Amplitude Control Research Articles

Foam gratings as an alternative to customized acoustic lenses.

This article describes a method of manipulating acoustic fields using transmission through foam gratings. The approach is investigated with an analytical model, a numerical model simulating full wave ultrasound propagation through the gratings, and experimental measurements. A grating is demonstrated that mimics a conventional ultrasound lens, modulating the phase of transmitted ultrasound while maximizing the transmitted amplitude. The performance of a foam grating is compared to a lens made of polydimethylsiloxane or three-dimensional printed resin. Using two gratings, independent control of amplitude and phase is demonstrated, with increased insertion loss. The primary advantages of this technique over conventional lenses are very rapid manufacture (<30 min), high repeatability due to the simplicity of manufacture, and the ability to control the amplitude of the transmitted ultrasound. Potential applications include generation of complex ultrasound fields for patient specific treatments in ultrasound therapy.

Amplitude control for an artificial hair cell undergoing an Andronov-Hopf bifurcation

The dynamics of an artificial hair cell is analyzed by considering the bifurcation behavior of a dominant mode model. It is shown that this model undergoes an Andronov-Hopf bifurcation similar to its biological counterpart, i.e., the hair cell in the mammalian cochlea. Consequently, this dynamical behavior is exploited to control the amplitude of the deflection of the artificial hair cell. In particular feedforward control with disturbance injection is designed based on an approximation of the oscillation using an envelope model to achieve a constant deflection amplitude. The approach is evaluated in numerical simulations.

Autonomous three-dimensional oscillator with five terms: spiking oscillations generation mechanism, microcontroller implementation and controls

This paper presents a report on the microcontroller implementation of an autonomous three-dimensional oscillator with five terms (ATDOFT) and performance analysis based on partial and total amplitude controls. ATDOFT displays periodic spiking behaviors, period-tripling bifurcation to chaos, chaotic spiking attractors, coexisting attractors and bistable attractors. ATDOFT is divided into two subsystems; namely the fast and slow subsystems to investigate the mechanism of the spiking dynamics. Relying on the stability analysis based on the fast subsystem with respect to the slow variable, it is shown that the spiking oscillations present in the ATDOFT arise from the system switching between the unstable state and the stable state of the lone equilibrium point of the fast subsystem. By inserting two controller parameters into the rate equations of the ATDOFT, total and partial amplitude controls are achieved. Finally, the dynamical behaviors found in ATDOFT are validated by the microcontroller implementation.

Filter-Less Photonic RF Image-Reject Mixing With Simultaneous Self-Interference Cancellation and Fiber Transmission

A filter-free photonic method to simultaneously realize radio frequency (RF) image-reject mixing, self-interference cancellation (SIC), and fiber transmission for in-band full-duplex (IBFD) radio-over-fiber (RoF) link is reported. The key to achieving multi-functions is the joint manipulation of fiber dispersion-induced intermediate frequency (IF) amplitude and time delay changes, which is implemented by sideband phase-shifted optical carrier suppression (SPS-OCS) modulation and frequency tuning of the optical carrier. Owing to the control of IF amplitude and delay variation introduced by fiber dispersion, simultaneous deep image rejection and SIC over wide bandwidth can be realized after fiber transmission. Since no optical filter is required, the proposed system can work at a lower frequency, featuring a large frequency tuning range. For 25 km single-mode fiber (SMF) transmission, simultaneous 20 dB SIC within 1 GHz bandwidth and 29 dB image rejection ratio (IRR) at 6.6 GHz RF frequency in the C band, 21 dB SIC and 19 dB IRR within 1 GHz bandwidth in the X band, 24 dB SIC within 1 GHz bandwidth and 20 dB IRR at 16 GHz RF frequency in the Ku band are experimentally demonstrated. Furthermore, weak SOI with various modulation formats are well recovered after the cancellation of strong interference and fiber transmission.

Rössler-like Neuronal Firing with Local Amplitude Control

Chaotic neuronal oscillation is fired up when a locally active memristor is introduced into the Rössler system. Such a memristive Rössler system has two independent parameters providing local amplitude control, one of which even adjusts the amplitude and frequency of variables in a specific intermittent mode. Different neuronal firing modes are modified by the system parameter. The coexistence of periodic oscillation and chaos is also captured along with basin of attraction. STM32-based experiment verified the numerical and theoretical results.

CMOS variable-gain phase shifter based on time-varying vector-sum method and its application to Ku-band phased array

In this paper, a new time-varying vector-sum method is proposed for variable-gain phase shifter design. By introducing a time variable into the conventional vector-sum phase shifter (VSPS) architecture, high-resolution phase shifting and wide amplitude control can be achieved simultaneously. The proposed time-varying phase shifter (TVPS) is fabricated in 0.13-μm CMOS technology with a core area of 1.76 mm2. A field-programmable gate array (FPGA) is utilized to generate gain-control timing sequences for phase shifting and on-off timing sequence for amplitude control, which are optimized to achieve a measured sideband suppression ratio of −17.2 dBc. For bidirectional operation, measured results present that the proposed TVPS can achieve a phase resolution of 10-bits, RMS (root mean square) phase error of 0.2–0.5°, RMS gain error of less than 0.2 dB, and gain tuning range of 10.1 dB in the frequency band of 12–18 GHz. The proposed TVPS is applied to a 4-element phased array, and the measured radiation patterns of scanned beams are presented.

Machine-Learning Clustering Methods Applied to Detection of Noise Sources in Low-Speed Axial Fan

Abstract The integration of rotating machineries in human-populated environments requires to limit noise emissions, with multiple aspects impacting on control of amplitude and frequency of the acoustic signature. This is a key issue to address and when combined with compliance of minimum efficiency grades, further complicates the design of axial fans. The aim of this research is to assess the capability of unsupervised learning techniques in unveiling the mechanisms that concur to the sound generation process in axial fans starting from high-fidelity simulations. To this aim, a numerical dataset was generated by means of large Eddy simulation (LES) simulation of a low-speed axial fan. The dataset is enriched with sound source computed solving a-posteriori the perturbed convective wave equation (PCWE). First, the instantaneous flow features are associated with the sound sources through correlation matrices and then projected on latent basis to highlight the features with the highest importance. This analysis in also carried out on a reduced dataset, derived by considering two surfaces at 50% and 95% of the blade span. The sampled features on the surfaces are then exploited to train three cluster algorithms based on partitional, density and Gaussian criteria. The cluster algorithms are optimized and their results are compared, with the Gaussian Mixture one demonstrating the highest similarity (&amp;gt;80%). The derived clusters are analyzed, and the role of statistical distribution of velocity and pressure gradients is underlined. This suggests that design choices that affect these aspects may be beneficial to control the generation of noise sources.

МЕТОД ГЕНЕРАЦИИ СВЕРХШИРОКОПОЛОСНЫХ СВЧ-СИГНАЛОВ С ЛИНЕЙНО-ЧАСТОТНОЙ МОДУЛЯЦИЕЙ НА ОСНОВЕ САМОГЕТЕРОДИНИРОВАНИЯ ИЗЛУЧЕНИЯ ЛАЗЕРНОГО ДИОДА

In this paper, microwave photonic technique of ultrawideband linearly frequency modulated signals generation is proposed. The proposed method based on direct modulation of the laser diode current, which provides a periodic change in the emission frequency. The Michelson interferometer summarizes laser signal and its replica with time delay exceeding 10 ms, which, in turn, is defined by time difference between arms. Optoelectronic conversion is performed in high-speed high-power photodiode. The proposed approach makes it possible to generate microwave signals with linear frequency modulation in the frequency range up to several tens of gigahertz by means of laser pump current modulation in the frequency range less than 100 MHz. The method of ultra-wideband microwave signals generation is implemented using a Michelson fiber-optic interferometer with Faraday mirrors. Such interferometer topology provides a doubling of the path length, and reduced gyroscopic effects due to a counter-propagating double pass. Changing the parameters of the generated microwave ultrawideband signals with frequency modulation is achieved by pump current shape and amplitude control. It is also proposed to use real-time oscilloscope without need of changing of the internal structure of such generator to pre-tune it. Time-frequency analysis is used to extract frequency versus time dependence. By so doing, direct impulse response estimation is performed. This method allows to characterize laser diode frequency response for arbitrary microwave waveform generation by means of pump current waveform calculation from experimental data.

Improved Position Sensorless Piston Stroke Control Method for Linear Oscillatory Machine via an Hybrid Terminal Sliding-Mode Observer

Since the piston stroke of linear oscillation machine (LOM) is very important for the safe and reliable operation of the system, it is necessary to effectively control the piston stroke. Besides, considering that the use of position sensor will reduce the system reliability, so the accurate position sensorless method is needed to obtain the stroke signals. In this article, a hybrid terminal sliding-mode observer is designed by combing a second-order nonsingular terminal sliding mode (SNTSM) and a high-order sliding-mode (HOSM) to estimate the back-electromotive force signals of the LOM. The SNTSM surface is selected to ensure that the system state variables can converge in a finite time and the HOSM control law is designed by introducing a variable exponential reaching law, which can strengthen the stability of the observer and greatly reduce the sliding chattering. Since the piston stroke is calculated by integrating the estimated piston velocity, the pure integral saturation will occur due to the presence of dc components in the measured current and voltage. In order to cope with this problem, one self-adaptive band-pass filter is introduced to replace the pure integrator, which can obtain smooth stroke signals with almost no amplitude and phase offset. Moreover, the current amplitude controller is designed to improve the control accuracy and response speed. Finally, comprehensive simulation and experimental results are provided to verify the effectiveness and the superiority of the proposed method.

Harnessing the plenoptic function for a directionally illuminated autostereoscopic display.

The plenoptic function is ideal to describe three-dimensional displays. We propose and demonstrate in this work that plenoptic function is a particularly suitable scenario in the directionally illuminated autostereoscopic display. Guided by this function, backlight structures and functional thin films are designed and applied for wave-vector and amplitude control so that homogeneous viewing is achieved in large viewing volume while display functionality with optical focusing and diverting can be fulfilled. The demonstration of high-quality displays by cloaking various optical defects in an otherwise severely distorted radiance distribution introduced by lens array is presented. We conclude that the scenario adopted in this work is immediately applicable to enhance general performance for autostereoscopy.

Broadband silicon-based tunable metamaterial microfluidic sensor

Tunable metamaterial absorbers play an important role in terahertz imaging and detection. We propose a multifunctional metamaterial absorber based on doped silicon. By introducing resonance and impedance matching into the absorber, a broadband absorption greater than 90% in the range of 0.8–10 THz is achieved. At the same time, the light regulation characteristics of the doped semiconductor are introduced into the absorber, and the precise amplitude control can be achieved in the range of 0.1–1.2 THz by changing the pump luminous flux. In addition, based on the principle of light-regulating the concentration of doped silicon carriers, the medium-doped silicon material is replaced by a highly doped silicon material, and a sensor with a sensitivity of up to 500 GHz/RIU is realized by combining the wave absorber with the microfluidic control. Finally, the broadband absorption characteristics and sensing performance of alcohol and water on the prepared device are verified by experiments, indicating that the absorber may have great potential in the field of sensor detection.

Memristor-coupled asymmetric neural networks: Bionic modeling, chaotic dynamics analysis and encryption application

With the rapid development of artificial intelligence, it has important theoretical and practical significance to construct neural network models and study their dynamical behaviors. This article mainly focuses on the bionic model and chaotic dynamics of the asymmetric neural network as well as its engineering application. We first construct a memristor-coupled asymmetric neural network (MANN) utilizing two asymmetrical sub-neural networks and a coupled multi-piecewise memristor synapse. Then, the chaotic dynamics of the proposed MANN is studied and analyzed by using basic dynamics methods like equilibrium stability, bifurcation diagrams, Lyapunov exponents, and Poincare mappings. Research results show that the proposed MANN exhibits multiple complex dynamical characteristics including infinitely wide hyperchaos with amplitude control, hyperchaotic initial-boosted behavior, and arbitrary number of hyperchaotic multi-structure attractors. More importantly, the phenomena of the infinitely wide hyperchaos and the hyperchaotic multi-structure attractors are observed in neural networks for the first time. Meanwhile, applying the hyperchaotic multi-structure attractors, a color image encryption scheme is designed based on the proposed MANN. Performance analyses show that the designed encryption scheme has some merits in correlation, information entropy, and key sensitivity. Finally, a physical circuit of the MANN is implemented and various typical dynamical behaviors are verified by hardware experiments.

Programmable Wavefront Control in the Visible Spectrum Using Low-Loss Chalcogenide Phase-Change Metasurfaces.

All-dielectric metasurfaces provide unique solutions for advanced wavefront manipulation of light with complete control of amplitude and phase at sub-wavelength scales. One limitation, however, for most of these devices is the lack of any post-fabrication tunability of their response. To break this limit, a promising approach is employing phase-change materials (PCMs), which provide fast, low energy, and non-volatile means to endow metasurfaces with a switching mechanism. In this regard, great advancements have been done in the mid-infrared and near-infrared spectrum using different chalcogenides. In the visible spectral range, however, very few devices have demonstrated full phase manipulation, high efficiencies, and reversible optical modulation. In this work, a programmable all-dielectric Huygens' metasurface made of antimony sulfide (Sb2 S3 ) PCM is experimentally demonstrated, a low loss and high-index material in the visible spectral range with a large contrast (≈0.5) between its amorphous and crystalline states. ≈2π phase modulation is shown with high associated transmittance and it is used to create programmable beam-steering devices. These novel chalcogenide PCM metasurfaces have the potential to emerge as a platform for next-generation spatial light modulators and to impact application areas such as programmable and adaptive flat optics, light detection and ranging (LiDAR), and many more.

Microcontroller Implementation, Controls, and Synchronization of Three-Dimensional Autonomous System with a Parabolic Equilibrium Point

The microcontroller implementation, controls, and synchronization of a three-dimensional (3D) autonomous system with a parabolic equilibrium point are investigated in this paper. The system in question displays a reverse period doubling route hidden chaotic attractors with two different shapes. Then, the partial and total amplitude controls of the system are achieved by inserting two parameters. A microcontroller implementation is performed in order to confirm the results obtained from the numerical simulations. It is found that the results from the numerical simulations and microcontroller implementation qualitatively agree with each other. The sliding mode controllers are designed to control chaos in the system under study. With the sliding mode control method, the numerical simulations confirm that chaos can be controlled in the 3D autonomous system with a parabolic equilibrium point. In addition, two chaotic 3D autonomous systems with a parabolic equilibrium point and the same parameters are synchronized by the use of a unidirectional linear error feedback coupling scheme. Finally, an active control technique is applied to bring about chaos synchronization between two chaotic 3D autonomous systems with a parabolic equilibrium and different parameters.

Polarization-insensitive amplitude and phase control based on interference metasurface

Extending the optical control capabilities of metasurfaces for broader functionalities has recently attracted extensive attention. Simultaneously achieving amplitude and phase control is an effective route as it allows rebuilding the full information of the field. However, related previous studies mostly rely on anisotropic meta-atoms, which restrict the available incident polarizations. Here, a polarization-insensitive amplitude and phase control method is proposed and experimentally demonstrated in the terahertz regime, which is actualized by introducing interference effect in reflective-type meta-molecules composed of isotropic meta-atoms. Two kinds of functional meta-mirror devices, i.e., multi-order meta-gratings and multi-focal meta-lenses, are designed and characterized, where the results verify this method very well. This proposed method further enriches the routes to control amplitude and phase and may also find broad applications in realizing flexible wavefront control devices with complex functionalities.

Independent control of both amplitude and phase for orthogonal circularly polarized electromagnetic waves through polarization conversions

Spin-selective multi-functional integrated metasurfaces have attracted much research attention due to its promising application prospects. However, the goal of independent and arbitrary control of both amplitude and phase for orthogonal circularly polarized (CP) waves still has not been achieved fully. This is because it requires mirror asymmetric structure to achieve such a goal but there is no apparent physical relation between the unit cell structure and the spin-selective properties. A simple method with clear physical pictures is proposed in this paper to achieve the goal of arbitrary spin-selective manipulations. The idea is to convert the incident orthogonal CP waves to orthogonal linearly polarized (LP) waves first, then manipulate the LP waves with matured techniques, and finally convert the LP waves back to the corresponding CP waves. Simulations and experiments have been carried out to validate the method. Using this idea, spin-selective focusing, spin-selective deflection and spin-selective orbital angular momentum vortex beam have been demonstrated.

Pixel level control of amplitude, phase, and polarization of an arbitrary vector beam

The generation of vector beams with complex spatial distributions is significant in the field of optical manipulation, optical metrology, optical microscopy, and so on. In this work, we propose a method to generate arbitrary vector beams, which is based on the complex amplitude beam shaping technology and the interferometric optical path configuration. With the method, we can achieve pixel-level control of amplitude, phase, and polarization of an arbitrary vector beam. Furthermore, different polarization states and orientations can be designed to coexist in one beam. The method has been verified with theoretical analysis and experimental results. The proposed method expands the application range of vector beams and provides a conducive way to explore the optical properties of the vector beams.

Dual-channel geometric meta-holograms with complex-amplitude modulation based on bi-spectral single-substrate-layer meta-atoms.

Metasurfaces with complex-amplitude modulation are superior in power regulation and hologram imaging resolution compared with those with phase-only modulation. Nevertheless, a single-cell metasurface with multi-band independent phase and amplitude controls is still a great challenge for the circularly polarized incidences. In this work, we propose and design a single-substrate-layer single-cell metasurface with independent complex-amplitude modulations at two discrete frequencies. Based on this emerging technique, a bi-spectral meta-hologram is designed and verified by both full-wave simulations and experiments, which could reconstruct two Chinese characters at the imaging plane at two frequencies. The proposed method shows great potential in multifunctional meta-devices with enhanced performance.

A mem-element Wien-Bridge circuit with amplitude modulation and three kinds of offset boosting

In the field of information processing, peripherals are often required to modulate the signal in terms of amplitude and position. At present, amplitude and offset boosting control of chaotic signals are mainly achieved by introducing additional constants or functions, and few systems rely on their parameters. In this work, a Wien-Bridge circuit is designed based on a voltage-controlled memristor. In addition to implementing the boosting control by introducing additional constants, the system exhibits both linear and nonlinear offset boosting behavior and amplitude control by changing the system’s parameters. This facilitates the reduction of the number of external devices for signal modulation. Besides, the system also presents coexisting symmetric attractors and bistability. These dynamic characteristics are investigated using Lyapunov exponents, bifurcation diagram, attractor projection, frequency spectra, attraction basin, and chaotic characteristic diagram. Finally, the system is implemented using DSP, which provides the basis for the application of chaotic modulation.

Design and Implementation of Simplified Symmetry Chaotic Circuit

In order to reduce the circuit cost and improve the stability and flexibility of the circuit, a simplified symmetry chaotic circuit was designed and implemented by using an inverse integration circuit and a voltage follower as isolators. The change of different symmetry chaotic dynamic behaviors caused by the change of parameters can be realized by adjusting the time constant. The behavior coexistence characteristics and amplitude control characteristics under different initial conditions were verified. The results of circuit experiments are in good agreement with those of numerical simulation and theoretical analysis. This method is effective and feasible.