Effects Of Amplitude Modulation Research Articles

Superposition and Amplitude Modulation Effects in Separated Flow

Abstract This article adopts direct numerical simulation method to study concave cavity flow with high Reynolds number, and explores the influence of outer region structure on inner region turbulence of concave cavity flow, as well as the mechanism of coherent structure in the near wall region of concave cavity flow. This article finds that the superposition and amplitude modulation effects of separated flow are weaker than those in smooth wall turbulence. At different positions within the concave cavity, the superposition effect in the reattachment zone is the strongest, while the superposition effect in the separation zone is the weakest, indicating that flow separation prevents large-scale structures from outer region penetrating into the near wall region. The amplitude modulation effect of the reattachment point is the strongest, which is related to the strong adverse pressure gradient of the reattachment point.

Magnetic field assisted laser propagation in plasmas with amplitude modulation effects

Magnetic field assisted laser propagation in plasmas with amplitude modulation effects

A novel capacitive sensor interface based on a simple capacitance-to-phase converter

Abstract A novel room temperature capacitive sensor interface circuit is proposed and successfully tested, which uses a modified All-Pass filter architecture combined with a simple series resonant tank circuit with a moderate Q-factor. It is fashioned from a discrete inductor with small dissipation resonating with a grounded capacitor acting as the sensing element to obtain a resolution of ∆C ~ 2 zF in a capacitance range of 10 – 30 pF. The circuit converts the change in capacitance to the change in the phase of a carrier signal in a frequency range with a central frequency set up by the tank circuit’s resonant frequency and is configured to act as a close approximation of the ideal All-Pass filter. This cancels out the effects of amplitude modulation when the carrier signal is imperfectly tuned to the resonance. The proposed capacitive sensor interface has been specifically developed for use as a front-end constituent in ultra-precision mechanical displacement measurement systems, such as accelerometers, seismometers, gravimeters and gravity gradiometers, where moving plate grounded air gap capacitors are frequently used. Some other applications of the proposed circuit are possible including the measurement of the electric field, where the sensing capacitor depends on the applied electric field, and cost effective capacitive gas sensors. In addition, the circuit can be easily adapted to function with very small capacitance values (1 - 2 pF) as is typical in MEMS-based transducers.

Mechanism analysis of the influence of rotor-to-rotor interactions on global rotor noise

Existing research mainly investigated the influence of rotor-to-rotor interactions on the aerodynamics performance and noise level, but did not reveal the mechanism by which loading fluctuation significantly increases the noise below the rotor. In this study, first, an acoustic modal analysis method was established by mapping the source modal domain to acoustic modal domain, to investigate the global noise generated by a twin rotor considering the rotor-to-rotor interactions. Then, it was concluded from the simulation that the rotor-to-rotor interactions have little influence on the distribution of the sound sources, while they obvious change the noise in region at high elevation angle. Next, the method proposed was verified through experiments in an anechoic chamber, and the prediction error of overall sound pressure level (OASPL) was less than 7%. Finally, acoustic modal analysis reveals that the mechanism is attributed to the high radiation efficiency of the higher-order source modal components and dominant vertical directivity pattern of new acoustic modal components. Moreover, the initial azimuth angle of the rotors has an amplitude modulation effect on those acoustic modal components. When the difference in initial azimuth angle is π/L for rotors with L blades, the new modal components generated by different rotors cancel out each other for the odd-order blade passing frequency (BPF) noises.

Experimental investigation of closed-loop active control to modulate coherent structures by mu-level method

Abstract The experimental research on zero-net-mass-flux jet closed-loop active control was conducted in the wind tunnel.The mu-level method successfully detected burst events of the coherent structures. The streamwise velocity signals in the turbulent boundary layer were measured by HWA. The drag reduction rate of 16.7% is obtained comparable to that of the open-loop control and saves 75% of the input energy at the ASYN 100V/160 Hz control case, which reflects the advantages of the closed-loop control.The experimental findings indicate that the intensity increases in the near-wall region. The perturbation of the PZT vibrators on skewness factor is concentrated in the region y + < 60 . The generation of high-speed fluids is depressed and the downward effect of high-speed fluids weakens. The alteration of energy distribution and the discernible impact of modulation between structures of varying scales is observed. The correlation coefficient exhibits a strong positive correlation, which indicates that the large-scale structures produce modulation effect on small-scale ones. The occurrence of burst events is effectively suppressed.The disturbance has the characteristics of stable periodicity, positive and negative symmetry, low intermittency and high pulsation strength.The conditional phase waveform shows the fluctuation amplitude increases, indicating amplitude modulation effects on coherent structures.

Buoyancy effects on very-large-scale motions and amplitude modulation in convective atmospheric surface layers

A large amount of high-Reynolds-number experimental data was obtained from long-term observations of the atmospheric surface layer in the Qingtu Lake Observation Array under different thermal stability conditions. To reveal the thermal effects, the variations of the scales of turbulent coherent structures, energy distribution and amplitude modulation as a function of thermal stability are investigated. Results show that in the convective atmospheric surface layer, the superposition of buoyancy and shear drives leads to a large enhancement of turbulent kinetic energy, an increase in the scales of coherent structures, and in particular, a more significant enhancement of the very-large-scale motions kinetic energy. This results in an increased energy proportion of very-large-scale motions, and thus enhancing the amplitude modulation effect on small scales. Moreover, the variations in the coherent structure scale, energy proportion of the very-large-scale motions, amplitude modulation coefficient and the corresponding modulating and carrier signal scales with the thermal stability parameter can all be characterized by the same parametric equation form. This study contributes to a better understanding of turbulence dynamics driven by both buoyancy and shear.

Amplitude modulation leads to the disappearance of relaxation oscillations in the Duffing system

Relaxation oscillations are pervasive in diverse areas of natural sciences and engineering, and exploring the dynamical mechanisms of relaxation oscillations is one of the most significant issues. Typical relaxation oscillations can be observed in the Duffing system. Recently, amplitude modulation has emerged as a novel control mechanism for investigating the behavior of fast-slow dynamics in systemic tension oscillations. It has demonstrated the ability to prolong the quasi-static slow process of the system and increase the number of bifurcation points. However, the exploration of the mechanistic aspects of amplitude modulation is still in its early stages, with many unreported dynamical mechanisms. Among these, investigating the modes of relaxation oscillations induced by amplitude modulation is one of the most important issues. Therefore, this manuscript focuses on studying the effect of amplitude modulation on relaxation oscillations, using the classical forced Duffing system as a representative model. Significantly, we report an intriguing finding for the first time, revealing a new amplitude-modulated mechanism by which the disappearance of relaxation oscillations can be induced. By employing the fast-slow analysis, we have examined the underlying dynamical mechanisms, revealing a strong correlation with the modulation index of amplitude modulation. Notably, when the system operates under low amplitude modulation, an extension of the quasi-static process is observed, manifesting as a prolonged slow process. Conversely, under high amplitude modulation, relaxation oscillations suddenly disappear. Our results serve to enrich the potential mechanisms of amplitude modulation, and our analysis provides a reference for investigating the dynamical behavior induced by amplitude modulation in other dynamical systems.

Amplitude modulation in turbulent boundary layer over anisotropic porous wall

In this study, the amplitude modulation effect in a turbulent boundary layer over anisotropic porous walls is investigated experimentally at the Reynolds number based on friction velocity of Reτ = 236–319. The streamwise and wall-normal velocity fields were measured using time-resolved particle image velocimetry. To clarify the coherent structures related to the amplitude modulation over the porous wall with skin friction reduction effect, the large-scale structures are extracted from the low-pass filtered streamwise velocity fluctuations. The small-scale events related to high fluctuation energy are detected by the variable-interval space-averaging technique. Over the porous wall, the induced upwash and downwash motion leads to a notable suppression of large-scale structures. The small-scale motions in the near-wall region are mainly caused by the ejection events, while the sweep events are significantly suppressed. The amplitude modulation effects indicate that the positive and negative large-scale velocity streaks produce suppression and enhancement effects to the near-wall small-scale turbulence, respectively, which is contrary to the conventional phenomenon over the smooth wall case. The interaction between outer large-scale and inner small-scale structures is significantly weakened by the porous wall, contributing to the overall skin friction reduction.

Vibration sideband modulation mechanism and analytical signal modelling of the ring gear in a planetary gear set

To address the vibration and modulation sideband mechanism problems, this paper proposes a dynamic model for the planetary gear transmission (PGT). Based on the time-varying vibration transfer path analysis, a novel analytical vibration signal model is derived using the mode superposition method to study the vibration characteristics of the ring gear. In the presented signal model, we analyze the complicated modulation sidebands in terms of frequency and reveal the amplitude modulation effect of the carrier. Results show that amplitudes of modulation sidebands are slightly asymmetric for a single planet system, while the amplitudes of modulation sidebands are asymmetric for the multiple planets system. Furthermore, methods for suppressing the vibration are proposed by designing the appropriate planet position angles, meshing phasing, and load sharing performance. Finally, simulation and experimental signals are compared to verify the proposed model. The result shows that experimental signals keep good consistency with the simulated signals.

Effect of inter-dot tunneling coupling on soliton dynamical behaviors in four-level triple quantum dot EIT medium

<sec>Soliton, which can travel over long distance without attenuation or shape change due to the balance of the interplay between dispersion (or diffraction) and nonlinearity in nonlinear medium, becomes a good information carrier in quantum information processing and transmission. Up to now, the study on the optical solitons mainly focuses on ultra-cold atomic electromagnetic induction transparency (EIT) medium. This is mainly because ultra-cold atomic system can generate strong nonlinear effect under low light excitation. However, for the practical application, it is a big challenge to control accurately the optical soliton dynamics in the atomic EIT medium due to its low temperature (which approaches to absolute zero) and rarefaction. Fortunately, with the maturity of semiconductor quantum production technology, quantum dots have extensive application prospect in quantum information processing and transmission. So, in the paper, we study the optical soliton dynamics in a four-level asymmetric array-type three-quantum-dot EIT medium.</sec><sec>Based on the current experimental results, we first propose a four-level asymmetric array-type three-quantum-dot EIT model. Subsequently, by using amplitude variable approach combined with multi-scale method, we study analytically the propagation of a probe pulse in this system. It is shown that when one (the another) inter-dot tunneling coupling is turned on (off), only a single transparency window appears in the center range of the probe field detuning. Only if two inter-dot tunneling couplings are turned on will two transparent windows be distributed on both sides of the central region of the probe field detuning. And the width of the single transparent window or the widths of two transparent windows become wider with the strength of the inter-dot tunneling coupling increasing. For the nonlinear case, by choosing appropriate parameters in the area of the transparency window, the stable propagation of soliton can be realized. Interestingly, we find that the strength of the inter-dot tunneling coupling has an important effect on the soliton dynamic behaviors. In the case that one (the another) inter-dot tunneling coupling is turned on (off), with the increase of strength of the inter-dot tunneling coupling, the velocity of the soliton exhibits a trend of first increasing and then decreasing, and the amplitude of the soliton presents a increasing trend for ever. For the case that two inter-dot tunneling couplings are turned on, with the strength of the two inter-dot tunneling coupling increasing, the velocity of the soliton presents a decreasing trend for ever, while the amplitude of the soliton exhibits a trend of first decreasing and then increasing. Thus, the amplitude modulation effect of optical soliton can be realized in semiconductor quantum dot devices.</sec>

Response of a Turbulent Boundary Layer to an Imposed Synthetic Large-Scale Structure

The dynamic response of a zero-pressure gradient turbulent boundary layer (TBL) to an active flow control actuator was experimentally investigated. The experimental TBL had a sufficiently low momentum thickness Reynolds number, such that there were no energetic organized large-scale structures in the outer region, as evidenced from measurements of the premultiplied wavenumber–frequency spectra. The periodically pulsed plasma actuator, placed inside the outer region of TBL, introduced a synthetic large-scale structure, and the boundary-layer response to this synthetic structure downstream of the actuator at select wall-normal and streamwise locations was investigated. The turbulence amplitude modulating effect of the synthetic large-scale structure, within the inner and log-linear regions of the boundary layer, was isolated and analyzed using a phase-locked analysis. The dynamic interaction of the synthetic large-scale structure and smaller-scale turbulent motions was quantified using a modulation coefficient, and a strong positive correlation within the inner and log regions of the boundary layer was measured. The streamwise development of the synthetic large-scale structure and its modulating effect on the near-wall turbulence across several streamwise locations are described. Profiles of the phase speed at these streamwise locations were extracted and were found to be constant within the log region, further confirming a strong coupling between the near-wall fluctuations in turbulence intensity and the synthetic large-scale motions introduced in the outer region. Overall, the turbulence amplitude modulation effect induced by the synthetic large-scale structure was found to be dynamically similar to the large-scale modulation measured in canonical TBLs at higher Reynolds numbers.

The effect of turbulent motions on particle spatial distribution in high-Reynolds-number particle-laden flows

The spatial relationship between turbulent and particle concentration structures is investigated based on the turbulent velocity and particle concentration data obtained synchronously at the Qingtu Lake Observation Array site. In addition to the observation of particle concentration structures that contain not only large-scale coherence but also significant energy in the high-Reynolds-number atmospheric surface layer (ASL), the scale of turbulent motions that have the most significant coherence with particle concentration is found to follow a 1/2 power scaling law with the local height and ASL thickness. Moreover, large-scale turbulent velocity fluctuations have a significant amplitude modulation effect on particle concentration fluctuations, but the modulating influence is different for small dust particles and large saltating particles. Based on the interphase amplitude modulation, there exists a particle–turbulence structure phase difference that varies with height, which further makes the structure inclination angle of the particle concentration larger than that of the turbulence. In this scenario, a conceptual model reflecting the relationship between the two is proposed, and a quantitative formulation is further derived and found to be in good agreement with the experimental results. These findings and the proposed model contribute insights into particle–turbulence interactions, thereby providing theoretical support for a unified model of turbulence dynamics and particle kinematics.

High-intensity laser guiding in a plasma: amplitude modulation effects

High-intensity laser guiding in a plasma: amplitude modulation effects

Frequency modulation laser spectroscopy method for methane isotopologue ratio and total concentration measurements at 1661 nm

Source identification and accurate measurements of methane gas concentration are key tools necessary for climate change management. Here we present a method for methane isotopologue ratio measurement using a laser-based frequency modulation (FM) spectroscopy technique in the near infrared at 1661 nm. We provide line shape analysis and discuss a fitting algorithm for accurate isotopologue ratio metrology and investigate and minimize the effects of residual amplitude modulation on the experimentally produced FM signal line shape. This FM technique is further evaluated for future development of a cavity-enhanced and noise-immune system capable of isotopologue ratio as well as ultrasensitive trace gas measurements, all accessible using a single distributed feedback laser.

Effects of amplitude modulation on mixed-mode oscillations in the forced van der Pol equation

Effects of amplitude modulation on mixed-mode oscillations in the forced van der Pol equation

Efecto de la técnica de modulación M-QAM para una infraestructura de red convergente Radio sobre Fibra (RoF)

The objective of the research is to analyze, at the simulation level, the effect of the M-Quadrature Amplitude Modulation (M-QAM) technique, in the downlink, for a converged Radio over Fiber (RoF) network infrastructure, implementing the Ortho-gonal Frequency Division Multiplexing (OFDM) technique and the Passive Optical Network architecture, with 10 Gbps capa-city (XG-PON). The evaluation of the effect of the M-QAM modulation technique was done through a pre-established simulation methodology and using the optsim sof-tware for the network model and tests. In the results of the research, the increase of the order of M-QAM modulation for a con-verged OFDM-RoF network infrastructure allows to represent more bits per symbol, however, it requires a higher transmission power. The conclusion derives in the pos-sibility of developing a robust converged OFDM-RoF network infrastructure of XG-PON type, implementing the M-QAM tech-nique, since it efficiently uses the available bandwidth.

Forced vortex merging and splitting events in ferrofluidic Couette flow

Time-dependent boundary conditions are ubiquitous in numerous natural and industrial flows. However, to date, the influence of such temporal modulations has been given minor attention. This research addresses ferrofluidic Couette flow in between co-rotating cylinders in a spatially homogeneous magnetic field subject to time-periodic modulation. Using a modified Niklas approximation, we study the effect of amplitude and frequency modulation onto the transition scenarios between different toroidal flow structures, non-propagating vortex (nV) states, via vortex merging and splitting. Thereby, the system response appears to be quite sensitive/dependent on the driving frequency ΩH, which can cause a notable “delay” in the system response. Further, as a result of the inertia of the ferrofluid, resisting the fast-changing accelerating Kelvin force, new, temporal nV states appear within an alternating field. These states are unstable under static fields. Finally, we show that within the same nV state, while keeping similar flow dynamics, large discrepancies in angular momentum and torque can be observed.

Masking effects of amplitude modulation on frequency-modulated tones

Human sensitivity to frequency modulation (FM) is best for low carrier frequencies (<∼4–5 kHz) and slow modulation rates (<5–10 Hz). This high sensitivity is thought to be afforded by neural phase locking to temporal fine structure (TFS). At faster rates and higher carriers, TFS cues may no longer be available, with sensitivity to FM relying instead on conversion to amplitude modulation (AM) via cochlear filtering. One way to test this hypothesis is to measure the masking produced by additional AM, with the prediction that AM masking will be more pronounced when FM is encoded via AM than via TFS cues. This study tested AM masking of FM and of “simulated FM,” which involves out-of-phase AM dyads. FM detection was measured for carrier frequencies of 1 and 6 kHz and modulation rates of 2 and 20 Hz with and without AM masking. Preliminary results suggest that FM and simulated FM sensitivity is more affected by AM at fast than slow rates at both low and high carrier frequencies. Overall, the results do not provide support for the idea that AM interference can be used to distinguish between TFS- and envelope-based codes for FM. [Work supported by NIH grant R21 DC019409.]

Investigation of the multiple characteristics of the self-mixing effect subject to a single particle.

As a compact interferometry technique, self-mixing interferometry (SMI) is a promising tool for micro particle detection in biochemical analysis and the monitoring of laser manufacturing processing, and currently SMI based micro particle detection is attracting increasing attention. However, unlike the typical displacement or vibration measurement driven by a macro target, only a small amount of literature has targeted the SMI effect induced by a single micro moving particle. In this paper, two numerical models were investigated to describe the characteristics of the signal sparked by individual particle. We compared the measurement results with the two models' simulations in three signal characteristic aspects: the temporal waveform, frequency spectrum, and phase profile. From these results, we established that both amplitude modulation and frequency modulation effects apply under different conditions in the self-mixing process. And for the first time, we analyzed the effect of the laser illumination spot size on the particle-induced SMI signal features with two optical arrangements. When the laser beam size is larger than the particle size, the signal bursts are likely to result from frequency modulation, and vice versa. Our results can improve the capability of SMI technology in particle size discrimination and particle sorting.

Passive resonant laser gyroscope with improvement of the suppression of residual amplitude modulation effects through correlation analysis

Passive resonant gyroscopes (PRGs) utilizing the Pound-Drever-Hall (PDH) method are expected to have a lower shot-noise limit in rotational rate measurement. However, there are also many technical obstacles in the way to touch the intrinsic noise floor. In this article, we find that the residual amplitude modulation (RAM) effect in the phase locking process deteriorates the accuracy and stability of the output signal of PRGs, and becomes a dominant limiting factor, especially in the low-frequency range. Since the suppression is not good enough in the PRGs due to the strict requirements, we propose to use the Pearson correlation coefficient to evaluate the correlation between the RAM signal and the PDH signal to achieve a sufficient correlation before active servo control. With the implementation of this improvement, the RAM-induced fractional frequency stability for the 12 m optical ring cavity is reduced down to . The contribution of the RAM effect to the rotational sensitivity of our 3 m × 3 m PRG is lowered to 8.0 × 10−9 rad s−1 at 1 mHz, which is one order of magnitude better than the unconstrained situation. With this upgrade, a rotational resolution of rad s−1 of the PRG is achieved, which is the best performance among all PRGs so far.