Low-frequency Modulation Research Articles

Experimental Study of a Nonthermal DBD-Driven Plasma Jet System Using Different Supply Methods

This article presents an experimental study of a DBD-driven plasma jet system. The aim of the study is to design a whole system (the jet reactor, its electrical power supply, and a gas-feeding apparatus) suitable for biomedical applications. The article describes the test bench developed for this purpose and discusses the parameters it controls. The measurements show that the studied solutions can be used to control critical parameters such as the jet temperature and dimensions. The best results were obtained for a bipolar short-pulse voltage power supply in the 10–20 kHz frequency range and for a series resonant inverter current power supply operated in “burst mode”, allowing low-frequency modulation.

Experimental Investigation on the Dynamic Propagation Characteristics of Low-Frequency Electromagnetic Waves in Cylindrical Time-Varying Enveloping Plasma Generated by a Shock Tube

A feasible solution for mitigating radio blackout has been proposed using the magnetic field component of low-frequency (LF) electromagnetic waves (referred to as the LF magnetic field) to transmit critical low-rate data because of the low attenuation of the LF magnetic field in the electrically small plasma. Previous works have modeled the hypersonic plasma flow field as spherical or cylindrical steady-state plasma, ignoring the time-varying properties of the plasma. This article presents the dynamic propagation of the LF magnetic field in a hypersonic plasma flow field generated by a shock tube, introducing a colored-Gaussian time-varying electron density model. Analytical expressions for the propagation characteristics of the LF magnetic field in cylindrical time-varying plasma are derived using an equivalent circuit. Meanwhile, a frequency-division-multiplex experimental method for a shock tube is presented to quantitatively measure the propagation characteristics of a multifrequency LF magnetic field. The experimental results are in good agreement with the theoretical results. As the fluctuation intensity of the electron density increases, the fluctuation intensities of the time-varying envelope and phase shift increase, and the power spectral density broadens. As the frequency of the LF magnetic field increases, the effects of the time-varying plasma on the propagation characteristics strengthen. These results are important to the design of LF communication systems and modulation algorithms in the scenario of shock-tube-generated plasma.

Non-equilibrium Sachdev-Ye-Kitaev model with quadratic perturbation

We consider a non-equilibrium generalization of the mixed SYK_44+SYK_22 model and calculate the energy dissipation rate W(\omega)W(ω) that results due to periodic modulation of random quadratic matrix elements with a frequency \omegaω. We find that W(\omega)W(ω) possesses a peak at \omegaω close to the polaron energy spliting \omega_RωR found recently in [1], demonstrating physical significance of this energy scale. Next, we study the effect of energy pumping with a finite amplitude at the resonance frequency \omega_RωR and calculate, in presence of this pumping, non-equilibrium dissipation rate due to low-frequency parameteric modulation. We found unusual phenomenon similar to “dry friction” in presence of pumping.

Hybrid Three-Phase Transformer-Based Multilevel Inverter With Reduced Component Count

This paper proposes a novel three-phase transformer-based multilevel inverter (MLI) topology to maximize the output voltage levels for high-power high-voltage applications while reducing component counts as compared to its transformer-based counterparts. The proposed hybrid topology is formed by connecting a three-level T-type module with full H-bridge cells through single-phase transformers. The T-type module is fixed while the full H-bridge cell can be repeated for enlarging the output voltage levels without increasing the voltage stress on switches. Key features of the proposed topology include low part count, capacitor-free, diode-free, voltage boosting, simple control, and modularity. Within the framework, a simple low-frequency pulse width modulation (LFPWM) switching scheme is used to control the output voltage, and the working principle is detailed for seven-, nine-, and N-level operation. The operability and performance of the proposed topology are numerically verified and experimentally validated at different loads. Moreover, its conversion efficiency is experimentally examined. Finally, a comparative study with existing transformer-based MLI circuits is conducted to prove its key merits.

Distribution of energy in propagation for ocean extreme wave generation in hydrodynamics laboratory

BACKGROUND AND OBJECTIVES: The hydrodynamic uncertainty of the ocean is the reason for testing marine structures as an initial consideration. This uncertainty has an impact on the natural structure of the topography as well as marine habitats. In the hydrodynamics laboratory, ships and offshore structures are tested using mathematical models as input to the wave marker. For large wavenumbers, Benjamin Bona Mahony's equation has a stable direction and position in the wave tank. During their propagation, the generated waves exhibit modulation instability and phase singularity phenomena. These two factors refer to Benjamin Bona Mahony as a promising candidate for generating extreme waves in the laboratory. The aim of this research is to investigate the distribution of energy in each modulation frequency change. The Hamiltonian formula that describes the phenomenon of phase singularity is used to observe energy. This data is critical in determining the parameters used to generate extreme waves.METHODS: The envelope of the Benjamin Bona Mahony wave group can be used to study the Benjamin Bona Mahony wave. The Benjamin Bona Mahony wave group is known to evolve according to the Nonlinear Schrodinger equation. The Hamiltonian governs the dynamics of the phase amplitude and proves the Nonlinear Schrodinger equation's singularity for finite time. The Hamiltonian is derived from the appropriate Lagrangian for Nonlinear Schrodinger and then transformed into the Hamiltonian with the displaced phase-amplitude variable.FINDINGS: Potential energy is related to wave amplitude and kinetic energy is related to wave steepness in the study of surface water waves. When , the maximum wave amplitude and steepness are obtained. When , extreme waves cannot be formed due to steepness. This is due to the possibility of breaking waves into smaller waves on the shore. In terms of position, the energy curve is symmetrical.CONCLUSION: According to Hamiltonian's description of the energy distribution, the smaller the modulation frequency, the greater the potential and kinetic energy involved in wave propagation, and vice versa. While the wave's amplitude and steepness will be greatest for a low modulation frequency, and vice versa. The modulation frequency considered as an extreme wave generator is , because the resulting amplitude is quite high and the energy in the envelope is also quite large.

Crystal Structure Algorithm (CryStAl) Based Selective Harmonic Elimination Modulation in a Cascaded H-Bridge Multilevel Inverter

This paper introduces an effective Selective Harmonic Elimination (SHE) modulation technique in a five, seven, and nine-level cascaded H-bridge (CHB) multilevel inverter (MLI). Minimization of the harmonics and device counts is the basis for the ongoing research in the area of MLI. Reduced harmonics and hence the lower Total Harmonic Distortion (THD), improve the output power quality. SHE is a low-frequency modulation scheme to achieve this goal. SHE techniques are used to eliminate the distinct lower-order harmonics by determining the optimum switching angles. These angles are evaluated by solving the non-linear transcendental equations using any optimization technique. For this purpose, the Crystal Structure Algorithm (CryStAl) has been used in this paper. It is a metaheuristic, nature-inspired, and highly efficient optimization technique. CryStAl is a simple and parameter-free algorithm that doesn’t require the determination of any internal parameter during the optimization process. It is based on the concept of crystal structure formation by joining the basis and lattice point. This natural occurrence can be realized in crystalline minerals in their symmetrically organized components: ions, atoms, and molecules. The concept has been utilized to solve non-linear transcendental equations. SIMULINK/MATLAB environment has been used for the simulation. The simulation result shows that the crystal structure algorithm is very effective and excels the other metaheuristic algorithm. Hardware results validate the performance.

Olivocochlear projections contribute to superior intensity coding in cochlear nucleus small cells.

Understanding communication signals, especially in noisy environments, is crucial to social interactions. Yet, as we age, acoustic signals can be disrupted by cochlear damage and the subsequent auditory nerve fibre degeneration. The most vulnerable medium- and high-threshold-auditory nerve fibres innervate various cell types in the cochlear nucleus, among which the small cells are unique in receiving this input exclusively. Furthermore, small cells project to medial olivocochlear (MOC) neurons, which in turn send branched collaterals back into the small cell cap. Here, we use single-unit recordings to characterise small cell firing characteristics and demonstrate superior intensity coding in this cell class. We show converse effects when activating/blocking the MOC system, demonstrating that small-cell unique coding properties are facilitated by direct cholinergic input from the MOC system. Small cells also maintain tone-level coding in the presence of background noise. Finally, small cells precisely code low-frequency modulation more accurately than other ventral cochlear nucleus cell types, demonstrating accurate envelope coding that may be important for vocalisation processing. These results highlight the small cell olivocochlear circuit as a key player in signal processing in noisy environments, which may be selectively degraded in ageing or after noise insult. KEY POINTS: Cochlear nucleus small cells receive input from low/medium spontaneous rate auditory nerve fibres and medial olivocochlear neurons. Electrical stimulation of medial olivocochlear neurons in the ventral nucleus of the trapezoid body and blocking cholinergic input to small cells using atropine demonstrates an excitatory cholinergic input to small cells, which increases responses to suprathreshold sound. Unique inputs to small cells produce superior sound intensity coding. This coding of intensity is preserved in the presence of background noise, an effect exclusive to this cell type in the cochlear nucleus. These results suggest that small cells serve an essential function in the ascending auditory system, which may be relevant to disorders such as hidden hearing loss.

Low switching frequency modulation for generalized three-phase multilevel inverters geared toward Grid Codes compliance

In this paper, a generalized three-phase multilevel power inverter (MLI) structure is proposed under asymmetric configurations. The operating mode and the switching combinations are briefly exposed according to the parity of the number of direct current (DC) voltage sources in use. Subsequently, the proposed topology is evaluated in terms of commonly used factors and then benchmarked against some of the state-of the-art cascaded MLIs featuring multiple DC voltage sources (MDCS-CMLIs) while putting emphasis on the reduction of power switching devices. Moreover, a new nearest level control (NLC)-based modulation technique is designed for the purpose of better comply with some quality grid codes, namely the European EN 50160 and the International IEC 61000-2-12. The identification of the optimal control thresholds is realized by a constrained optimization algorithm (e.g., particle swarm optimization (PSO)) which is implemented in python script and validated through SIMULINK fast fourier transform (FFT) analysis tool. Lastly, the harmonic performance of the proposed technique is compared side-by-side with that of the conventional NLC scheme and exhibits significant reduction in harmonic distortion.

Method for power reduction of demodulation driver circuit in indirect time-of-flight CMOS image sensor.

To improve the depth accuracy of an indirect time-of-flight CMOS image sensor, high modulation frequency is often adopted. It will result in high power consumption of an on-chip demodulation driver, and this problem will be much more serious when the resolution of the sensor is much higher. In this paper, a power reduction method that can lower the power consumption of the demodulation driver circuit during the integration time while obtaining accurate high-resolution depth maps is proposed and analyzed theoretically. The method decreases the number of driven pixels at a high-modulation frequency by a programmable resolution adjustment circuit to obtain an accurate low-resolution depth map. A low-depth accuracy high-resolution depth map is obtained at a low modulation frequency, and then a modified super-resolution algorithm is used to obtain an accurate high resolution solution depth map. To demonstrate the effectiveness of the proposed method, a model is established based on the actual indirect time-of-flight sensor architecture, then the depth error and power consumption are analyzed by the simulation results of the model. In the simulation, 25 MHz and 100 MHz are used as the low modulation frequency and high modulation frequency, respectively. With the best scenario in depth accuracy kept, average power consumption decreases 38.47% and peak power consumption decreases 49.83% while the depth error that is represented by RMSE merely increases 8.08%.

Secondary vortex, laminar separation bubble and vortex shedding in flow past a low aspect ratio circular cylinder

Large eddy simulation of flow past a circular cylinder of low aspect ratio ( $AR=1$ and $3$ ), spanning subcritical, critical and supercritical regimes, is carried out for $2\times 10^3 \le Re \le 4\times 10^5$ . The end walls restrict three-dimensionality of the flow. The critical $Re$ for the onset of the critical regime is significantly lower for small aspect ratio cylinders. The evolution of secondary vortex (SV), laminar separation bubble (LSB) and the related transition of boundary layer with $Re$ is investigated. The plateau in the surface pressure due to LSB is modified by the presence of SV. Proper orthogonal decomposition of surface pressure reveals that although the vortex shedding mode is most dominant throughout the $Re$ regime studied, significant energy of the flow lies in a symmetric mode that corresponds to expansion–contraction of the vortex formation region and is responsible for bursts of weak vortex shedding. A triple decomposition of the time signals comprising of contributions from shear layer vortices, von Kármán vortex shedding and low frequency modulation due to the symmetric mode of flow is proposed. A moving average, with appropriate size of window, is utilized to estimate the component due to vortex shedding. It is used to assess the variation, with $Re$ , of strength of vortex shedding as well as its coherence along the span. Weakening of vortex shedding in the high subcritical and critical regime is followed by its rejuvenation in the supercritical regime. Its spanwise correlation is high in the subcritical regime, decreases in the critical regime and improves again in the supercritical regime.

Optomechanical temporal sampling of terahertz signals

Various detection schemes are currently investigated in the terahertz frequency range (<2 THz), as an alternative to the widespread bolometers and Golay cells that feature very high sensitivity but low modulation frequencies (<10 kHz). In this work, we report an alternative concept based on an optomechanical detector able to read out an arbitrary periodic modulation imprinted on a terahertz beam. The detector is a based on a combination of a split-ring resonator, acting as a terahertz antenna, and a high-quality mechanical resonator with typical resonant frequency ω0/2π = 1 MHz. We demonstrate two methods for Fourier sampling the envelope of the terahertz signal, in which the mechanical resonator is used as a reference oscillator. With our methods, signals with an arbitrary period T can be sampled, even those that are much faster than the oscillation period of the mechanical resonator, 1/T ≫ ω0.

A Novel Hexagonal-Shaped Multilevel Inverter with Reduced Switches for Grid-Integrated Photovoltaic System

To date, the grid-connected solar photovoltaic (PV) system has drawn consideration from researchers and academicians due to the speedy improvement and the declining price of solar panels. The proficiency and dependability of a grid integrated PV system rest mainly on the power conversion unit and the proper controlling mechanism. This paper introduces a novel asymmetric hexagonal-shaped fifteen-level inverter designed to feed a grid-integrated solar PV system. First, it aims to reduce the number of components and thereby decrease the installation space and cost of the multilevel inverter. Moreover, it has a low total blocking voltage (TBV) and total device rating (TDR) and uses few switching devices for generating per level of output voltage. The proposed topology utilizes only eight switching devices for generating fifteen levels at the output, which is lower than conventional multilevel inverter topologies. Here, a low-frequency modulation scheme using the half-height (HH) method generates switching pulses to minimize the complexity. The proposed multilevel inverter topology is also validated through the simulations in the MATLAB SIMULINK environment. The proposed inverter need for filters is illustrated according to different grid codes for integrating PV systems to the grid.

Right-hemisphere coherence to speech at pre-reading stages predicts reading performance one year later

ABSTRACT Neural entrainment to the low-frequency modulations of speech might contribute significantly to reading acquisition. Still, no previous study has actually attempted to establish a longitudinal link between them. The present study tested Basque-speaking children twice: once before reading was formally instructed (t 1; 5–6 years old) and once after they had received a full school year of reading instruction (t 2; 6–7 years old). At t 1, speech-brain coherence was recorded via EEG. At t 2, in addition to the coherence measure, reading performance was assessed. Our results show that children with larger pre-reading delta-band (<1 Hz) speech-brain coherence at right sites of the scalp performed better in the reading tasks one year later. Overall, our results provide preliminary support for a relevant contribution of right-hemisphere speech-brain coherence to successful reading development and point towards pre-reading neural coherence indexes as useful tools for the early detection of developmental reading disorders.

Modulation and Feed-Forward Based Damping Matching Strategy for Linear Generators

This article presents an active damping matching control strategy to optimize the output power of linear generators in energy harvesting applications. The method adjusts the magnitude of the current command responsible for active power set-point. The proposed approach combines a simple model-based feed-forward term with a slow but accurate correction based on the response of output power to a low-frequency modulation in set-point current magnitude. The correction is derived from the phase of output power oscillations and used to adjust the power set-point to achieve active-load matching conditions. In order to remove the low-frequency oscillations in the power at steady state, the method automatically stops the current amplitude modulation when maximum output power is reached. In addition, the proposed control incorporates an overstroke protection, which increases the active current component thereby reducing the stroke rapidly to a safe limit. The overall control principle is validated experimentally.

Bichromatic synchronized chaos in driven coupled electro-optomechanical nanoresonators

Chaos and synchronization are important and ubiquitous phenomena in nature. Chaos synchronization spontaneously emerges in the collective dynamics of coupled nonlinear oscillators; however, its control remains a challenge at the nanoscale. Here, we present an experimental and theoretical investigation of synchronization on the route to chaos and in the chaotic regime in mechanically coupled electro-optomechanical nanocavities. In this system an integrated electroactuation enables one to drive the mechanical normal modes in the nonlinear regime while the mechanical displacement is transferred to an optical probe which provides a direct readout access to both their amplitude and phase responses. Using a single low-frequency modulation of the force applied to each normal mode, we induce a chaotic dynamics in the coupled nanoresonators. By applying a simultaneous force modulation on each of the normal modes, we generate chaos at two distinct carrier frequencies referred to as bichromatic chaos. The mode amplitudes are synchronized all the way on the route to chaos as well as in the chaotic regime. Meanwhile, their phases experience complex dynamics with imperfect synchronization in the chaotic regime. These results set the ground for applications of mechanical nanoresonators in areas such as metrology, multispectral chaotic encryption, and analog computing.

Temporal integration of monaural and dichotic frequency modulation.

Frequency modulation (FM) detection at low modulation frequencies is commonly used as an index of temporal fine-structure processing. The present study evaluated the rate of improvement in monaural and dichotic FM across a range of test parameters. In experiment I, dichotic and monaural FM detection was measured as a function of duration and modulator starting phase. Dichotic FM thresholds were lower than monaural FM thresholds and the modulator starting phase had no effect on detection. Experiment II measured monaural FM detection for signals that differed in modulation rate and duration such that the improvement with duration in seconds (carrier) or cycles (modulator) was compared. Monaural FM detection improved monotonically with the number of modulation cycles, suggesting that the modulator is extracted prior to detection. Experiment III measured dichotic FM detection for shorter signal durations to test the hypothesis that dichotic FM relies primarily on the signal onset. The rate of improvement decreased as duration increased, which is consistent with the use of primarily onset cues for the detection of dichotic FM. These results establish that improvement with duration occurs as a function of the modulation cycles at a rate consistent with the independent-samples model for monaural FM, but later cycles contribute less to detection in dichotic FM.

Exposure to industrial noise: impacts on cognitive performance

Research on the relation between exposure to noise and cognitive performance inside industrial environments is not as broad as on office environments. For a better understanding of the specific industrial noise problems, participants performed arithmetic tests inside a hemi anechoic room while they were exposed to sounds of five typical industrial noise sources. The subjects also classified how annoying they perceived the noise signals. The effect of noise on the arithmetic test's performance was larger on accuracy than on velocity, which was verified using a Student t-test. Spectral-temporal characteristics - especially high frequency content and strong low frequency modulation - appear to relate better with lower performance on the test than high sound levels. Subjects that evaluated noise as more annoying performed worse in a final arithmetic test (under silence) after being exposed to the noises, indicating a possible cumulative effect of noise on performance. The findings provide a better insight in the cognitive behavior of people who are exposed to industrial noise. Hence, the study will proceed with the specific noise analysis of single industrial workplaces.

In-situ thermal transport measurement of flowing fluid using modulated photothermal radiometry

In situ thermal transport measurement of flowing fluid could be useful for the characterization and diagnosis of practical thermal systems such as fluid heat exchangers and thermal energy storage systems. Despite abundant reports on the ex-situ thermal conductivity measurement of stagnant fluids, a suitable technique for the thermal conductivity measurement of flowing fluid has been rarely reported. This paper presents the thermal conductivity measurement of flowing fluid within a pipe using a non-contact modulated photothermal radiometry (MPR) technique, where the surface of the pipe is heated by an intensity-modulated laser and the heat diffuses into the fluid with suitable modulation frequency. We design a tube section with small wall thickness suitable for the MPR measurements to maximize the sensitivity of the thermal response to the fluid properties while minimizing the lateral heat spreading effect. Intrinsic thermal conductivity of different fluids was obtained within a proper range of frequency and flow velocity where the forced convection effect is negligible. The forced convection effect became prominent at high flowing velocity and at low modulation frequency, leading to higher effective thermal conductivity of the fluid. It is found that the intrinsic thermal conductivity could be obtained when the flow velocity is less than 100 mm/sec and ReD1/2Pr1/3 < 100 for DI water and Xceltherm oil under the specified experimental conditions, where ReD is the Reynolds number and Pr is the Prandtl number.

Design and Analysis of Grid Interfaced 43-Level CHB Multilevel Converter for Integrating 10 MW Solar PV Plant

Megawatt solar plants are the reality now with nations looking for GW installed capacity. This high power is possible because of increased power levels in photovoltaic (PV) energy conversion systems. The multilevel converter (MLC) is the emerging technology for interfacing medium and higher voltage grids. This paper gives the design and analysis of transformerless grid interfaced single-stage 43-level Cascaded H-bridge (CHB)-based MLC for integrating large-scale solar PV plants with improved Total Harmonic Distortion (THD). Transformerless integration and reduced filter size, due to improved THD, contribute appreciable savings in the Capital Expenditure and Operation and Maintenance cost of the big solar PV plant. This paper also showcases the design-based strategy for deciding the levels used in the MLC, making it both efficient and economical. The control scheme comprises voltage-oriented control (VOC) with synchronous reference frame (SRF) and phase-locked loop (PLL). The low-frequency phase-shifted pulse width modulation (PWM) suitable for the cascaded MLC is used for modulation. The separate incremental conductance (InC) algorithm is used for the extraction of maximum power from each solar PV array. This algorithm takes care of the unforeseen insolation level changes, shading effect, ambient temperature, and other related factors of the multi-string SPV system. The simulation is performed in MATLAB/Simulink and validated on an OPAL RT simulator. Both steady-state and dynamic behaviors at different insolation levels of the considered system are studied. The performance is validated as per the IEEE-519 standard requirement. Decent decrease in THD of grid current is observed with low switching losses.

Numerical investigation on the flow around an inclined prolate spheroid

Numerical simulations are performed for the flow around an inclined 5:2 prolate spheroid in a uniform freestream. The Reynolds number (Re = 300, 500, 700, and 1000) and incidence angle (α = 0°–90°) are considered as significant parameters affecting the wake transitions, where α = 0° indicates flow parallel to the major axis of the prolate spheroid, and the Re is based on the inflow velocity U0 and the volume-equivalent sphere diameter De of the spheroid. In the range considered of Re and α, eight flow regimes are identified: (i) steady axisymmetric (SA) flow regime; (ii) steady planar symmetric flow regime; (iii) steady asymmetric (SAS) flow regime; (iv) periodic planar symmetric flow regime with non-zero mean lift or “Zig-zig-like” (Zz-like) mode; (v) periodic asymmetric flow regime with double-sided vortex shedding; (vi) multi-periodic asymmetric flow regime with double-sided vortex shedding and low frequency modulation (MPADL); (vii) multi-periodic asymmetric flow regime with single-sided vortex shedding and low frequency modulation (MPASL); and (viii) weakly chaotic state. Three of them are new and first reported, i.e., SAS, MPADL, and MPASL modes. The wake structure of the Zz-like mode is different from that of the zig-zig mode in the sphere/disk wake with a pair of streamwise vortices extending to the near wake. It is found that the elongated body can delay the onset of unsteadiness at small incidence angles. A flow regime map in the considered (Re, α) space is then provided. Finally, the physical mechanisms of the low-frequency phenomena observed at different wake modes are explored.