Nonlinear Switching Research Articles

Nonlinear optical switch based on coherent perfect absorption.

Coherent perfect absorption (CPA) or reflection (CPR) are methods to realize the extreme manipulation on an optical field. We propose a scheme to operate a bistable switch with convertible CPA and/or CPR. Generally, CPA and CPR occur with different input-field phases. For example, CPA is realized when two input probe beams are in phase; instead, CPR is achieved when they are out of phase. In this scheme, a CPA state can be converted to a CPR state by an incoherent field although two input fields are in phase. When we use the incoherent field as a switching field, the CPA (CPR) state is treated as the closed (open) state. As a result, the switching efficiency can theoretically reach a maximum value, i.e., η = 1. In addition, the switch can be operated in the linear regime with a weak input field, and in the nonlinear or bistable regime with a strong input field. Moreover, the efficiency of the bistable switch is sensitively dependent on the input-field intensity. It provides a potential application of this work on sensitive optical detecting.

Deep reservoir computing based on self-rectifying memristor synapse for time series prediction

Herein, a self-rectifying resistive switching memristor synapse with a Ta/NbOx/Pt structure was demonstrated for deep reservoir computing (RC). The memristor demonstrated stable nonlinear analog switching characteristics, with a rectification ratio of up to 1.6 × 105, good endurance, and high uniformity. Additionally, the memristor exhibited typical short-term plasticity and dynamic synaptic characteristics. Based on these characteristics, a deep memristor RC system was proposed for time series prediction. The system achieved a low normalized root mean square error (NRMSE) of 0.04 in the time series prediction of the Henon map. Even at 90 °C, deep RC retains good predictive power with an NRMSE of only 0.07. This work provides guidance for efficient deep memristive RC networks to handle more complex future temporal tasks.

Coupled electro-aeroelastic energy harvester model based on piezoelectric transducers, VIV-galloping interaction and nonlinear switching circuits

Miniaturization, multi-functionality, and low power consumption are key features in the development of electronic devices today. These characteristics open up the possibility for the development of small, self-powered systems. Piezoelectric materials have emerged as a promising solution due to their ability to convert mechanical energy into electrical energy from the surrounding environment, such as wind. In this research work, we investigate an aeroelastic piezoelectric energy harvester based on the interaction between vortex-induced vibrations and galloping. The device, a bimorph cantilevered beam with a square-section bluff body attached to its tip, produces mechanical oscillations that are extracted by various electrical circuits, including a nonlinear switching interface. A numerical model, implemented in a Simulink environment, is developed to solve the coupled electro-aeroelastic problem for each electrical interface. The results are compared to experimental data collected from wind tunnel tests conducted at various wind velocities and load resistances, and a satisfactory correlation is observed. The validated model is finally used to carry out a parametric analysis aimed at optimizing the performance of the harvester in a low wind speed range. This investigation could contribute to a better understanding of an aeroelastic harvesting system and potentially assist in the optimization of design parameters and electrical interfaces for specific applications.

Coupled analysis of a compact autoparametric vibration energy harvester with synchronized switch circuits

We previously developed a high-performance autoparametric vibration energy harvester (VEH) with a self-powered synchronized switch circuit, which can realize miniaturization, a low acceleration threshold for triggering the autoparametric resonance, and milliwatt-level power output. However, the mechanical and electrical nonlinearities considering nonlinear stiffness hardening and electrical switching complicate the performance analysis. We established a simpler analysis technique for the autoparametric vibration energy harvester with a synchronized switch circuit. We first derived governing equations and then introduced an equivalent impedance model to simplify the analysis coupled with a synchronized switch circuit. The simulation replicated experimental results well at an acceleration sufficiently higher than the acceleration threshold but not around the acceleration threshold because the acceleration dependency of the inversion coefficient and the switching delay were ignored in the analysis. The analysis technique revealed a complex coupling interaction of the upper and lower oscillators (i.e., the piezoelectric cantilever and the microfabricated oscillator with a seismic mass) and the synchronized switch circuits. The analysis technique is a useful tool for predicting the performance or designing the structure of a compact autoparametric VEH connecting to switch circuits.

Discrete-Time Switching Systems as Difference Inclusions: Deducing Converse Lyapunov Results for the Former From Those for the Latter

Nonlinear discrete-time switching systems under mode-dependent switching and dwell-time constraints are modeled by difference inclusions. Novel proofs of converse Lyapunov results are obtained for the switching systems as consequences of a converse Lyapunov result for a difference inclusion.

An approach on nonlinear integration of MMC to linear model of ROPS in transient analysis

SummaryThe modular multilevel converter (MMC) is a novel prospective multilevel converter topology for high‐voltage or high‐power applications. This paper presents the 3‐ model integrated into a linear model in transient analysis and the design of current controller for MMC. This paper analyzes the control interactions of MMC on nearby turbine generator. The eigenvalue analysis is used to evaluate the impact of different controller modes of MMC. The impact of converter control with nonlinear switches is analyzed through the transient simulation. The eigenvalue analysis and controller design are carried out on a linear model, and the transient simulation analysis is performed on both the D‐Q model and a three‐phase model of MMC using MATLAB‐Simulink. The results show that the transient simulation of three‐phase model on the proposed approach is consistent with the transient simulation of D‐Q model. Also, the transient simulation results show a satisfactory response with the current controller parameters of the MMC at various operating cases. To validate the results of MATLAB‐Simulink model, the proposed system is implemented in hardware‐in‐the‐loop (HIL) simulation with an integrated subsystem built in two real‐time simulators. The subsystem of mathematical model is implemented in dSPACE, and the subsystem of 3‐ MMC with controller is implemented in Typhoon. The HIL simulation results show a satisfactory response and consistent with MATLAB‐Simulink model results.

Event-triggered H∞ robust filtering for nonlinear semi-Markov switching systems

This paper studies the filtering problem for a class of discrete-time semi-Markov switching repeated scalar nonlinear systems with an event-triggered scheme. Considering the limitation of bandwidth, the mode-dependent event-triggered mechanism is introduced to determine whether the currently sampled sensor data is transmitted to the filter, in which the parameters of the event generator depend on the system mode. By means of a constructed time-varying Lyapunov function, the two stages of the systems jump instant and mode residence are analysed, and a linear matrix inequality technique is used to ensure the mean-square stability and performance of the filter error system. Accordingly, the co-design method of the mode-dependent time-varying filter and the event-triggered mechanism is derived for semi-Markov switching systems. Finally, a numerical simulation is given to illustrate the effectiveness and feasibility of the method proposed in this paper.

Exploring Routes to Enhance the Calculation of Free Energy Differences via Non-Equilibrium Work SQM/MM Switching Simulations Using Hybrid Charge Intermediates between MM and SQM Levels of Theory or Non-Linear Switching Schemes.

Non-equilibrium work switching simulations and Jarzynski's equation are a reliable method for computing free energy differences, ΔAlow→high, between two levels of theory, such as a pure molecular mechanical (MM) and a quantum mechanical/molecular mechanical (QM/MM) description of a system of interest. Despite the inherent parallelism, the computational cost of this approach can quickly become very high. This is particularly true for systems where the core region, the part of the system to be described at different levels of theory, is embedded in an environment such as explicit solvent water. We find that even for relatively simple solute-water systems, switching lengths of at least 5 ps are necessary to compute ΔAlow→high reliably. In this study, we investigate two approaches towards an affordable protocol, with an emphasis on keeping the switching length well below 5 ps. Inserting a hybrid charge intermediate state with modified partial charges, which resembles the charge distribution of the desired high level, makes it possible to obtain reliable calculations with 2 ps switches. Attempts using step-wise linear switching paths, on the other hand, did not lead to improvement, i.e., a faster convergence for all systems. To understand these findings, we analyzed the solutes' properties as a function of the partial charges used and the number of water molecules in direct contact with the solute, and studied the time needed for water molecules to reorient themselves upon a change in the solute's charge distribution.

Nonlinear optical properties of PVD-grown Cr2Te3 film and its nonlinear switching application

Recently, two-dimensional (2D) nanomaterials have been investigated extensively in the field of nonlinear photonics. Cr2Te3, which is one of the 2D transition metal chalcogenides, has garnered attention in the field of spintronics and optoelectronics because of its fascinating magnetic and optical properties. Despite its potential in optoelectronics, Cr2Te3 has rarely been studied in the field of nonlinear photonics. This study investigates the nonlinear optical responses of nanoscale-layered Cr2Te3 films grown by physical vapor deposition at telecommunication wavelengths. A large nonlinear absorption coefficient of –(1.43 ± 0.06) × 105 cm/GW and a nonlinear refractive index of –1.22 ± 0.04 cm2/GW at 1560 nm obtained through Z-scan measurements indicate that the Cr2Te3 film shows saturable absorption and self-defocusing properties at telecommunication wavelengths. Density functional theory calculation show that Cr2Te3 is suitable for broadband optical device. The potential of the nanoscale-layered Cr2Te3 film as a base medium for a nonlinear optical switch was evaluated by fabricating a saturable absorption mirror (SAM). Stable Q-switched pulses with a maximum repetition rate of 33.35 kHz and minimum temporal width of 2.62 μs were readily achieved from a fiber laser cavity incorporating the SAM.

Analytically pricing variance and volatility swaps under a Markov-modulated model with liquidity risks

This paper determines strike prices of discretely sampled variance/volatility swaps taking into account stochastic liquidity risks and the switching of economic conditions. We adopt nonlinear regime switching volatility to reflect how asset prices are affected by economic cycles, and market prices of assets are discounted according to the level of market liquidity. We then establish a risk-neutral measure under regime switching Esscher transform, so that analytical valuation of variance/volatility swaps can be completed based on the closed-form forward characteristic function. The limiting behavior of discretely sampled variance/volatility swaps is also considered through the investigation of pricing continuously sampled variance/volatility swaps. Finally, based on the results from numerical implementation, we confirm that the new model is very flexible in reflecting different influence associated with common real market observations.

Thermal nonlinearity and all-optical switching of synthesized Azo-Cl compound

Azo-Cl compound is synthesized and fully characterized via NMR and mass spectroscopies. The Azo-Cl compound thermal properties, theoretical chemical shifts, chemical structure, electron absorption spectrum, frontier molecular orbitals, the atomic dipole moment, corrected Hirshfeld charge analysis and electrostatic molecular potential of the Azo-Cl compound are studied in details. The Azo-Cl compound nonlinear refractive index (NLRI) is estimated via diffraction patterns (DPs) and the Z-scan, using low power continuous wave (cw) laser beam. The all-optical switching (AOS) property is recognized in the Azo-Cl compound using two laser beams. We found that the value of the NLRI of sample calculated by the diffraction patterns is greater than the value calculated by the Z-scan, due to the use of different input powers in both cases. The experimental results proved that the sample showed a high NLRI in the range of 10−7 calculated by the Z-scan method under low input power of 5 mW, which indicates that the Azo-Cl compound is a good candidate to be used in optical device applications.

Adaptive super-twisting-based nonsingular fast terminal sliding mode control of permanent magnet linear synchronous motor

In this study, to reduce the impact that permanent magnet linear synchronous motor (PMLSM) servo system on the sensitivity of external and internal interferences, an adaptive super-twisting-based nonsingular fast terminal sliding mode control (AST-NFTSMC) scheme is put forward. First of all, the mathematical model of PMLSM contains uncertainties is set up, and the control law is established to make position signal converge to given state asymptotically. Second, by introducing the super-twisting algorithm, the chattering caused by nonlinear switching function in traditional method is weakened. However, in actual industrial situations, it is difficult to determine the boundary of lumped disturbance, which makes the switching gains in super-twisting algorithm cannot be accurately selected. Therefore, an adaptive law is introduced to adjust the switching gains online, so that the gains can be dynamically adjusted within a limited range during operation, so as to further weaken chattering. Finally, the practicability of AST-NFTSMC is proved in theory and verified by system experiments. The experimental results prove that AST-NFTSMC can significantly weaken chattering, and result in robust control performance.

Nonlinear feedback switching rule design for sector‐bounded switched systems

AbstractThis article presents a robust switching rule design technique for a class of nonlinear and uncertain switched systems. The approach is based on a state transformation that allows for nonlinear state feedback. The results are given in terms of linear matrix inequality problems and they guarantee global asymptotic stability of the closed‐loop system even if sliding modes occur on any switching surface. The class of systems considered is general enough to include multiple time varying sector‐bounded nonlinearities associated with real‐time changes in the operation point. The potential of the method is illustrated through photovoltaic systems, in which the nonlinear I–V characteristic of the modules is treated as a sector‐bounded function. As the slope of the sectors depend on the environmental conditions, robust sectors containing the nonlinearities for any uncertain uniform operation condition are derived.

Distributed event-triggered consensus control for a class of nonlinear multi-agent systems under switching topologies

A distributed event-triggered consensus control protocol is proposed for a class of nonlinear multi-agent systems with switching topologies. The nonlinear dynamics and switching topologies are considered simultaneously to adapt to some actual scenarios. To economize the communication resources, a distributed event-triggered mechanism is established to decrease the consumption of communication resources. The new event-triggered mechanism is constructed by the information of distributed errors, which can fully utilize communication relationships among agents to control the timing of events. A class of negative exponential functions is added to the event-triggered condition as the event-triggered mechanism is applied for the presented multi-agent systems. The design of event-triggered condition can reduce the occurring frequency of events when the adjusting time of control scheme begins at an initial small amount period of time. Finally, the simulation results are provided, which verify the feasibility and effectiveness of the designed event-triggered consensus control strategy for the presented multi-agent systems with switching topologies.

Switching Transition Modeling of eGaN HEMT in Power Converters

Selection of power switch driver resistance is crucial for power converter design, and an improper resistance value can lead to reduced efficiency and undesired operational behavior such as over-voltage and false turn-on. To select appropriate resistance, this letter proposes an accurate switching transition modeling method for switches in DC-DC converters, which can help guide engineers design switch drivers. For a converter with multiple components, i.e., a high-order converter system, the traditional analytical methods become very complex due to a large number of operating modes. To alleviate this problem, in the proposed modeling method, all nonlinear switches are modeled as linear systems, and various operating modes are combined into one mode in the proposed model. With the simplified mode, the driver parameters can be easily obtained. To verify the proposed model, we take the enhanced gallium nitride high electron mobility transistor (eGaN HEMT) high-order DC-DC converter as an example for experimentation. The eGaN HEMT is highly sensitive to parasitic parameters and switching frequency, and thus the high-order converter can demonstrate the ease of design with the proposed modeling method. Experiments on a Z-source converter and a quadratic-boost converter validate the feasibility of the proposed modeling method.

Leveraging Voltage-Controlled Magnetic Anisotropy to Solve Sneak Path Issues in Crossbar Arrays

In crossbar array structures, which serves as an “in-memory” compute engine for artificial intelligence (AI) hardware, write sneak path problem causes undesired switching of devices that degrades network accuracy. While custom crossbar programming schemes have been proposed, device-level innovations leveraging nonlinear switching characteristics of the cross-point devices are still under exploration to improve the energy eff iciency of the write process. In this work, a spintronic device design based on magnetic tunnel junction (MTJ) exploiting the use of voltage-controlled magnetic anisotropy (VCMA) effect is proposed as a solution to the write sneak path problem. In addition, insights are provided regarding appropriate operating voltage conditions to preserve the robustness of the magnetization trajectory during switching, which is critical for proper switching probability manipulation.

Unusual nonlinear switching in branched carbon nanotube nanocomposites

In this experimental study, we investigate the nonlinear dynamic response of nanocomposite beams composed of polybutylene terephthalate (PBT) and branched carbon nanotubes (bCNTs). By varying the weight fraction of bCNTs, we obtain frequency response curves for cantilever specimens under harmonic base excitations, measuring the tip displacement via 3D scanning laser vibrometry. Our findings reveal a surprising nonlinear softening trend in the steady-state response of the cantilevers, which gets switched into hardening for higher bCNT weight fractions and increasing oscillation amplitudes. The interaction of bCNTs with the thermoplastic hosting matrix results in stick-slip hysteresis, causing a softening nonlinearity that counteracts the geometric hardening associated with the nonlinear curvature of the first mode of the cantilever. However, when the weight fraction of bCNTs is greater than 1%, the bridging of the branched CNTs leads to the formation of a strong network that contributes to the hardening response at higher oscillation amplitudes. This mechanical behavior is detected by the trend of the nonlinear harmonic spectra and the equivalent damping ratio estimated using the half-power bandwidth method. To predict the observed unusual experimental behavior, we use a nonlinear mathematical model of the nanocomposite cantilever samples derived from a 3D mesoscale hysteretic model of the PBT/bCNT material. Our results suggest that the presence of bCNTs in a thermoplastic matrix is the main driver of the highly tunable nonlinear stiffness and damping capacity of the material. The reported experimental and modeling results provide valuable insights into the nonlinear dynamic behavior of PBT/bCNT nanocomposites and have potential applications in the design of advanced materials with tailored mechanical properties.

Optical Multiplexer

In this paper, we present an all-optical multiplexer based on a Terahertz Optical Asymmetric Demultiplexer (TOAD) device. The TOAD is used as a nonlinear optical switch to selectively route optical signals based on their wavelength or frequency, allowing for the multiplexing of multiple optical channels onto a single fiber optic cable. We describe the design and implementation of the TOAD-based multiplexer, including the optical components and signal processing algorithms used to achieve high-speed, low-error-rate operation. We also present experimental results demonstrating the performance of the multiplexer, including its ability to maintain signal quality over long distances and under various noise and interference conditions. Our results show that the TOAD-based multiplexer offers a promising approach to all-optical multiplexing for high-speed, high-capacity optical communications systems.

Multi-Stimuli Responsive Luminescence and Domino Phase Transition of Hybrid Copper Halides with Nonlinear Optical Switching Behavior.

Although phase transition materials (PTMs) under external stimuli are of great research interest duo to their rich potential applications, it is still challenging to explore multi-responsive PTMs. Herein, two different phases of organic-inorganic hybrid copper-based halides, α- and β-Gua3 Cu2 I5 (Gua+ =CN3 H6 + ), were synthesized by solvent evaporation method, which they crystalize in the noncentrosymmetric space group Fdd2 with zero-dimensional structure and centrosymmetric space group C2/c with one-dimensional metal-halogen framework, respectively. Interestingly, it is firstly demonstrated that Gua3 Cu2 I5 simultaneously possesses reversible PL conversion and NLO switching properties in response to thermal stimulus. Strikingly, apart from heat, its structural phase transition can also be triggered by crystalline-phase-recognition (CPR) and mechanical force. These new findings may pave a path for future exploration of PTMs with multiple physical properties.

Multi‐Stimuli Responsive Luminescence and Domino Phase Transition of Hybrid Copper Halides with Nonlinear Optical Switching Behavior

AbstractAlthough phase transition materials (PTMs) under external stimuli are of great research interest duo to their rich potential applications, it is still challenging to explore multi‐responsive PTMs. Herein, two different phases of organic–inorganic hybrid copper‐based halides, α‐ and β‐Gua3Cu2I5(Gua+=CN3H6+), were synthesized by solvent evaporation method, which they crystalize in the noncentrosymmetric space groupFdd2 with zero‐dimensional structure and centrosymmetric space groupC2/cwith one‐dimensional metal‐halogen framework, respectively. Interestingly, it is firstly demonstrated that Gua3Cu2I5simultaneously possesses reversible PL conversion and NLO switching properties in response to thermal stimulus. Strikingly, apart from heat, its structural phase transition can also be triggered by crystalline‐phase‐recognition (CPR) and mechanical force. These new findings may pave a path for future exploration of PTMs with multiple physical properties.