Sinusoidal Phase Research Articles

Detection of Acoustically Induced Interface Waves Using a Dual-Frequency Sinusoidal Phase Modulating Laser Interferometer and a Normalized PGC-Arctan Demodulation Algorithm

Detection of Acoustically Induced Interface Waves Using a Dual-Frequency Sinusoidal Phase Modulating Laser Interferometer and a Normalized PGC-Arctan Demodulation Algorithm

Active linearized PGC demodulation with fusion of PGC-Arctan and PGC-DCM schemes for nonlinear error elimination in SPM interferometer.

To eliminate the nonlinear error of phase generated carrier (PGC) demodulation in sinusoidal phase modulating interferometer (SPMI), an active linearized PGC demodulation with fusion of differential-and-cross-multiplying (PGC-DCM) and the arctangent (PGC-Arctan) schemes is proposed. In this method, the periodic integer multiple of π (π-integer phases) of PGC-Arctan without nonlinear error and the corresponding PGC-DCM results recorded at the same time are fused to obtain a calibration coefficient for PGC-DCM demodulation. Combining the accurate π-integer phases of PGC-Arctan and the calibrated fractional phase in the range of π of PGC-DCM, a linearized PGC demodulation result can be achieved, effectively eliminating the nonlinear error caused by drifts of phase demodulation depth (m) and carrier phase delay (θ). The distinct advantage of the proposed method is that it actively and linearly calibrates the fractional result of PGC-DCM without needing to measure or compensate m and θ. Simulation and displacement measurement experiments with different m and inherent arbitrary θ are performed to validate the proposed method. The experimental results show that nonlinear error of the proposed method can be reduced to about 0.1 nm with real-time linearization.

Spin-phonon and magnetoelectric coupling in oxygen-isotope substituted TbMnO3 investigated by Raman scattering

In order to investigate the effects leading to the strong magnetoelectric coupling in the type II multiferroic $\mathrm{Tb}\mathrm{Mn}{\mathrm{O}}_{3}$ we have studied the thermal properties and temperature dependence of the lattice vibrations of ${\mathrm{TbMn}}^{16}{\mathrm{O}}_{3}$ and its isotopically substituted counterpart ${\mathrm{TbMn}}^{18}{\mathrm{O}}_{3}$. Heat capacity measurements on powder samples revealed no significant change in the ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Tb}}^{3+}$ magnetic phase transition temperatures, as well as the multiferroic ordering temperature upon isotope substitution, indicating that a change in the dynamical modulation of the $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedral distortions and rotations altering the Mn-O-Mn bond angles has no influence on the magnetic properties of $\mathrm{Tb}\mathrm{Mn}{\mathrm{O}}_{3}$. Raman light scattering experiments have been performed on isotopically substituted single crystals to determine the temperature induced changes in phonon energies and linewidths at the sinusoidal and multiferroic phase transitions. A detailed modeling indicates that the spin-phonon coupling can be accounted for the pronounced anomalies in the temperature dependence of the phonon behaviors at the transition to the sinusoidal spin phase at ${T}_{\mathrm{N}}^{\mathrm{Mn}}=41$ K and to the multiferroic spin-spiral phase at ${T}_{\mathrm{FE}}=28$ K. No further effects such as the appearance of the electric polarization or the electromagnon were required to explain the data, especially below the multiferroic phase transition.

Generation of high performance optical chirped pulse for distributed strain sensing application with high strain accuracy and larger measurement range.

A photonic approach for generating low frequency drifting noise, arbitrary and large frequency chirping rate (FCR) optical pulses based on the Kerr effect in the nonlinear optical fiber is theoretically analyzed and experimentally demonstrated. Due to the Kerr effect-induced sinusoidal phase modulation in the nonlinear fiber, high order Kerr pulse with a large chirping rate is generated. In the concept-proof experiments, the FCR of the mth Kerr pulse has been significantly improved by a factor of 2m+1. In addition, dynamic strain measurement along with a random fiber grating array (RFGA) sensor by using different order Kerr pulse is carried out for demonstrating a large strain measurement range with lower uncertainty sensing capability. Benefiting from the use of a single laser source and large FCR Kerr pulse, the system exhibits a 3.9 µɛ static strain measurable range, 0.24 µɛ measurement uncertainty by using -4th order Kerr pulse that has an FCR up to 0.8 GHz/ns. Note that the FCR of the chirped pulse could be further enhanced by using larger FCR chirped pulse seed or choosing higher order Kerr pulses.

The Fucoxanthin Chlorophyll a/c-Binding Protein in Tisochrysis lutea: Influence of Nitrogen and Light on Fucoxanthin and Chlorophyll a/c-Binding Protein Gene Expression and Fucoxanthin Synthesis

We observed differences in lhc classification in Chromista. We proposed a classification of the lhcf family with two groups specific to haptophytes, one specific to diatoms, and one specific to seaweeds. Identification and characterization of the Fucoxanthin and Chlorophyll a/c-binding Protein (FCP) of the haptophyte microalgae Tisochrysis lutea were performed by similarity analysis. The FCP family contains 52 lhc genes in T. lutea. FCP pigment binding site candidates were characterized on Lhcf protein monomers of T. lutea, which possesses at least nine chlorophylls and five fucoxanthin molecules, on average, per monomer. The expression of T. lutea lhc genes was assessed during turbidostat and chemostat experiments, one with constant light (CL) and changing nitrogen phases, the second with a 12 h:12 h sinusoidal photoperiod and changing nitrogen phases. RNA-seq analysis revealed a dynamic decrease in the expression of lhc genes with nitrogen depletion. We observed that T. lutea lhcx2 was only expressed at night, suggesting that its role is to protect \\cells from return of light after prolonged darkness exposure.

Algorithms for Real-Valued Noisy Damped Sinusoid Parameter Estimation

In this paper an improved version of three state-of-the-art Interpolated Discrete-Time Fourier Transform (IpDTFT) algorithms for the estimation of the frequency and the damping factor of noisy damped sinusoids is proposed. Sinusoid amplitude and phase are also estimated. Improvement is obtained by both compensating the effect on the estimated parameters of the spectral leakage from the fundamental image component and minimizing the estimator variance through a suitable selection of the interpolation points. The obtained estimates are then further improved by applying a linear signal fit (LSF) algorithm. The accuracies of the proposed algorithms are compared with each other and with the related Cramer-Rao Lower bound through computer simulations. The required computational times are also briefly analyzed in order to assess the algorithms usefulness in real-time applications.

Nonlinear errors correction based on trapezoidal plus sinusoidal phase shifting algorithm

相移轮廓术是一种广泛使用的光学三维测量方法，其精度不仅受相位展开算法本身的影响，也受测量系统中投影仪和摄像机的非线性影响。理论上，投射更多的相移条纹可减弱非线性误差的影响，但是增加了测量时间。为了提高误差校正的效率，提出了一种基于梯形正弦相移的测量方法。该方法需要两组改进的梯形相移条纹和一幅正弦条纹。梯形条纹提供图像强度信息和条纹级次信息，图像强度信息用来求取系统的非线性响应曲线，进一步消除系统的非线性。正弦条纹经过希尔伯特变换可求得额外的条纹图像，用来计算截断相位信息。经过校正的截断相位信息，可进一步获取精度较高的三维信息。相较于先前的梯形与正弦误差校正方法，该方法的测量效率提高了28%。

Square-wave drive for synchronous reluctance machine and its torque ripple analysis

Synchronous reluctance machine (SynRM) can be perceived as a special type of permanent magnet synchronous machine (PMSM), and shares similar control method, i.e. the sine-wave current drive with sinusoidal phase currents. In this paper, square-wave drive, which is employed for permanent magnet brushless (BLDC) motors, is employed for the SynRM, in order to economically reduce the cost of rotor position sensor. It is revealed that the torque density and efficiency are slightly sacrificed, whereas torque ripple is deteriorated, proving the SynRM with square-wave drive still promising for the cost-sensitive application if torque ripple is not considered as a critical issue. To further investigate the additional pulsating torque under square-wave drive, mathematical model based on a-b-c phase inductance and d-q axis inductance are established, together with the time-stepping FE calculated currents. It is concluded that the harmonics in the currents tend to cause non-sinusoidal variation of the magnetic reluctance, which can be represented as additional inductance harmonics. The harmonics of the current and inductance interact with each other, thus undesirable torque ripple components are produced.

Group-velocity dispersion emulator using a time lens.

We report a novel method to continuously track the temporal evolution of an arbitrary complex waveform as it propagates through a group-velocity dispersion medium by using a single-frequency-driven phase modulator. The proposed method exploits the fact that the frequency spectrum of a given (input) waveform, following a suitable sinusoidal temporal phase modulation, exhibits the same shape as that of a dispersed version of the same temporal waveform after propagation through a prescribed amount of dispersion. In experiments, we track the dispersion-induced temporal evolution of different optical picosecond pulsed waveforms by tuning the frequency and/or amplitude of the phase modulation signal and observing the resulting shapes in the optical frequency domain. A good agreement is obtained between the measured spectra and predicted temporal shapes of the propagating waveform for different amounts of dispersion. Moreover, the method is successfully applied on a chirped optical pulse to find the optimal pulse compression conditions.

New class of fractal elements with log-periodic corrections: Confirmation on experimental data

In this paper, the authors propose a theory to describe the behavior of the new type of fractal element which exihibit complex-conjugated power-law exponents. To explain the impedance behaviour of these elements, log-periodic corrections are employed. So far, the impedance of fractal elements are studied which shows power law behaviour in a limited frequency band; and they are modeled as band limited constant phase element. However, the proposed theory is able to describe the impedance behaviour of the fractal element in the entire frequency zone of measurement. To validate the theory, NanoTubes (MWCNTs) based 10 fractal elements are fabricated which exihibit sinusoidal type phase response in the frequency zone from 1 Hz to 4 MHz (it is to be noted that the measurement range of the instrument is 10 mHz to 4 MHz). The derived fitting formula is expressed in the squared log-normal term and contain log-periodic corrections. The proposed fitting formula, incorporated in the paper, will facilitate to explore the deterministic nature of the log-periodic oscillations in complex systems. Earlier these oscillations were considered random or counterintuitive and is misinterpreted as the results of measurement artifacts. Besides, it will find application in modelling the spatially extended systems and also to the analysis of nonlinear dynamics in a complex system. Moreover, one can combine the conventional resistance, capacitance and inductance in one “hybrid” combination using the theory.

Nb/Au/NbSe2 hybrid Josephson junctions

We fabricated thin film Nb/Au/NbSe2 hybrid Josephson junctions by a dry transfer technique with only a single lithography step in the process. A thin Au layer is deposited on Nb to prevent oxidation during the fabrication process. The superconducting van der Waals (vdW) material NbSe2 is placed on top of the Nb/Au layer. Electrical transport properties are studied in detail and are compared to numerical simulations. The current–voltage characteristics we observe are typical for superconductor-normal metal-superconductor junctions and we do not observe an effect of a potential insulating barrier between NbSe2 and Au. The modulation of the critical current in magnetic fields indicates an inhomogeneous distribution of supercurrent density, presumably caused by the roughness of the Nb/Au interface to NbSe2. Nevertheless, we observe clear integer Shapiro steps, indicating a sinusoidal current phase relation of junctions. We do not see an impact of the anisotropic s-wave and the charge density wave in NbSe2 on the Josephson effects. Our method presents a viable and simple way to fabricate hybrid Josephson junctions between superconducting films and two-dimensional (2D) vdW superconducting materials, which might offer a chance for widespread applications.

Self-correction of air refractive index in distance measurement using two-color sinusoidal phase modulating interferometry

A two-color sinusoidal phase modulating (SPM) interferometer based on electro-optic modulator (EOM) is devised for self-correction of air refractive index in distance measurement. Two laser sources with high frequency stability and close wavelengths (633 nm and 782 nm) are used in this scheme. High-accuracy phase demodulation was realized using phase generated carrier (PGC) demodulation techniques with an FPGA-based signal processing board. Experimental results of nanometer displacement measurements show that the resolution and accuracy of PGC demodulation is better than 1°, and the nonlinear error is less than 0.2°. Performance tests of two-color SPM interferometer compared with one-color interferometers under dynamic environment were implemented with an arm length difference of 4 m. The results show that, the measured distance of one-color interferometer drifts 4.8 μm in 600 s, which is caused by the deviation between the measured value of air refractive index and the actual value along the laser propagation path, and this drift reduces to ±1.5 μm using two-color interferometer without environmental sensing.

Generation of Flexible hyperbolic Airy-like beams using a truncated acousto-optical effect

In this paper, we demonstrate the shaping of an incident Gaussian beam into a tunable hyperbolic Airy-like beam, using an acoustooptics cell. The latter contains a transparent liquid (water), where an ultrasound wave propagating and creating a sinusoidal refractive index variation (giving rise to a sinusoidal phase transmittance). By adding an aperture, this sinusoidal phase transmittance becomes equivalent to a cubic phase (sin(x)≈x−x3/3! for x<0.2λa, λa is the ultrasound wavelength), which allows the generation of a tunable Airy-like beam. Using the Fresnel-Kirchhoff diffraction integral, we derive analytical expressions for the diffracted Gaussian beam by the acoustooptics cell in two cases; (a) with and (b) without the aperture. For the first case, the algebra is straightforward and the field has a closed analytical expression, however for the second case, the diffraction integral has no analytical expression, thus, we expand the aperture into a weighted sum of Gaussian functions, to overcome such problem. Based on the obtained mathematical expressions, we study the effect of each parameter of the acoustooptics interaction, on the propagation behavior of the generated Airy-like beam. We believe that the results of this paper could be useful for many interesting applications, involving Airy beams, such as particle manipulation, optical tweezing, and optical communication.

Accurate Measurement for the Subsequent Perturbation in the Coherent Φ-OTDR System with Small Laser-Frequency-Drift

In the coherent Φ-OTDR system with small laser-frequency-drift less than 50 kHz, the phase change in the quiet region without external perturbation is theoretically deduced to be linear with the fiber length while its waveform in the direction of pulse sequence is highly similar with the external perturbation acting on the fiber before the quiet region. Moreover, the phase information of one position contains the perturbation information of all foregoing positions. Consequently, a simple and accurate solution of differential operation for acquiring the phase information of subsequent perturbation which is behind the initial perturbation occurring on the fiber is proposed. The fitted phase change trace between the foregoing and the subsequent perturbation is extended to the region behind the subsequent perturbation. Then, behind the subsequent perturbation, the extended phase change trace is subtracted by the fitted phase change trace containing two perturbations. Moreover, in order to afford the fitting data with less noise as much as possible, the phase changes at positions where the value of modulus of coherent Φ-OTDR is lower than the set threshold value is firstly eliminated. To verify these methods, an experiment with two PZT vibrations in this paper is described. For the subsequent PZT vibration, the sinusoidal phase signal with a frequency of 50 Hz is perfectly retrieved when the threshold is set to be 10 mV. And the discussion about threshold value shows that it is satisfactory for the accuracy of phase extraction of the subsequent perturbation if the threshold is set as or above the noise level in the form of modulus in the experiment.

Research on resonance splitting under sinusoidal modulation in resonant optic fiber gyro

In this study, the sinusoidal phase modulation and demodulation principle in resonant fiber optic gyro (RFOG) are introduced. The RFOG simulation system is established, through which the relationship between resonance splitting and modulation frequency of dual-frequency sawtooth and sinusoidal signal is obtained. The resonance splitting is then explained based on sideband spectrum theory. The experimental device is built and the results show that there are obvious resonance splitting and distortion in linear region of demodulation output, when the sinusoidal frequency is higher than FWHM/2. Finally, the feasibility of the sideband frequency locking technology is verified by resonance splitting based on sideband spectrum theory, providing theoretical support for this novel technology, which can suppress backscattering noise effectively.

A comparison of strategies for state‐selective coherent Raman excitation

AbstractWe report on the theoretical and experimental evaluation of state‐selective bond activation for coherent Raman spectroscopy and control of chemical reactivity. We compare six different strategies for state‐selective activation using shaped broadband femtosecond laser pulses. Results for a pair of long pulses with different wavelengths are also considered. For each of these approaches, we report on their theoretical and experimental ability to excite a desired vibrational mode while minimizing excitation of other modes including harmonics. We find that the double parabola spectral phase function gives the most intense Raman excitation with 10 cm−1 selectivity with the lowest background. The sinusoidal phase function produces intense Raman excitation with high selectivity but gives a series of harmonic excitations which could hinder selectivity. Implications of this study on several fields ranging from sensing, to controlling chemical reactions, and selective excited state excitation by X‐ray pulses are discussed.

Focusing characteristics of linearly polarized Lorentz-Gaussian vortex beams with sinusoidal phase modulation.

Based on the vector diffraction theory, this paper investigates the focusing properties of linearly polarized Lorentz-Gaussian vortex beams with sinusoidal phase modulation and discusses the focused light intensity under different parameters in detail. Results show that the focus pattern in the horizontal direction at the focal region can be compressed by increasing the relative Gaussian parameter wx. As the relative Lorentz parameter γy increases, the focus pattern will separate in the vertical direction of the optical field. With the topological charge number m increases, a special tunable optical dark trap focusing mode can be obtained. Through changing the sinusoidal modulation parameter n, the regular trilateral, quadrangle, pentagon, and hexagon shapes of the focusing mode can be correspondingly constructed. Besides, on increasing propagation distance z, the focusing mode in the near focusing region gradually extends outside and always exhibits hexagon-shaped patterns, which reflects that this special focusing mode has a good stability. In addition, the optical gradient force distributions and the field intensity distributions in the longitudinal plane are also investigated to illuminate the applications of these alterable focal patterns. Those novel, to the best of our knowledge, findings may be helpful in applications such as optical manipulation, optical focusing, and imaging.

Prevalence of Vestibular Disorders in Independent People Over 50 That Experience Dizziness.

People aged over 50 are the most likely to present to a physician for dizziness. It is important to identify the main cause of dizziness in order to develop the best treatment approach. Our goal was to determine the prevalence of benign paroxysmal positional vertigo (BPPV), and peripheral and central vestibular function in people that had experienced dizziness within the past year aged over 50. One hundred and ninety three community-dwelling participants aged 51–92 (68 ± 8.7 years; 117 females) were tested using the clinical and video head impulse test (cHIT and vHIT) to test high-frequency vestibular organ function; the head thrust dynamic visual acuity (htDVA) test to test high-frequency visual-stability; the dizziness handicap inventory (DHI) to measure the impact of dizziness; as well as sinusoidal and unidirectional rotational chair testing to test low- to mid-frequency peripheral and central vestibular function. From these assessments we computed the following measures: HIT gain; htDVA score; DHI score; sinusoidal (whole-body; 0.1–2 Hz with 30°/s peak-velocity) vestibulo-ocular reflex (VOR) gain and phase; transient (whole-body, 150°/s2 acceleration to 50°/s constant velocity) VOR gain and time constant; optokinetic nystagmus (OKN) gain and time constant (whole-body, 50°/s constant velocity rotation). Our study showed that BPPV, and peripheral or central vestibular hypofunction were present in 34% of participants, suggesting a vestibular cause to their dizziness. Over half (57%) of these with a likely vestibular cause had BPPV, which is more than twice the percentage reported in other dizzy clinic studies. Our findings suggest that the physical DHI score and VOR time constant were best at detecting those with non-BPPV vestibular loss, but should always be used in conjunction with cHIT or vHIT, and that the htDVA score and vHIT gain were best at detecting differences between ipsilesional and contralesional sides.

Entropy generation of a nanofluid in a porous cavity with sinusoidal temperature at the walls and a heat source bellow

PurposeThis paper aims to focus on the analysis of the entropy generation in an inclined square cavity filled with a porous media saturated by a nanofluid with sinusoidal temperature distribution on the side walls, adiabatic conditions on the upper wall and a heat source at the lower wall.Design/methodology/approachThe two-phase nanofluid model including the Brownian diffusion and thermophoresis effects has been used for simulation of nanofluid transport inside the porous cavity. The governing equations and the entropy generation owing to fluid friction, heat and mass transfer are transformed in terms of the dimensionless variables, and the results are obtained by using the finite difference method of the second-order accuracy.FindingsThe numerical results of the model are investigated, and the effect of different important parameters, such as inclination angle of the cavity, amplitude ratio of the sinusoidal temperature or phase deviation, is discussed. The results for no inclination of the cavity is compared and successfully validated with previous reported results of the literature. The important findings of the study are focused mainly on the existence of the irreversibility phenomena which are affected by the conditions of the model and the values of the studied parameters.Originality/valueThe originality of this work is given by the presented mathematical model, the numerical solution with new results for entropy generation in an inclined porous cavity filled by a nanofluid and the applications for design of electronic or energy devices.

Fault-Tolerant Control of Dual Three-Phase PMSM Drives With Minimized Copper Loss

In this article, a minimum-copper-loss fault-tolerant control scheme is proposed for open-phase fault and open-switch fault of dual three-phase permanent magnet synchronous motor (DT-PMSM) drives. Both the winding configurations of isolated neutral points and connected neutral points are studied in this article. In conventional minimum-copper-loss fault-tolerant control schemes, the constraints of sinusoidal phase currents result in insufficient copper-loss reduction. Different from them, the current references with the theoretically lowest copper losses are first derived and applied for different fault cases of DT-PMSM drives without using any unnecessary constraints in the proposed fault-tolerant control scheme. Thus, all phase currents in the proposed minimum-copper-loss fault-tolerant control scheme are optimized to be nonsinusoidal waveforms. Besides, the copper losses are further reduced by fully utilizing the remaining healthy switch in the faulty inverter leg for the open-switch fault of DT-PMSM drives with the proposed scheme. It has been theoretically and experimentally proved that the proposed fault-tolerant control scheme can reduce copper losses than all existing fault-tolerant schemes for both open-phase fault and open-switch fault in typical two-level voltage-source-inverter-fed DT-PMSM drives.