Effect Of Frequency Variation Research Articles

Effects of Stimulus Frequency and Location on Vibrotactile Discrimination Performance Using Voice Coil Actuators on the Forearm

What are the effects of frequency variation of vibrotactile stimuli on localization acuity? The precise localization of vibrotactile stimuli is crucial for applications that are aimed at conveying vibrotactile information. In order to evaluate the ability to distinguish between vibrotactile stimuli based on their frequency and location on the forearm, we used a relative point localization method. Participants were presented with pairs of sequential vibrotactile stimuli at three possible locations on the forearm and asked to determine whether the second stimulation occurred at the same location as the first one in the pair or not. The stimulation frequency varied between 100 Hz, 150 Hz, 200 Hz and 250 Hz, which covers the range of frequencies that human observers are most sensitive to. The amplitude was kept constant. Our results revealed that the ability to discriminate between actuators remained unaffected by variations in the frequency of vibrotactile stimulation within the tested frequency range. The accuracy of the tactile discrimination task was heavily dependent on the location of the stimulation on the forearm, with the highest accuracy close to the wrist and elbow, locations that may serve as tactile anchor points. Our results highlight the critical role of stimulation location in precise vibrotactile localization and the importance of careful consideration of location in the design of forearm-mounted vibrotactile devices.

Distributed Economic Dispatch Control Method with Frequency Regulator for Smart Grid under Time-Varying Directed Topology

The paper studies a new distributed control method to solve the economic dispatch problem (EDP) under directed topology based on consensus protocol. Electrical equipment is closely related to frequency, and the frequency of each generator varies independently during operation. Therefore, it hinders the realization of economic dispatch. To solve the problem, we combine a frequency regulator with a consensus protocol, which eliminates the effect of frequency variation on the designed consensus algorithm. Meanwhile, considering the problem of excessive communication cost and low computational efficiency in large-scale power systems, an event-triggered mechanism is introduced into the designed algorithm. Furthermore, in order to overcome the unexpected loss of communication links, the time-varying topology mechanism is employed to develop the distributed economic dispatch (DED) algorithm to improve the robustness. Then, the stability of the above algorithm is proved by graph theory and convergence analysis. Finally, several simulations illustrate that our proposed methods are effective.

Grid power quality enhancement using an ANFIS optimized PI controller for DG

Grid frequency variation causes phase angle deviation in current with respect to voltage. This is sensed at the phase-locked loop in the controller. In past studies the effect of grid frequency variation is neglected while designing the controller for power quality restoration. When modern grids are connected to large numbers of non-linear loads and various types of distributed generation (DG), it results in continuous variation in grid frequency. Thus it is necessary to consider the grid frequency variation for effective power quality restoration. However, tuning of conventional PI controller gains considering frequency variation is very difficult. Thus it is necessary to develop an adaptive intelligent nonlinear controller to tackle the effects of frequency variation, voltage distortion and non-linear load simultaneously. This paper presents the importance of considering the effects of the frequency variation, grid voltage distortion and non-linear load, while designing and deploying a controller for power quality restoration. The proposed controller supplies power to local load as well as transferring surplus power to the grid from DG along with the additional benefit of improving grid power quality. A DG with an ANFIS optimized PI current controller for power quality enhancement is proposed. The method is economical as it requires no additional hardware. Results are compared with PI, PI-RC and fuzzy current controllers to validate the effectiveness of the proposed controller.

DC offset rejection in a frequency-fixed second-order generalized integrator-based phase-locked loop for single-phase grid-connected applications

Fast and accurate monitoring of the phase, amplitude, and frequency of the grid voltage is essential for single-phase grid-connected converters. The presence of DC offset in the grid voltage is detrimental to not only grid synchronization but also the closed-loop stability of the grid-connected converters. In this paper, a new synchronization method to mitigate the effect of DC offset is presented using arbitrarily delayed signal cancelation (ADSC) in a second-order generalized integrator (SOGI) phase-locked loop (PLL). A frequency-fixed SOGI-based PLL (FFSOGI-PLL) is adopted to ensure better stability and to reduce the complexity compared with other SOGI-based PLLs. A small-signal model of the proposed PLL is derived for the systematic design of proportional-integral (PI) controller gains. The effects of frequency variation and ADSC on the proposed PLL are considered, and correction methods are adopted to accurately estimate grid information. The simulation results are presented, along with comparisons to other single-phase PLLs in terms of settling time, peak frequency, and phase error to validate the proposed PLL. The dynamic performance of the proposed PLL is also experimentally validated. Overall, the proposed PLL has the fastest transient response and better dynamic performance than the other PLLs for almost all performance indices, offering an improved solution for precise grid synchronization in single-phase applications.

Frequency Domain Characteristic Analysis of Fault Electrical Quantities in HVDC Transmission System

The transient frequency domain characteristics of different fault electrical quantities in HVDC transmission system are studied in this paper firstly using analytical calculation. Firstly, the equivalent model of LCC converter suitable for DC system fault characteristic analysis and the equivalent model of DC line considering parameter frequency variation effect are established. On this basis, the DC system fault equivalent circuit is constructed. The frequency domain expressions of relevant electrical quantities under different DC line fault conditions are obtained according to the solution of equivalent circuit. On the basis of the frequency domain expression of fault electrical quantity, the frequency component diagram of fault electrical quantity is obtained. Finally, the frequency spectrum of fault voltage under different fault conditions is analyzed and compared.

ANALISIS MATERIAL SERAT ALAM TEBU SEBAGAI BAHAN PEREDAM SUARA

Abstract 
 Material Sugarcane natural fiber material can be used as a sound absorber material. In measuring the value of the sound absorption coefficient of the cane natural fiber silencer using the sound level meter application on the smartphone to measure the intensity of sound (dB) and the frequency generator application connected to the speaker as a sound source (Hz). The test uses an acoustic box as a miniature room that will be tested for its sound absorption coefficient values coated with sugarcane natural fibers. The purpose of this study is to find out the influence of sugarcane fibers in reducing noise and to find out the effect of frequency variations on the value of the sound absorption coefficient. Measurement of the noise level of the sugarcane natural fiber material on the acoustic wall produces different sound absorption coefficient values based on variations in the frequency of the sound source. The greater the frequency value, the higher the absorption coefficient value. Frequency variations used include 500 Hz, 1000 Hz, 1500 Hz, 2000 Hz, 2500 Hz, and 3000 Hz. The value of the sound absorption coefficient drops at a frequency of 1000 Hz but there is a re-increase at frequencies above 1500 Hz. The smallest sound absorption coefficient is obtained at the time of frequency 1500 Hz with a value of = 0.01047 and the largest at the time of frequency 3000 Hz with a value of = 0.10139. The coefficient value is too small, so it is not effective in muffling the sound.

Suppression of Spurious Cavity Modes Using Lossy Dielectric Material in X-Band Tunable Coaxial Pulse Magnetron

This article presents the electromagnetic and particle-in-cell (PIC) simulation results of an X-band coaxial magnetron obtained using commercially available 3-D simulation tools CST particle studio. The operating frequency of the magnetron is 9.5 GHz with the tuning range of 8.5-9.5 GHz and the output power of 200 kW. It is observed by simulation that stable operation is not possible without eliminating the spurious cavity modes. For this purpose, the inner wall of the anode block has been loaded with the lossy dielectric material in the form of an annular cylinder having dielectric permittivity 23 and loss tangent 0.24. When the anode wall is loaded with lossy dielectric material, eight space charge spokes are observed during the stable operation of the magnetron which correspond to π-mode of operation in a coaxial magnetron having 16 vanes. A clear oscillation spectrum with a single peak is observed at 9.350 GHz with no other noticeable peaks. The radiated output power obtained in simulations is about 235 kW, with an anode voltage of 23 kV and an anode current of 30 A. The applied external magnetic field is 0.36 T and the corresponding efficiency of the magnetron operation is ~34%. The frequency tunability of the magnetron and the effect of frequency variation on the output power of the magnetron have also been studied by varying the length of the outer coaxial cavity. The frequency has been varied from 8.65 to 9.577 GHz and the corresponding variation in the output power is about 16%.

Characterisation of Signal Amplitude-Frequency for Indoor Power Line Communication Channel in the 1 — 30 MHz Broadband Frequencies

The transmission of data signals over power lines is a very promising technique for delivering indoor broadband communication services. However, since power grids were originally designed for high-voltage low-frequency signal transmission, there is a frequency mismatch between the power grid and high-frequency data signals. This mismatch poses a challenge to deploying power lines as a communication channel. Although, studies and researches conducted in several countries have made transmission of data over power lines possible, the behaviour and properties of the power grid cannot be generalised. Hence, the need for in-depth experiment and measurement on the suitability and capability of the Nigerian power grid for data transmission is crucial for proper characterising and modelling of the power line communication (PLC) channel. In this paper, we present experimental measurements and results of the effects of frequency variations on the attenuation experienced by broadband high-speed data signals transmitted over the Nigerian indoor power line network.

Effects of Frequency on the Induced Fields of Deep Transcranial Magnetic Stimulation Systems: A Numerical Case Study

Transcranial Magnetic Stimulation (TMS) is a neurophysiological technique that is used as a noninvasive diagnostic and therapeutic tool for neurological conditions. This paper addresses the effects of frequency variation on magnetic and induced electric fields for deep brain stimulation scenario, considering the hippocampus region of the brain. A modified magnetic resonance coupling (MMRC) coil is designed and utilised to stimulate a realistic human head model at frequencies from 1 to 30 kHz, with constant and variable excitation current scenarios, while considering safety guidelines inside the brain. Sensitivity analysis is performed to quantify the reliability of field estimates. It is found that, although the maximum value of the induced electric field increases linearly with frequency, the general pattern of that field distribution inside the head demonstrates frequency-independent behaviour. Both depth of stimulation and field focality demonstrate a noticeable change with frequency below 12 kHz, while these attributes are almost saturated above this frequency band when using MMRC coil. It is also noted that, although increasing operating frequency can reduce the excitation current, the safety of the patient is prone to be jeopardized. Hence, to choose the optimum frequency range for the TMS system, several factors including, safety limits, stimulation threshold, desired magnetic flux density, power consumption, and target depth should be considered. This study provides a systematic approach to analyse the efficacy of deep TMS (dTMS) systems by making adequate trade-offs for the frequency selection to stimulate the targeted depth without exceeding safety limits, while using minimum possible power.

Investigation on Electrical Properties of Solid Polymer Sheets (HDPE AND LDPE) at Audio Frequency Range

Two different groups of solid polymer sheets: low density polyethylene (LDPE) sample of thickness 0.006 cm and 0.007 cm along with high density polyethylene (HDPE) sample of the thickness of 0.009 cm, 0.010 cm were taken in this work. The measurement of electrical properties such as dielectric constant, ε' and dielectric loss, ε'' for LDPE and HDPE polymer sheets have been measured using a dielectric cell. The dielectric cell has been fabricated which consists of two circular parallel plates of pure stainless steel each of 5 cm diameter and 2 mm thickness. An impedance bridge (GRA 650A) was used for measurement of capacitance, C, and dissipation factor, D in the audio frequency (AF) range, 100 Hz to 10 kHz. Different samples were loaded in between the two plates of the cell and the capacitance as well as the dissipation factor were estimated from the dial readings of the bridge. Effect of frequency variation on ε', ε'', relaxation time, τ , dissipation factor, tanδ and ac conductivity, σ were also discussed at audio frequency range. The complex permittivity, ε*, related to free dipole oscillating in an alternating field and loss tangent, tanδ were calculated. The frequency-dependent conductivity, dielectric behavior, and electrical modulus, both real (M') and imaginary (M") parts of LDPE and HDPE have been studied in this work. The values of the real part of the electrical modulus (M') did not equal to zero at low frequencies and it is expected that the electrode polarization may develop in both sheets. These findings reveal an increased coupling among the local dipolar motions in a short-range order localized motion. The analysis of real (ε') and imaginary (ε'') parts of dielectric permittivity and that electrical modulus real (M') and imaginary (M") parts signify poly dispersive nature of relaxation time as observed in Cole-Cole plots.

Neural Network Model for Magnetization Characteristics of Ferromagnetic Materials

The magnetic characteristics of silicon steel sheet 30Q120 under different AC frequencies were measured by an Epstein frame in order to analyze the effects of frequency variation on the hysteresis loop of ferromagnetic materials and compare the differences of such materials at different frequencies. First, the forecasting method of the magnetic properties of ferromagnetic materials under the influence of frequency using neural network was proposed based on the measured experimental data. Hysteresis loops at different frequencies were obtained. Then, the obtained results were compared with the measured results. Second, the dynamic Jiles–Atherton hysteresis model was established based on the Jiles–Atherton hysteresis theory, and hysteresis loops at different frequencies were obtained. The accuracies of the neural network model and Jiles-Atherton hysteresis model were verified by comparing the simulation results with the measured data. Upon comparing the dynamic Jiles–Atherton hysteresis and the neural network hysteresis models, results show that the latter has better accuracy. Furthermore, the correctness and effectiveness of the proposed method are verified.

Effect of resonant frequency variation on the ultrasonically assisted deep drawing process: numerical and experimental study

This paper focuses on the system frequency variation effect on the ultrasonically assisted deep drawing (UADD) process, based on experimental and numerical approaches. A special ultrasonic die is precisely designed and fabricated to improve draw-ability and reduce the forming force. The longitudinal resonance frequency of the vibratory system is established as 20 kHz prior to forming load application on the system. Consequently, a three-dimensional finite element model of the deformation process is developed. The output of this simulation shows good agreement with the experimental test results. The UADD test with 5 μm amplitude demonstrated 5.6% decrease in maximum average force and 12.2% increase in the drawing ratio when compared with the conventional deep drawing (CDD). In addition, the resonant frequency variation effect on the forming force is revealed during the experimental tests. Since the excitation frequency is tuned out with the natural frequency of the system at the beginning of the test, no forming force reduction was observed at this stage. To further investigate this effect, two complementary steps are implemented in this work. In the first phase, the natural frequency of the system is determined by numerical modal analysis and reshaping the blank at various deformation stages. Consequently, forced vibrations with frequencies very close to the natural frequencies, calculated from the first phase, are applied to the system in the second phase, to simulate the forming process. Based on the validated numerical model, the forming force, friction force, and material flow stress distributions are disclosed for UADD in various excitation frequencies.

Modeling and Analyzing the Effect of Frequency Variation on Weak Grid-Connected VSC System Stability in DC Voltage Control Timescale

The effect of frequency variation on system stability becomes crucial when a voltage source converter (VSC) is connected to a weak grid. However, previous studies lack enough mechanism cognitions of this effect, especially on the stability issues in DC voltage control (DVC) timescale (around 100 ms). Hence, this paper presented a thorough analysis of the effect mechanism of frequency variation on the weak grid-connected VSC system stability in a DVC timescale. Firstly, based on instantaneous power theory, a novel method in which the active/reactive powers are calculated with the time-varying frequency of voltage vectors was proposed. This method could intuitively reflect the effect of frequency variation on the active/reactive powers and could also help reduce the system order to a certain extent. Then, a small-signal model was established based on the motion equation concept, to depict the effect of frequency variation on the weak grid-connected VSC system dynamics. Furthermore, an analytical method was utilized to quantify the effect of frequency variation on the system’s small-signal stability. The quantitative analysis considered the interactions between the DC voltage control, the terminal voltage control, phase-locked loop, and the power network. Finally, case studies were conducted, and simulation results supported the analytical analyses.

Design, fabrication and reliability study of piezoelectric ZnO based structure for development of MEMS acoustic sensor

This paper reports a piezoelectric zinc oxide (ZnO) based acoustic sensor for high sound pressure level (SPL) with wide bandwidth for audio and aeroacoustic applications. The proposed structure has been simulated using finite element method (FEM) based MEMS-CAD tool Coventorware and optimized the dimensions of the diaphragm for a large dynamic range of 100-180 dB sound pressure level (SPL) and large bandwidth (22 kHz). The resonant frequency of the simulated structure is 67 kHz. Optimized structure dimensions have been chosen and fabricated the structure. The diaphragm structure has been released using bulk micromachining wet etching process. The ZnO thin film of 1.71 µm has been deposited using radio frequency (RF) sputtering technique and characterized using X-ray powder diffraction (XRD) and atomic force microscopy (AFM). The resonant frequency of the fabricated device is measured using laser doppler vibrometer (LDV) and found to be 65 kHz. The experimental sensitivity of the fabricated device is measured and is found to be 80 μV/Pa. The reliability testing of the fabricated structure was performed. The maximum current that can be passed across aluminum (Al) and deposited ZnO edge was found to be 2.69 A without any damage. The electrical characterization such as capacitance, loss (tan $$\delta$$) of fabricated device parameters were measured and the effects of frequency variation on both were also studied.

Pre-stretch and frequency variation effect on the dielectric permittivity of a dielectric elastomer: an amended permittivity model

In the present letter, we model the pre-stretch and frequency parameter effect on the dielectric permittivity of a dielectric elastomer. The present work is the extension of our most recent work (Kumar and Sarangi in Mech Mater 128:1–10, 2019) in case of deformable smart material. In particular, pre-stretching as well as frequency parameter variables majorly affect the deformation mechanism of a dielectric elastomeric material. In line with this, we first develop a new amended permittivity model of a dielectric elastomeric material based on the fundamental laws of physics. This amended permittivity model successfully enrols the pre-stretch and frequency parameter effect on the dielectric permittivity of a dielectric elastomer. Additionally, the amended permittivity model also successfully resolves the existing numerical inaccuracies of the previously known permittivity models in large deformations. Next, the formulated amended permittivity model is calibrated with some available experimental data, and compared to a known permittivity model existing in the literature.

Harmonic Virtual Impedance Design for Parallel-Connected Grid-Tied Synchronverters

In recent years, synchronverters have become a preferred control solution for the integration of renewable energy sources and battery systems to power networks. In this control strategy, the converter acts as a fundamental frequency voltage source and, as such, is unable to deal with harmonic power quality issues. In this paper, the harmonic control is frequently addressed using virtual impedances; however, they have been seldom studied for synchronverters. This paper presents a detailed design procedure for harmonic virtual impedances applied to parallel-connected synchronverters. The proposed method offers a tailor-made design of the converter output impedance and large stability margins. The method is used to decouple the dynamics of the synchronverter control, and the proposed virtual-impedance is explained in detail. The obtained results showed the output impedance of each synchronverter can be designed to achieve a tradeoff in power quality between current and voltage. In addition, the effect of frequency variations was explored and two solutions were provided and compared. All the control system improvements were experimentally validated using two 15-kVA battery-supported synchronverters connected to a distorted weak grid.

Analysis of Current Harmonics Compensation and the Effect of Frequency Variation for Single-Phase Stand-Alone PV Inverters using PR Controller

ABSTRACTThis paper presents the analysis of current harmonics compensation using the proportional-resonant controller for single-phase stand-alone photovoltaic inverter applications. The effect of frequency variation in the reference signal to the controller performance was also analyzed. The controller parameters (Kp, Ki, and ωc) and the inductor-capacitor (LC)-filter parameters are optimally selected to obtain a very low current total harmonic distortion . The control algorithm was implemented using a low-cost digital signal processor (DSP) TMS320F28335 eZdsp development board. Both simulation and experimental results validate the performance and the effectiveness of the control technique used.

Investigation of Flutter Mechanisms of a Contra-Rotating Open Rotor

The growing pressure to reduce fuel consumption and cut emissions has triggered renewed interest in contra-rotating open rotor (CROR) technologies. One of their potential issues is self-excited or forced vibration of the unducted, light-weight, highly swept blades. This paper presents a numerical study into the flutter behavior of a CROR rig at take-off conditions. The study presented in this paper aimed to validate the numerical approach and provide insights into the flutter mechanisms of the open rotor under investigation. For the initial validation, pressure profiles and thrust coefficients from steady-state mixing plane calculations were compared against rig measurements. A full domain unsteady analysis predicted front rotor instability at low advance ratios. Flutter occurred in the first torsional mode in 0 and 1 nodal diameter (ND) which agreed with experimental observations. Subsequent unsteady computations focused on the isolated front rotor and first torsional mode. The flow field and aerodynamic damping over a range of advance ratios were studied. It was found that minimum aerodynamic damping occurred at low advance ratios when the flow was highly three-dimensional on the suction side. A correlation between the quasi-steady loading on the blade and aeroelastic stability was made and related to the numerical results. The effects of variations in frequency were then investigated by linking local aerodynamic damping to the unsteady pressure on the blade surface.

Robust phase locked‐loop algorithm for single‐phase utility‐interactive inverters

An accurate, robust and efficient transport-delay based phase-lock loop (TDPLL) algorithm is proposed for single phase utility interactive inverters. The traditional TDPLL has low complexity and its transient response is smooth, but its performance is significantly affected by the change in the grid frequency. The proposed TDPLL is designed to have robustness against grid frequency variations. The proposed method uses two delays instead of one to cancel the grid frequency variation effect. Since the grid voltage could be polluted by harmonics and may suffer from sag/swell anomalies, the proposed method is enhanced further to be robust against these sources of disturbances. Moreover, a method is proposed to tune the parameters of the system. The performance of the proposed PLL is validated through simulations and experimental results.

Effect of frequency variation and covariation on auditory streaming of tone sequences

Recent results from our lab show the masking of one tone sequence by another to be strongly related to the information divergence of sequences, a measure of statistical separation of signals [Gilbertson et al., POMA 19, 050028 (2013)]. The present study was undertaken to determine if the same relation holds for the auditory streaming of tone sequences. An adaptive procedure was used to measure thresholds for streaming of ABAABA tone sequences wherein the frequencies of the A and B tones varied independently of one another (r = 0) or covaried within the sequence (r = 1). The procedure adapted on the difference Δ in the mean frequencies of A and B tones (normally distributed in cents) with the mean frequency of A tones fixed at 1000 Hz. For most listeners, Δ increased monotonically with increases in the variance of the tone frequencies (σ = 0-800 cents), but did not differ significantly for r = 0 and r = 1. For other listeners, Δ was a nonmonotonic function of variance and differed for r = 0 and r = 1. The results fail to support a strong relation between auditory streaming and the information divergence of tone sequences.