Longitudinal Impedance Research Articles

Resistive and impedimetric properties of elastic composite based on graphene and CNT under uniaxial compressive displacement

In this paper the fabrication of built–in rubber graphene and CNT based elastic composite samples under uniaxial compressive displacements is presented along with the investigation of their resistive and impedimetric properties. Thin layer structure of CNT-graphene-CNT was deposited on one side of a rectangular prism elastic rubber substrate through rubbing-in technology. The requirements of the resistance and impedances along the three orthogonal axis at the frequencies of 100Hz, 1kHz, 10kHz, 100 kHz and 200 kHz respectively were investigated from uniaxial compressive displacements that were applied in the longest axis directions of the sample. The anisotropy for the requirements of the resistance and impedances on the compressive displacements along the longest axis of the sample was also observed. The longitudinal resistance and impedance of the samples were decreased under the effect of both longitudinal compressive displacement and for the displacement in the direction perpendicular to the surface of graphene film. The longitudinal resistance and impedances increased with increase of the transverse displacement along the surface of graphene film. Influence of the uniaxial compressive displacements on the interatomic distances was investigated through XRD. Magnitude of resistance and impedances of the samples were decreased with increase of temperature and humidity.

Estimating the impedance of a synchrotron component from beam-induced power loss

A method for a first-order approximation estimation of the longitudinal impedance of a synchrotron component, starting from power loss measurements on the device, is proposed. This method also estimates the resonance frequency and the quality factor of the impedance after the execution of several machine runs, without disconnecting the device. After a detailed description of the method, its suitability is demonstrated through a practical case study using power loss measurements of the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN).

Quantification of resistive wall instability for particle accelerator machines

The aim of this study is to quantify longitudinal resistive wall impedances, corresponding wake functions, and wake potentials for different accelerator machines of interest. Accurate calculations of wake potentials by particle-in-cell codes are extremely difficult for the investigated parameters; therefore, we use an analytical approach and consider large domains with fine discretization for the required numerical integrations. The semianalytical wake potential computations are benchmarked against numerical general purpose 2D/3D Maxwell solver software codes and a different analytical approach for a certain set of parameters. We report examples to illustrate limitations of wake potential estimations from coupling impedances, and computations for the machines using realistic beam parameters and machine conditions. A numerical example where the aim is to find the wake potential of the machine from the 5$\%$ noisy impedance data is given.

New spiral beam screen design for the FCC-hh injection kicker magnet

The injection kicker system for the Future Circular Collider (FCC-hh) must satisfy demanding requirements. To achieve low pulse ripple and fast field rise and fall times, the injection system will use ferrite loaded transmission line type magnets. The beam coupling impedance of the kicker magnets is crucial, as this can be a dominant contribution to beam instabilities. In addition, interaction of the high intensity beam with the real part of the longitudinal beam coupling impedance can result in high power deposition in the ferrite yoke. This gives a significant risk that the ferrite yoke will exceed its Curie temperature: hence, a suitable beam screen will be a critical feature. In this paper, we present a novel concept - a spiral beam screen. The fundamental advantage of the new design is a significant reduction of the maximum voltage induced on the screen conductors, thus decreased probability of electrical breakdown. In addition, the longitudinal beam coupling impedance is optimized to minimize power deposition in the magnet.

HOM damping options for the Z-Pole operating scenario of FCC-ee

The Z-pole option of FCC-ee is an Ampere class machine with a beam current of 1.39 A. Due to high HOM power and strong HOM damping requirements, the present baseline of FCC-ee considers a single-cell cavity at 400 MHz. In this paper, different HOM damping schemes are compared for the Z-pole operating scenario with the aim of lowering the parasitic longitudinal and transverse impedance. The HOM power for each damping scheme is also calculated.

Design studies of a compact superconducting rf crab cavity for future colliders using Nb/Cu technology

The design of a compact crab cavity using Nb/Cu technology is presented. The cavity shape is based on a ridged waveguide resonator with wide-open apertures to provide access to the inner surface of the cavity and facilitate coating. It also provides natural damping for higher-order modes (HOMs) and comparatively low longitudinal and transverse impedances. A first prototype is being fabricated, originally within the HL-LHC framework and now for the Future Circular Collider study. The optimized shape is characterized and compared with respect to peak surface field balance, multipolar momentum components, and longitudinal and transverse impedances. Further investigations include the identification of multipacting barriers, the frequency sensitivity to pressure fluctuations in the helium bath, the radio frequency (rf) design of a fundamental mode coupler, and considerations of HOM damping. Along these topics, several methods have been established serving a wider range of applications, in particular, for the rf loss evaluation, the postprocessing of multipacting simulations, and a detailed error analysis of the pressure sensitivity simulations.

The natural matching of harmonic responses in the pulmonary circulation.

Key points The right ventricle of the mammal heart is highly sensitive to the afterload imposed by a combination of the pulmonary circulation and the retrograde contribution of the left heart.Right ventricular afterload can be analysed in terms of pulmonary artery input impedance, which we were able to decompose as the result of the harmonic frequency responses of the pulmonary vessels and the left heart attached in series.Using spectral methods, we found a natural matching between the pulmonary vasculature and the left chambers of the heart. This coupling implies that the upstream transmission of the left heart frequency‐response has favourable effects on the pulmonary tree.This physiological mechanism protects the right ventricle against acute changes in preload, and its impairment may be a relevant contribution to right ventricle dysfunction in pulmonary hypertension. The right ventricle (RV) of the mammal heart is highly sensitive to the afterload imposed by the pulmonary circulation, and the left heart (LH) retrogradely contributes significantly to this vascular load. Transmission‐line theory anticipates that the degree of matching between the frequency responses of the pulmonary vasculature and the LH should modulate the global right haemodynamic burden. We measured simultaneous high‐fidelity flow (pulmonary artery) and pressure (pulmonary artery and left atrium) in 18 healthy minipigs under acute haemodynamic interventions. From these data, we decomposed the impedance spectra of the total right‐circulation system into the impedance of the pulmonary vessels and the harmonic response of the LH. For frequencies above the first harmonic, total impedance was below the pulmonary impedance during all phases (P < 0.001; pooled phases), demonstrating a favourable effect of the LH harmonic response on RV pulsatile load: the LH harmonic response was responsible for a 20% reduction of pulse pulmonary artery pressure (P < 0.001 vs. a theoretical purely‐resistive response) and a 15% increase of pulmonary compliance (P = 0.009). This effect on compliance was highest during acute volume overload. In the normal right circulation, the longitudinal impedance of the pulmonary vasculature is matched to the harmonic response of the LH in a way that efficiently reduces the pulmonary pulsatile vascular load. This source of interaction between the right and left circulations of mammals protects the RV against excessive afterload during acute volume transients and its disruption may be an important contributor to pulmonary hypertension.

Beam-based Measurement of Broadband Longitudinal Impedance at NSLS-II

Beam-based Measurement of Broadband Longitudinal Impedance at NSLS-II

Model for the Evaluation of an Angular Slot’s Coupling Impedance

In high energy particle accelerators, a careful modeling of the electromagnetic interaction between the particle beam and the structure is essential to ensure the performance of the experiments. Particular interest arises in the presence of angular discontinuities of the structure, due to the asymmetrical behavior. In this case, semi-analytical models allow one to reduce the computational effort and to better understand the physics of the phenomena, with respect to purely numerical models. In the paper, a model for analyzing the electromagnetic interaction between a traveling charge particle and a perfectly conducting angular slot of a negligible thickness is discussed. The particle travels at a constant velocity along a straight line parallel to the axis of symmetry of the strip. The longitudinal and transverse coupling impedances are therefore evaluated for a wide range of parameters.

All-angle Brewster effect observed on a terahertz metasurface

In physics, the Brewster effect initially refers to a reflectionless transmission of a transverse-magnetic wave that impinges on an interface separating two different regular media at a particular angle, known as the Brewster angle. Nowadays, people have recognized that the Brewster effect can also be observed under transverse-electric incidences such as in magnetic media. However, all Brewster effects observed so far were associated with a unique incident angle. In this work, we demonstrate a Terahertz metasurface on which the Brewster effect can be observed at all angles of incidence. The underlying physics behind this all-angle Brewster effect is the dispersion engineered at each angle of incidence to strictly match the longitudinal wave impedance on both sides of the surface. Theoretical analysis, full-wave simulation, and experimental results are consistent with each other. The proposed approach is simple but robust and scalable to other frequencies, implying promising applications such as perfect polarizers and space phase shifters.

Remote Monitoring of Joints Status on In-Service High-Voltage Overhead Lines

This work presents the feasibility study of an on-line monitoring technique aimed to discover unwanted variations of longitudinal impedance along the line (also named “impedance discontinuities”) and, possibly, incipient faults typically occurring on high voltage power transmission lines, like those generated by oxidated midspan joints or bolted joints usually present on such lines. In this paper, the focus is placed on the application and proper customization of a technique based on the time-domain reflectometry (TDR) technique when applied to an in-service high-voltage overhead line. An extensive set of numerical simulations are provided in order to highlight the critical points of this particular application scenario, especially those that concern the modeling of both the TDR signal injection strategy and the required high-voltage coupling devices, and to plan a measurement activity. The modeling and simulation approach followed for the study of either the overhead line or the on-line TDR system is fully detailed, discussing three main strategies. Furthermore, some measurement data that were used to characterize the specific coupling device selected for this application at high frequency—that is, a capacitive voltage transformer (CVT)—are presented and discussed too. This work sets the basic concepts underlying the implementation of an on-line remote monitoring system based on reflectometric principles for in-service lines, showing how much impact is introduced by the high-voltage coupling strategy on the amplitude of the detected reflected voltage waves (also named “voltage echoes”).

Beam-induced HOM power in CEPC collider ring cavity

The power loss of cavity high-order modes (HOMs) is a key issue in Circular Electron and Positron Collider (CEPC) RF system design. A large HOM power may cause a quench of SC cavity. The purpose of this article is to study the beam-induced HOM power for CEPC collider ring. The factors influencing the cavity HOM power are also investigated. Starting with the beam filling patterns, the beam spectrums of different beam time structures are deduced. Then, the longitudinal impedance is simulated for CEPC 2-cell 650 MHz cavity. Finally, the cavity HOM power is calculated for CEPC CDR design. The cavity HOM power is 459 W for Higgs, 506 W for W and 1026 W for Z-pole. These values are smaller than the average values. There is no overlap between beam spectral lines and cavity HOM frequency. The filling patterns of CEPC CDR Higgs, W and Z are safe. The dangerous filling patterns can be identified for CEPC Z-pole by scanning different parameters.

FDM analysis on pulsatile two-phase MHD rheology of blood in tapered stenotic blood vessels

The pulsatile two-phase flow of blood in a tapered narrow artery with overlapping stenosis in the presence of magnetic field is analysed, modelling the suspension of all the erythrocytes in the inner phase region as Herschel-Bulkley fluid and the cell depleted plasma in the outer-phase region as Newtonian fluid. Explicit finite difference method is employed to obtain the numerical solution to various flow measurements from the modelled initial boundary value problem. It is found that when the magnetic field parameter increases, the velocity increases and wall shear stress and longitudinal impedance to flow increase. The estimates of the increase in the longitudinal impedance to flow for the two-phase H-B fluid model is higher than that of the single-phase H-B fluid model.

A PDMS-based broadband acoustic impedance matched material for underwater applications

Having a material that is matched in acoustic impedance with the surrounding medium is a considerable asset for many underwater acoustic applications. In this work, impedance matching is achieved by dispersing small, deeply subwavelength sized particles in a soft matrix, and the appropriate concentration is determined with the help of Coherent Potential Approximation and Waterman & Truell models. We show experimentally the validity of the models using mixtures of Polydimethylsiloxane (PDMS) and TiO2 particles. The optimized composite material has the same longitudinal acoustic impedance as water and therefore the acoustic reflection coefficient is essentially zero over a wide range of frequencies (0.5–6 MHz). PDMS-based materials can be cured in a mold to achieve desired sample shape, which makes them very easy to handle and to use. Various applications can be envisioned, such the use of impedance-matched PDMS in the design and fabrication of acoustically transparent cells for samples, perfectly matched layers for ultrasonic experiments, or superabsorbing metamaterials for water-borne acoustic waves.

Impedance evaluation of in-vacuum undulator at KEK Photon Factory

The estimate of impedance and kick factors of the recently installed at KEK Photon Factory (PF) four In-Vacuum Undulators (IVU) is currently a very important issue, because they could be considerable contributors to the total impedance of PF. Moreover, the coupling impedance of the IVUs could lead to the beam energy loss, changes in the bunch shape, betatron tune shifts and, finally, to the various beam instabilities. Using the simulation tool (CST Particle Studio), longitudinal and transverse impedances of the IVUs were evaluated and compared to analytical formulas and measurement results. The study provides a basis for the subsequent mitigation of unwanted impedance, for the accurate estimate of its effects on the beam quality and beam instabilities and also for the impedance budget of a newly designed next-generation machine which has many IVUs and small-aperture beam pipes.

Measurements of electromagnetic properties of ferrites as a function of frequency and temperature

Fast kicker magnets are used to inject beam into and extract beam out of the CERN accelerator rings. These kickers are often ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. The interaction of the beam with the resistive part of the longitudinal beam coupling impedance leads to power dissipation and heating of different elements in the accelerator ring. In particular, power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. In addition, the imaginary portion of the beam coupling impedance contributes to beam instabilities. A good knowledge of electromagnetic properties of materials up to GHz frequency range is essential for a correct impedance evaluation. This paper presents the results of transmission line measurements of complex initial permeability and permittivity for different ferrite types. We present an approach for deriving electromagnetic properties as a function of both frequency and temperature; this information is required for simulating ferrite behaviour under realistic operating conditions.

A Computerized Time Domain and Spectral Analysis System for Acoustic Characterization of Tissue Mimicking Materials

In this study, an integrated computerized system for acoustic characterization of tissue mimicking materials (TMMs) was developed. It is used to determine the longitudinal velocity and acoustic impedance of TMMs for time domain analysis and frequency dependent phase velocity and attenuation coefficient of TMMs for spectral analysis. It utilizes the pulse echo immersion technique and consists of a pulser/receiver generator, a transducer as both transmitter and receiver, a digital oscilloscope and a personal computer installed with a custom-developed program. The program is developed on LabVIEW 2012 platform and its graphical user interface consists of three parts; signal acquisition and selection panel, signal display panel and acoustic properties panel. Its performance is validated using KB-Aerotech Alpha R Series transducer with 5.0 MHz center of frequency and RIGOL DS2202 2 Channel 200 MHz 2 GSa/s digital oscilloscope for poly(methyl methacrylate) (PMMA) sample with (1.000 ± 0.050)cm thickness at (24.0 ± 0.1) °C water temperature. Findings indicated that the developed system produced accurate and consistent results less than 2.00% error compared to reference values. The developed computerized system offers a user-friendly interface, fast results display and convenient connection.

Measurements of Electromagnetic Properties of Ferrites as a Function of Frequency and Temperature

Fast kicker magnets are used to inject beam into and extract beam out of the CERN accelerator rings. These kickers are often ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. The interaction of the beam with the resistive part of the longitudinal beam coupling impedance leads to power dissipation and heating of different elements in the accelerator ring. In particular, power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. In addition, the imaginary portion of the beam coupling impedance contributes to beam instabilities. A good knowledge of electromagnetic properties of materials up to GHz frequency range is essential for a correct impedance evaluation. This paper presents the results of transmission line measurements of complex initial permeability and permittivity for different ferrite types. We present an approach for deriving electromagnetic properties as a function of both frequency and temperature; this information is required for simulating ferrite behaviour under realistic operating conditions.

On vertical dynamic stability and cross‐section optimization of closed‐ended hollow pile by considering soil compaction effects

SummaryThis paper conducts a comprehensive study on the effects of expansion force after pile driving on the vertical vibration of the hollow pile. The initial radially inhomogeneous strain field of soil in disturbed soil region and dynamic shear modulus of remolded soil are constructed by applying the cylindrical cavity expansion method. The equation governing the incremental motion of the soil is consequently deduced on the basis of incremental deformations superposed on an underlying finite deformation. The longitudinal impedance of the top of the pile and the velocity response in frequency and time domains are also numerically studied. The relations between the expansion force after pile driving and the velocity response of the pile with different wall thickness are discussed accordingly. The results suggest that a pile has a better dynamical stability when the characteristics of the section are optimized and interacting force with soil medium gets smaller.

A model of electrical impedance tomography implemented in nerve-cuff for neural-prosthetics control

Objective: In neural interfaces for peripheral nerve a trade-off exists between the level of invasiveness and the selectivity of neural recordings. In this study, we implement electrical impedance tomography (EIT) in a nerve cuff with the aim to investigate the achievable level of selectivity. Approach: Established modelling approaches in neural-EIT are expanded on to be used, for the first time, on myelinated fibres which are abundant in mammalian peripheral nerves and transmit motor commands. The model is then used to evaluate the viability of using EIT with a nerve cuff to record neural activity in peripheral nerves. Main results: Fibre impedance models indicate activity in unmyelinated fibres can be screened out from activity in myelinated fibres using operating frequencies above 100 Hz. At 1 kHz the transverse impedance magnitude, which is perpendicular to the fibre length axis, of inactive intra-fascicle tissue and the fraction change during neural activity are estimated to be 1142 Ω cm and −8.8 × 10−4, respectively. At 1 kHz and 10 mm spacing between the impedance measurement electrode pair, the longitudinal impedance magnitude, which is parallel to the fibre length axis, and the fraction change during neural activity are estimated to be 328 Ω cm and −0.30, respectively. We show that a novel EIT drive and measurement electrode pattern which utilises longitudinal current and longitudinal differential boundary voltage measurements could distinguish activity in different fascicles, as well as simultaneous activity in multiple fascicles, of a three-fascicle mammalian nerve using simulated data. Significance: The results of this study provide an estimate of the transient change in impedance of intra-fascicle tissue during neural activity in mammalian nerve, and present a viable EIT electrode pattern, both of which are critical steps towards implementing EIT in a nerve cuff for a recording neural interface.