Surface Modes Research Articles

Observation of Higher-Mode Rayleigh Waves from Ambient Noise in the Tarim Basin, China

Abstract Higher mode surface waves, which can provide additional constraints on subsurface structures in addition to fundamental modes in surface-wave tomography, have been observed from ambient noise cross-correlation functions (CCFs) in sedimentary basins in oceans or near coastlines. However, few studies show that higher mode surface waves can be observed and extracted directly from ambient noise CCFs in inland basins. In this study, we report observations of high signal-to-noise ratio fundamental and the first higher mode Rayleigh waves at a period range of 0.2–1.90 s and 0.2–1.35 s, respectively, from ambient noise CCFs in the southeastern margin of the Tarim basin, the biggest inland basin in China. We confirm the credibility of the first higher mode surface waves by showing that the observed first higher mode dispersion curves are matched with predicted ones calculated from S velocity models solely constrained by fundamental-mode dispersion curves. After the verification of the credibility of the first higher mode surface waves, we demonstrate that the inclusion of the first higher mode dispersion curves helps image deeper structures with an increase of average depths from ∼0.73 to ∼1.24 km, which will be beneficial to future explorations of deep oil and gas resources in the Tarim basin.

Third‐order integral sliding mode control of piezoelectric actuators based on rate‐amplitude‐dependent Prandtl‐Ishlinskii model

AbstractAiming at trajectory tracking control of piezoelectric actuators (PEAs), this article proposes a third‐order integral sliding mode control (3‐ISMC) based on rate‐amplitude‐dependent Prandtl‐Ishlinskii (PI) inverse model feedforward (3‐RAPI) scheme, which can achieve finite time convergence and avoid singular problems, while ensuring the continuity of the control signal. In this control scheme, a rate‐amplitude‐dependent PI (RAPI) model is proposed to describe the hysteresis characteristics of PEA, and the RAPI hysteresis inverse model is used to realize the feedforward control. The simulation results verify the improvement of the modeling accuracy of the RAPI model compared with the traditional PI model. In order to reduce the influence of modeling error and improve the robustness of the system, a 3‐ISMC scheme based on integral non‐singular fast terminal sliding mode surface is proposed. Simulation and experimental results demonstrate that the tracking performance of 3‐ISMC is improved compared with the existing third‐order integral terminal sliding model control (3‐ITSMC). Finally, the composite control algorithm is realized by combining the RAPI hysteresis inverse model feedforward with the 3‐ISMC algorithm. The experimental results further show that the control algorithm can track the input signal in a wide range of rate and amplitude.

Composite Control Based on Feed-Forward and FISMC Method for Accurate Speed of Gimbal System With Harmonic Drive

In the gimbal system of single gimbal magnetically suspended control moment gyroscope (SGMSCMG), harmonic drive is usually installed to ensure the large output torque and reduce the volume and weight of the servo motor. Nevertheless, its nonlinear characteristics make the transmission torque fluctuate and decrease the performance of the gimbal system. The disturbance torque fluctuations can be divided into ‘gear wave torque’ and ‘non-gear wave torque,’ and to suppress the different types of fluctuations, a composite control method based on model-based feed-forward and fuzzy integral sliding mode control (FISMC) method is proposed. The former method is adopted to restrain the gear wave torque. Then, for the rest of the disturbance torques, the FISMC with new dynamic sliding mode surface is put forward to enhance the robustness and improve the performance of the speed. Finally, the simulation and experiments are carried out on SGMSCMG to validate the effectiveness of the composite method. The results show that the torque fluctuation can be effectively suppressed and the performance of the gimbal system can be significantly improved.

Determination of the resistance of water-repellent properties to ultraviolet radiation on self-hydrophobized surface textures of AISI 304 steel

In this work, the object of the study were femtosecond laser textured steel samples. Using a femtosecond laser to texture the surface both in the direct-beam mode, which provides microtextures, and in the reflection mode, which leads to the formation of LIPSS-type nanostructures on the surface. Such hybrid complexes are optimal in terms of water repellency as they embody the principle of hierarchical textures. This approach is one of the promising ways to solve the problem of scaling the process of obtaining superhydrophobic metal surfaces. The aim of the work is to establish the stability of water-repellent properties of micro- nanotextures obtained on the surface of AISI 304 steel after spontaneous hydrophobization under the action of UV radiation. The study of the obtained textured surface by scanning electron microscopy to confirm the presence of nanotexture and by energy-dispersive X-ray spectroscopy to establish the elemental composition of the obtained microtexture were made in the work. The paper shows that the water repellency of AISI 304 steel surfaces textured at micro and nano levels by femtosecond laser after long exposure to the atmosphere increases to a superhydrophobic state with the value of contact angles up to 155°. It has been shown that such surfaces are sensitive to UV radiation. Depending on the type of structure, the loss of hydrophobicity under experimental conditions occurs in 15-45 minutes of exposure, and complete hydrophilization of the surface occurs after 100 minutes of irradiation. As a result, the obtained self-hydrophobic surfaces are not suitable for operation under the influence of sunlight. However, ultraviolet radiation can be used to pre-clean such surfaces from adsorbed organic contaminants.

Experimental study on the sloshing of a three-layer liquid system with a free surface

Laboratory experiments have been conducted on the sloshing of three immiscible liquids in a rectangular tank subjected to harmonic horizontal excitation. The three working liquids are water, machine oil and ethanol, respectively. Their depths to tank length are all equal to 0.2. Dozens of experimental cases including a wide range of excitation amplitudes (0.04–8.0 cm) and frequencies (0.111–2.614 Hz) are considered. The experiments produce some results that are unique to the three-layer liquid sloshing. When the excitation frequency is equal to the first mode natural frequency of the bottom interface as well as very close to the third mode natural frequency of the middle interface, the typical resonance phenomenon can be observed both at the middle and the bottom interfaces. Meanwhile, the amplitudes of the free surface displacement are negligibly small compared to the middle and the bottom interfaces. With the increase of the excitation amplitude, the wave pattern on the bottom interface changes from 2D standing wave to 3D gravity-capillary wave. In addition, detailed comparisons between higher resonant modes of the free surface, the middle and the bottom interfaces are carried out. When the excitation frequency is equal to the fifth mode natural frequency of the bottom interface, the typical secondary resonance occurs at the free surface and subsequently influences the other two interfaces. In brief, the present study reveals that in the case of three-layer liquid sloshing, the relevant physics can be much more complicated compared to sloshing of single-layer or two-layer liquid.

Acoustic surface modes on metasurfaces with embedded next-nearest-neighbor coupling

We design, simulate, and experimentally characterize an acoustic metasurface comprising of a one-dimensional (1D) array of open, sound-hard cavities modulated with beyond-nearest-neighbor (BNN) couplings in the form of additional connecting cavities embedded beneath the surface. The hidden complex structure is realized readily with additive manufacturing techniques [three-dimensional (3D) printing]. The dispersive properties of the supported localized acoustic surface waves are influenced by competing power-flow channels provided by the BNN couplings, that generate extrema in the dispersion spectra within the first Brillouin zone. The structure supports negatively dispersing ``backwards'' waves that we experimentally verify. Such structures thereby provide a route to enhanced acoustic sensing by acoustic metasurfaces.

Sliding-mode anti-disturbance speed control of permanent magnet synchronous motor based on an advanced reaching law

In order to improve the performance of a permanent magnet synchronous motor (PMSM) speed controller, an advanced reaching law sliding mode control (ASMC) strategy is proposed in this study. The advanced sliding mode reaching law (ASMRL) introduces a power term of the system state and a checkmark function term about the sliding mode function based on the traditional constant-proportional rate reaching law(TSMRL) , and replaces the sign function with a hyperbolic tangent function. A detailed theoretical analysis of the characteristics of the ASMRL is then presented. The theoretical analysis shows that the ASMRL converges to the sliding mode surface more quickly and with less chattering than the TSMRL. In addition, a sliding mode disturbance observer (SMDO) is designed to estimate the total disturbance of the system, and the estimated disturbance is compensated to ASMC. Then the stability of the system with ASMC and the stability of the system with ASMC+SMDO is proved by Lyapunov’s theorem. Finally, the proposed control strategy is validated on an experimental platform of PMSM. The experimental results show that the ASMC has a faster convergence speed, smaller chattering, better disturbance rejection performance than the traditional constant-proportional rate reaching law sliding mode control(TSMC), and better performance with the addition of SMDO.

An improved global fast terminal high-order sliding mode control strategy based on novel reaching law for improving PMLSM dynamic performance

Due to its better power density and efficiency, permanent magnet linear synchronous motor (PMLSM) is ideal for generating electricity with wave power device (WPD). Nevertheless, when the PMLSM for the WPD control system is impacted by changes in motor characteristics and interference from the outside environment, it typically is unable to deliver high-quality dynamic performance on schedule. Although sliding mode control (SMC) has been introduced to improve the robustness of the system greatly in recent decades, traditional methods still have problems such as slow dynamic response, poor anti-disturbance performance, large chattering amplitude, and phase delay. To solve the above defects in SMC, an improved global fast terminal high-order SMC strategy based on novel reaching law for improving PMLSM dynamic performance is proposed in this paper, as well as the sliding mode surface and control law of the speed controller is designed based on this control strategy. The proposed strategy would not only shorten the dynamic response time but also weaken the chattering magnitude in the sliding mode stage, improving the dynamic performance of both speed and current. The simulation results demonstrate that in comparison to the traditional PI and SMC control methods, the improved strategy proposed in this paper can further enhance the control performance of the linear motor, demonstrating the method’s enormous potential in the double closed-loop vector control system of PMLSM for WPD.

Fixed-time fault-tolerant attitude control for rigid spacecraft with torque saturation

This paper investigates the fixed-time attitude control problem for spacecraft under input saturation, actuator faults, and system uncertainties. Three novel saturated fixed-time nonsingular terminal sliding mode surfaces (NTSMSs) are designed, which can keep the system states fixed-time stable after the establishment of their sliding manifolds. Two of them are time-varying and firstly designed. Each of the two NTSMSs has an adjustment parameter that is adjusted dynamically and used to handle saturation and cancel the attitude dynamics. According to other related predesigned parameters, a conservative lower bound of this parameter is obtained. A saturated control scheme is then designed in conjunction with a newly proposed saturated reaching law. A modification strategy is carried out to facilitate the engineering applications of our methods. The fixed-time stability of the closed-loop systems is validated by Lyapunov stable theory. Simulation results validate the effectiveness and superiority of the proposed control scheme.

Heterogeneous swarm control based on two‐layer topology

SummaryIn this paper, we propose a heterogeneous swarm control method based on a two‐layer communication topology, which solves the problems of great difficulty in controller design and high computational complexity of communication topology in large‐scale heterogeneous swarm control. Firstly, we divide large‐scale heterogeneous swarms into several independent isomorphic sub‐swarm and design corresponding sub‐swarm controllers, which dramatically reduces the difficulty of swarm controller design. Secondly, we introduce a two‐layer communication topology to treat the followers in the first‐layer communication topology as leaders in the second‐layer communication topology, which establishes the connection between each sub‐swarm and the global leader and reduces the computational complexity of the communication topology. Finally, based on the two‐layer communication topology, the swarm controllers in the first‐layer and second‐layer communication topologies are designed using the sliding mode and dynamic surface methods. The Lyapunov function is designed to prove its stability. The simulation results verify the effectiveness of the controllers.

The impact of 3D Raman imaging and HR-TEM analysis on the observed changes in the orientation of the crystallites in 3D flower-like nanostructured layers

The presented study aims to explain the formation phenomena of titanium dioxide flower_like forms on Ti foil. TiO2 nanoforms were obtained by chemical oxidation using H2O2 and further crystallization at 600 °C under an argon atmosphere. The morphology of layers is determined by reaction time. Understanding the factors that indicate the transition sequence and control the phase stability may provide insight into how the properties of titanium dioxide nanomaterials can be manipulated. A cross-sectional view of the samples reveals the complex arrangement of grains and their different shapes. HR-TEM and 3D Raman spectroscopy allowed to gain new insights into the structure formation. Observations of vibrational modes of anatase (101) and (001) surfaces allow quantitatively defining the percentage of facets exposition. Moreover, the spectra collected from different z-heights for the sample and the analysis of the integrated intensity ratio of Eg (144 cm−1) and A1g (514 cm−1) anatase bands show the grains' variable nature. The results present that the inner layer of the nanostructure is composed of more oriented crystallites, in contrast to the oxide/substrate interface and the sample surface. The model of the growth mechanism of a multilayered TiO2 scale formed on Ti has been proposed. Data availability statementThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Implementation of NATO standards to improve the electromagnetic immunity and compatibility of equipment of the critical infrastructure objects

Ensuring that domestic technical equipment meets modern safety and reliability requirements in accordance with NATO standards is a pressing problem in Ukraine. Without metrological support for testing the electromagnetic compatibility and immunity to powerful electromagnetic fields of natural and artificial origin, it is impossible to ensure reliable and safe use of modern electronic, electroenergetics and electric equipment in critical infrastructure facilities.
 The paper presents the metrological traceability paths of the state measurement standards in the field of electromagnetic measurements, established at the NSC “Institute of Metrology”, to the SI units. The results of the research on the measurement standard of the electromagnetic field strength unit in the frequency range from 0.01 MHz to 43 GHz (NDETU EM-05-2021), established at the NSC “Institute of Metrology”, are described. The connection of the NDETU EM-05-2021 measurement standard with the measurement standards of the power unit of electromagnetic oscillations in coaxial and waveguide transmission lines and the standard of AC electric voltage is demonstrated.
 The lists of tests in accordance with the AESTR-500 standard, which are supported by the measurement standards of the NSC “Institute of Metrology”, and the equipment that can be calibrated by the national measurement standards are given. The examples of tests for electromagnetic compatibility carried out in the testing centre of the State Enterprise “Kharkivstandartmetrologiya” are provided.
 Based on the results of the developed statistical models at the Research and Design Institute “Molniya” for predicting the vulnerability to electromagnetic effects of atmospheric phenomena on critical infrastructure facilities, the examples of the distribution of lines of the equal potential (in kilovolts) on the ground surface in the short circuit mode and the distributions of probability density of lightning strikes are presented. The distributions of the equal potential lines on the ground surface in the short-circuit mode of high-voltage substations are modelled based on calculations.

Zigzag Edge States in Graphene in the Presence of In‐Plane Electric Field

Herein, the edge states in a finite‐width graphene ribbon and a semi‐infinite geometry subject to a perpendicular magnetic field and an in‐plane electric field, applied perpendicular to a zigzag edge, are explored. To accomplish this, a combination of analytic and numerical methods within the framework of low‐energy effective theory is employed. Both the gapless and gapped Dirac fermions in graphene are considered. It is found that a surface mode localized at the zigzag edge remains dispersionless even in the presence of electric field. This is shown analytically by employing Darwin's expansion of the parabolic cylinder functions of large order and argument.

Dual Jitter Suppression Mechanism-Based Cooperation Control for Multiple High-Speed Trains with Parametric Uncertainty

Parameter uncertainty is one of the key factors that affect the performance of train systems. In order to obtain good tracking and cooperation performances and to improve line utilization, this paper proposes a sliding mode surface-based cooperation control scheme for multiple high-speed trains subject to parameter uncertainty. Based on the single-mass point model, multiple high-speed trains can be modeled as a quasi-multi-agent system with the leader–follower model. Considering the parameter uncertainty of the system, the non-singular terminal sliding mode surface is applied and adaptive control laws are designed to estimate the unknown parameters and external disturbances. A dual jitter suppression mechanism-based cooperation control drive strategy is presented in order to achieve the following objectives: (1) the leading train can track the desired trajectory very well; (2) one train can follow the adjacent train in front at the desired safe interval; and (3) the cooperation performances can be obtained for the quasi multi-agent system. Lyapunov functions are defined to prove the stability of the system, and simulation experiments show that the proposed cooperation control scheme is feasible and effective. According to the presented control scheme applied for multiple high-speed trains, the line utilization rate can be greatly improved.

Robust [formula omitted]-dissipative event-triggered sliding mode control of discrete T-S fuzzy descriptor systems with partial unmeasurable premise variables

In this paper, the admissibility analysis and dissipative sliding mode control (SMC) based on event-triggered mechanism (ETM) are studied for discrete T-S fuzzy descriptor systems (D-TSFDS). The problem of partial unmeasurable premise variables in D-TSFDS is dealt with by nonlinear dynamic programming. Based on ETM, a sliding mode surface based on measurable premise variables is proposed for the first time. Since the delay between the sensor and the controller in ETM, a Lyapunov-Krasovskii function is used to acquire the sufficient conditions for the closed-loop system to be admissible with dissipative performance. A new SMC law is given to ensure the reachability conation. The simulation results demonstrate the effectiveness of the proposed method.

Fixed-time synchronization of multiplex networks by sliding mode control

Multiplex networks involve different types of synchronization due to their complex spatial structure. How to control multiplex networks to achieve different types of synchronization is an interesting topic. This paper considers the fixed-time synchronization of multiplex networks under sliding mode control (SMC). Firstly, for realizing three types of synchronization of multiplex networks in a fixed time, a unified sliding mode surface (SMS) is established. After that, based on the theory of SMC, a sliding mode controller (SMCr) which is more intelligent and has a simpler form than those in the existing literature is put forward for multiplex networks. It can not only guarantee the emergence of sliding mode motion, but also can realize three different kinds of synchronization by adjusting some parameters or even one parameter of the controller. Based on some theories of fixed-time stability, this paper deduces several sufficient conditions for the trajectories of the system to reach the preset SMS in a fixed time, and derives some sufficient conditions for multiplex networks to realize three different types of fixed-time synchronization. At the same time, the settling time which can reveal what factors determine the fixed-time synchronization in multiplex networks is obtained. Finally, in numerical simulations, different chaotic systems are set for each layer of multiplex networks to represent the nodes of different layers, which can prove that the theoretical results are practical and effective.

Modeling of very high frequency large-electrode capacitively coupled plasmas with a fully electromagnetic particle-in-cell code

Phenomena taking place in capacitively coupled plasmas with large electrodes and driven at very high frequencies are studied numerically utilizing a novel energy- and charge-conserving implicit fully electromagnetic particle-in-cell (PIC)/Monte Carlo code ECCOPIC2M. The code is verified with three model problems and is validated with results obtained in an earlier experimental work (Sawada et al 2014 Japan. J. Appl. Phys. 53 03DB01). The code shows a good agreement with the experimental data in four cases with various collisionality and absorbed power. It is demonstrated that under the considered parameters, the discharge produces radially uniform ion energy distribution functions for the ions hitting both electrodes. In contrast, ion fluxes exhibit a strong radial nonuniformity, which, however, can be different at the powered and grounded electrodes at increased pressure. It is found that this nonuniformity stems from the nonuniformity of the ionization source, which is in turn shaped by mechanisms leading to the generation of energetic electrons. The mechanisms are caused by the interaction of electrons with the surface waves of two axial electric field symmetry types with respect to the reactor midplane. The asymmetric modes dominate electron heating in the radial direction and produce energetic electrons via the relatively inefficient Ohmic heating mechanism. In the axial direction, the electron energization occurs mainly through an efficient collisionless mechanism caused by the interaction of electrons in the vicinity of an expanding sheath with the sheath motion, which is affected by the excitation of the surface modes of both types. The generation of energetic electron populations as a result of such mechanisms is shown directly. Although some aspects of the underlying physics were demonstrated in the previous literature with other models, the PIC method is advantageous for the predictive modeling due to a complex interplay between the surface mode excitations and the nonlocal physics of the corresponding type of plasma discharges operated at low pressures, which is hard to reproduce in other models realistically.

A computational study of adsorption of H2S and SO2 on the activated carbon surfaces

An effort has been made to explore the adsorption potential of activated carbon (AC) structures for adsorption of hydrogen sulfide (H2S) and sulfur dioxide (SO2) employing density functional theory (DFT) at GGA level. 2-ring, 3-ring, 6-ring, and 9-ring carbon structures are used as adsorbent surfaces. The above mentioned rings are examined by creation of defect and inclusion of hydrogen as well to get the clear view close to experimental observations of adsorption properties of activated carbon. The adsorption properties depend upon many factors including whether adsorbate adsorbs in planer or non-planer mode, defect creation in the adsorbent substrate, atomic hydrogen insertion in the system and size of the adsorbent system. Our calculations show that side by side (planer) interaction binds the molecules much more strongly in comparison with molecules adsorbed upon the surface in non-planer mode. If vacancy is created at the central position of the surface, the molecules bind with substantial binding energy. However, overall Eads of the molecules varies randomly and no consistency could be achieved. Additionally, smaller sized structures are favorable relative to the bigger surfaces. The highest Eads for both the molecules is −2.97 eV, though not on the same substrate system. Finally, it can be argued that activated carbon is very useful material for adsorbing the noxious gases.

Multichannel waveguide QED with atomic arrays in free space

We study light scattering off a two-dimensional array of atoms driven to Rydberg levels. We show that the problem can be mapped to a generalized model of waveguide QED, consisting of multiple one-dimensional photonic channels (transverse modes), each of which is directionally coupled to a corresponding Rydberg surface mode of the array. In the Rydberg blockade regime, collective excitations of different surface modes block each other, leading to multichannel correlated photonic states. Using an analytical approach, we characterize interchannel quantum correlations, and elucidate the role of collective two-photon resonances of the array. Our results open new possibilities for multimode many-body physics and quantum information with photons in a free-space platform.

Coordinated Optimal Control of AFS and DYC for Four-Wheel Independent Drive Electric Vehicles Based on MAS Model.

The problem that it is difficult to balance vehicle stability and economy at the same time under the starting steering condition of a four-wheel independent drive electric vehicle (4WIDEV) is addressed. In this paper, we propose a coordinated optimal control method of AFS and DYC for a four-wheel independent drive electric vehicle based on the MAS model. Firstly, the angular velocity of the transverse pendulum at the center of mass and the lateral deflection angle of the center of mass are decoupled by vector transformation, and the two-degree-of-freedom eight-input model of the vehicle is transformed into four two-degree-of-freedom two-input models, and the reduced-dimensional system is regarded as four agents. Based on the hardware connection structure and communication topology of the four-wheel independent drive electric vehicle, the reduced-dimensional model of 4WIDEV AFS and DYC coordinated optimal control is established based on graph theory. Secondly, the deviation of the vehicle transverse swing angular velocity and mass lateral deflection angle from their ideal values is oriented by combining sliding mode variable structure control (SMC) with distributed model predictive control (DMPC). A discrete dynamic sliding mode surface function is proposed for the ith agent to improve the robustness of the system in response to parameter variations and disturbances. Considering the stability and economy of the ith agent, an active front wheel steering and drive torque optimization control method based on SMC and DMPC is proposed for engineering applications. Finally, a hardware-in-the-loop (HIL) test bench is built for experimental verification, and the results show that the steering angle is in the range of 0-5°, and the proposed method effectively weighs the system dynamic performance, computational efficiency, and the economy of the whole vehicle. Compared with the conventional centralized control method, the torque-solving speed is improved by 32.33 times, and the electrical consumption of the wheel motor is reduced by 16.6%.