Admittance Method Research Articles

An optimized parallel admittance matrix approach using the adjacence-graph recursive-thresholding technique

The admittance method is an accurate approach for the analysis of electromagnetic circuits. Unfortunately, until now it has suffered from two main limitations, i.e., its high numerical complexity and its lack of robustness, due to the risk of numerical ill conditioning in a linear system representing the core of the approach. In a previous paper, both drawbacks have been solved, using a strategy based on the system partitioning into many independent and well-conditioned reduced-size subsystems, thanks to the exploitation of the matrix adjacence graph properties. In this paper, we demonstrate that the use of this strategy paves the way to a natural, straightforward, and low-cost migration on distributed platforms, with a consequent substantial reduction in computer times. Furthermore, the use of suitable optimization strategies proposed here allows an optimum partitioning of the system in order to maximize the parallel efficiency.

ADMITTANCE FIELD METHOD FOR THE CALCULATION OF THE SPECTRAL DENSITY OF CURRENT FLUCTUATIONS

In the framework of the Green-function formalism the admittance field method is proposed for the calculation of the spectral density of current fluctuations of two and more terminal devices. The usefulness of the theory is illustrated by hydrodynamic calculations performed for a submicron GaAs structure. The unifying property of the formalism evidences the same physical ground of both the admittance and impedance field methods when instantaneous fluctuations of carrier accelerations during scattering events are taken as noise sources.

A stable and efficient admittance method via adjacence graphs and recursive thresholding

The generalized admittance method is a rigorous full-wave approach for the analysis of waveguide circuits. Unfortunately, it may present the risk of ill conditioning, especially when very complex structures are analyzed with a considerably high number of modes. In this paper, the concepts of adjacence graph and recursive thresholding are proposed to solve its numerical problems. By applying the proposed strategy, the linear system representing the core of the analysis is partitioned into many independent and well-conditioned subsystems, thus improving the numerical stability of the approach and its efficiency. The attractive features of the proposed approach are its simplicity and immediate implementation. Results are given, referred to a real industrial case, a complex E/H-plane filter, whose analysis could not be performed via a standard admittance method when a very high number of modes were considered. With the present approach, the ill conditioning is avoided and considerable enhancements in computing times is achieved.

New computerised tools for building design in different climates

SYNOPSIS The present paper describes two new computer programs, BTS and COMFORT. The first was written to help simulate the performance of a new passive cooling and heating system, designed by the author for buildings in North Africa. BTS is based on a simplified version of the admittance method. The main algorithms empolyed in the program are presented. Finally a validation proceedure was applied against an independent full scale experiment. Good agreement was obtained. The second program was written for the prediction and analysis of human thermal comfort. The program incorporates six thermal comfort indices; three original and three modified versions of the original. The original indices are: Fanger's Comfort Equation, Charma's Tropical Summer Index and Madsen's Equivalent Temperature. Results produced by the program are presented, for the six indices, in terms of the same Predicted Mean Vote, (PMV scale). The six indices are, however, classified as three for summer and three for winter.

Comparison of peak load predictions and treatment of solar gains in the admittance and heat balance load calculation procedures

Calculation of design cooling loads is of critical concern to designers of HVAC systems. The work reported here has been carried out under a joint ASHRAE-CIBSE research project to compare design cooling calculation methods. Peak cooling loads predicted by the ASHRAE heat balance method are compared with those predicted by a number of implementations of the admittance method using different window models. The results presented show the general trends in overprediction or underprediction of peak load. Particular attention is given to different window modelling practices. The performance of the methods is explained in terms of some of the underlying assumptions in the window models, and by reference to specific inter-model comparisons.

Qualitative Comparison of North American and U.K. Cooling Load Calculation Methods

A qualitative comparison is presented between three current North American and U.K. design cooling load calculation methods. The methods compared are the ASHRAE Heat Balance Method, the Radiant Time Series Method and the Admittance Method, used in the U.K. The methods are compared and contrasted in terms of their overall structure. In order to generate the values of the 24 hourly cooling loads, comparison was also made in terms of the processing of the input data and the solution of the equations required. Specific comparisons are made between the approximations used by the three calculation methods to model some of the principal heat transfer mechanisms. Conclusions are drawn regarding the ability of the simplified methods to correctly predict peak-cooling loads compared to the Heat Balance Method predictions. Comment is also made on the potential for developing similar approaches to cooling load calculation in the U.K. and North America in the future.

Unconstrained physiological monotoring in daily living for health care

This paper deals with the recent development of two types of non-invasive physiological monitoring systems for possible application in an unconstrained manner to normal subjects for health care as well as to patients and/or outpatients with disorders or with life support systems (artificial organs and organ transplantations). One is an ambulatory monitoring system which allows automatic acquisition of blood pressure, cardiac output and other cardiovascular hemodynamic parameters on a beat-by-beat basis using the volume-compensation and transthoracic electrical admittance method. The other is a home monitoring system installed in a lavatory which can measure body and excreta weight together with the ballistocardiogram as an index of cardiac ejecting function in an unaware fashion without attachment of any sensors to the subject's body and without special operations for measurement during toilet use. Outlines of these two systems and monitoring results of laboratory and field testings are presented, and these suggest that the ambulatory and non-conscious physiological monitoring techniques described herein appear promising as a valuable and helpful means for use in research as well as in the practical field of health monitoring at home during daily living.

Tunnel-fluctuation model of the MIS admittance

A tunnel-fluctuation model of the MIS admittance accounting for surface potential nonuniformity and tunnel trapping of charge carriers in the insulator is proposed. A trap distribution profile in the dielectric is considered: a uniform and an exponential type. For both types expressions for the normalized conductance G p/ ω of a MIS structure are obtained. A technique for determination of tunnel-fluctuation (standard deviation of the surface potential, trap depth in the insulator) and interface (time constant, capture cross section and spectral density of interface states) parameters of MIS structures combining the admittance method and nonequilibrium capacitance methods is proposed.

Comparison of cardiac-induced endogenous fields and power frequency induced exogenous fields in an anatomical model of the human body

Time-domain potentials measured at 64 points on the surface of a large canine heart, considered comparable with those of a human heart, were used to calculate the electric fields and current densities within various organs of the human body. A heterogeneous volume conductor model of an adult male with a resolution of approximately and 30 segmented tissue types was used along with the admittance method and successive over-relaxation to calculate the voltage distribution throughout the torso and head as a function of time. From this time-domain voltage description, values of and were obtained, allowing for maximum values to be found within the given tissues of interest. Frequency analysis was then used to solve for and in the various organs, so that average, minimum and maximum values within specific bandwidths (0-40, 40-70 and 70-100 Hz) could be analysed. A comparison was made between the computed results and measured data from both EKG waveforms and isopotential surface maps for validation, with good agreement in both amplitude and shape between the computed and measured results. These computed endogenous fields were then compared with exogenous fields induced in the body from a 60 Hz high-voltage power line and a 60 Hz uniform magnetic field of 1 mT directed from the front to the back of the body. The high-voltage power line EMFs and 1 mT magnetic field were used as `bench' marks for comparison with several safety guidelines for power frequency (50/60 Hz) EMF exposures. The endogenous electric fields and current densities in most of the tissues (except for organs in close proximity to the heart, for example lungs, liver, etc) in the frequency band 40-70 Hz were found to be considerably smaller, between 5% and 10%, than those induced in the human body by the electric and magnetic fields generated by the 60 Hz sources described above.

A simple approach to the capacitance technique for determination of interface state density of a metal–semiconductor contact

In this study we attempt to interpret the experimentally observed nonideal Al–pSi Schottky diode I– V and C– V characteristics. The expressions for the capacitance–voltage relationship at low frequency and high frequency are derived considering two non idealities, namely interface states and series resistance. After extracting the diode parameters from the I– V and C– V characteristics, theoretical plots for the high frequency and low frequency capacitance are obtained using the expressions derived. A comparison of the latter with available experimental plots reveals that the expressions for the low frequency and high frequency capacitance derived here are simpler, more accurate and closer to experimental results than those used in the past. The variation of interface state density with the applied bias voltage is obtained from the low frequency and high frequency C– V plots by using the capacitance technique. To examine the validity of the present approach, the value of density of interface states is compared with that obtained by the multifrequency admittance method. It is observed that there is good agreement between the results obtained by both methods.

New approach to the calculation of electrical transients, part II: Applications

AbstractThe calculation of electrical transients in power systems is important for insulation coordination. Most of the computer programs in current use are based on the nodal admittance method. This paper describes a computer program for the calculation of electrical transients based on a new approach which enables the use of more sophisticated numerical integration routines. The program can cope with linear network elements like resistors, capacitors, reactors, voltage and current sources and with non‐linear network elements like surge arresters and arc models. The descriptions of the models and their parameters are stored in libraries separate from the main program. The user can define his own models.

New approach to the calculation of electrical transients, Part I: Theory

AbstractThe calculation of electrical transients in power systems is important for insulation coordination. Most of the compiiter programs in current use are based on the nodal admittance method. This paper describes a computer program for the calculation of electrical transients based on a new approach which enables the use of more sophisticated numerical integration routines. The program can cope with linear network elements like resistors, capacitors, reactors, voltage and current sources and also with non‐linear network elements like surge arresters and arc models. The description of the models and their parameters is stored in libraries separate from the main program. The user can define his own models.

Effect of Microstructure and Composition on Ionic Conductivity of Rare‐Earth Oxide‐Doped Ceria

Polycrystalline ceria doped with several rare‐earth oxides (, and ) at various concentrations were fabricated. Conductivity was measured by ac admittance and dc four‐probe methods. The conductivity was separated into grain and grain boundary contributions using complex admittance technique as well as the grain size dependence of conductivity. The effect of dopant type and concentration on grain boundary conductivity was examined. Grain size dependence of polycrystalline conductivity, which can be adequately described by the so‐called brick layer model, appears to give a more reliable measure of the grain conductivity compared to the complex admittance method. Polycrystalline resistivity (1/conductivity) increases linearly with the reciprocal of grain size. The intercept of resistivity vs. inverse grain size plot gives a measure of the grain resistivity, and the slope gives a measure of the grain boundary resistivity. Activation energies of polycrystalline conductivity, grain conductivity, and grain boundary conductivity were determined. A compositional analysis of fractured samples was carried out by Auger spectroscopy. The dopant concentration near grain boundaries was estimated to be lower than that in the bulk.

Dielectric multilayers with absorption at layer boundaries

The concept of a conducting surface is applied to the description of dielectric multilayers with very thin absorbing films at layer boundaries. Recursive formulas are derived for calculation of multilayer parameters on the basis of the admittance method with arbitrary incidence angles. An expression is found for the characteristic matrix of a conducting surface. Quarter-wavelength dielectric mirrors with boundary losses are investigated, and some simple analytical expressions are found. The possibility of use of the proposed method in the case of boundaries that scatter the light is discussed. Surface radiation conductance is introduced as a characteristic of integral light scattering at a boundary.

Effective elastic thickness of the lithosphere along the Easter Seamount Chain

Bathymetry and gravity data collected during Legs 5, 6, and 7 of the 1993 GLORIA Expedition and the recently released 2‐min altimetry‐derived global gravity grid are used to determine the effective elastic thickness of the lithosphere along the Easter Seamount Chain (ESC). Forward modeling, admittance, and coherence methods yield consistent results. With the exception of the eastern and western ends of the ESC the effective elastic thickness along the chain is ∼1–4 km. The thin elastic thickness for the majority of the ESC seamounts is compatible with a young seafloor age at the time of loading derived from new radiometric ages of the seamounts along the chain and a magnetic isochron age interpretation of the Nazca plate seafloor age. The elastic thickness southeast of the Nazca fracture zone is ∼6 km, apparently because of the seafloor age discontinuity across the fracture zone. The elastic thickness near the San Felix Island, at the eastern end of the ESC, is even greater (∼11 km), which is compatible with the estimated seafloor age at the time of loading. A slight increase in the effective elastic thickness of the far western part of the ESC suggests dynamic compensation or less thermal weakening of lithosphere above a plume channel versus directly above the plume center. These findings combined with published geochemistry support a hotspot origin for the ESC, complicated by large‐scale plate boundary reorganizations and channeling of plume material to the East Pacific Rise.

A self-consistent technique for the analysis of the temperature dependence of current–voltage and capacitance–voltage characteristics of a tunnel metal-insulator-semiconductor structure

A new formalism is reported for the analysis of the current–voltage (I–V) characteristics of a tunnel metal-insulator-semiconductor (MIS) device, which considers a bias dependent distribution of interface states and barrier lowering due to the image force. Our theoretical expression for the I–V characteristics is general in the sense that it is applicable even under conditions when both the thermionic emission and the diffusion mechanisms of current transport compete with each other. The method is ideal for new epitaxial materials and devices where the carrier density is not known precisely beforehand. A self-consistent method of analysis is reported to determine the characteristic parameters of MIS diodes, using simultaneously the I–V and capacitance–voltage data as a function of temperature. This computational analysis has been used to examine the current transport mechanism in an Au/p-InP epitaxial MIS diode. The experimental verification of the theory and computational analysis is done by comparing the values of the interface state density distribution in thermal equilibrium with the semiconductor Nss, obtained from the forward I–V characteristics, with those directly measured by the multifrequency admittance method. Excellent agreement from these comparisons strongly supports the validity of the theory. Over the temperature range of 200–393 K, our results indicate that the interfacial layer-thermionic emission was clearly the dominant mechanism of the forward current transport in an MIS fabricated on a lightly doped InP:Zn epitaxial layer. The transmission coefficient through the insulator layer obtained from the reverse I–V characteristics was θp=1.43×10−3±7% from which we estimate an oxide thickness of 2.2 nm. The analysis of the barrier height φb0 versus temperature, obtained from 1 MHz C–V data provided a value φ0=1.06 V±10% for the zero bias and zero temperature barrier height.

Investigation of interfacial states in MIS structures by a single-frequency admittance method

Two models of tunneling charge exchange on interfacial states buried in the insulator are examined. In one model the spatial distribution of these states is assumed to be uniform and in the other model the volume density of traps decreases exponentially with increasing depth. Analytical expressions are obtained for the width and position of the peak in the normalizedconductance curves in both models, and the accuracy and limitations of these expressions are indicated. A new procedure for investigating interfacial states by the admittance method is proposed, based on the use of G-V characteristics of metal-insulator-semiconductor (MIS) structures measured at a fixed frequency.

Fast Fourier transform admittance analysis method applied to thickness-shear-mode acoustic wave sensors

A fast Fourier transform admittance analysis (FFT-AA) method, applied to thickness-shear-mode (TSM) acoustic wave sensors, is first proposed and the corresponding theory is presented. Based on the FFT-AA, an oscillatory waveform with the feature of a damped free oscillation is obtained experimentally. It can illustrate dynamically and directly the vibratory characteristics of TSM sensors, which can be considered as an important advantage over an admittance spectrum obtained by admittance analysis. Compared with the motional resistance in equivalent circuit, the decay time, obtained by Levenberg-Marquardt algorithm through the fit of the oscillatory equation to oscillatory waveform, is more suitable for characterization of the electrical energy dissipated in the quartz crystal. The oscillatory features of TSM sensor are investigated by FFT-AA in different medium. The decay times are 0.1807, 0.0761 and 0.2300 μs with the media being air, water and dry coating film respectively. Finally, the proposed method has been successfully applied to monitor a curing process of coating polymer. It is therefore shown to be a useful technique to study oscillatory behavior of TSM acoustic wave sensors.

Insertion of Hydrogen and/or Lithium Into Cesium Tungsten Bronze

Hydrogen and/or lithium insertion into hexagonal cesium tungsten bronze, Cs0.3WO3, was studied using voltammetric and a.c. admittance methods. The close values of stoichiometric coefficients for hydrogen and/or lithium in coinsertion bronzes as well as the close values of diffusion coefficients DH and DLi are ascribed to a lattice distortion caused by large cesium species which influence both equilibrium and the mobility of inserting species regardless of their different chemical nature.

Thermal behavior of a building with a slanted roof

The roof angle of a building can influence its energy consumption. To evaluate this influence, we have used a computer program, BRE-ADMIT, based on the admittance method. An additional program was written in order to analyse sloping structures. The new software transforms the data on buildings with one or two-pitched roofs to that of a building of cubical shape such that it can be analyzed by BRE-ADMIT. From this cubical-shaped building, the thermal behavior of the our pitched-roof building could be obtained by running BRE-ADMIT. To verify the validity of our mathematical model, experiments were performed on one-pitch roof buildings. For a roof sloped north with an optimal slope angle, we have found that one can save up to 20% of the cooling energy. For a one-slope building facing south, when the roof has an optimal slope angle, 11% of the heating energy is saved but for a building with a two-pitch roof, energy consumption during winter does not depend on the angle of the slope. This new program can give useful information to building designers on roof slope angle in order to obtain the lowest cooling and heating energy consumption.