Frequency Admittance Research Articles

The Influence of Climatic Factors on the Provocation of Epileptic Seizures.

Background/Objectives: Recent studies provide the first indications of the impact of climate factors on human health, especially with individuals already grappling with internal and neurological conditions being particularly vulnerable. In the face of escalating climate change, our research delves into the specific influence of a spectrum of climatic factors and seasonal variations on the hospital admissions of patients receiving treatment for epileptic seizures at our clinic in Kaiserslautern. Methods: Our study encompassed data from 9366 epilepsy patients who were admitted to hospital due to epileptic seizures. We considered seven climate parameters that Germany's National Meteorological Service made available. We employed the Kruskal-Wallis test to examine the correlation between the frequency of admittance to our hospital in the mentioned patient group and seasons. Furthermore, we used conditional Poisson regression and distributed lag linear models (DLMs) to scrutinize the coherence of the frequency of patient admittance and the investigated climate parameters. The mentioned parameters were also analyzed in a subgroup analysis regarding the gender and age of patients and the classification of seizures according to ILAE 2017. Results: Our results demonstrate that climatic factors, such as precipitation and air pressure, can increase the frequency of hospital admissions for seizures in patients with general-onset epilepsy. In contrast, patients with focal seizures are less prone to climatic changes. Consequently, admittance to the hospital for seizures is less affected by climatic factors in the latter patient group. Conclusions: The present study demonstrated that climatic factors are possible trigger factors for the provocation of seizures, particularly in patients with generalized seizures. This was determined indirectly by analyzing the frequency of seizure-related emergency admissions and their relation to prevailing climate factors. Our study is consistent with other studies showing that climate factors, such as cerebral infarcts or cerebral hemorrhages, influence patients' health.

Algorithm for identifying RLC parameters

The article discusses an algorithm capable of determining the substitution scheme of the investigated circuit and calculating the parameters of its elements without operator intervention, based on the admittance frequency characteristics. This algorithm enhances the functional capabilities of RLC meters and can be applied to solve practical problems related to identifying the substitution scheme of the investigated circuit. As an RLC meter measures the total resistance only at one or several fixed frequencies, obtaining an understanding of the substitution scheme from these measurements is challenging. To select the substitution scheme, an analysis of the impedance or admittance frequency characteristics is required. Typically, this analysis is performed manually and is time- consuming. The proposed algorithm automates the analysis of the admittance frequency characteristics. The algorithm associates values and the sequence of slopes of the admittance frequency characteristics with an array of known sequences and slope values for known substitution schemes. The calculation of substitution scheme parameters is based on the resonance frequencies and the heights of zero slopes. To minimize the impact of noise on result accuracy, a synchronous signal detection method is employed. The article introduces a criterion for assessing the algorithm's performance and conducts testing on several types of circuits. During testing, the relative error in calculating substitution scheme parameters was evaluated, with a maximum value not exceeding 6 %.

Power-frequency admittance model of multi-VSGs grid-connected system considering power coupling

The high penetration of renewable energy decreases the inertia of power systems. The virtual synchronous generator (VSG) control technology has good inertia compensation effect and has attracted considerable attention because of the similar external characteristics of synchronous generators. However, the power and frequency oscillation of multi-VSG grid-connected systems seriously threatens the stability of power system. Existing multi-VSG power frequency admittance (PFA) models ignore the power coupling caused by the large line impedance ratio in medium- and low-voltage microgrids, and the accuracy of these models needs improvement. Thus, this study aims to establish a multi-VSG grid-connected PFA model considering power coupling. The influence of power coupling on model accuracy is analyzed, and the impacts of line impedance and reactive loop coefficient on the power-frequency response characteristics are investigated. Simulation results verify that the proposed model has higher accuracy over existing models.

Fast, Accurate and Full Extraction of Coupling-of-Modes Parameters by Finite Element Method

This paper presents a new numerical approach for the full extraction of the coupling-of-modes (COM) parameters by stationary and eigenfrequency analyses in the finite element method (FEM). This is a fast method extracting from the results of static analysis and eigenfrequency analysis. It avoids the long calculation time of admittance frequency response analysis, which is commonly used in extracting COM parameters. In addition to the usual COM parameters (velocity, reflection coefficient, transduction coefficient and capacitance), the phases of reflection and transduction coefficient can be also extracted with this method. The proposed method was applied to different cutting types LiNbO3 with different types of thicknesses in a varying interdigital transducer (IDT). These examples show that our approach has great potential in extracting all the COM parameters of the Rayleigh SAW for all kinds of IDT structures. Therefore, it is a fast, accurate, general and full extraction approach of COM parameters.

Effects of Age and Middle Ear on the Frequency Tuning of the cVEMP and oVEMP.

Upward shift in the air conducted (AC) frequency tuning of vestibular evoked myogenic potentials (VEMPs) as an effect of aging is hypothesized to be due to the microstructural stiffening changes in the inner ear. However, with an AC stimulus, it may be possible that the shift in the frequency tuning of VEMPs as an effect of aging may also be due to contributions from the middle ear. The main aim of this study was to examine the effects of age on the frequency tuning of the cervical VEMP (cVEMP) and ocular VEMP (oVEMP) and determine the role of middle ear transmission characteristics in shaping these effects. Standard group comparison. One-hundred seven participants divided in three groups: young adult, middle-age, and older adults with "normal" middle ear and negative history of neurological or vestibular complaints. Middle ear measures included static admittance and middle ear resonant frequency. cVEMP and oVEMPs were elicited with AC tone bursts at 500, 750, and 1,000 Hz. No significant effect of age was observed on any of the middle ear measures. There was a significant effect of age on the amplitude of the cVEMP, but this effect was frequency specific. The age-related reduction in cVEMP corrected amplitude was only observed when the eliciting stimulus was 500 or 750 Hz, with no significant effect observed with a 1,000 Hz stimulus. For the oVEMP, the effects of age were apparent at all stimulus frequencies. We also observed a general upward shift in the frequency tuning of both the cVEMP and oVEMP for middle-age and older adults, with 750 and 1,000 Hz yielding higher response rates and larger amplitudes among middle-aged and older adults. Measurements of middle ear did not significantly contribute to the observed findings. The upward shift in frequency tuning of VEMPs among middle age and older adults could be due to the changes in the vestibular system and not from the middle ear. These results support the use of different frequency stimuli (i.e., 750 or 1,000 Hz) to elicit a VEMP if a response is absent using a 500 Hz stimulus, especially in patients over the age of 40.

Assessment of the Influence of Ground Admittance Correction and Frequency Dependence of Electrical Parameters of Ground of Simulation of Electromagnetic Transients in Overhead Lines

Assessment of the Influence of Ground Admittance Correction and Frequency Dependence of Electrical Parameters of Ground of Simulation of Electromagnetic Transients in Overhead Lines

Finite element simulation and characterization of one-port heterostructured surface acoustic wave resonator

The research work presents the study of a heterostructured surface acoustic wave (SAW) resonator consisting of an interdigital transducer (IDT), lithium niobate (LN), and silicon (Si) substrate. In the proposed structure, Silicon is the base substrate, above it layer of LN is placed then IDT is designed on it. The presented analysis includes the variation of the quality factor and electromechanical coupling coefficient with the change in the width of the piezoelectric layer. The electromechanical coupling coefficient (K 2), quality factor (Q-factor), velocity, resonance, admittance, and anti-resonance frequency have been studied for the thickness of the different layers of LN film. The higher quality factor of one port SAW devices reduces the energy loss and the K 2 of the devices indicates faster energy conversion. The Q-factor and K 2 are found to be depending on the thickness of LN, resonance, and anti-resonance frequency.

Coulomb interactions and effective quantum inertia of charge carriers in a macroscopic conductor

We study the low frequency admittance of a quantum Hall bar of size much larger than the electronic coherence length. We find that this macroscopic conductor behaves as an ideal quantum conductor with vanishing longitudinal resistance and purely inductive behavior up to f<1MHz. Using several measurement configurations, we study the dependence of this inductance on the length of the edge channel and on the integer quantum Hall filling fraction. The experimental data are well described by a scattering model for edge magnetoplasmons taking into account effective long range Coulomb interactions within the sample. This demonstrates that the inductance's dependence on the filling fraction arises from the effective quantum inertia of charge carriers induced by Coulomb interactions within an ungated macroscopic quantum Hall bar.

Cellulose Ester Insulation of Power Transformers: Researching the Influence of Moisture on the Phase Shift Angle and Admittance

This study investigates the frequency–temperature relations between the phase angle φ and admittance Y for composites of cellulose, synthetic ester, and water nanoparticles. We determined the activation energy value for the relaxation time of a phase shift angle ΔWφ ≈ (0.783 ± 0.0744) eV, which was related to the shift of φ(f) waveforms in higher frequency area with increasing temperature. We found that the position of admittance frequency waveforms in double logarithmic coordinates was simultaneously influenced by the temperature dependence of admittance and its relaxation time. Activation energy values for the relaxation time of admittance ΔWτ ≈ (0.796 ± 0.0139) eV and the activation energy value of admittance ∆WY ≈ (0.800 ± 0.0162) eV were determined. It was found that all three activation energy values were identical and their average was ΔW ≈ (0.793 ± 0.0453) eV. Impregnation with synthetic ester resulted in a decrease of activation energy by 0.26 eV compared to the impregnation with insulating oil. This was related to higher dielectric permittivity of the synthetic ester.

Piezoelectric Electro-Mechanical Impedance (EMI) Based Structural Crack Monitoring

To detect small cracks in plate like structures, the high frequency characteristics of local dynamics were studied with the piezoelectric electro-mechanical impedance (EMI) method, and damages were monitored by the changes of the EMI. The finite element simulation model of EMI was established, and numerical analysis was conducted. The simulation results indicated that the peak frequency of the piezoelectric admittance signal is a certain order resonance frequency of the structure, and the piezoelectric impedance method could effectively detect the dynamic characteristics of the structure. The piezoelectric admittance simulation and experimental study of aluminum beams with different crack sizes were performed. Simulation and experimental results revealed that the peak admittance frequency decreases with the increase of crack size, and the higher resonance frequency is more sensitive to the small-scale damage. The proposed method has good repeatability and strong signal-to-noise ratio to monitor the occurrence and development of small-scale crack damage, and it has an important application prospect.

High-frequency vibration analysis of LiTaO3 piezoelectric plates excited by lateral electric fields produced by surface electrodes under viscous liquid loadings for sensing

In this work, the coupled thickness-shear and flexural vibrations of the LiTaO3 piezoelectric plates excited by lateral electric fields produced by surface electrodes under viscous liquid loadings are modeled and analyzed based on Mindlin’s plate theory. The influences of liquid properties on the admittance characteristics and frequency shifts of the piezoelectric bulk acoustic wave devices operate in the lateral field excitation (LFE) mode are examined. In addition, the effects of the structure parameters, such as the electrode gap width, electrode/plate mass ratio and the electrode width, on the frequency sensitivity are investigated. It is shown that with the increasing electrode/plate mass ratio R, the sensitivities of the device on liquid viscosity and density increase first and then decrease, there is a maximal sensitivity when R is with a certain value. The varying trends of the frequency shifts with various liquid properties and sensitivities with various structural parameters are verified by the FEM simulations. The results are crucial to obtain good vibration characteristics and sensitivities for liquid-phase LFE piezoelectric sensors by using LiTaO3 piezoelectric crystals.

Measurement-based frequency-dependent model of a HVDC transformer for electromagnetic transient studies

A wide-band, frequency-dependent five-terminal model is developed that represents one HVDC transformer unit in the French-English IFA2000 HVDC interconnection. Three such interconnected 1-ph units constitute one 3-ph transformer bank needed in 12-pulse conversion. The model is obtained via admittance frequency sweep measurements on the transformer's terminals, including common-mode measurements to capture the high-impedance coupling to earth at lower frequencies. The data set is modified to reduce the magnetizing current to a realistic level by a novel eigenvalue scaling procedure. The final data set is subjected to modeling by a stable and passive rational model while utilizing a mode-revealing transformation to retain the accuracy of the small eigenvalues that are related to the high-impedance coupling to earth. The paper describes details related to the measurements and modeling steps as well as the many intermediate accuracy validations that were done. Also is described challenges in the measurements that resulted due to interference of the measurements by a nearby 400 kV overhead line. The model is applied in a time domain simulation of the complete HVDC link in normal operation where voltage waveforms resulting from line commutations are compared against those by a classical model with added stray capacitances.

Analysis methods for highly radiation-damaged SiPMs

Prototype SiPMs with 4384 pixels of dimensions 15×15μm2 produced by KETEK have been irradiated with reactor neutrons to eight fluences between 109 and 5×1014 cm−2. For temperatures between −30∘C and +30∘C capacitance–voltage, admittance–frequency, current–forward voltage, current–reverse voltage and charge–voltage measurements with and without illumination by a sub-nanosecond laser have been performed. The data have been analysed using different methods in order to extract the dependence on neutron fluence and temperature of the electrical parameters, the breakdown voltage, the activation energy for the current generation, the dark-count rate and the response to light pulses. The results from the different analysis methods are compared.

Admittance Characteristics of Radial and Thickness Vibrations of Thin Piezoceramic Disks

Experimental results on the forced radial and thickness vibrations of circular piezoceramic plates are analyzed. Experimental and theoretical amplitude–frequency plots for admittance and its active and reactive components are compared. It is established that the admittance–frequency characteristics are very dependent on the vibration mode and interelectrode capacitance. The calculations of admittance are in agreement with the experimental data.

A QCM humidity sensor based on fullerene/graphene oxide nanocomposites with high quality factor

This paper described a quartz crystal microbalance (QCM) humidity sensor based on fullerene (C60)/graphene oxide (GO) nanocomposites. Humidity sensing properties such as the quality factor, frequency response property, response/recovery time, and humidity hysteresis were measured and quantitatively compared with a GO based QCM humidity sensor. The experiments provided evidences that the GO film was viscous even at low relative humidity, which had a large impact on the measurable result of a GO coated QCM humidity sensor. As a result, the proposed sensor showed better performances at quality factor and dynamic response/recovery behavior than the GO based QCM humidity sensor. Based on the admittance analysis and frequency response analysis of the sensors, it was speculated that the introduction of C60 molecules into GO reduced the aggregation of the GO sheets and formed some hydrophobic isolation layers between the GO sheets, which could inhibit the water molecules permeation and maintain the mechanical stiffness of the C60/GO film.

Shaping of PWM Converter Admittance for Stabilizing Local Electric Power Systems

This paper suggests the concept of shaping the pulsewidth-modulated (PWM) converter admittance. The analytic admittance matrix equation, which is derived from the small signal model of a PWM converter, is formulized. Based on the damping coefficient and the natural frequencies of phase-locked loop and dc voltage loop, the variations in admittance frequency responses are discussed. In addition, the frequency response can be adjusted through pole placement using the gain of the current controller. The controller gain for a stable operation is designed by detailed understanding of the frequency response shape. Furthermore, to stabilize the local electric power systems (EPSs) that invoke instability through the interaction between constant power load PWM converters, the admittance shaping loop is utilized for the distributed generator PWM converters. Through computer simulation and hardware experiments, the proposed shaping guidance can effectively stabilize local EPS.

Out-of-equilibrium quantum dot coupled to a microwave cavity

We consider a superconducting microwave cavity capacitively coupled to both a quantum conductor and its electronic reservoirs. We analyze in details how the measurements of the cavity microwave field, which are related to the electronic charge susceptibility, can be used to extract information on the transport properties of the quantum conductor. We show that the asymmetry of the capacitive couplings between the electronic reservoirs and the cavity plays a crucial role in relating optical measurements to transport properties. For asymmetric capacitive couplings, photonic measurements can be used to probe the finite low frequency admittance of the quantum conductor, the real part of which being related to the differential conductance. In particular, when the quantum dot is far from resonance, the charge susceptibility is directly proportional to the admittance for a large range of frequencies and voltages. However, when the quantum conductor is near a resonance, such a relation generally holds only at low frequency and for equal tunnel coupling or low voltage. Beyond this low-energy near equilibrium regime, the charge susceptibility and thus the optical transmission offers new insights on the quantum conductors since the optical observables are not directly connected to transport quantities. For symmetric lead capacitive couplings, we show that the optical measurements can be used to reveal the Korringa-Shiba relation, connecting the reactive to the dissipative part of the susceptibility, at low frequency and low bias.

Finite Element Modeling and Synthesis of c-axis Tilted AlN TFBAR for Liquid Sensing Applications

Thin film bulk acoustic resonator (TFBAR) with c-axis tilted AlN finite element modeling was performed using COMSOL Multiphysics simulation software. Depending on the AlN c-axis tilt angle, dual mode TFBAR can be obtained that operate in longitudinal and shear mode: the former mode is a thickness-extensional mode, while the latter is a thickness-in plane-shear mode that is suitable for liquid sensing applications. The acoustic wave displacement, the resonator frequency and equivalent admittance of the TFBARs with different tilt angles and electrode thicknesses were simulated to obtain the optimum design (high electroacoustic coupling efficiency and large quality factor Q) for shear mode operation. Furthermore, AlN films having the c-axis tilted up to about 30̊ from the substrate normal were successfully grown on silicon (100) substrates by reactive rf magnetron sputtering technique at 200̊C.

A condensed transfer function method as a tool for solving vibroacoustic problems

Substructuring approaches are nowadays widely used to predict numerically the vibroacoustic behavior of complex mechanical systems. Some of these methods are based on admittance or mobility frequency transfer functions at the coupling interfaces. They have already been used intensively to couple subsystems linked by point contacts and enable to solve problems at higher frequency while saving computation costs. In the case of subsystems coupled along lines, a Condensed Transfer Function method is developed in the present paper. The admittances on the coupling line are condensed in order to reduce the number of coupling forces evaluated. Three variants are presented, where the transfer functions are condensed using three different functions. After describing the principle of the CTF method, simple structures will be given as test cases for validation.

Charge relaxation resistance in the cotunneling regime of multichannel Coulomb blockade: Violation of Korringa-Shiba relation

We study the low frequency admittance of a small metallic island coupled to a gate electrode and to a massive reservoir via a \emph{multi channel} tunnel junction. The ac current is caused by a slowly oscillating gate voltage. We focus on the regime of inelastic cotunneling in which the dissipation of energy (the real part of the admittance) is determined by two-electron tunneling with creation of electron-hole pairs on the island. We demonstrate that at finite temperatures but low frequencies the energy dissipation is ohmic whereas at zero temperature it is super-ohmic. We find that (i) the charge relaxation resistance (extracted from the real part of the admittance) is strongly temperature dependent, (ii) the imaginary and real parts of the admittance do not satisfy the Korringa-Shiba relation. At zero temperature the charge relaxation resistance vanishes in agreement with the recent zero temperature analysis [M. Filippone and C. Mora, Phys. Rev. B {\bf 86}, 125311 (2012) and P. Dutt, T. L. Schmidt, C. Mora, and K. Le Hur, Phys. Rev. B {\bf 87}, 155134 (2013)].