introduces a reflection coefficient, ρx, at the connection between the blades and the tower. Disregarding the generation of upward leaders, this paper calculates the electric field of subsequent return strokes for different distances from the wind turbine and for different model parameters. The results demonstrate that changes in the reflection coefficient ρx affect oscillation amplitude and also slightly influence the pulse width, with a negative ρx leading to smaller and more frequent pulses. Contrasts with measured waveforms indicate that models with a constant reflection coefficient are inaccurate. Adopting variable reflection coefficient values yields a more accurate match. This approach offers a new perspective for electromagnetic field calculations in lightning-struck structures, emphasizing the significance of impedance dynamics of return stroke channel.

Uncertainty propagation for microwave scattering parameter measurements subject to time-domain and time-gating transformations

Analysis of the scattering (S-)parameters of devices and materials often involves the inspection of a particular interface or feature. Time-gating functions offered by vector network analysers have routinely been used to gate S-parameters in the time-domain to separate the device or material interface from other physical features of the network. To date, explicit uncertainty propagation through this process has not been demonstrated. PyDynamic, a Python software package, has been developed to explicitly propagate uncertainty between domains (i.e., frequency and time) and through the gating process. This paper presents the application of PyDynamic to S-parameter measurements of a coaxial device, namely a Beatty line, where the analysis presents results in the transformed time-domain and time-gated frequency-domain with uncertainties. In this demonstration, following time-gating of a Beatty line impedance discontinuity, the time-gated and transformed reflection S-parameters show a reduction in uncertainty from up to approximately 0.0025 U linear magnitude and up to 5 degrees in phase to less than 0.0005 U linear magnitude and 0.2 degrees in phase.

Leak detection in an operational underground water distribution network using active acoustics

Leaks present in the water distribution networks (WDNs) lead to an enormous loss of a valuable resource, not only affecting the economic efficiency of water utilities but also posing significant potential safety hazards, and an increased burden on infrastructure maintenance. In the past, several studies have focused on passive acoustic-based leak detection by primarily sensing and analyzing the acoustic signals emitted from the leak source. In this study, we installed a low-frequency transducer in the water column of an operational WDN near Los Angeles, California, and excited the system using steady-state sinusoidal and sine burst signals. The acoustic pressure signals inside the pipe network were measured at multiple locations using state-of-the-art hydrophone-enabled devices retrofitted to fire hydrants. The experiments were conducted in the presence of a simulated leak in the network. The leak acts as an impedance discontinuity for the acoustic wave propagation, and therefore, the excited signals undergo partial reflection at the leak location. Based on signal processing techniques, we attempt to detect and localize the leaks in the WDN. The goal of using the active acoustics is to detect small leaks and increase the range of sensing.

Applying Characteristic Impedance Compensation Cut-Outs to Full Radio Frequency Chains in Multi-Layer Printed Circuit Board Designs.

Modern wireless communication systems are of utmost importance to various sectors such as healthcare, education, the household, and the advancement of emerging technologies like the internet of things, autonomous vehicles, and the enhancement of 5G. Further development and improvement of these systems drives the need for small dimension, high integration and density, and cost-effective electronic devices. Achieving optimal performance in wireless electronic devices involves overcoming engineering challenges related to microstrip line signal integrity. This research addresses the impact of surface mount technology (SMT) component pads on signal integrity, proposing a novel high-frequency microstrip line structure for mitigating impedance discontinuities. The study introduces stepped microstrip lines and explores characteristic impedance compensation techniques. A six-layer printed circuit board (PCB) structure is presented, and the effects of compensation on signal integrity are analyzed using time-domain reflectometry and scattering parameter measurements. The results demonstrate the effectiveness of compensation methods in aligning characteristic impedance with desired values, thereby ensuring improved impedance matching and transmission coefficients. The average over-the-length impedance for the proposed structure with compensation applied was measured to be 52.7 Ω, which is only 1.3 Ω (2.5%) more than that of the reference microstrip. Applying reference plane cut-outs leads to a maximum compensated absolute value of more than 30 Ω to reach the target impedance with a 10% tolerance. This research contributes valuable insights for advancing wireless communication systems and maintaining robustness in high-frequency microstrip transmission lines.

Trifurcated lined ducts: A comprehensive study on noise reduction strategies.

The present research is centered on analyzing and modeling the scattering characteristics of a trifurcated waveguide that includes impedance discontinuities. A mode-matching method, grounded in projecting the solution onto orthogonal basis functions, is devised for the investigation. The impedance disparities at the interfaces are represented in normal velocity modes, which, when combined with pressure modes, result in a linear algebraic system. This system is subsequently truncated and inverted for numerical experimentation. The convergence of scattering amplitudes is assured by reconstructing matching conditions and adhering to conservation laws. The computational results indicate that optimizing attenuation behavior is achievable through manipulating variation bounding properties and impedance discontinuities.

An Improved 1X De-Embedding Method for Fixtures With Impedance Discontinuities

An Improved 1X De-Embedding Method for Fixtures With Impedance Discontinuities

A New Insight on the "S" Shape Pattern of Soft Faults in Time-Domain Reflectometry.

This paper proposes a new interpretation of the commonly observed, very specific, time-domain response associated with a soft defect in an electrical line under test using time-domain reflectometry. The reflectometry reveals the nature of a defect by analyzing the reflections undergone by an injected pulse at the impedance discontinuities present on the line. The faulty section considered in this work is modeled as a local modification of the characteristic impedance. Using the developed model, we explain how, depending on the physical and electrical characteristics of the faulty section, the associated signature yields a very specific "S"-shaped pattern. The influence of the probing signal is also investigated. Finally, it is shown that the amplitude of the reflected signal cannot be interpreted straightforwardly as a mirror of the severity of the defect and that consequently, small echoes can mask more significant defects.

Dual-band Via-less Band-pass Filter Based on Cascaded Closed Ring Resonator

A band-pass filter (BPF) is an essential part of a wireless communication system as it functions to reduce interference and noise. Many structures have been proposed to achieve a high-quality BPF. Typically, these structures utilize vias. However, vias has several drawbacks, including impedance discontinuities, increased resistance values, and complex structures. In this study, we propose a dual-band BPF based on a cascaded closed ring resonator (CCRR) without using vias. Specifically, the proposed structure consists of multiple CCRRs connected at the corner pattern and incorporates capacitive coupling to the input impedance. Additionally, the CCRR configuration has dual sizing to achieve dual-band performance. Subsequently, the proposed BPF is simulated and fabricated using Duroid Rogers RT 5880 with dielectric constant εr = 2.2, dissipation factor tan δ = 0.0009, and thickness h = 1.575 mm. The measurement results demonstrated that the dual-band BPF operated at a resonant frequency of 2.50 GHz with a transmission coefficient (S21) value of -2.18 dB in the first band. In the second band, a resonant frequency of 3.70 GHz was obtained with an S21 value of -1.43 dB. The bandwidth in the first band was 160 MHz, and in the second band, it was 110 MHz. Moreover, based on the measurement results, the reflection coefficient (S11) in the first band was -11.05 dB, while in the second band, it was -23.3 dB. The excellent agreement between the simulation and measurement validates the proposed method.

Thinned array ultrasonic imaging of debonding defects in discontinuous impedance bonded structures

Ballastless track is a typical bonding structure with discontinuous impedance. Under the influence of heavy load, deteriorating environment and other situations, the circumstance of debonding occurs frequently and seriously affects the safety of train operation. In this work, a high-precision array ultrasound fast imaging method is proposed. Based on the propagation path and time of sound wave in the medium obtained by ray tracing method, a theoretical model of sound velocity of discontinuous impedance bonding structure is established when the difference in sound velocity among dielectric layers is taken into account. High degree of freedom sparse array based on real number coding as well as synthetic aperture focusing technology (SAFT) imaging method is used to improve detection efficiency. The results of the experiments carried out on ballast less track structure are shown below. The ray tracing method can accurately calculate the propagation path and propagation time of ultrasonic wave and improve the detection accuracy. The optimized thinned array pattern has narrowed the main lobe width and low side lobe gain, which improves the detection efficiency and sound field directivity. The efficiency of thinned array SAFT imaging method is improved by 30.9% when the imaging error of debonding defects is within ±5%, which provides a theoretical support fordetecting such debonding defects.

Crosstalk Analysis of Printed Circuit Board Traces With Right-Angled Bent Corners via Time Domain Hybrid Method

Discontinuous impedance exists when bent corners are introduced into the traces of printed circuit board (PCB). By combining transmission line (TL) equations, higher order finite-difference time-domain (FDTD) method, state variable method, and Norton's theorem, an efficient time domain hybrid method is proposed to realize the fast crosstalk simulation of the traces with right-angled bent corners (RABCs) in this work. First, the whole structure of the traces is decomposed into a cascade network, which consists of multiple equal length parallel microstrip lines (EL-PMSLs) and the RABC structures. Then, the crosstalk responses on these EL-PMSLs can be quickly solved by applying TL equations combined with the higher order FDTD method. With the application of Norton's theorem, the equivalent circuit model of whole PCB traces is constructed. Finally, the equivalent circuits of the RABC structures are extracted, and the port voltages of these RABCs are calculated via state variable method and fed back to these EL-PMSLs as boundaries, thus the round-trip transmission of interference signals on the PCB traces is realized. Numerous crosstalk simulations of PCB traces with typical RABC structures, as well as extracted from a practical PCB, are presented and compared with the results of commercial software CST to verify the correctness and efficiency of the proposed method.

Multi-Mode Excitation by Interleaved EBG Structure for Suppression of Power/Ground Noise in Multi-Layer PCBs

Signal line transition with layer transition via is inevitable in multi-layer PCB. The return current can generate voltage noise between the cavities due to the discontinuity of the return current path. Other layer transition vias passing through the cavity can pick up the voltage noise and result in problems of signal integrity. In this paper, an electromagnetic bandgap (EBG) structure is proposed for suppression of the broadband cavity noise. The impedance discontinuity between layers of interleaved EBG cell enhances the efficiency of noise suppression, and the slots embedded in the EBG cell excite multi-mode resonances for extending the bandwidth of noise suppression. The dispersion diagram is utilized to preliminarily analyze the characteristic of the proposed EBG cell, and a 5×5 cells EBG board is further analyzed for characterizing the efficiency of noise suppression. Both simulation and measurement results prove the proposed structure can effectively suppress the cavity noise under −35 dB over the frequency range from 0.56 GHz to the highest measurement frequency, 20 GHz.

Constant intensity acoustic propagation in the presence of non-uniform properties and impedance discontinuities: Hermitian and non-Hermitian solutions.

Propagation of sound through a non-uniform medium without scattering is possible, in principle, if the density and acoustic compressibility assume complex values, requiring passive and active mechanisms, also known as Hermitian and non-Hermitian solutions, respectively. Two types of constant intensity wave conditions are identified: in the first, the propagating acoustic pressure has constant amplitude, while in the second, the energy flux remains constant. The fundamental problem of transmission across an impedance discontinuity without reflection or energy loss is solved using a combination of monopole and dipole resonators in parallel. The solution depends on an arbitrary phase angle that can be chosen to give a unique acoustic metamaterial with both resonators undamped and passive, requiring purely Hermitian acoustic elements. For other phase angles, one of the two elements must be active and the other passive, resulting in a gain/loss non-Hermitian system. These results prove that uni-directional and reciprocal transmission through a slab separating two half spaces is possible using passive Hermitian acoustic elements without the need to resort to active gain/loss energetic mechanisms.

Application of the finite element method to atmospheric sound propagation over impedance discontinuities

Outdoor noise propagation typically involves the propagation of sound over mixed ground conditions, including variations in the surface impedance. Diffraction occurs at the interface between different ground conditions, and this can significantly affect local sound attenuation. Popular approaches to modelling impedance discontinuities include the boundary integral method, parabolic equations, and semi-empirical methods. This paper presents an alternative approach that takes advantage of the generality of the finite element method. It was shown recently that the semi analytic finite element method can be used to solve the exact governing wave equation for atmospheric sound propagation in a complex vertically stratified medium. This allows for the inclusion of arbitrary temperature and wind profiles provided the problem is range independent. It is shown here that it is relatively straightforward to extend this approach to include multiple surface impedance discontinuities, provided each discrete surface is uniform in the axial direction. This is achieved using point collocation to enforce the axial boundary conditions over each discontinuity. Predictions are generated for single and multiple discontinuities, and comparisons are made against predictions obtained using other computational methods.

Effect of Impedance Discontinuity Induced by Line Bending on Passive Intermodulation in Connector-Microstrip Assemblies

Scattering parameters (S-parameters) and passive intermodulation (PIM) characterize the signal integrity for small signal excitation and nonlinearity for high-power excitation. In this letter, a model that relates the S-parameters and PIM is theoretically proposed and experimentally verified. A simplified PIM model is presented to investigate the effect of impedance mismatch between two nonlinear points on the reflected intermodulation (IM) powers. Considering the impedance discontinuity induced by line bending, the impact of different bending angles on transmission phase and signal reflection is simulated. Through the combination of S-parameter modeling and passive nonlinear transfer functions, an equivalent circuit is developed to simulate the IM3 powers resulting from connector–microstrip assemblies with different line bending angles. In addition, a series of PIM tests are conducted with customized samples. Experimental results are consistent with the predictions, showing the effect of the scattering characteristics on the PIM.

Feasibility of soil erosion measurement using time domain reflectometry

Scientific research and control technology of soil erosion both rely on accurate and efficient soil erosion measurements. Based on the principles of locating interfaces in layered media and measuring dielectric properties by time domain reflectometry (TDR), we developed TDR-based measurement of changes in the air–soil interface along the TDR probe for soil erosion measurement, and simultaneously measuring volumetric soil moisture content (θv). Part of a three-rod TDR probe was inserted in the soil and the rest exposed to air, so changes in the air–soil interface could be denoted by changes in the length of exposed probe (Lair). TDR waveforms were analyzed using a combination of tangent line method and second-order bounded mean oscillation methods to identify time points at positions of impedance discontinuity in electromagnetic propagation, then converting these data to Lair and θv by calibrated equations. According to the laboratory experiment using sandy loam and silt loam, Lair could be effectively measured within a wide soil moisture range by the calibrated equation and the thickness of the eroded soil layer could thus be determined. The RMSE of θv measurement ranged between 0.003 and 0.025 cm3 cm−3, which enabled the identification of the appropriate soil moisture range for measuring Lair, and achieve reliable simultaneous measurement of soil erosion and soil moisture content. The simulated rainfall experiment using sandy loam and silt loam and field scouring experiment conducted in loam also indicated that the proposed method could achieve high measurement accuracy in erosion environments, for which Lair with the RMSE from 1.8 to 2.1 mm and θv with the RMSE from 0.007 to 0.024 cm3 cm−3. The proposed method has various advantages, including versatility, minimal disturbance, easy automation of measurement at multiple positions, etc., could serve as a new technical option for soil erosion measurement, and extend the utilization of TDR.

Acoustic liners for jet-installation noise reduction

A Helmholtz resonator with a curved cavity is studied for reducing jet-installation noise in a configuration comprised by a subsonic jet and a nearby flat plate. The face-sheet and cavity are designed with the Guess method and the impedance is verified through an experiment and a simulation of an impedance tube. Both single and double degree-of-freedom liners, the latter with a perforated septum inside the cavity, are studied. A good agreement is obtained for the impedance curves from the design method and the experimental and numerical impedance tube, particularly at frequencies close to the absorption peak. Numerical simulations of the installed jet are performed with an array of resonators placed inside the plate with the face-sheet on the lower side, targeting noise reduction at a ground observer. Far-field spectra show that noise reduction in the order of 7 dB is obtained with respect to the baseline solid plate, at the resonance frequency of the single degree-of-freedom liner. Moreover, there is a broad frequency range around the resonance in which the sound pressure levels of the lined plate are lower. For the configuration with the double degree-of-freedom resonator, further noise reduction (approximately 3 dB) is obtained at higher frequencies, around the second peak in the absorption coefficient curve. The results also show that a slight noise reduction (2 - 3 dB) occurs for an observer on the shielded side of the plate, but in a significantly narrower band around the resonance frequency. This is attributed to the absorption of acoustic waves from the jet itself prior to their scattering at the trailing edge, coupled with a less abrupt impedance discontinuity at the trailing edge. Consequently, the resonators also act by reducing the strength of the acoustic source at the designed resonance frequency.