Characteristic Impedance Research Articles

Determination of the characteristic impedance and the complex wave number by five different approaches

This study presents several methods to determine the characteristic impedance and the complex wave number of porous materials. These methods include the two-cavity method by Utsuno et al., the two-thickness method by Dunn and Davern, the four-microphone transfer-matrix method by Song and Bolton, the empirical method by Miki and theoretical calculation by the inverse method of Johnson-Champoux-Allard (JCA) model. Glass wool and polyester materials are used to compare different approaches. The results indicate a clear correlation among all methods. The theoretical calculation based on the inverse method of the JCA model can predict well without direct measurement of the non-acoustical parameters. However, there are disadvantages to several methods including sharp peaks in some frequency ranges for the two-cavity method, data fluctuation at low frequency for the four-microphone method, and inaccuracy in predicting the characteristic impedance of thick materials at middle and high frequencies for the two-thickness method. The results imply that the inverse method of the JCA model is a reliable method to predict the characteristic impedance and the complex wave number with comparable accuracy to traditional experimental methods.

Experimental and theoretical basic research on sound absorption characteristics of foam materials with and without membrane

A basic study was conducted to theoretically estimate the acoustic properties of a sound-absorbing foam material. Generally, the lattice of sound-absorbing foam materials contains membranes. Herein, for simplicity, a mathematical model was constructed assuming a cubic frame structure as the basic frame structure of the foam, which included a membrane. Accordingly, the sound absorption coefficient was obtained and compared with the experimental results. In the mathematical model, the clearance in the frame structure (with membrane) was divided into elements and was approximated as a clearance surrounded by two parallel planes, considering the exact shape of each element. Herein, the characteristic impedance and propagation constant of the approximated clearance were obtained and treated as a one-dimensional transfer matrix, and the sound absorption coefficient was calculated using the transfer matrix method. For the experiments, the samples were fabricated using a 3D printer and the sound absorption coefficient was measured using a two-microphone impedance tube. Overall, the experimental and theoretical results exhibited similar trends.

Least-squares approach for improving the accuracy of bulk acoustic property measurements using an impedance tube

The bulk acoustic property (characteristic impedance, propagation wave number, or propagation constant) of porous acoustic material with an impedance tube is generally calculated by the two-cavity method, which is calculated from the specific acoustic impedance obtained by the two-microphone transfer function method (ASTM E1050, ISO 10534-2) or from the transfer matrix measured by the four-microphone transfer matrix method (ASTM E2611). These methods can obtain the bulk acoustic property from the results of up to two measurements with different termination conditions. However, the bulk acoustic property may not be obtained correctly due to calculation singularities caused by the test specimen and/or measurement conditions, and calculation errors caused by setting errors regarding the dimensions or environmental conditions of the tube nd/or test specimen. As a result, to reduce the errors in the bulk acoustic property, workarounds such as measuring the specific acoustic impedance or transfer matrix under multiple termination conditions (n conditions) and averaging the bulk acoustic properties obtained for all combinations of two termination conditions have sometimes been used. Therefore, to improve the error in the bulk acoustic properties, a new calculation method based on the least squares method using all the data measured under multiple termination conditions is proposed.

Tunable electrical and impedance characteristics of Co–Zn doped M-type Sr Hexaferrites: Role of grain, grain boundaries, electrical transport mechanisms and software/circuit modeling

M-type hexaferrites SrCoxZnxFe12-2xO19 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) have been synthesized using the sol-gel method. The structural, dielectric, and electrical properties of Zn2+ and Co2+ substituted strontium ferrite have been carried out. The dielectric and electric properties of prepared hexaferrites have been examined over the frequency range of 100 Hz to 2 MHz. The formation of the hexagonal phase has been confirmed by the X-ray diffraction (XRD) analysis. The substitution of Co2+ and Zn2+ causes a reduction in crystallite size from 39.50 to 26.42 nm being the smallest in the case of x = 1.0. Scanning electron microscopy (SEM) indicates the formation of honeycomb-like grain structures in composition x = 1.0. The dielectric spectrum shows that the dielectric constant and loss tangent vary non-monotonically with the doping of Co–Zn content. A non-Debye type relaxation is shown by the electric modulus of the prepared compositions. There is a reduction in relaxation time with the increase in doping of Co–Zn. The impedance spectra indicate the effects of both grain and grain boundaries on the electrical properties. The impedance analysis has been presented with the modeling of electrical processes in the samples using an equivalent circuit model comprising of parallel RC circuit for grains and grain boundaries. The obtained simulated results are in agreement with the measured results.

Sequence Impedance Modeling and Analysis of Modular Multilevel Converter Considering DC Port Characteristics

The extensive deployment of Modular Multilevel Converters (MMCs) in AC/DC systems can lead to complex resonance issues. Impedance modeling forms the foundation for analyzing the stability of interconnected system. Existing investigations primarily address resonance concerns on the AC side of MMC. In the process of impedance modeling, the DC system is generally approximated as an ideal voltage source, thereby neglecting its dynamic impact on the impedance characteristic of MMC. Such simplification may result in inaccuracies within stability analysis findings. Based on the multi-harmonic linearization method, this paper introduces an impedance modeling approach that takes into account the characteristics of the DC port. Taking DC voltage control as a case study, the impedance model for the AC side of the MMC is established. The results of programming calculation and simulation measurement of sequence impedance are mutually verified. Finally, the MMC impedance responses determined by different DC port characteristics are analyzed. Significant alterations in MMC impedance characteristics are introduced by DC side resistance and capacitance, which may result in negative damping effects and a decrease in system stability margins. The DC side inductance has a relatively minor impact on MMC impedance responses. The analysis results show that the sequence impedance model of MMC considering DC port characteristics can improve the accuracy of stability analysis results.

Acoustic impedance measurement method using spherical waves

The mechanical properties and composition of materials can be better understood through ultrasonic non-destructive testing. Ultrasound is a valuable tool for characterizing elastic moduli, material microstructure, morphological conditions, and correlated acoustical/mechanical properties. Although ultrasound measurement techniques like transmission and pulse-echo are well-established, there is a growing demand for new technologies to facilitate automated inspection and enhance the widespread application of this method. This paper presents a novel approach to evaluate the characteristic acoustic impedance of a sample using measurements of reflected spherical waves. Employing a spherical sound source makes the energy distribution more uniform in all directions, minimizing measurement errors caused by system alignment. Additionally, that configuration aids in determining the experiment's geometry. The impedance was evaluated by analysis of the spherically reflected Gaussian-modulated sinusoidal pulses, which are less susceptible to noise interference. The acquired signal is fitted into a mathematical model to calculate the acoustic impedance, considering the decrease in sound pressure amplitude at the spherical wavefront according to the inverse distance law. Materials with a wide range of impedances (2 MRayl < Z < 46 MRayl) were measured to validate the method. The experimental impedances exhibited statistically significant agreement with values obtained via through-transmission impedance evaluation. The linear regression indicates a bias of 0.02 MRayls and an overall relative error of 1.7 % between the methods. This experimental setup holds promise for accurately assessing submerged structures, offering potential advantages for quantitative inspection.

Detecting loss of excitation condition of synchronous generator in the presence of unified power flow controller based on data mining method

Loss-of-excitation (LOE) conditions may cause devastating effects on both the generator and power system. If LOE is not meticulously detected, two dangerous events may emerge: 1. unnecessary trip signal, 2. not detecting this abnormal condition or detecting it with time delay. Both mentioned flaws have considerable harmful consequences on the generator and power system. Conventional techniques for detecting LOE conditions are based on impedance measurement. The presence of flexible alternating current transmission (FACT) system devices can considerably affect the impedance characteristic of the system and as a result, the operation of impedance-based relays. This paper simulates LOE and stable power swing (SPS) conditions causing failures and errors in the LOE protection in the presence or absence of a unified power flow compensator (UPFC), and parameters with different behaviors are determined. Then, the most sensitive parameters are combined using an intelligent method. The single parameter, achieved from a combination of features in the previous process, is applied to a learning vector quantization (LVQ) neural network. The LVQ is a type of artificial neural network that is based on a prototype supervised learning classification algorithm and trained its network through a competitive learning algorithm. The simulation results show that, in a single machine infinitive bus (SMIB) test system, R-X directional scheme has 2 mal-operations and the proposed algorithm has no mal-operation without UPFC in the system. With UPFC in the system, the R-X directional scheme has four mal-operations and the proposed algorithm has no mal-operation. In the IEEE 9-bus test system, the R-X directional scheme has five mal-operations and the proposed algorithm has no mal-operation. Moreover, applying the proposed algorithm, LOE is detected very quickly in the presence or absence of the UPFC in the system and this approach prevents electrical and mechanical stresses enforced to the machine and power system. © 2017 Elsevier Inc. All rights reserved.

Analysis of the suitable thawing endpoint of the frozen chicken breast using video recording analysis, shear force, and bioelectrical impedance measurement.

This study focuses on analyzing the texture properties and bioelectrical impedance characteristics of frozen chicken breasts during low-temperature thawing, meanwhile, we also compared the differences in physiochemical properties. Frozen chicken breasts were thawed at 4 ± 2°C for 2, 4, 6, 8, and 10 h separately, then the physiochemical properties (color, pH, water-holding capacity, water distribution), the texture properties (easy-to-cut level), and the bioelectrical impedance were determined and analyzed. The easy-to-cut level of the samples was evaluated by the sensory panel and two indexes, one is Warner-Bratzler shear force measured by texture analysis machine, and the other is cutting speed value calculated by the consumer-oriented cutting behavior analysis using frame-by-frame video recording analysis method. These two methods were used to characterize the easy-to-cut level of the frozen samples during thawing from the industrial processing and home cooking standpoint. Strong correlations were observed between the easy-to-cut level and the bioelectrical impedance of the frozen chicken breasts during thawing. The impedance magnitude at 100 kHz showed a high correlation coefficient (R2 = .9417) with Warner-Bratzler shear force, and the impedance magnitude at 50 Hz showed a high correlation coefficient (R2 = .8658) with cutting speed. Our results indicated the acceptability of using bioelectrical impedance to evaluate the easy-to-cut thawing endpoint for both industry processing and home cooking.

Structural, dielectric, impedance, and electric modulus characteristics of Y2CaCuO5 high-k dielectric ceramics

With the increasing trends of integrated circuit densification, device miniaturization, and exponential growth of microelectronic components there is a huge responsibility on the part of material researchers to derive, design, and develop new materials. Materials that can overcome the existing limitations in the present compounds available in the market or can expedite the process of material fabrication are of great interest. This feat can be achieved by the fabrication of new materials, and analysis of various characterizations viz. (structural, dielectric, transport behavior, and impedance spectroscopy). With this perspective, in this communication, a high permittivity dielectric material belonging to the Y-Ba-Cu-O ternary systems where barium is replaced by calcium (Y2CaCuO5) is synthesized using solid-state reaction route. X-ray diffraction, scanning electron micrograph, and energy-dispersive X-ray spectroscopic study confirm the phase and microstructure of the sample. The observed higher value of the dielectric constant is understood from Koop’s phenomenological theory and internal barrier layer capacitance model. The dispersive behavior of conductivity is interpreted by Jonscher’s power law. Overlapping large polaron tunneling model for conduction is observed. Impedance spectroscopy analysis reveals non-Debye type of relaxation with variable time constants. According to Nyquist plots; up to 250 °C only grain effect (bulk) is dominantly present; however, at higher temperatures, the contribution from both grain and grain boundary is seen.

Impedance-Based Stability Analysis of Grid-Connected Inverters under the Unbalanced Grid Condition

As a common interface circuit for renewable energy integrated into the power grid, the inverter is prone to work under a three-phase unbalanced weak grid. In this paper, the instability of grid-connected inverters under the unbalanced grid condition is investigated. First, a dual second-order generalized integrator phase-locked loop (DSOGI-PLL)-based inverter under balanced and unbalanced conditions is modeled. A fourth-order impedance model is established to describe its impedance characteristics under the unbalanced grid condition. To analyze this multi-input multi-output system, a simplified stability analysis method based on the generalized Nyquist stability criterion and matrix theory is proposed. Then, the influences of circuit and control parameters on the stability of the grid-connected inverter system under the unbalanced grid condition are investigated. Finally, the accuracy of the derived frequency-coupled impedance model is verified via simulations, and the effectiveness of the proposed simplified stability analysis method on the system stability analysis is verified via both simulations and hardware experiments.

A study about the relationships between surface structures and electrical impedance characteristics in single-walled carbon nanotube/polyester composites

The present study aims to understand the relation between impedance characteristics and fractal behaviours. The pure and single-walled carbon nanotube (SWCNT) reinforced unsaturated polyester resin (UPR)-based composite specimens were produced by the hot press process with this aim. The Nyquist variation in the neat sample shows a straight line, which can describe the great resistance in the material and its insulating nature, while the Nyquist plots of the carbon nanotube doped sample show an almost semi-circular shape, indicating the presence of electrical conductivity. In addition, fractal analysis with statistical scaling method is used to determine the relationships between the superficial heteromorphology and electrical properties of samples. The surface particle coverage rates, fractal dimensions, cluster pattern structures, Feret diameters and Feret angles were calculated for samples. Feret angle decreases indicating that the distance between clusters is decreasing as coverage ratio, fractal dimension and Feret diameter increases.

Time domain response of corrugated transmission lines

AbstractIn order to employ periodic corrugated microstrip lines for reducing or suppressing electromagnetic interference in high‐speed or high‐frequency circuits, a precise method is necessary to calculate and measure the characteristic impedance of periodic microstrip lines. The equation for characteristic impedance (depending on frequency) of lossless periodic microstrip lines was obtained based on the transfer matrix method. A time domain pulse was used to measure the instantaneous impedance of conventional microstrip lines, and when the instantaneous impedance does not change with distance, it can be identified as the characteristic impedance of microstrip lines. However, when the time‐domain pulses are employed to measure the instantaneous impedance of periodic microstrip lines, rapid oscillations occur with distance. Therefore, a standard for spacing between adjacent grooves in the microstrip line can be suggested by analysing the interaction between the time‐domain pulses and the microstrip line grooves. Once such a standard is satisfied, many grooves etched along the microstrip line would no longer be distinguished by the time‐domain pulses. Such a principle and method can be used to determine the instantaneous impedance for the microstrip lines that have periodic grooves. On the other hand, when several periodic structures with different lattice constants coexist on a microstrip line, they can also be distinguished via the instantaneous impedance. A time domain reflectometer was used for measuring the instantaneous impedance of periodic microstrip lines, and the measured results are in agreement with the theoretical analysis.

Space-Confined multiple interface in super-structured TiO2@PPy composite for enhanced electromagnetic wave absorption

Microwave absorption (MA) has become an important challenge with the development of electronic technology where fine structural design and interface modification of absorbing materials play a crucial role in optimizing their MA performance. In this study, hydrogenated hollow multi-shelled structure (HoMS) TiO2 (HH-T) was prepared using the sequential template method combined with hydrogenation treatment, followed by the synthesis of HH-T/PPy composite by in-situ polymerization. The HH-T/PPy composite possesses a uniform disordered interface and a uniform 3D conductive network. The HH-T/PPy composite exhibits an improved minimum reflection loss (RL) of −40.2 dB, and an effective absorption bandwidth (RL < -10 dB) of 5.02 GHz with a relatively thin matching thickness of 2.0 mm. The enhanced MA performance is mainly due to the excellent impedance characteristics, interface polarization, and conductive loss. This research offers new insights into the design and analysis of advanced microwave materials with superior performance.

Impedance characterization of substrate leakage in wafer bonded CMUTs

This work investigates substrate leakage in Capacitive Micromachined Ultrasonic Transducers, (CMUTs) having thin backings. CMUTs produced with solid or rigid substrates have a high Q resonance with flat baseline. However, if the operating wavelength of CMUT becomes larger than the thickness of substrate the real part of cell impedance shows elevated baselines with more leakage at DC than at higher frequencies. When a clamped CMUT membrane is excited harmonically the vibrations produced are counterbalanced by the backing medium. Hence some of the energy is coupled to substrate as loss resulting in a lower mechanical Q of resonance. We first derive this energy coupled to the backing medium using FEA analysis considering the velocity field and associated tensile stresses in a thin backing. Substrate impedance is found numerically from isotropic damping of dispersive elastic waves in the backing. This backing impedance is introduced as a shunt mechanical loss across the transduction force in equivalent circuit model. We characterize the measured impedance of CMUT cells with both FEMs and linear circuit models. Simulations results closely agree with the measured impedance levels, frequency and bandwidth of resonance.

A multi‐band open‐ended waveguide antenna by using groove loading technique

AbstractA new multi‐band frequency response controlling method using groove loading technique on the narrow wall of an open‐ended waveguide is proposed by the authors. The feature of this scheme is a larger stopband spacing that is independent of the position of the loading structure. A tri‐band antenna is designed as an example to verify the effectiveness of the idea. Two notches are introduced, and the bandwidths, as well as stopband spacings, can be adjusted by independent parameters. The tri‐band prototype can be fabricated using 3D printing technology or machining technology. Reasonable agreement between the measured and simulated results of impedance and radiation characteristics have been achieved.

Measures of aortic function independently predict adverse events in females with thoracic aortic aneurysms

Abstract Background/Introduction Thoracic aortic aneurysm (TAA) is a disease associated with high morbidity and mortality. TAA is more common in males, but females with TAA experience faster aneurysm growth and a higher risk of acute aortic syndromes and death. We have previously demonstrated that measures of aortic function, correlating with abnormal aortic wall architecture and reflecting worse aortic health, are independently associated with aneurysm size and expansion, specifically among females. To date, international guidelines focus on aneurysm size to determine timing for prophylactic surgical intervention, however adverse outcomes can occur before surgical thresholds are met, highlighting the need for novel risk assessment tools in TAA. Purpose We sought to evaluate whether measures reflecting proximal aortic function (where the TAA is located) would independently predict adverse outcomes in men and women with TAA. These measures include: aortic characteristic impedance (Zc), proximal aortic compliance (PAC), proximal aortic pulse wave velocity (PAoPWV) and the aortic stiffness-thickness product (Eh). Study summary is illustrated in Picture 1. Methods We performed a prospective study of 102 males and 48 females with TAA. Measures reflecting proximal aortic function were non-invasively assessed with validated methodology combining arterial tonometry with transthoracic echocardiography at the time of enrollment. The primary outcome was a composite of acute aortic syndromes, death, or guideline-directed aortic surgery. We used Cox proportional hazard models to determine the independent associations of aortic function measures with the primary outcome. PAoPWV and Eh were log-transformed to reduce skewness. Models were adjusted for variables previously demonstrated to predict adverse outcomes in TAA: age, sex, aneurysm size and etiology, and mean arterial pressure (MAP). Sex-specific models were performed if the interaction of sex *aortic function measure was significant (P≤0.05). Results Mean age was 62±12 years, 70 (47%) had degenerative etiology, baseline aneurysm size was 46.3±4.3mm, and MAP was 90±10 mmHg (not different between and women, P&amp;gt;0.07 for each). Mean follow up was 4.6±2.4 years in females and 5.5±2.3 years in males, P=0.031. Our primary outcome occurred in 37 (25%) participants (3 dissections, 3 intramural hematomas, 1 aortic rupture, 22 elective surgical repairs and 8 deaths). Interaction terms of sex with each of the aortic function variables were significant (P&amp;lt;0.04 for each). Results of the sex-specific models are summarized in Picture 2. We observed that higher Zc, PAoPWV and Eh, and lower PAC were each independently associated with an increased risk of adverse outcomes among females only. Conclusions Among females with TAA, measures of proximal aortic function are independent predictors of adverse events, highlighting novel markers for risk stratification and therapeutic targeting.Illustrative Summary

Pavement damage monitoring using electromechanical impedance of embedded piezoelectric plate

Piezoelectric transducers have seen widespread usage in the monitoring of structural health. It has tremendous potential for monitoring the health of infrastructure, especially pavement monitoring. In the present study, the impedance characteristics of a piezoelectric plate embedded in the pavement is utilized to monitor the health status of the pavement. Based on the piezoelectricity principle, a model of an electromechanical piezoelectric plate embedded in pavement is established. The damage of the pavement is considered as the thickness decreasing of the pavement layer. The present proposed model is verified by comparing its degeneration with the exact solution of a single layer model. Numerical results demonstrated that with the deceasing of the thickness of the pavement, which is considered as the deterioration of the pavement, the achievable maximum electromechanical impedance characterization including impedance, admittance and conductance decreased. This demonstrated that the achievable maximum impedance, admittance and conductance of an embedded piezoelectric plate could be used as the indicator of pavement health monitoring. This study primarily presents theoretical underpinnings for pavement monitoring using electromechanical impedance of piezoelectric plates.

Comparing acoustic prediction methods for additively manufactured porous structures

While macroscale methods for predicting the acoustic properties of porous structures have been popular in the past, they often require time-consuming manufacturing and testing workflows. Meanwhile, microscale approaches allow the prediction of transport parameters based exclusively on a periodic structure's unit cell geometry. Here, we compare these methods to predict the characteristic impedance of additively manufactured porous structures. We use the microscale approach to estimate the geometry's transport parameters, then predict the characteristic properties using the Johnson-Champoux-Allard (JCA) model. We measure the acoustic properties of the printed structures using a normal incidence impedance tube and estimate the transport parameters using an inverse characterization approach. We use the twothickness method as a macroscale approach to predict the characteristic properties from the measured surface impedances of two sample thicknesses. Finally, we compare these characteristic prediction methods. Our results show that the inverse characterization and twothickness methods offer the closest match to the measured values at low frequencies.

A neural network-augmented two-microphone impedance tube method to estimate sound propagation characterisics

Two-microphone impedance tubes are a popular method to measure the normal incidence sound absorption coefficient. However, a single measurement with this method does not offer enough information to identify the sound propagation characteristics, i.e. the characteristic impedance and the wave number of absorbent samples. Instead, more elaborate measurement techniques that require more time, more equipment and enhanced user knowledge need to be applied. This contribution presents a technique combining neural networks and the two-microphone impedance tube method to estimate the propagation characteristics of a highly porous sample from a single two-microphone impedance tube measurement. The measured surface impedance serves as input to a U-net architecture, which preserves the high frequency resolution of the data and returns an estimate of the surface impedance mimicking an air cavity attached behind the sample. Then, the two cavity method is used to calculate the propagation characteristics from the measured and the networks predicted surface impedances. The presented approach gives precise estimates of the propagation characteristics of simulated highly porous samples and for two different, physically measured melamine foam samples, while drastically reducing the required resources and expenses. In this way, it provides an efficient way to estimate the propagation characteristics of absorbent samples.

Enhanced Non-Communication-Based Protection Coordination and Advanced Verification Method Using Fault Impedance in Networked Distribution Systems

In recent years, the networked distribution system (NDS), which is normally connected to the distribution line (DL), was actively studied as the topology of the future distribution system for reasons such as improving supply reliability, improving line utilization, and increasing the capacity of distribution generators (DGs). However, the NDS creates new issues in terms of protection coordination because of its bidirectional power flow and fault current flow. The issues associated with conventional protection schemes in the NDS include malfunction of protective devices due to bi-directional fault currents and failure of protection coordination due to communication failures between protective devices. When applying a conventional protection method in the NDS, the protection schemes become complicated, and there is a risk of protection coordination failure due to communication failure between protective devices. To solve this problem, this paper proposes an effective and innovative non-communication-based protection algorithm for protection coordination in the NDS. The proposed protection algorithm utilizes fault impedance characteristics, which allow not only determination of whether a fault occurred, but also the ability to identify the exact fault point. Therefore, the proposed method is expected to be sustainably utilized and contribute to developing protection schemes and devices in various system topologies and scenarios in the future. Additionally, this paper addresses the overall concept of hardware-in-the-loop simulation (HILS) and directly verifies the proposed protection algorithm using HILS. Therefore, this study establishes a sustainable foundation for future research on protection coordination using HILS.