Theoretical Impedance Research Articles

Development of a high-time/spatial resolution self-impedance probe for measurements in laboratory and space plasmas.

Plasma impedance probes are often used in laboratory experiments as well as in space to make measurements of important plasma parameters such as the electron density. Conventional impedance probe methods involve sweeping the frequency applied to the probe through a range containing the plasma frequency, which can take on the order of a second to complete. This acquisition time leads to very low spatial resolution when making measurements from sounding rockets in the ionosphere. A high-time resolution impedance probe is under development at the U.S. Naval Research Laboratory with the goal of increasing the spatial resolution of measurements in space. To achieve this, a short-time Gaussian monopulse with a center frequency of 40MHz and containing a full spectrum of frequencies is applied to an electrically short dipole antenna. Laboratory experiments were performed with the Gaussian monopulse triggered once every 10 µs and averaged over ten shots, equating to a spatial resolution of 13cm for a typical sounding rocket speed. This paper discusses the development of the new high-time/spatial resolution self-impedance probe and illustrates that the short-time pulse method yields results that match well with data taken using conventional methods. It is shown that plasma parameters such as the electron density, sheath frequency, and electron-neutral collision frequency can also be derived from the data. In addition, data from the high-time/spatial resolution impedance probe are shown to compare well with those from theoretical impedance models.

Remote RF excitation for small-bore MR imager at 15.2 T

We report a method for remote excitation of the RF signal for preclinical-equivalent ultra high field Magnetic Resonance Imaging (MRI). A parallel-plate waveguide together with a bio-inspired surface coil were used to perform remote excitation experiments to acquire images with a small-bore MR imager at 15.2 T. The imager bore size limits the RF coil transmitter dimensions, so the Gielis super-formula was used to design an RF coil with small dimensions. Electromagnetic simulations of the principal mode were run to study the waveguide filled with air and loaded with a saline solution-filled tube. Radiation patterns were also computed in a semi-anechoic chamber for the same scenarios as above. A saline solution-filled spherical phantom and a formaldehyde-fixed mouse phantom were used to acquire images. Radiation patterns showed an omnidirectional distribution with no side lobes, and a very smooth behaviour with almost no loss of information in the saline solution-filled tube and without. The theoretical wave impedance was calculated and compared with simulated results showing an excellent correspondence. Spherical phantom image data and simulation results of B1 were contrasted and showed an important correlation. Ex vivo mouse images were of high quality and exhibited clear delineation of anatomical structures. These imaging results are in very good agreement with the simulations. Numerical, theoretical and experimental results validate this approach, using a bio-inspired surface coil with a simple waveguide for preclinical small-bore MRI at ultra high field.

Analysis of Electrical Model of Data Center Power System

The electrical structure of the power distribution system in data center is generally a tree-like structure, with fewer branches closer to the power supply side and more branches closer to the load side. In this article, the electrical topology structure diagram is established, and the structure of power distribution network between 10kV input line and power distribution units is discussed. In the electrical structure of power system, 10kV distribution cabinets and 400V distribution cabinets are connected with electrical equipment such as electrical cable, transformer or enclosed busbar. By analysing the equivalent impedance model of equipment above, the theoretical impedance values are obtained.

Design of Log Periodic Dipole Array Antenna Ranging from 30 to 150 MHz

This paper describes construction of 16 element frequency independent and high bandwidth Log Periodic Dipole Array antenna which works within the frequency range of 30 to 150 MHz. The antenna of gain 8 dBi is designed by calculating the parameters from Matlab. Matlab program is used to calculate the parameters like length of elements, separation between elements, theoretical impedance, standing wave ratio, etc. Thus, the designed antenna was fabricated. The antenna element is a cylindrical aluminum pipe of diameter 9mm and the boom used is rectangular antenna pipe of dimension 1”X1”. Fabrication also includes other materials like M-seal, zip tie, etc for physical stability of the antenna. Log Periodic Dipole Array antenna design described in this paper is fed with 75 ohm coaxial cable to 1:1 balun. Balun is also used for impedance matching between the antenna and coaxial cable. Antenna analyzer is used to measure Standing Wave Ratio and Impedance which are found to be 1.623 and 71.5625 ohm respectively. The antenna can be a receiver or a transmitter type for operating with the signals within Very High Frequency band.

Impedance Model of a Water-Filled Pt Nanopore: Interfacial Charging and Chemisorption Effects

The impedance response contains rich information about an electrochemical system under investigation. Disentangling this highly convoluted information requires physical models. In this work, we develop a theoretical impedance model for a water-filled Pt nanopore, as a representative element in electrocatalytically active layers of polymer electrolyte fuel cells or electrolysis cells. The model accounts for double-layer charging, proton conduction and oxygen transport in the pore as well as chemisorption and oxygen reduction reaction at the Pt surface. It relaxes two widely used assumptions, namely, electroneutrality in solution phase and infinitely fast adsorption kinetics. Analytical impedance expressions are obtained for different limiting cases and impedance fingerprints of interfacial charging and chemisorption effects are identified.

Novel broadband measurement technique on PCB cells for the field- and stress-dependent impedance in ferromagnetic wires

The lack of broadband impedance measurements has restricted the potential capabilities of ferromagnetic wire composites, which have been mainly evaluated through theoretical impedance calculated from existing models without considering wire domain microstructure. Here, we have developed an accurate method for measuring the impedance of ferromagnetic wires in a wide frequency range, from 100 kHz up to 15 GHz, under magnetic and stress stimuli. The broadband measurements were ensured by a more accurate microwave calibration on the PCB cell, extending the reference planes up to the wire sample ends and by compensating the sample waveguide properties using the phase unwrapping technique proposed in this work. In addition, a specially designed dogbone PCB measurement cell allows both field- and stress-dependent impedance measurements, efficiently transferring the tensile stress from the cell to the wire sample fixed onto it. The measured wire impedance can be then recalculated into the surface impedance, which constitutes the boundary condition in the antenna equation, describing the microwave scattering properties of a wire. The developed approach will make it possible to build a practically predictive scattering theory in composite materials with embedded wire inclusions and thus their implementation in real-world applications, such as remote stress monitoring.

Acoustic performance of countersunk micro-perforated panel in multilayer porous material

This study investigates the acoustic performance of a countersunk micro-perforated panel, along with two distinct porous materials used in a multilayer porous absorber configuration. Additive manufacturing is applied to create sub-millimeter perforation with different hole spacings on polymer micro-perforated panels. Experiments are conducted in an impedance tube, in which the effects of the perforation ratio, air gap, and varying porous layer configurations on the sound absorption capabilities are investigated. For validation, considering the converging hole profile in the micro-perforated panel, an integration method with end correction is used to calculate the tapered section impedance, and the traditional Maa theory is used for the uniform hole. The theoretical impedance of the multilayer absorber is calculated using the transfer matrix method and subsequently compared to the experimental results. The results demonstrate that the countersunk hole micro-perforated panel exhibits a significant improvement in sound absorption, and the introduction of porous materials extends the sound absorption bandwidth. Furthermore, the results indicate that the sound absorption capability depends on the porous material placement in the multilayer absorber configuration.

EIS at carbon fiber cylindrical microelectrodes

The theoretical mass-transport impedance at cylindrical microelectrodes has been known for some time, but an experimental verification is given here for the first time, using carbon fiber electrodes taken from a commercial carbon felt. Nonlinear least-squares fitting of the impedance spectrum of a redox couple at the reversible potential enables accurate evaluation of a composite parameter containing the standard rate constant and mean diffusivity, without measuring the fiber diameter, length or area.

Modeling of the Electrochemical Reactions at the Electrode-Electrolyte Interface of Nickel/Metal Hydride Batteries by an Equivalent Electrical Circuit

Based on the experimental impedance spectra, the electrochemical reactions that are deposed at the electrode-electrolyte interface can be modeled by equivalent electrical circuits. Each element used in the circuit must have a physical correspondence in the electrochemical system. In this work, a model has been proposed to a NiMH battery electrode to describe, in detail, the electrochemical process at the interface of this electrode. The theoretical impedance of a proposed circuit is a function of several variables. These adjusted variables to reach a good agreement between the theoretical spectra and the experimental spectra in the studied frequency. The Z-simplex software allows refining the experimental results. These results show a good superposition between the experimental spectra and the theoretical spectra corresponding to the proposed electric circuit. This leads to the conclusion that the proposed circuit describes the phenomena that take place at the interface of the hydride electrode.

Coal Seam Roof: Lithology and Influence on the Enrichment of Coalbed Methane

To identify the lithology of coal seam roof and explore the influence of these roofs on the enrichment of coalbed methane, low-frequency rock petrophysics experiments, seismic analyses and gas-bearing trend analyses were performed. The results show that the sound wave propagation speed in rock at seismic frequencies was lower than that at ultrasound frequencies. Additionally, the P-wave velocities of gritstone, fine sandstone, argillaceous siltstone and mudstone were 1,651 m/s, 2,840 m/s, 3,191 m/s and 4,214 m/s, respectively. The surface properties of the coal seam roofs were extracted through 3D seismic wave impedance inversion. The theoretical P-wave impedance was calculated after the tested P-wave velocity was determined. By matching the theoretical P-wave impedance of the four types of rocks with that of the coal seam roofs, we identified the lithology of the roofs. By analyzing known borehole data, we found that the identified lithology was consistent with that revealed by the data. By comparing and analyzing the coal seam roof lithology and the gas-bearing trends in the study area, we discovered that the coal seam roof lithology was related to the enrichment of coalbed methane. In the study area, areas with high gas contents mainly coincided with roof zones composed of mudstone and argillaceous siltstone, and those with low gas contents were mainly associated with fine sandstone roof areas. Thus, highly compact areas of coal seam roof are favorable for the formation and preservation of coalbed methane.

A feasibility study on achieving mode coalescence in acoustic waveguides

In a previous talk at ASA it was shown that the double root, commonly referred to as an exceptional point (EP), for modal frequencies in a 2-D or 3-D waveguide can exhibit almost perfect absorption over a relatively broad frequency range. The key to the phenomenon is that the wall impedance is such that modes coalesce at a complex-valued frequency. In this talk, we consider how to feasibly achieve the aforementioned wall impedance with the use of simple resonators. Within the frequency ranges supporting scale separation, it can be shown that a wall aligned with resonators can be modelled as an effective surface with a unique admittance. It is with this concept that we arrive at results showing distinct frequencies at which mode coalescence can occur. Strategies capable of deriving the necessary resonators parameters, and therefore, its dimensions are given. Numerical results are shown for reflection and transmission from a waveguide with the tuned effective surface composed of resonators in addition to the theoretical impedance boundary associated with constant EP behavior. Computer simulations and preliminary experimentation of the phenomena are referenced. Future attempts of utilizing more complicated metasurface designs are discussed for next iterations. [Work supported by NSF.]In a previous talk at ASA it was shown that the double root, commonly referred to as an exceptional point (EP), for modal frequencies in a 2-D or 3-D waveguide can exhibit almost perfect absorption over a relatively broad frequency range. The key to the phenomenon is that the wall impedance is such that modes coalesce at a complex-valued frequency. In this talk, we consider how to feasibly achieve the aforementioned wall impedance with the use of simple resonators. Within the frequency ranges supporting scale separation, it can be shown that a wall aligned with resonators can be modelled as an effective surface with a unique admittance. It is with this concept that we arrive at results showing distinct frequencies at which mode coalescence can occur. Strategies capable of deriving the necessary resonators parameters, and therefore, its dimensions are given. Numerical results are shown for reflection and transmission from a waveguide with the tuned effective surface composed of resonators in addition to th...

The Theoretical Mass Transfer and Impedance at an Impinging Jet Electrode: Copper Electrodissolution Studies

The fluid flow near the stagnation point of an impinging jet electrode is an example of a uniformly accessible surface for diffusive transport. The characteristic convective faradaic impedance function has been derived and found to be identical to that of the rotating disk electrode (RDE) at infinite Schmidt number. At finite, but large, Schmidt number, the impedance shows an important dependence on the flow characteristics. Analysis of the low frequency impedance allows one to determine the diffusion coefficient, as previously shown for the rotating disk electrode. The analysis is illustrated for the impedance of Cu dissolution in acid chloride media, and complements earlier studies of the reaction system on a RDE.

Absorption performance optimization of perforated plate using multiple-sized holes and a porous separating partition

This research proposes a new type of sound absorptive perforated plate with multiple-sized holes and a porous separating partition in an attempt to extend the sound absorption bandwidth. Separating different sized holes with a porous partition instead of a conventional rigid partition is an unprecedented idea. However, existence of a porous separating partition makes it hard to use theoretical surface impedance models to predict absorption performance. So we introduce appropriate finite element simulation method using the effective density of hole. To consider the end correction effects for hole length and viscosity length of a perforated plate, the effective density of the Johnson-Champoux-Allard model is modified and the end correction lengths of the modified effective density are corrected again in connection with finite element simulation. Material property of a porous separating partition is modeled by the Delany-Bazley material model. After constructing the finite element model, we analyzed the absorption coefficient graphs of perforated plates with two-sized holes and four-sized holes according to the separating partition types: no partition, rigid partition and porous partition. To enhance the wide-band absorption performance, flow resistivity value and thickness of a porous separating partition as well as hole sizes are optimized. From the analysis and design examples, we confirmed that the perforated plate using multiple-sized holes and a porous separating partition can make a continuous frequency range of high absorption coefficient compared to the perforated plate with a conventional rigid partition.

Measurement of Young’s Modulus and Internal Damping of Pork Muscle in Dynamic Mode

Automotive shocks involve various tiers’ speed for different human body tissues. Knowing the behavior of these tissues, including muscles, in different vibration frequency is therefore necessary. The muscle has viscoelatic properties. Dynamically, this material has variable mechanical properties depending on the vibration frequency. A novel technique is being employed to examine the variation of the mechanical impedance of pork muscle as a function of frequency. A force is imposed on the lower surface of the sample and acceleration is measured on its upper surface. These two parameters are measured using sensors. The sample is modeled by Kelvin–Voigt model. These measures allow deducing the change in the mechanical impedance modulus (/[Formula: see text]/ [Formula: see text] /Force: Acceleration/) of pork muscle as a function of vibration frequency. The measured impedance has a resonance of approximately 60[Formula: see text]Hz. Best-fit parameters of theoretical impedance can be deduced by superposition with the experiment result. The variation of Young’s modulus and internal damping of pig’s muscle as a function of frequency are determined. The results obtained between 5[Formula: see text]Hz and 30[Formula: see text]Hz are the same as determined by Aimedieu and al in 2003, therefore validating our technique. The Young’s modulus of muscle increases with the frequency, on the other hand, we note a rating decrease of internal damping.

Mesoscopic Framework Enables Facile Ionic Transport in Solid Electrolytes for Li Batteries

Li‐ion‐conducting solid electrolytes can simultaneously overcome two grand challenges for Li‐ion batteries: the severe safety concerns that limit the large‐scale application and the poor electrolyte stability that forbids the use of high‐voltage cathodes. Nevertheless, the ionic conductivity of solid electrolytes is typically low, compromising the battery performances. Precisely determining the ionic transport mechanism(s) is a prerequisite for the rational design of highly conductive solid electrolytes. For decades, the research on this subject has primarily focused on the atomic and microscopic scales, where the main features of interest are unit cells and microstructures, respectively. Here, it is shown that the largely overlooked mesoscopic scale lying between these extremes could be the key to fast ionic conduction. In a prototype system, (Li0.33La0.56)TiO3, a mesoscopic framework is revealed for the first time by state‐of‐the‐art scanning transmission electron microscopy. Corroborated by theoretical calculations and impedance measurements, it is demonstrated that such a unique configuration maximizes the number of percolation directions and thus most effectively improves the ionic conductivity. This discovery reconciles the long‐standing structure–property inconsistency in (Li0.33La0.56)TiO3 and also identifies mesoscopic ordering as a promising general strategy for optimizing Li+ conduction.

Acoustic metasurface-based perfect absorber with deep subwavelength thickness

Conventional acoustic absorbers are used to have a structure with a thickness comparable to the working wavelength, resulting in major obstacles in real applications in low frequency range. We present a metasurface-based perfect absorber capable of achieving the total absorption of acoustic wave in an extremely low frequency region. The metasurface possessing a deep subwavelength thickness down to a feature size of ∼λ/223 is composed of a perforated plate and a coiled coplanar air chamber. Simulations based on fully coupled acoustic with thermodynamic equations and theoretical impedance analysis are utilized to reveal the underlying physics and the acoustic performances, showing an excellent agreement. Our realization should have an high impact on amount of applications due to the extremely thin thickness, easy fabrication, and high efficiency of the proposed structure.

Complex Impedance Measurement System for the Frequency Range from 5 kHz to 100 kHz

The improved design of previously developed complex impedance measurement system is described. Realized system for measurement of complex impedance is based on integrated circuit AD5933 which is controlled by microcontroller ATmega128. Device has full standalone capabilities with LCD for displaying of results and keyboard for configuration on the field. Created report with measured values of impedance magnitude and phase angle is stored on micro SD card in format compatible with MS Excel which ensures easy off-line analysis on PC. Realized device is equipped with self-calibration system which ensures high accuracy in wide range of impedance and frequency. In the aim of the verification of developed system, the measurement results are plotted and compared with theoretical impedance values. Realized system can be used for complex impedance measurement, impedance spectrometry, biomedical and automotive sensors, proximity sensors, FFT processing, structural health monitoring, etc.

Boosting power conversion efficiencies of quantum-dot-sensitized solar cells beyond 8% by recombination control.

At present, quantum-dot-sensitized solar cells (QDSCs) still exhibit moderate power conversion efficiency (with record efficiency of 6-7%), limited primarily by charge recombination. Therefore, suppressing recombination processes is a mandatory requirement to boost the performance of QDSCs. Herein, we demonstrate the ability of a novel sequential inorganic ZnS/SiO2 double layer treatment onto the QD-sensitized photoanode for strongly inhibiting interfacial recombination processes in QDSCs while providing improved cell stability. Theoretical modeling and impedance spectroscopy reveal that the combined ZnS/SiO2 treatment reduces interfacial recombination and increases charge collection efficiency when compared with conventional ZnS treatment alone. In line with those results, subpicosecond THz spectroscopy demonstrates that while QD to TiO2 electron-transfer rates and yields are insensitive to inorganic photoanode overcoating, back recombination at the oxide surface is strongly suppressed by subsequent inorganic treatments. By exploiting this approach, CdSe(x)Te(1-x) QDSCs exhibit a certified record efficiency of 8.21% (8.55% for a champion cell), an improvement of 20% over the previous record high efficiency of 6.8%, together with an additional beneficial effect of improved cell stability.

Mathematical solutions of comprehensive variations of a transmission-line model of the theoretical impedance of porous electrodes

Mathematical solutions were obtained for the impedance of one-dimensional transmission-line (TML) models with all possible variations of the boundary conditions and connections to an external circuit. First, three types of connection (Z-type, T-type, and E-type) were considered. A more generalized connection that includes the characteristics of both Z-type and T-type (universal-type) was also considered. All four of the resulting general solutions were versatile, but quite complicated. Next, comprehensive variations of the general solutions depending on specific boundary conditions, which are generally simpler, were also considered. Finally, an equivalent transform from a three-terminal TML model to a simple Y-circuit was calculated. This enables calculation of the serial connection of multiple TML models with different parameters, which represents a multi-layered electrode.

HOMs of the SRF Electron Gun Cavity in the BNL ERL

The Brookhaven Energy Recovery Linac (ERL) is operated as an R&D test bed for high-current, low emittance electron beams. It comprises a superconducting five-cell cavity and a half-cell superconducting RF photo-injector electron gun. The ERL is undergoing commissioning with focus on the performance of the electron gun, not the least on the cavity Higher Order Modes (HOM). Among the various alternative solutions, a beam tube damper based on a layer of ferrite tiles was adopted for the five-cell accelerator cavity. For the gun, a ceramic-ferrite damper consisting of a lossless ceramic cylinder surrounded by damping ferrite tiles has been investigated. This design is innovative in its damper approach and combines a variety of goals including broadband HOM damping and protection of the superconducting cavity vacuum from potential damage by the separately cooled absorber. In this paper the empirical performance of an installed ceramic-ferrite damper is described by the Q reduction of a few selected gun cavity resonances. The theoretical coupling impedance presented to a traversing beam is numerically analyzed in terms of radial waveguide modes in the damper section. Strong damping of the gun cavity HOMs by the fundamental power coupler (FPC) is found and discussed. Finally, the measured Q-values of the operational gun cavity without the ceramic-ferrite damper at superconducting temperatures are presented