Constant Frequency Modulation Research Articles

Low Conducted-EMI Single-Phase Boost PFC with Sliding Frequency Modulation.

A boost Power Factor Correction (PFC) circuit is connected between the AC grid and converters to meet Electromagnetic Interference (EMI) and Total Harmonic Distortion (THD) standards. An EMI filter should be utilized at the input of the PFC to attenuate high-frequency noise injected into the grid. This article discusses the low-conducted EM emission boost PFC with Sliding Frequency Modulation (SFM) proposed by Power Integrations. The proposed boost PFC is compared with a conventional boost PFC operated using Constant Frequency Modulation (CFM) at 120 kHz. Both PFCs are rated for the same nominal power (i.e., 300 W) and output voltage (i.e., 383 V). An analytical loss model is also developed to compare the performance of the SFM and CFM PFCs. The analytical findings are verified by means of simulations and experiments.

Visualization of oscillatory electron dynamics on the surface of liquid helium

We investigate the time traces of currents induced in five segmented electrodes by the motion of electrons on the surface of liquid $^{4}\mathrm{He}$ at $\ensuremath{\sim}0.3$ K, that are placed in a perpendicular magnetic field and exposed to microwave radiation. Nonlinear dynamics methods are utilized to explore the characteristic features of the current oscillations in the electrodes for different electron densities and pressing voltages. The wavelet phase coherence and phase shift are calculated to obtain the coherence relationships between the signals in all five electrodes as functions of the pressing voltage. Coupling analysis of the ridge-extracted instantaneous frequencies revealed the directions of motion of electrons inside the cell and provided evidence of strong phase coupling at a pressing voltage of 4.20 V. These classical methods reveal that the motion is oscillatory, with a varying frequency subject to a constant frequency modulation. High harmonics due to nonlinearity arise at higher frequencies where the resonance condition is satisfied at a pressing voltage of 4.20 V for low-electron density. Our approach provides a platform for investigating these phenomena analytically. We show that slow gravity waves on the helium surface modulate the electronic oscillatory behavior and illustrate that the model in fact produces three-dimensional dynamics. Motion of electrons on the surface of liquid helium is shown to be a paradigmatic example of a chronotaxic system, i.e., a system that undergoes continuous perturbation but is nonetheless capable of maintaining its stability.

Experimental and theoretical investigations on the modulation capabilities of a sample of vertical cavity surface emitting laser diodes for atomic vapour applications

This paper discusses various frequency modulation and intensity modulation capabilities within a sample of direct laser current modulated identical vertical cavity surface emitting laser diodes. The presented analysis is based on measurements of the spectral amplitudes as a function of the applied modulation power at a constant modulation frequency of 3.517 GHz. Their evaluation by Bessel function fits produces the three modulation parameters: frequency modulation index, intensity modulation index (via the alpha parameter) and the side band asymmetry of the first order side bands. The variation of the laser diode’s modulation capability is discussed. It is found that the individual laser diodes show a significant variations in their modulation capabilities. Thus an experimental preselection of the laser diode is required to find laser diodes which are suitable as a light source for atomic vapour applications, with special emphasis on a coherent population trapping-based scalar magnetometers.

Maximum-Power-Per-Ampere Variable Frequency Modulation for Dual Active Bridge Converters in Battery-Balancing Application

Varying the operating frequency helps dual-active bridge topologies increase the system efficiency since the soft-switching is regained at low-load condition. This article proposes a conduction-loss-based variable frequency modulation (VFM) that decouples the phase-shift from the frequency control that conventional VFM applies. The power losses for the shared-bus battery-balancing topology are elaborated as switching frequency varies. The results show that increasing the operating frequency within the reasonable boundaries can benefit not only the switching loss but also the conduction losses. The switching loss is nearly constant, whereas the conduction losses decrease significantly. A factor of output power and transformer current, namely power-per-ampere, is derived as a function of operating conditions and phase-shift independent of switching frequency. The operating setpoints are selected to minimize the factor using both online and offline optimizations. The proposed control strategy outperforms constant frequency modulation by up to 30% below 30% rated power. Furthermore, compared with conventional VFM, the proposed method improves the efficiency of the system under test by 1.5% below 50% normalized power, with significantly less computational resources needed.

The Optics and Optimal Control Theory Interpretation of the Parametric Resonance

The aim of the article is the elaboration of parametric resonance theory at piecewise constant frequency modulation. The investigation is based on the analogy with optics and optimal control theory (OCT) application. The exact expressions of oscillation frequency, gain/damping coefficients, dependencies of these coefficients on the modulation depth, duty ratio and initial phase are derived. First of all, the results obtained on the basis of the energy behavior analysis (at the conjunction conditions execution) in frictionless systems are presented. The well-known parametric resonance triggering condition is revised and adjusted. The heuristic feedback introduction (based on the energy behavior analysis) in the oscillation equation permits one to prove that the frequency modulation satisfying the parametric resonance condition is not necessary and sufficient condition of the oscillations unlimited increase. Their damping/shaking up formally corresponds by the frequency and duty ratio to the condition of the equality of optical paths to the quarter-wavelength characteristic of the interference filter or mirror. The unity of space-time coordinates shows itself in this specific form of the optical-mechanical analogy due to the general Hill’s equation description. It is marked that this equation theory underlies most of metamaterials advantages because all transport phenomena imply different wave – electromagnetic, acoustic, spin etc. propagation one way or another. The question about control uniqueness arises that is modulating frequency, duty ratio and signature sign uniqueness. Another question of characteristic index extremum at different controls is tightly bound with the former. The answers to these questions are obtained on the basis of OCT. The similarity of the optimal control problem solution and the one obtained at the heuristic feedback introduction through fundamental solutions product permits one to introduced the new form named general or mixed Hamiltonian along with the ordinary and OCT Hamiltonians. Besides this mixed Hamiltonian equality to zero together with the Wronskian constancy (almost everywhere) is the useful analogous in form to the Liouville’s theorem equation. The nonlinearity accounting using the OCT formalism is described too.

Microscopía fototérmica para el estudio de transformaciones de fase

RESUMEN Se presenta el desarrollo de un novedoso sistema que permite el mapeo con alta resolución espacial de la difusividad térmica en función de la temperatura hasta 1800K. El sistema se basa en una técnica fototérmica recientemente desarrollada por el grupo, consistente en la medición con un láser de prueba de la curvatura inducida por el calentamiento con un láser modulado. La utilización de tecnología de fibras ópticas provee una alta robustez al equipo. Un horno para microscopio permite realizar rampas a velocidad controlada para el estudio de transiciones de fase y la medición de la difusividad térmica en función de la temperatura. Se pueden establecer mesetas para hacer barridos espaciales con resolución microscópica para el estudio de la evolución de las fases o hacer tratamientos térmicos in situ para estudiar luego la distribución espacial de las fases presentes. En este trabajo se presenta un ejemplo, donde la señal es colectada para un punto fijo y para una dada frecuencia de modulación, en función de la temperatura de la muestra. Se diseña para ello un sistema de corrección de enfoque que compensa la deriva térmica generada por la expansión térmica del sistema. El desplazamiento lateral es corregido utilizando un algoritmo de correlación y la imagen de la cámara. Este dispositivo fue utilizado para determinar la transición de fase de una muestra testigo. Estas capacidades se muestran a partir de la determinación de la energía de activación de la transformación de fase amorfo-cristal de una aleación de Fe-B-Si.

Unified Equivalent Circuit Model and Optimal Design of <inline-formula><tex-math>$V^{2}$</tex-math> </inline-formula> Controlled Buck Converters

$V^{2}$ control has advantages of simple implementation and fast transient response and is widely used in industry for point-of-load applications. This control scheme is elegant when output capacitors with large RC time constant are employed, such as OSCON capacitors. However, in most cases using capacitors with small RC time constant, such as ceramic capacitors, instability problem will occur. Previous modeling methods including sampled-data modeling, discrete-time analysis, time-domain analysis, and describing function are all very mathematical and difficult to apply for practical engineers as little physical insight can be extracted. Up to now, no equivalent circuit model is proposed which is able to predict the instability issue and serve as a useful design tool for $V^{2}$ control. This paper proposes a unified equivalent circuit model which is applicable to all types of capacitors by considering the effect of capacitor voltage ripple. The equivalent circuit provides the physical insight of $V^{2}$ control as a nonideal voltage source, a dual concept of previous nonideal current source for current-mode control. The equivalent circuit model is a simple yet accurate complete model and is very helpful for design purpose. Optimal design guidelines for point-of-load applications are provided. The proposed equivalent circuit model is applicable to both variable frequency modulation and constant frequency modulation. The equivalent circuit model and design guidelines are verified with Simplis simulation and experimental results.

A study of surface texturing using piezoelectric tool holder actuator on conventional CNC turning

Tribology studies have recently shown the beneficial reduction in the friction coefficient of various mechanical components by application of surface texturing. This study presents a study of surface texturing using a piezoelectric tool holder actuator whereby the tool holder installed on a conventional computerized numerical controlled (CNC) machine lathe. The tool holder used in surface texturing a workpiece surface, yields average strokes up to 26 ?m and has a natural frequency of approximately 480 Hz. A piezo actuator of 15 μm maximum displacement was utilized, and a single parallel four-bar flexure hinge mechanism magnified the input displacement from the piezo actuator by an amplification ratio of 3:1. In this study, a piezo actuator that operated under the open-loop condition, in modulation frequency range from 100 Hz to 135 Hz, was imposed to cut into the workpiece surface to build a pattern of dimples. Moreover, the characteristics of the dimple-pattern topography were investigated by varying the spindle rotation rate between 30 rpm and 100 rpm at constant modulation frequency of 120 Hz. According to the experimental results, Al 6061-T6 and AISI 1045 were successfully textured by using the piezoelectric tool holder actuator. The results showed that the maximum errors of the dimple feature on Al 6061-T6 and AISI 1045 were approximately 10.14% and 47.97%, respectively, between the analysis and experimental results.

Complex-optical-field lidar system for range and vector velocity measurement

A coherent lidar system based on the measurement of complex optical field is demonstrated for the first time. An electro-optic in-phase/quadrature (I/Q) modulator is used in the lidar transmitter to realize carrier-suppressed complex optical field modulation in which the positive and the negative optical sidebands can carry independent modulation waveforms. A fiber-optic 90° hybrid is used in the lidar receiver for coherent heterodyne detection and to recover the complex optical field. By loading a constant modulation frequency on the lower optical sideband and a wideband linear frequency chirp on the upper sideband, vector velocity and target distance can be measured independently. The wide modulation bandwidth of this lidar system also enabled unprecedented range resolution and the capability of measuring high velocity unambiguously.

Cascade amplification of self-similar frequency-modulated pulses in normal group velocity dispersion active fibres

This paper examines the possibility of efficient amplification of self-similar frequency-modulated wave packets in longitudinally inhomogeneous active fibres. We analyse the dynamics of parabolic pulses with a constant frequency modulation rate and derive algorithms for optimising the group velocity dispersion profile in order to ensure self-similar propagation of such pulses. We demonstrate that the use of a cascade scheme can ensure efficient amplification of individual subpicosecond pulses of this type.

Amplification of frequency-modulated soliton-like pulses in inhomogeneous optical waveguides with normal dispersion

The possibility of effective amplification of self-similar frequency-modulated pulses (FMPs) in longitudinally inhomogeneous active optical waveguides is studied. Peculiarities of the dynamics of parabolic pulses with a constant frequency modulation rate are considered. An optimal profile of variation of the group velocity dispersion was obtained in correspondence with optimal amplification of a similariton-like pulse. The use of FMPs in amplifying and longitudinally inhomogeneous optical waveguides with a correspondingly matched profile of normal dispersion of group velocities is shown to be capable of providing for an amplification of subpicosecond pulses up to energies above 1 nJ.

Digital Pulsewidth Modulation Technique for a Synchronous Buck DC/DC Converter to Reduce Switching Frequency

It has been shown that the resolution of a digital pulsewidth modulator (DPWM) can be dramatically increased by either constant on-time modulation control or constant off-time modulation control as compared to that for constant frequency modulation. However, the switching frequency increases dramatically for the constant on/off-time modulation method under heavy/light load conditions, respectively. The increase of switching frequency results in more switching losses and requires a higher performance controller. The objective of this paper is to propose a new digital pulsewidth modulation (PWM) technique with constant on/off-time control for a synchronous buck dc/dc converter in order to reduce the switching frequency and switching losses. Moreover, the switching frequency can be limited to a certain range. Experimental results of the proposed new digital PWM technique are presented for confirmation. It will be shown that the proposed technique can significantly reduce the switching frequency of the converter, thereby improving DPWM resolution and the efficiency.

Full range complex spectral domain optical coherence tomography for volumetric imagingat 47 000 A-scans per second

In this paper we demonstrate a high speed spectral domain optical coherence tomography(SDOCT) system capable of achieving full range complex imaging at a line scan rate of47 kHz. By applying a beam-offset method, a constant modulation frequency is introducedinto each B-scan that enables reconstruction of the full range complex SDOCTimages of in vivo tissue samples. To make use of the full capacity of the detectioncamera used in the system, system control software is developed that streams theraw spectral fringe data directly into the computer memory. In order to assessperformance of the high speed full range SDOCT system for imaging biologicalspecimen, we present results imaged from the cuticle of the fingernail of a humanvolunteer in vivo and from chick embryos ex vivo. We also show the high sensitivityadvantages of full range complex imaging as compared to conventional SDOCT. Tothe best of our knowledge, an imaging rate of 47 000 A-scans per second is thehighest imaging rate that has ever been reported for full range complex imaging.Notwithstanding, the method reported here has no limitations on the imaging speed andthus offers a useful tool to achieve volumetric imaging of living samples where the highsensitivity region around zero delay line in the system can be utilized for imaging.

Optical Microangiography: A Label-Free 3-D Imaging Technology to Visualize and Quantify Blood Circulations Within Tissue Beds In Vivo

Optical microangiography (OMAG) is a recently developed volumetric imaging technique that is capable of producing 3D images of dynamic blood perfusion within microcirculatory tissue beds in vivo. The imaging contrast of OMAG image is based on the intrinsic optical scattering signals backscattered by the moving blood cells in patent blood vessels, thus it is a label free imaging technique. In this paper, I will first discuss its recent developments that use a constant modulation frequency introduced in the spectral interferograms to achieve the blood perfusion imaging. I will then introduce its latest development that utilizes the inherent blood flow to modulate the spectral interferograms to realize the blood perfusion imaging. Finally, examples of using OMAG to delineate the dynamic blood perfusion, down to capillary level resolution, within living tissues are given, including cortical blood perfusion in the brain of small animals and blood flow within human retina and choroids.

Directional blood flow imaging in volumetric optical microangiography achieved by digital frequency modulation

An effective digital frequency modulation approach to achieve directional blood flow imaging within microcirculations in tissue beds in vivo for optical microangiography is presented. The method only requires the system to capture one three-dimensional data set within which the interferograms are modulated by a constant frequency modulation that gives one directional flow information. The result is that the imaging speed is doubled and the computational load is halved. The method is experimentally validated by a flow phantom and is tested for imaging of cerebral vascular blood perfusion in a live mouse with the cranium left intact.

Spectral domain polarization sensitive optical coherence tomography achieved by single camera detection

We present a spectral domain polarization sensitive optical coherence tomography (PSOCT) system that incorporates: 1) a spectrometer configured with a single line-scan camera for spectral interferogram detection, 2) a reference delay line assembly that provides a fixed optical pathlength delay between the lights of two orthogonal polarization states, and 3) a moving reference mirror that introduces a constant modulation frequency in the spatial spectral interferograms while the probe beam is scanned over the sample. The system utilizes the full range of complex Fourier plane for polarization sensitive imaging, where OCT images formed by the vertical and horizontal polarization beam components appear adjacent to each other. It is able to provide imaging of retardation, fast optic axis and backscattered intensity of the interrogated biological tissue. The system is experimentally demonstrated both in vitro and in vivo with an imaging rate at 10,000 A scans per second.

Frequency-resolved photocurrent studies of a-

In-quadrature frequency-resolved photocurrent (FRPC) measurements were performed on amorphous (a-) thin films between 20 K and 290 K, and as a function of excitation intensity. These measurements yield lifetime distributions directly. We have obtained a recombination lifetime of about s for . This lifetime was found to be independent of excitation intensity and temperature. It is explained in terms of the capture of nonequilibrium carriers. We also present the temperature and intensity dependences of the FRPC response of at a constant modulation frequency. They give information about recombination kinetics.

Detection thresholds of random amplitude modulation

The main objective of this study was to determine the detection thresholds of random amplitude modulation (RAM) as a function of modulation and carrier frequency. Two experiments were performed. Experiment 1 concerned the detection thresholds of AM stimuli for only random amplitude changes at constant modulation frequency. Experiment 2 dealt with detection thresholds for simultaneous, random changes in amplitude and modulation frequency. The data obtained showed that for low modulation frequency, the detection thresholds for sinusoidal amplitude modulation (SAM), random amplitude modulation at constant modulation frequency [RAM(fm const)], and random amplitude and modulation frequency [RAM(fs random)] overlapped one another in the limit of SD. However, for higher carriers and modulation frequencies the RAM(fm const) thresholds were, in a limited range offm , much lower than the SAM ones. When random changes in modulation frequency were combined with random changes in amplitude, the RAM(fm random) thresholds decreased relative to the RAM(fm const) thresholds. a)Permanent address: Institute of Acoustics, Adam Mickiewicz University, Poznan ul. Matejki 48/49, Poland.

Step-scan FT-IR photothermal spectral depth profiling of polymer films

Abstract In step-scan Fourier transform infrared (FT-IR) spectroscopy, a constant modulation frequency can be applied to the entire spectral range. This is particularly useful for photoacoustic (PA) detection since, in the absence of saturation, the PA response at all wavelengths in step-scan FT-IR PA spectroscopy will correspond to the same depth in the sample, whereas in a typical continuous-scan FT-IR PA spectrum each wavelength corresponds to a different sampling depth. A step-scan FT-IR PA spectral depth profile can be obtained by changing the modulation frequency for different scans. Alternatively, depth information can be obtained from the phase of the PA signal. The step-scan mode of data collection permits easier access to the PA phase than does the continuous-scan mode. The combined use of modulation frequency variation and analysis of the phase allows a wider range of depths to be probed. This type of spectrally resolved depth information is particularly useful when applied to polymeric materials with special surface properties. This includes not only characterization of surface-coated and laminar materials, but also studies of weathering, aging, curing and the diffusion of species into or out of a polymer matrix. Step-scan FT-IR PA spectral depth profiling of some of these types of samples is illustrated and the theory and techniques involved are discussed.

Improved current control technique of VSI PWM inverters with constant modulation frequency and extended voltage range

A hysteresis control method for three-phase, current-controlled, VSI PWM (pulse width modulation) inverters characterized by constant switching frequency is presented. The method is based on substantial improvement of the principle of minimization of interference among modulations of the various phases, which does not require any knowledge of load parameters or EMF, provided the load is symmetric. Interference minimization allows PLL (phase-locked loop) control of switching frequency. The inherent benefits of the proposed technique are full exploitation of inverter voltage capabilities and a definite reduction ion commutation losses. The method minimizes commutation losses and current ripple while allowing maximum output AC voltage to be obtained from the inverter. The method exhibits all the favorable characteristics of hysteresis controls: fast response, good accuracy, and robustness. Experimental tests confirmed theoretical forecasts, showing excellent performance of the control.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>