Multiples Of Frequency Research Articles

Electron spin noise under the conditions of nuclei-induced frequency focusing

We study theoretically the electron spin noise in quantum dots under non-equilibrium conditions caused by the pumping by a train of circularly polarized optical pulses. In such a situation, the nuclear spins are known to adjust in such a way, that the electron spin precession frequencies become multiples of the pump pulse repetition frequency. This so called phase synchronization effect was uncovered in [Science {\bf 317}, 1896 (2007)] and termed nuclei-induced frequency focusing of electron spin coherence. Using the classical approach to the central spin model we evaluate the nuclear spin distribution function and the electron spin noise spectrum. We show that the electron spin noise spectrum consists of sharp peaks corresponding to the phase synchronization conditions and directly reveal the distribution of the nuclear spins. We discuss the effects of nuclear spin relaxation after the pumping is over and analyze the corresponding evolution of nuclear spin distributions and electron spin noise spectra.

Harmonics and Mitigation Techniques Through Advanced Control in Grid-Connected Renewable Energy Sources: A Review

With more renewable energy based distributed generation (DG) units connected to utility power grids, deterioration of power quality at the point of common coupling (PCC) becomes a major concern. There are two types of harmonics associated with DG units, and together they may cause excessive harmonic distortion at the PCC. The first type of harmonics is generated by power electronic devices in DG units such as photovoltaic systems, which contains high-frequency harmonic components at multiples of the carrier frequency of the DG interfacing inverter. Such harmonics are first reviewed in this paper, and the potential operational effect at the system level due to LCL or LC filters installed at the inverter output to mitigate such harmonics are discussed. The second type of harmonics is generated by other nonlinear local, PCC, and utility loads in the system, which are common type of harmonics at multiples of the power grid frequency, 50/60 Hz. Harmonic mitigation for such harmonics achieved through advanced control of the DG interfacing inverter operated as a power quality conditioner are reviewed and summarized. This systematic review can facilitate better understanding of harmonics associated with renewable energy based DG units and provide guidelines on advanced control schemes to realize ancillary harmonic compensation service through DG interfacing inverters.

Harmonic Error Cancellation for Accurate Square-wave-based Bio-Impedance Measurements.

Bio-impedance spectroscopy, which measures impedance of the tissue over a frequency range, has been widely used to provide crucial information for monitoring human health. Its conventional methods using sine wave current stimulation of the tissue and sine wave demodulation of the resultant voltage provide an accurate impedance measurement, but involve bulky components and power inefficiency due to sinusoidal waveform generation and analog signal multiplication. Instead, the method using square wave clocks can be much more area and power efficient, but inherently has substantial errors in the measured result due to the presence of harmonics in square waves. In this paper we propose a technique to cancel the errors caused by harmonics of the square wave stimulation and demodulation. The technique, based on the fact that the magnitude ratio of all the harmonics of a square wave are known, cancels out harmonic errors by subtracting or adding the square-wave-based measured results at higher harmonics to the fundamental output as a simple post-processing calculation. Simulation results using a generic electrode and tissue model show that this technique can provide a precise measurement of the bio-impedance with <0.5% magnitude error and < 0.2 phase error considering just five frequency multiples. Because this method does not involve sinusoidal signal generation and analog mixing, it is adequate to be integrated in a wearable health monitoring device at low area and power overhead.

An investigation of spectral characteristic of displacement fluctuation and its effect on surface quality in precision machining

In precision machining, the machining conditions play an important role in part surface quality, because the characteristic of the exciting source in machine tools has a close relationship with the machining conditions. Therefore, this paper investigates the spectral characteristic of displacement fluctuation and its effect on the part surface quality for ball screw feed systems. The spectral characteristic is deduced by an equivalent disturbance model that considers the error sources of permanent magnet synchronous motor drives. In the spectrum of displacement fluctuation, the amplitudes of some spectral components increase with the load force; the corresponding frequencies are even multiples of the fundamental frequency of phase current and of the fundamental frequency of phase current plus or minus the rotor frequency. The resonance due to the variation of spectrum seriously deteriorates the part surface quality, leading to visible and characteristic patterns on the surface of machined parts. In the paper, two solutions to improve the surface quality are proposed and validated, i.e., the control method based on an adaptive filter and the method with constraint of feed rate.

Inflow-based flap control on a 10MW-scale wind turbine using a spinner anemometer

In the paper, an individual flap control (IFC) algorithm based on wind speed measurements obtained with a spinner anemometer is presented. The controller uses flap actuators with the aim to remove any deterministic source of load variation on blades, associated with asymmetries of the inflow. Such load variations are concentrated on multiples of the rotational frequency (p multiples) and they are mainly due to wind yaw, inclination and atmospheric boundary layer (ABL) shear. The aim of the controller is to assist operation of the conventional feed-back individual pitch controller (IPC) and thereby reduce its control duty cycle. The performance of the proposed controller is assessed through aero-elastic simulations for the 10MW DTU Reference Wind Turbine. A subset of normal operation fatigue and ultimate Design Load Cases (DLCs) of the IEC has been simulated and load reduction capabilities of the control algorithm have been compared against those of the standard individual pitch control (IPC) loop.

HARMONIC DOMAIN MODEL OF AN OPEN-LOOP CONTROLLED PWM CONVERTER

An harmonic domain model is developed for open-loop controlled voltage source inverters, which provides the steady-state solution for integer multiples of the fundamental frequency. The convolution of the switching function spectrum with the converter currents and voltages is used to describe the coupling of the AC side and the DC side. The modeling is based on a single phase leg and is extended to a single-phase and a three-phase voltage source inverter, which results in a non-linear algebraic equation system. For open-loop control the switching function is independent of the converter currents and voltages and the model is simplified to a linear equation system. This straightforward and fast model is verified by time domain simulations and experimental results. The modeling can be adapted to systems of coupled converters, which is presented for a back-to-back converter system showing the harmonic interaction of the connected subsystems.

Inharmonic speech reveals the role of harmonicity in the cocktail party problem

The “cocktail party problem” requires us to discern individual sound sources from mixtures of sources. The brain must use knowledge of natural sound regularities for this purpose. One much-discussed regularity is the tendency for frequencies to be harmonically related (integer multiples of a fundamental frequency). To test the role of harmonicity in real-world sound segregation, we developed speech analysis/synthesis tools to perturb the carrier frequencies of speech, disrupting harmonic frequency relations while maintaining the spectrotemporal envelope that determines phonemic content. We find that violations of harmonicity cause individual frequencies of speech to segregate from each other, impair the intelligibility of concurrent utterances despite leaving intelligibility of single utterances intact, and cause listeners to lose track of target talkers. However, additional segregation deficits result from replacing harmonic frequencies with noise (simulating whispering), suggesting additional grouping cues enabled by voiced speech excitation. Our results demonstrate acoustic grouping cues in real-world sound segregation.

Helicity asymmetry in strong-field ionization of atoms by a bicircular laser field.

Ionization of atoms by an intense bicircular laser field is considered, which consists of two coplanar corotating or counterrotating circularly polarized field components with frequencies that are integer multiples of a fundamental frequency. Emphasis is on the effect of a reversal of the helicities of the two field components on the photoelectron spectra. The velocity maps of the liberated electrons are calculated using the direct strong-field approximation (SFA) and its improved version (ISFA), which takes into account rescattering off the parent ion. Under the SFA all symmetries of the driving field are preserved in the velocity map while the ISFA violates certain reflection symmetries. This allows one to assess the significance of rescattering in actual data obtained from an experiment or a numerical simulation.

Characterization of Harmonic Signal Acquisition with Parallel Dipole and Multipole Detectors.

Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is a powerful instrument for the study of complex biological samples due to its high resolution and mass measurement accuracy. However, the relatively long signal acquisition periods needed to achieve high resolution can serve to limit applications of FTICR-MS. The use of multiple pairs of detector electrodes enables detection of harmonic frequencies present at integer multiples of the fundamental cyclotron frequency, and the obtained resolving power for a given acquisition period increases linearly with the order of harmonic signal. However, harmonic signal detection also increases spectral complexity and presents challenges for interpretation. In the present work, ICR cells with independent dipole and harmonic detection electrodes and preamplifiers are demonstrated. A benefit of this approach is the ability to independently acquire fundamental and multiple harmonic signals in parallel using the same ions under identical conditions, enabling direct comparison of achieved performance as parameters are varied. Spectra from harmonic signals showed generally higher resolving power than spectra acquired with fundamental signals and equal signal duration. In addition, the maximum observed signal to noise (S/N) ratio from harmonic signals exceeded that of fundamental signals by 50 to 100%. Finally, parallel detection of fundamental and harmonic signals enables deconvolution of overlapping harmonic signals since observed fundamental frequencies can be used to unambiguously calculate all possible harmonic frequencies. Thus, the present application of parallel fundamental and harmonic signal acquisition offers a general approach to improve utilization of harmonic signals to yield high-resolution spectra with decreased acquisition time. Graphical Abstract ᅟ.

STUDY ON PROCESS COORDINATION CAPABILITY FOR EARTH SURFACE IMAGING VIA VNREDSAT-1 OF VIETNAM AND BKA OF BELARUS

Leading companies in the field of obtaining data from Earth remote sensing from space are building Satellite constellations to increase the frequency (multiplicity) and monitor various parts of the Earth’s surface. The Satellite constellation remote sensing equipment from Airbus (France) allows daily observation of any point on the Earth’s surface with high spatial resolution, and the grouping of DigitalGlobe (USA) – with ultra-high spatial resolution. The analysis of the mutual exploitation of the national space systems of the Socialist Republic of Vietnam and the Republic of Belarus has been carried out. There have been analyzed the joint capabilities of VNREDSat-1 (Vietnam) and BKA (Belarus) Earth Observation Systems for the monitoring of natural resources, the environment and natural disasters by comparison of their space and temporal characteristics (orbit parameters and re-visit time) as well as spectral-energetic characteristics (space, spectral and radiometric resolutions). The accepted correlation of technical parameters for solving the previously mentioned tasks having into account the different phases of the mentioned satellites has been determined. The conclusions have been reinforced by the results of live experiments with archival and instant data from both EO satellites.

On the Robustness of CMOS-Chopped Operational Amplifiers to Conducted Electromagnetic Interferences

This paper deals with the robustness of low power chopped CMOS operational amplifiers (OpAMPs) to electromagnetic interferences (EMI) conducted at the device input stage. The main differences between chopped amplifiers and standard offset uncompensated ones are analyzed in terms of EMI susceptibility, achieving three main results. First, a new model is developed to show how chopping influences the amplifier susceptibility in a broadband sense, demonstrating that chopped OpAMPs generate a lower amount of EMI-induced offset from the nonlinear distortion with respect to standard ones because of the topological differences between the respective input stages. Second, a model to predict the effects of EMI appearing at the multiples of the chopping frequency is derived, showing that chopped OpAMPs can experience dc shift peaks because of the linear distortion of the disturbances whose frequencies hit the even multiples of the chopping frequency. Finally, the simultaneous presence of the technological offset and the offset produced by the nonlinear and the linear distortion of EMI in chopped OpAMP is illustrated by means of dedicated EMI susceptibility measurements performed on several devices designed to validate the analysis.

Effects of Noisy and Modulated Interferers on the Free-Running Oscillator Spectrum

A new methodology for the prediction of oscillator phase dynamics under the effect of an interference signal is presented. It is based on a semianalytical formulation in the presence of a noisy or modulated interferer, using a realistic oscillator model extracted from harmonic-balance simulations. The theoretical analysis of the phase process enables the derivation of key mathematical properties, used for an efficient calculation of the interfered-oscillator spectrum. The resulting quasi-periodic spectrum is predicted, as well as the impact of the interferer phase noise and modulation over each spectral component, in particular over the one at the fundamental frequency. It is demonstrated that under some conditions, the phase noise at this component is pulled to that of the interference signal. Resonance effects at multiples of the beat frequency are also predicted. In addition, the effects of interferer phase and amplitude modulation on the oscillator phase dynamics have been studied and compared. For that analysis, efficient simulation techniques have been developed. The analyses have been validated with experimental measurements in an FET-based oscillator at 2.5 GHz, obtaining excellent agreement.

Effects of Therapy With Semi-occluded Vocal Tract and Choir Training on Voice in Adult Individuals With Congenital, Isolated, Untreated Growth Hormone Deficiency

Voice is produced by the vibration of the vocal folds expressed by its fundamental frequency (Hz), whereas the formants (F) are fundamental frequency multiples, indicating amplification zones of the vowels in the vocal tract. We have shown that lifetime isolated growth hormone deficiency (IGHD) causes high pitch voice, with higher values of most formant frequencies, maintaining a prepuberal acoustic prediction. The objectives of this work were to verify the effects of the therapy with a semi-occluded vocal tract (SOVTT) and choir training on voice in these subjects with IGHD. We speculated that acoustic vocal parameters can be improved by SOVTT or choir training. This is a prospective longitudinal study without control group. Acoustic analysis of isolated vowels was performed in 17 adults with IGHD before and after SOVTT (pre-SOVTT and post-SOVTT) and after choir training (post training), in a 30-day period. The first formant was higher in post training compared with the pre-SOVTT (P = 0.009). The second formant was higher in post-SOVTT than in pre-SOVTT (P = 0.045). There was a trend of reduction in shimmer in post-choir training in comparison with pre-SOVTT (P = 0.051), and a reduction in post-choir training in comparison with post-SOVTT (P = 0.047). SOVTT was relevant to the second formant, whereas choir training improved first formant and shimmer. Therefore, this speech therapy approach was able to improve acoustic parameters of the voice of individuals with congenital, untreated IGHD. This seems particularly important in a scenario in which few patients are submitted to growth hormone replacement therapy.

Characterization and suppression of stripe artifact in velocity-selective magnetization-prepared unenhanced MR angiography.

To characterize and suppress stripe artifact associated with velocity-selective (VS) magnetization for unenhanced MRA. Extended phase graph formalism was used to show that the stripe artifact contains multiples of the fundamental frequency that is determined by the area of unipolar VS gradient. Four VS preparation pulses whose excitation profiles are spatially shifted by quarter the fundamental period of the stripes, were applied alternately. For further suppression of the artifact, k-space data at kz = 0 were averaged over the 4 VS preparations. The proposed schemes were tested in a chicken breast phantom and healthy human subjects. When the standard VS preparation scheme was used, stripe artifact was shown in all the reconstructed images and appeared as artifactual peaks in k-space that corresponded to the first and second order harmonics of the fundamental frequency. Alternate application of the 4 phase-shifted VS preparation pulses suppressed the stripes, but not completely, as evidenced by residual erroneous peaks in k-space. After the k-space averaging, the stripe artifact was nearly eliminated. Stripe artifact in VS-MRA consists of multiples of the fundamental frequency and can be effectively suppressed through alternate application of phase-shifted VS preparations along with k-space averaging.

Proposing a non‐linear microwave ring resonator for efficient multi‐tone generation

This research proposes a microstrip non-linear ring resonator (MNLRR) as a frequency comb generator. Due to multiple circulations of waves along the ring, they interact with the non-linear components several times; thus, in comparison with a microstrip non-linear transmission line with the same number of non-linear components, the MNLRR achieves a higher harmonic-conversion-efficiency. Furthermore, we distinguish three regimes of multi-tone generation for the proposed MNLRR. In the first regime of operation, generation of harmonics at integer multiples of the excitation frequency is observed. In the second regime, one recognises generation of spectral lines at the resonance frequencies of MNLRR in addition to degenerate four-wave mixing tones. Furthermore, we have shown that integer multiples of these spectral components are also excited. In the third regime, we encounter the generation of frequency components whose frequencies are input-power dependent. According to our measurement results, a higher level of excitation power is required for this regime. Here, the number of components increases while their spacing reduces by growing power level.

Analysis of the impact of interferers on VCO-based continuous time delta-sigma modulators

Analog to digital converters (ADCs) used in receivers, face desired and undesired signals. Undesired signals are located out-of-band (OOB) of interest and are stronger than the desired signal and degrade the performance of the ADCs. Continuous time (CT) delta-sigma modulators (DSMs) can provide inherent anti-aliasing and hence they relax the requirement of the dynamic range. In this paper the behavior of CT-DSMs, utilizing voltage controlled oscillators (VCOs), for receiver applications are studied. The results indicate that, due to the frequency modulation occurring in the VCOs, when interfering signals are applied at the half of the sampling frequency (fs), integer multiples of the carrier frequency (fc) and fc/2,fc/3…, modulation tones appear in the bandwidth of the desired channel. This leads to degradation of the signal to noise and distortion ratio (SNDR). An analytical expression for the output signal of the VCO-based integrator in the presence of the interferers has been derived. In addition, behavioral simulations are done for both cascade of integrators in the feedback structure (CIFB) and cascade of integrators in the feedforward structure (CIFF) as well as multi-stage noise shaping (MASH) structures. It will be discussed how the designer should choose the suitable structure.

Investigation on three‐phase seven‐level cascaded DC‐link converter using carrier level shifted modulation schemes for solar PV system applications

Three-phase seven-level cascaded DC-link converter (CDCLC) is proposed for solar photovoltaic (PV) applications. The proposed configuration is integrated with stepped DC-link module (DCLM) and H-bridge inverter. In CDCLC configuration, the stepped DC-link voltage is attained through DCLMs with reduced inverter voltage stress. Compared with conventional two-level and three-level inverters, power spectral density in the multiples of switching frequency is significantly reduced. Elimination of inverter end filter components emphasises the advantage of CDCLC systems over conventional inverters. A reduction in DC sources, power switches, and gate driver units make the system more cost-effective over conventional cascaded multilevel inverter. To achieve the quality of power output in the proposed converter, carrier level shifted pulse width modulation (CLSPWM) schemes are developed for the DC-link converter switching. Simulated and experimental models of three-phase seven-level CDCLC configuration are developed and its performance is analysed for CLSPWM switching schemes.

Micro-piezoelectric pulse diagnoser and frequency domain analysis of human pulse signals

BackgroundThe theory of pulse diagnosis is to assess the physiological condition of the human body using radial pulse. However, pulses can vary markedly from person to person. Further, pulse diagnosis is difficult to learn and requires one-on-one teaching. MethodsTo address this problem, we built a home-made pulse diagnoser and measured human pulses for studying the standardization of pulse diagnosis. Our pulse diagnoser was composed of a piezoelectric transducer, differential amplifier, data acquisition instrument, and a Matlab analysis program. The measured pulses were converted into electronic signals by a piezoelectric transducer and saved on a computer. The digitalized data were then refined and analyzed by fast Fourier transform for frequency analysis. Simulations were performed to assess the factors that affected the pulse, including phase shifts of reflected pulse waves (generate sub-peaks in pulses), inconsistent heart rates (deform pulse waves), the vessel stiffness (alter harmonic frequencies of the pulses), and the wave amplitudes (determined by the pulse strength). ResultsBy comparing a published report and our simulation findings, we characterized the pulse types and the effects of various factors, and then applied the findings to study actual pulses in patients. Three types of pulses were determined from the frequency spectrum—choppy pulse (Se mai) without apparent harmonic peaks, the harmonic frequencies of wiry pulse (Xian mai) that are non-integer multiples of the fundamental frequency, and surging pulse (Hong mai) that exhibit strong amplitudes in the spectrum of frequency. A normal pulse and a slippery pulse were differentiated by a phase shift, but not by assessing the frequency spectrum. ConclusionThese findings confirm that frequency domain analysis can avoid ambiguity arising in assessing the three types of pulses in the time domain. Further studies of other pulses in the frequency domain are required to develop a precise electronic pulse diagnoser.

Harmonic dynamic loading response of reinforced concrete column

A reinforced concrete column is classified as compression structural element mostly analyzed and designed due to the applied combinations of dead and live loading with other considered loadings. Industries of considerable or relatively great size, production and electrical utilities are very concerned about the presence of dynamic loads in their electrical power systems. This behavior provides current with different components that are multiples of the fundamental frequency of the system which are called harmonics. Reinforced concrete elements such as column must be checked for the strength capacity and the response due to applied harmonic loading after completed the static analysis and design. In present article evaluations of reinforced concrete columns under the effects of dynamic harmonic loadings are studied. The main parameters are the reinforcement ratio and harmonic ranged loadings. Finite elements approach was adopted to analyze the columns by ANSYS software and all models are simulated in three dimensions. The analysis results indicated that the square cross sections with that rectangular of the same cross sectional area are closed in performance against static and dynamic loadings.

Effect of external magnetic field on locking range of spintronic feedback nano oscillator

In this work we have studied the effect of external applied magnetic field on the locking range of spintronic feedback nano oscillator. Injection locking of spintronic feedback nano oscillator at integer and fractional multiple of its auto oscillation frequency was demonstrated recently. Here we show that the locking range increases with increasing external magnetic field. We also show synchronization of spintronic feedback nano oscillator at integer (n=1,2,3) multiples of auto oscillation frequency and side band peaks at higher external magnetic field values. We have verified experimental results with macro-spin simulation using similar conditions as used for the experimental study.