Admittance Model Research Articles

Impact of Injector Mass Flow Fluctuations on Combustion Dynamics in Liquid Engines

Reynolds-averaged Navier–Stokes simulations were carried out to study the influence of acoustically driven injector mass flow fluctuations on combustion dynamics in a liquid propellant rocket engine. First, a framework of transfer functions is introduced, showing the links between pressure fluctuations in the chamber and resulting heat release modulation on the basis of the subprocesses involved. An analytical model for the injector admittance is evaluated, and computational-fluid-dynamics results for a single-injector configuration are obtained. The impact of mass flow fluctuations on evaporation dynamics and on heat release modulation is studied for four load points. Results show that the combustion dynamics are controlled by the droplet evaporation time. Dynamic mode decomposition results explain the convective transport of the droplets and give a detailed insight into the fluctuating fields. A weak mutual influence of the fuel evaporation is observed, whereas the fluctuations of the heat release rate are governed by the oxidizer evaporation rate. Evaporation rates and heat release rates are found to be linearly dependent on the mass flow excitation amplitude allowing for the superposition of transfer functions. Finally, a flame transfer function in the form of a low-pass filter is derived, providing a linear feedback model as input for low-order combustion instability assessment tools.

Electric characteristics analysis on power drive system based on negative input‐resistance compensator

A power drive system is a typical load for the 270 V DC power distribution systems of more electric aircraft. It may cause instability of power grid, including voltage transients and current transients. A negative input-resistance compensator with current limitation is proposed to solve the stability problem as well as to decrease both voltage transients and current transients. The main emphasis is placed on the transient characteristics research of power drive system with the proposed compensator. A dc network admittance model is established to select proper parameters for the compensator. Simulation and experiments show that the designed compensator increases system stability while satisfying the transient requirements of the power distribution system.

(Invited) The Use of Eqcm-D for in-Situ Characterization of Dimensional Changes in Cycled Battery Electrodes

Ions adsorption/desorption in nanoporous carbon electrodes and, especially, Li-ion insertion/extraction to/from typical battery electrodes are accompanied by significant volume changes, which complicates enormously gravimetric analysis by EQCM of the ionic fluxes involved in these processes. [1, 2] Gravimetric analysis by EQCM is based on the use of the classical Sauerbrey’s equation, which transforms ions insertion-induced resonance frequency changes into mass (or ions population) changes. Such an approach implies that additional mass onto quartz-crystal coating is of pure inertial origin, so that the dissipation factor of the oscillating crystal, and hence the related resonance width, remain constant. Figure 1 shows a drastic increase in the resonance width accompanying frequency change during Li-ion extraction from a thin LiFePO4 electrode. A finite difference of about 20% exists between the experimentally measured frequency shift and that calculated from the Sauerbrey’s equation (based on the electrochemical data that enable calculations of mass changes). As has been recently reported, [3] measuring frequency differences together with the changes in the resonance peak width can provide input parameters of the hydrodynamic admittance models of composite battery electrodes. With such information it is possible to obtain important potential-dependent structural parameters of the composite electrodes, namely, effective thickness of the porous active mass and its permeability (linked to porosity). This new approach to characterization of composite battery materials has been recently developed in collaboration with researchers from Tel-Aviv University [1,2], and was applied successfully to describe dynamics of Li ion batteries electrodes [3] and to understand the capacitive paradox of Ti3C2 MXene phase electrodes [4] in collaboration with research teams at the Leibnitz Institute (Germany) and Drexel University (USA), respectively. The method is based on the fact that intercalation-induced changes in geometric structural parameters of electrodes, modify their hydrodynamic interactions of with the electrolyte solutions. These are nicely recorded by EQCM-D and analyzed in terms of suitable admittance models. Until recently, we applied this approach to composite electrodes containing only rigid binders (such as PVdF in contact with aqueous solutions). Herein we are going to extend the EQCM-D based methodology for structural characterization of composite electrodes containing viscoelastic polymeric binders, developing thus a non-invasive in-situ dynamic monitoring of elastic properties of composite battery electrodes (using EQCM-D) [5]. This unique method can be adjusted for the characterization of viscoelastic behavior of polymeric binders during long-term cycling of composite electrodes used in all kinds of batteries. References (1) Levi, M.D; Sigalov S.; Aurbach, D.; Daikhin, L. J. Phys. Chem. C 2013, 117, 14876−14889. (2) Daikhin, L.; Levi, M.D.; Sigalov, S.; Salitra, G.; Aurbach, D. Anal. Chem., 2011, 83, 9614–9621. (3) Levi, M.D; Sigalov S.; Salitra, G.; Elazari, R.; Aurbach, D.; Daikhin, L.; Presser, V. J. Phys. Chem. C 2013, 117, 1247−1256. (4) Levi, M. D.; Lukatskaya , M. R.; Sigalov, S.; Beidaghi, M.; Shpigel, N.; Daikhin, L.; Aurbach, D.; Barsoum, M. W.; Gogotsi, Y.;. Adv. Energy Mater. 2015, 1400815. (5) Shpigel, N.; Levi, M.D; Sigalov, S.; Girshevitz,O.; Aurbach, D.; Daikhin, L.; Jäckel, N.;] Presser, V. Angew. Chemie, 2015 (accepted) DOI: 10.1002/anie.201501787. Figure 1

Closed‐form impedance model for annular through‐silicon via pairs in three‐dimensional integration

Annular through-silicon via (TSV) is one of the promising solutions for vertical interconnects in three-dimensional integration, which diminishes mismatch effects of the coefficients of thermal expansion between two different materials and saves cost, as compared with other TSV structures. In this study, an analytical impedance model is proposed. Closed-form formulas for calculations of the per-unit-height resistances and inductances are derived by calculating the electromagnetic field quantities in the cylindrically multilayered media, via solving the longitudinal current densities in the conducting layers. Combining with the conventional admittance model, a compact transmission line model is obtained, which can be used to model the electrical properties of annular TSVs. These formulas appropriately capture the real current distribution because of skin effects in metal conductors as well as the eddy current loss in semiconductor regions. The results from these analytical formulas have comparable accuracy as those obtained by the full-wave solver in a wideband frequency range, yet much higher computational efficiency than existing modelling methods.

Impact and admittance modeling of the Isidis Planitia, Mars

In this study, the impact event that produced the Martian Isidis basin (0–20°N and 70–100°E) was modeled using the iSALE hydrocode, and the current lithospheric structure was obtained comparing the calculated admittance from topography and gravity data, with the admittance from top-load and bottom-load flexure models. The best-fit admittance model was obtained using a bottom-load flexure with a thinned crust of 10km, likely formed by cooling of the surficial melt pool after the impact, and an elastic thickness of 36km. We found that the impact produced crustal excavation and thickening, surficial melt pool and temperatures >1500K beneath the area where the free-air maxima is observed. The geometry resulting from the impact modeling is compatible with the radius of the Isidis basin. Derived thermal gradient and heat flux are in agreement with an early-Noachian epoch for the Isidis impact event and with the intense volcanic activity that followed the impact.

On MOS admittance modeling to study border trap capture/emission and its effect on electrical behavior of high-k/III–V MOS devices

In this paper, we present results of a study on border trap capture/emission (C/E) process and its effect on small signal admittance of III–V devices. A MOS admittance model using a non-radiative multi-phonon phenomenon as the basis of the border trap capture/emission process is developed and utilized to investigate the effect of parameters like temperature, gate voltage, oxide thickness and trap distribution on capture/emission process. The simulation results are found to match closely with experimentally observed temperature, voltage and dielectric thickness dependencies in experimental admittance data.

Small-signal admittance model of multi-traps distributed over energy and space in the insulator of MIS tunnel structures

A theoretical model is developed which allows computing the current and small-signal conductance and capacitance of MIS tunnel structures containing surface or border traps with their arbitrary space and energy distribution. Results of the theoretical simulations are discussed and compared with measurement data.

Multi-port admittance model for quantifying the scattering response of loaded plasmonic nanorod antennas.

In this paper we demonstrate the feasibility of using multiport network theory to describe the admittance properties of a longitudinally loaded plasmonic nanorod antenna. Our analysis reveals that if the appropriate terminal ports are defined across the nanorod geometry then the corresponding voltage and current quantities can be probed and thus it becomes feasible to extract the admittance matrix of the structure. Furthermore, it is demonstrated that by utilizing cylindrical dielectric waveguide theory, closed form expressions can be derived that uniquely characterize the loading material in terms of its admittance. The combination of the admittance matrix information along with the load admittance expressions provides an effective methodology for computing the nanorod's input admittance/impedance for arbitrary loading scenarios. This is important because the admittance resonances are associated with the structure's scattering peaks which are excited by a plane wave polarized parallel to its long dimension. Subsequently, the proposed approach provides a fast and computationally efficient circuit-based methodology to predict and custom engineer the scattering properties of a loaded plasmonic nanorod without having to rely on repetitive lengthy full wave simulations.

Design-dependent performance of self-actuated and self-sensing piezoelectric-AlN cantilevers in liquid media oscillating in the fundamental in-plane bending mode

In this work the electrical performance of micromachined piezoelectric cantilevers having different designs is investigated in liquid environment, thus making most beneficially use of their self-actuated and self-sensing capability. The impact of parasitic effects originating from e.g. the electrical feedlines, on the sensing characteristics is discussed. The focus is set on in-plane bending modes excited in a large viscosity range from 1.09cP to 238.82cP and the corresponding influence on the conductance peak, which is important especially for liquid monitoring purposes. Furthermore, an analytical model for the dynamic admittance and the conductance peak is presented and compared to the measurements. Based on these results design guidelines for optimizing the performance of piezoelectric in-plane resonators are presented.

Study of carrier dynamics of N,N′-diphenyl-N,N′bis (1,1′-biphenyl)-4,4′-diamine (NPB) through the frequency dependence of impedance spectroscopy and particle swarm optimization algorithm

In this paper, carrier dynamics in N,N′-diphenyl-N,N′bis(1,1′-biphenyl)-4,4′-diamine (NPB) was studied using impedance spectroscopy (IS) and particle swarm optimization algorithm (PSO). We applied PSO to fit the frequency dependence of impedance spectroscopy of NPB, and achieved the charge-carrier transit time and the dispersive parameters of NPB, and then obtained carrier mobility. The impacts of the dispersive degree on the impedance had been analyzed. Though PSO, the three unknown parameters, charge-carrier transit time τdc and dispersive degree M, α in the admittance model were achieved simultaneously. The results verified the reliability of this method. Furthermore, we have presented the advantages of PSO compared with the traditional nonlinear least squares algorithm. In our limited knowledge, this paper begins the work to study materials in the deep level of algorithm

Research on Admittance Model of Primary Electricity Equipments Based on LCC

Because of the unsatisfied present situation of bidding evaluation in the field of electric power equipment, the LCC theory is introduced into the bidding evaluation method, which can be used to evaluate the total cost of electric power equipment. Combining with ADC method, the paper proposes a comprehensive procurement model and verifies it by a practical case.

Identification for hole transporting properties of NPB based on particle swarm optimization algorithm

In order to study the carrier transporting properties in organic semiconductors (OSCs), the samples of single layer structure ITO/NPB/Ag are prepared, and the corresponding admittance model in theory is built. Impedance samples of the structure under different DC bias voltages are obtained by small sinusoidal signal frequency test method. The particle swarm optimization (PSO) algorithm, in which fitness function includes both the real part and the imaginary part of OSC impedance, is used to identify the model parameter including dispersion coefficient M, α and charge-carrier transit time τdc. To validate the proposed method, an equivalent circuit model of the structure, whose time constant τc is identified by least squares method, is built. Two single-layer structures, whose NPB thickness values are respectively 1000 nm and 1200 nm, are tested. Test results show that the charge-carrier transit time τdc is proportional to the time constant τc and the two hole mobility μdc values both satisfy the famous Poole-Frenkel formula.

Robust impedance active control of flight control devices

This paper focuses on the control of the mechanical impedance of an aircraft yoke. The control architecture involves an inner position servo-loop and an outer loop feedbacking the torque/force measurement to the position reference input through the required admitance model. Two different approaches are presented for the inner position servo-loop design: a classical Proportional-Derivative control and a structured H∞ control. These two approaches are compared from the performance/robustness trade off point of view. The performance and robustness indexes are respectively the maximal variation on the required admittance model and the maximal pilot own impedance supported by the closed loop system before to become unstable. These indexes are computed using real μ-analysis. Both approaches are implemented on an experimental test-bed. Analysis and exprimental results with a pilot in the loop confirm that the structured H∞ controller is the best solution.

Stabilization of Medium-Frequency Modes in Isolated Microgrids Supplying Direct Online Induction Motor Loads

Driven by the economical and environmental concerns, the importance of distributed generation-based microgrids is increasing. However, the presence of induction motor (IM) loads in converter-based microgrids might induce source-load admittance mismatch between the IM load and microgrid converters leading to medium-frequency instabilities, particularly in isolated microgrids. To overcome this issue, this paper presents detailed small-signal admittance models, analysis, and stabilization of a voltage-source inverter (VSI)-based microgrid with direct online IM load. The resultant source (VSI) and load (IM) admittances form a multi-input-multi-output (MIMO) system. Using the generalized Nyquist stability criterion, it is shown that the interactions between the lightly-damped dynamics of IMs and isolated VSI-based microgrid have significant destabilizing effect. Active compensation techniques are proposed to maintain the system stability. Time-domain simulations and experimental results are presented to validate the theoretical analysis.

Comments to “A Distributive-Transconductance Model for Border Traps in III-V/High-$k$ MOS Capacitors”

In this paper, we have found the missing factor in the derivation to the transconductance model [1] and reaffirmed that, when all the physics are taken into account, the distributed admittance model published in [2] is correct.

Comments to “A Distributive-Transconductance Model for Border Traps in III-V/High-k MOS Capacitors”

The commentors state that in the article named above [ibid., vol. 34, no. 6, pp. 735-737, Jun. 2013] the authors derived a distributed transconductance gm for the equivalent circuit of oxide traps in an MOS capacitor. Their gm expression, the right-hand side of (7), is mathematically identical to the expression of ΔYbt/Δx, (5), of the commetors' work "A Distributed Bulk-Oxide Trap Model for Al2O3- InGaAs MOS Devices" published in IEEE TRANSACTIONS ON ELECTRON DEVICES in August, 2012. The commentors have found the missing factor in the derivation to the transconductance model in the article commented-on and reaffirmed that, when all the physics are taken into account, the distributed admittance model they published in 2012 is correct.

A Biodynamic Feedthrough Model Based on Neuromuscular Principles

A biodynamic feedthrough (BDFT) model is proposed that describes how vehicle accelerations feed through the human body, causing involuntary limb motions and so involuntary control inputs. BDFT dynamics strongly depend on limb dynamics, which can vary between persons (between-subject variability), but also within one person over time, e.g., due to the control task performed (within-subject variability). The proposed BDFT model is based on physical neuromuscular principles and is derived from an established admittance model-describing limb dynamics-which was extended to include control device dynamics and account for acceleration effects. The resulting BDFT model serves primarily the purpose of increasing the understanding of the relationship between neuromuscular admittance and biodynamic feedthrough. An added advantage of the proposed model is that its parameters can be estimated using a two-stage approach, making the parameter estimation more robust, as the procedure is largely based on the well documented procedure required for the admittance model. To estimate the parameter values of the BDFT model, data are used from an experiment in which both neuromuscular admittance and biodynamic feedthrough are measured. The quality of the BDFT model is evaluated in the frequency and time domain. Results provide strong evidence that the BDFT model and the proposed method of parameter estimation put forward in this paper allows for accurate BDFT modeling across different subjects (accounting for between-subject variability) and across control tasks (accounting for within-subject variability).

Compensation of piezoceramic bonding layer degradation for structural health monitoring

The compensation of the degradation of the bonding layer of piezoceramics used in structural health monitoring is addressed in this article. A simple admittance model is first used to measure and extract the variation of admittance parameters using the same acquisition chain which is used by the structural health monitoring system for damage monitoring. More precisely, the method uses measurable changes in physical transducer modal damping at frequencies around piezoceramic resonance to estimate the extent of degradation. Then, a finite element model is used to obtain calibration curves linking the variations in transducer modal damping to amplitude and phase of the ultrasonic signals generated or measured by the piezoceramics. Such calibration curves are obtained by simulating with the FEM the effect of varying the bonding layer coverage area and Young’s modulus on (a) admittance and (b) amplitude and phase of the ultrasonic signals. From this, a signal correction factor is developed for the dominant bonding layer coverage area degradation failure mode to compensate for the changes in amplitude and phase of guided waves generated and measured by degraded piezoceramic transducers. The measured modal damping determines the amount of bonding layer degradation from the simulated modal damping calibration curves and then the quantified bonding layer degradation amount selects the amplitude and phase correction to be applied to measured signals from the calibration curves. The benefits of the signal correction factor are demonstrated below piezoceramic resonance to improve damage imaging and localization using the Embedded Ultrasonic Structural Radar algorithm (delay and sum method) when a single transducer in a sparse array of transducers fixed to an aluminum plate is damaged due to the close proximity of drop-weight impacts. Up to a certain damage extent, the signal correction factor could allow an extension of the service life of the structural health monitoring system.

Effect of high current density on the admittance response of interface states in ultrathin MIS tunnel junctions

The effect of a high current density on the measured admittance of ultrathin Metal–Insulator–Semiconductor (MIS) tunnel junctions is investigated to obtain a reliable energy distribution of the density, DS(E), of defects localized at the semiconductor interface. The behavior of admittance Y(V, T, ω) and current density J(V, T) characteristics is illustrated by rectifying Hg//C12H25Si junctions incorporating n-alkyl molecular layers (1.45nm thick) covalently bonded to n-type Si(111). Modeling the forward bias admittance of a nonequilibrium tunnel junction reveals several regimes which can be observed either in C(ω≈0) vs. (J) plots of the low frequency capacitance over six decades in current or in M″(ω) plots of the electrical modulus over eight decades in frequency. At low current density, the response of interface states above mid-gap is unaffected and a good agreement is found between the interface states densities derived from the modeling of device response time τR(V) and from the low–high frequency capacitance method valid for thick MIS devices; the low defect density near mid-gap (DS<1011eV−1cm−2) results from a good passivation of dangling bonds at the C12H25n Si interface. In the high current density regime (J>1mAcm−2), the admittance depends strongly on both the density of localized states and the dc current density, so that the excess capacitance method overestimates DS. For very high current densities (J>10mAcm−2), the observation of a linear C(ω≈0) vs. (J) dependence could indicate some Fermi level pinning in a high interface density of states located near the Si conduction band. The temperature-independent excess capacitance C(ω≈0)−C(1MHz) observed at very small J, not predicted by the admittance model, is attributed to some dipolar relaxation in the molecular junction.

Small-signal admittance model as a characterization tool of the MOS tunnel diode

The tunnel leakage through the insulator layer of metal–insulator–semiconductor tunnel diodes and its small-signal admittance is investigated by means of a theoretical model of the metal–oxide–semiconductor tunnel diode based on a steady-state algorithm and the minority carrier relaxation time. The conclusions are reviewed using an experimental Al-SiO2-Si structure with an ultrathin oxide layer.