Array Model Research Articles

Theoretical Model and Experiments of Focused Phased Array for Cross-Medium Communication in Misaligned Transmitter/Receiver Scenarios

Direct communication across the water-air interface has attracted wide attention because of its potential applications in integrated air-sea networking. In this article, three different cross-medium communication systems have been proposed, including line-of-sight (LOS) optical links, laser-induced acoustic (LIA) systems, and translational acoustic radio frequency (TARF) systems. However, LOS optical links are sensitive to turbid water, misalignment of the transmitters/receivers, and the influence of surface waves. LIA systems are unstable with poor repeatability. TARF systems require the alignment of transmitters/receivers. Moreover, in situations where the location of detection points is required to be frequently moved for flexible communication, LOS optical links, and TARF systems both failed. This article proposes a cross-medium focused phased array (CMFPA) model, which is a multiple-input single-output system, to enlarge the detection area and increase the overall wave amplitude at the water surface. Theoretical analyses and experimental results indicate that the CMFPA can relax the requirement of precise alignment between communication nodes and improve performance in cross-medium communication when compared to a single-input single-output system. The study is expected to provide a foundation for cross-medium communication between underwater and airborne nodes in misaligned transmitters/receivers scenarios.

Novel Coil Array Design and Modeling for Independent Control of Multiple Magnetic Microrobots

The independent control of microrobot swarms is a major challenge in the field of micro/nano manipulation. In this paper, a new localized magnetic field generating system is presented that can be used for the independent control of multiple magnetic microrobots. Such a system will allow for cooperative or parallel microassembly tasks with teams of magnetic microrobots. Firstly, the performance of the novel circular microcoil is modeled by analyzing the effect of input current to study the magnetic field distribution characteristics in the workspace, which is validated by finite element analysis and simulation; then, an actuation and control strategy of microrobots for microcoil array is proposed. Meanwhile, the independent closed-loop control of the microrobot is realized based on visual feedback; finally, an experimental platform for the microcoil actuation system is built to validate the newly designed structure. The results show that the microrobot can move flexibly and accurately with the tracking error within 0.444mm. At the same time, the system is capable of independently controlling multiple microrobots and holds great potential in performing micromanipulation tasks.

Energy Balance Analysis for Water Resources Satellite Operation Orbit Selection

In order to supply enough power for the satellite mission and at the same time to suppress cost increase through over-design, it is necessary to select an appropriate solar array and battery capacity. In the initial stage of satellite design, the required capacity must be analyzed to determine the solar array and battery model, which will be reflected throughout the overall satellite design. This study verifies that the CAS500 satellite platform can provide the power required for the mission in the initial stage of water resources satellite, and furthermore, it found the solar panel and battery capacity required for the water resources satellite. To this end, it was confirmed that the energy balance was satisfied by selecting the worst case one-day mission scenario of the water resources satellite under various conditions.

Modeling of Magnetoelectric Microresonator Using Numerical Method and Simulated Annealing Algorithm.

A comprehensive understanding of the linear/nonlinear dynamic behavior of wireless microresonators is essential for micro-electromechanical systems (MEMS) design optimization. This study investigates the dynamic behaviour of a magnetoelectric (ME) microresonator, using a finite element method (FEM) and machine learning algorithm. First, the linear/nonlinear behaviour of a fabricated thin-film ME microactuator is assessed in both the time domain and frequency spectrum. Next, a data driven system identification (DDSI) procedure and simulated annealing (SA) method are implemented to reconstruct differential equations from measured datasets. The Duffing equation is employed to replicate the dynamic behavior of the ME microactuator. The Duffing coefficients such as mass, stiffness, damping, force amplitude, and excitation frequency are considered as input parameters. Meanwhile, the microactuator displacement is taken as the output parameter, which is measured experimentally via a laser Doppler vibrometer (LDV) device. To determine the optimal range and step size for input parameters, the sensitivity analysis is conducted using Latin hypercube sampling (LHS). The peak index matching (PIM) and correlation coefficient (CC) are considered assessment criteria for the objective function. The data-driven developed models are subsequently employed to reconstruct/predict mode shapes and the vibration amplitude over the time domain. The effect of driving signal nonlinearity and total harmonic distortion (THD) is explored experimentally under resonance and sub-resonance conditions. The vibration measurements reveal that as excitation levels increase, hysteresis variations become more noticeable, which may result in a higher prediction error in the Duffing array model. The verification test indicates that the first bending mode reconstructs reasonably with a prediction accuracy of about 92 percent. This proof-of-concept study demonstrates that the simulated annealing approach is a promising tool for modeling the dynamic behavior of MEMS systems, making it a strong candidate for real-world applications.

Research on deflection and focusing technology of pipeline annular ultrasonic phased array

Relevant theoretical knowledge of ultrasonic phased array and the propagation characteristics of a sound field are combined to establish the Rayleigh integral mathematical model of a phased array focused sound field and analyze the spatial distribution law. The deflection focusing delay rule of annular phased array is deduced by using the reverse phase matching method. The detection experiment is carried out with the carbon steel pipeline. The effects of the number of working array elements and deflection angle on the amplitude change of echo signal and the effect of defect detection are analyzed, and focusing conditions. Results show that the deflection focusing delay rule of an ultrasonic phased array can focus sound beams with different focal lengths and deflection angles. The number of working array elements is kept at 6–8, which can obtain good detection effect, and the deflection angle is within 10°, which can maintain good defect detection accuracy.

Passive array micro-magnetic stimulation device based on multi-carrier wireless flexible control for magnetic neuromodulation.

Objective.The passive micro-magnetic stimulation (µMS) devices typically consist of an external transmitting coil and a single internal micro-coil, which enables a point-to-point energy supply from the external coil to the internal coil and the realization of magnetic neuromodulation via wireless energy transmission. The internal array of micro coils can achieve multi-target stimulation without movement, which improves the focus and effectiveness of magnetic stimulations. However, achieving a free selection of an appropriate external coil to deliver energy to a particular internal array of micro-coils for multiple stimulation targets has been challenging. To address this challenge, this study uses a multi-carrier modulation technique to transmit the energy of the external coil.Approach.In this study, a theoretical model of a multi-carrier resonant compensation network for the arrayµMS is established based on the principle of magnetically coupled resonance. The resonant frequency coupling parameter corresponding to each micro-coil of the arrayµMS is determined, and the magnetic field interference between the external coil and its non-resonant micro-coils is eliminated. Therefore, an effective magnetic stimulation threshold for a micro-coil corresponding to the target is determined, and wireless free control of the internal micro-coil array is achieved by using an external transmitting coil.Main results.The passiveµMS array model is designed using a multi-carrier wireless modulation method, and its synergistic modulation of the magnetic stimulation of synaptic plasticity long-term potentiation in multiple hippocampal regions is investigated using hippocampal isolated brain slices.Significance.The results presented in this study could provide theoretical and experimental bases for implantable micro-magnetic device-targeted therapy, introducing an efficient method for diagnosis and treatment of neurological diseases and providing innovative ideas for in-depth application of micro-magnetic stimulation in the neuroscience field.

Instability mechanism and failure criteria of large-span flexible PV support arrays under severe wind

Compared with independent flexible PV support, the entire structure force performance and transfer mechanism of inter-row cables and inter-span rods of flexible PV support arrays are more complex, it is easy to have large vibration or even instability failure under strong wind. In this study, the three-span and five-row flexible PV support array of a 66 MW Fishery-PV Complementary demonstration site in the eastern coastal region of China is used as the research object. The rigid body pressure measurement wind tunnel test was designed and carried out, and the wind pressure distribution characteristics of the PV panels surface were analyzed. A three-dimensional explicit dynamics model of the flexible PV support array considering inter-row cables and inter-span rods is established, and the wind-induced dynamic response characteristics and instability processes of the large-span flexible PV support array are effectively simulated. Finally, the instability mechanism of the large-span flexible PV support array is revealed, and the dual failure criteria based on structural deformation and energy increment are proposed. Results demonstrated that the maximum values of displacement and von Mises stress of the large-span flexible PV support array are concentrated in the 1st row of the span in the windward side. The array under 0° and 180° wind direction angles induces local instability and failure at wind speeds of 51 m/s and 46 m/s due to the failure of the 1st row of triangular rods and crossed diagonal rods on the windward side, respectively, and the rods instability mechanisms are Eulerian buckling mechanism and Limit point buckling mechanism, respectively. When the axial compression ratio [Δ] > 0.1 or the strain energy increment [ΔU] > 1.0 × 105J of the instability rod, the structure will be locally destabilized. This paper presents a systematic work around the wind-induced response and instability characteristics of the large-span flexible PV support array, the results are of significance for the engineering application of solar energy generation structures.

Location and Tracking Mode of Sports Rehabilitation Training With Self-Powered Sensors Based on Particle Swarm Optimization Algorithm

With the growth of the country’s economic strength, people’s living standards have steadily improved. Sports have become the main means to change physical fitness and maintain the per capita health index. The state also puts forward higher requirements for the security work of athletes, elderly groups and rehabilitation patients. Traditional rehabilitation training mainly relies on various sensor devices, such as acceleration sensing, pressure sensing and so on. These devices need a lot of energy to supply power for the equipment in the process of use, which is no longer suitable for today’s modern development environment. Based on the concept of self-powered sensors, this paper proposes a sports rehabilitation training model updated by particle swarm optimization algorithm. First of all, the performance and indicators of self-powered sensor devices are analyzed, and the self-powered electrical components are optimized using friction nano new energy technology. Starting from the basic characteristics of wearable models, we can ensure the consistency of posture in sports rehabilitation. During training, the wearing process will stretch 10% of the length in advance to ensure comfort and sensitivity. According to the results of the test record, the pulse index is clear and obvious, consistent with the actual number of minutes per minute. Finally, the sensor array model and function model are improved under the particle swarm optimization algorithm to realize the positioning and tracking function in sports rehabilitation training. The results show that the wearable training equipment optimized by particle swarm optimization can better locate and track the movement track than the traditional sports rehabilitation equipment. It can adjust the movement posture and protect the safety of trainers. At the same time, it is more prominent in performance and power supply duration.

On tidal array layout sensitivity to regional and device model representation

In-stream tidal devices are ready to be deployed, yet the largest operational commercial array is limited to 6MW. Upcoming government support should see the size of such arrays increase by orders of magnitude, and thus the optimal placement of turbines within tidal arrays is an emerging challenge for successful commercial integration. Hydrodynamic models are required to predict the power produced by an array and the impact on the surrounding environment. The influence of common model inputs to layout optimisation are investigated herein. This is achieved using a shallow water equation based tidal array modelling framework, Thetis, coupled with a low cost analytical wake model (FLORIS) that allows for rapid assessment of the impact of small changes in hydrodynamic results on array micro-siting. The sensitivity of array optimisation at an intermediate development point (43 turbines) is interrogated through both artificial flow field manipulation and the variation of model input pertinent to the optimisation. A small margin exists in which an optimised array layout will perform efficiently for a deviation in flow prediction accuracy. However, incorrect flow predictions by a range sensitive to model inputs had a reduction of almost 8% on array efficiency relative to a control case. The sensitivity of flow field variance by model input changes, on extractable energy and array layout are substantial. Comparing arrays sited on flow fields using different bathymetry resolution leads to a discrepancy on average of over 2% to average array power. Arrays sited for different mesh resolution and friction representation also see average changes up to and exceeding 0.75%. For array developers and the future of this nascent industry, re-calibration of the model at every stage of data collection coupled with early acquisition of bathymetry data is critical not just for accurate power quantification, but also array efficiency. At a regional scale, quantification of the potential tidal resource must consider the consequences of uncertainty in model input data and site constraints that cannot yet be accounted for.

Fast time-domain model for an array of interactive point-absorbers


 
 
 A fast time-domain model is developed for an array of six interacting point-absorber wave energy converters, based on the design originated at Uppsala University. The point-absorbers are placed in a symmetric grid, were each row contains one pair. The devices interact by scattered and radiated waves, while they are restricted to move in one degree of freedom, heave. Under the assumption of linear potential flow theory, the hydrodynamic coefficients for the excitation and radiation forces are obtained using an analytical multiple-scattering method. The equations of motion are solved directly in the time domain following the Cummins’ formulation. Modelling an array of wave energy converters in the time domain comes down to solving a system of integro-differential equations, were convolution terms appear in the computation of the excitation and radiation forces. In the majority of wave farm models, frequency-domain approaches are used to solve the equations of motion, since time-domain models are more computationally demanding and significantly more challenging to develop. This is not only because of the numerical integration involved, but especially due to the computation of the convolution term accounting for the radiated water waves on the free-surface, implying that waves radiated by the body in the past continue to affect the dynamics in the future. Regardless the computational effort associated with time-domain approaches, their use is required for realistic control applications and complex device dynamics, like non-linearities due to the power take-off configuration. In particular the non-linear effects that arise during the wave energy conversion chain are treated as time-varying coefficients within the system of differential equations describing the motion. Input to the numerical scheme are irregular, long-crested waves, obtained from the Bretschneider spectrum, corresponding to four, different sea states. It is of high interest to study whether the linear numerical model simulates accurately the performance of each interactive surface buoy in response to the irregular waves. Therefore, the numerical results for the full array configuration are compared with experimental data. At this point we emphasize that there are not a lot of experimental works considering arrays of point- absorbers, due to the complexity and costs associated with the task. Therefore, finding a set of data to validate the array model is not trivial. The experimental results we use were carried out in the COAST Lab at Plymouth University, UK, corresponding to a 1:10 scaled prototype of an array of point-absorbers. The set-up consists of six ellipsoid floats free to move in six degrees of freedom and connected via ropes and pulleys to individual power take-off systems. Despite the highly non-linear effects in the physical experiment, the free motion of the buoys in all directions, and the power take-off configuration, the numerical scheme is able to accurately capture the heaving motion of the buoys and their power absorption.
 
 

Micro-seismic monitoring using sparse planar array and a weak signal enhancement method

Abstract Traditional ground micro-seismic monitoring is performed by laying long survey lines. This is expensive and difficult to implement in complex mountainous areas and deep marine shale gas reservoirs in China. To address these challenges, this study proposes a ground micro-seismic monitoring method using a sparse planar array that offers greater flexibility in implementation. This study presents a weak signal enhancement method based on a broadband-array adaptive beamforming algorithm to improve the signal-to-noise ratio (SNR) of micro-seismic data collected by sparse planar arrays and to suppress coherent noise. The proposed method involves establishing a signal model for a broadband planar array, estimating the direction of arrival (DOA) of broadband signals using a grid search method, and setting constraint conditions and objective functions based on the DOA results. The optimal weight vector is then calculated by solving the objective function to obtain the desired signal and suppress noise. This study demonstrates that the proposed method effectively improved the SNR and suppressed coherent noise in synthetic and real data. It also highlights the effectiveness of the sparse planar array as a ground micro-seismic monitoring method and the adaptive broadband beamforming method as a practical weak signal enhancement technology.

Towards complementary operations of offshore wind farm and photovoltaic array: A centralized reinforcement learning enabled control approach

Integrated offshore wind and photovoltaic (PV) power generation has high potential in significantly improving renewable power utilization, but the complementary operation of the integrated power system is fundamentally challenging, especially under high uncertainties of meteorological conditions. In this paper, the joint regulation of the offshore wind farm and the PV array is considered where the generator torque of each wind turbine and the tilt angles of the PV array are regarded as the control actions to simultaneously maximize the overall power generation and improve power quality. The model of the offshore wind farm including wake models and the turbine drive-train dynamic model is established while model of the PV array using the tilt angle as the regulation variable is also constructed. By considering the control of the integrated power system of the wind farm and the PV array as a typical partially-observable Markov decision process (MDP), a twin-delayed deep deterministic policy gradient (TD3) algorithm is developed to jointly regulate the wind farm and PV array. Design experiments have been conducted to evaluate the potential and effectiveness of the proposed TD3 control method for the integrated offshore wind and PV power system. The test results demonstrate that the TD3 method has good convergence performances in the overall power output and power variation rate regulations. The control objectives of improving the overall power output and smoothing the power variations can be simultaneously achieved by using appropriate parameter settings in the TD3 algorithm.

Novel radiation hard position sensitive detector using YAG:Ce fibers for ion beam instrumentation at FRIB

We are investigating the feasibility of a new detector concept for use in the beam line at the Facility for Rare Isotope Beams (FRIB). The detector is designed to withstand the high ion beam intensities and the high radiation environment while providing position, timing, and energy information. Based on the concept of a fiber detector, the device uses YAG:Ce crystals as sensing material, chosen for their extreme radiation tolerance to electromagnetic or hadronic exposure. The crystals are machined into long and thin rods which are laid out in orthogonal horizontal and vertical arrangements to obtain spatial sensitivity to impinging particles. The readout is performed at the extremities of the rods with strip Multi Pixel Photon Counters (MPPC) also referred to as Silicon Photomultipliers (SiPM) arrays model S13552 from Hamamatsu mounted on ribbon cables with connector ends.

Low-Rank and Row-Sparse Decomposition for Joint DOA Estimation and Distorted Sensor Detection

Distorted sensors could occur randomly and may lead to the breakdown of a sensor array system. We consider an array model within which a small number of sensors are distorted by unknown sensor gain and phase errors. With such an array model, the problem of joint direction-of-arrival (DOA) estimation and distorted sensor detection is formulated under the framework of low-rank and row-sparse decomposition. We derive an iteratively reweighted least squares (IRLS) algorithm to solve the resulting problem. The convergence property of the IRLS algorithm is analyzed by means of the monotonicity and boundedness of the objective function. Extensive simulations are conducted regarding parameter selection, convergence speed, computational complexity, and performances of DOA estimation as well as distorted sensor detection. Even though the IRLS algorithm is slightly worse than the alternating direction method of multipliers in detecting the distorted sensors, the results show that our approach outperforms several state-of-the-art techniques in terms of convergence speed, computational cost, and DOA estimation performance.

Programmable Multi-stable Structure Based on Cosine Beam

Mechanical metamaterials with multi-stable properties are an emerging field of interest. In this paper, we present a novel 3D bi-stable cell element with negative stiffness characteristics designed based on a cosine-curved beam. Static compression simulations were performed for the single-cell model and the series model. Using “E” and “F” states as programming units, five array models were designed to analyze the stiffness variation rules. Dynamic simulations were conducted to compare the energy absorption rate and collision force of the model with variable stiffness. The conclusion shows that the structure has multi-stable and negative stiffness characteristics, and its stiffness can be adjusted in the range of 113.0 to 197.6 N/mm. Additionally, the energy absorption rate can be adjusted in the range of 8% to 65%. This study has made the structure configurable after manufacturing, breaking through the application limitations of predefined objects, and broadening its application prospects.

Mechanically Controlled, Wide-Angle Scanning, Series-Fed Antenna Array With Low Profile for High-Power Radar Systems

This paper presents the design and implementation of a mechanically-controlled, series-fed antenna array featuring wide-angle beamsteering at the X-band. A theoretical model of a series-fed array, including phase shifters inserted between consecutive elements, is initially developed to derive design rules and gain insight into crucial performance trade-offs. Subsequently, a mechanically-controlled, reflection-type phase shifter consisting of a branch line coupler and two Pi-network reflective loads is presented. A movable metallic overlay tunes the impedance of the reflective loads, thus effectively modifying the output phase. While requiring a minimal linear displacement of only 0.06λ0, this topology provides a maximum phase shift of 300° with an average insertion loss of 1 dB and is exploited for synthesizing a series-fed patch array. Based on simulations and measurements, the proposed antenna offers an almost constant realized gain of about 15 dBi within a wide scanning range of ±50°, and the side lobe level is better than -12 dB. The average total efficiency is 50%, and the cross-polarization levels are at least 11 dB below the maximum realized gain. The main weaknesses are the narrow bandwidth of 2.5% and the slight beam squint as the frequency varies. The proposed design is ideal for radars due to its excellent performance and high power-handling capability.

High-Resolution Parameter Estimation for Wideband Radio Channel Sounding

Multidimensional channel sounding measures the geometrical structure of mobile radio propagation. The parameters of a multipath data model in terms of directions, time-of-flight and Doppler shift are estimated from observations in frequency, time and space. A maximum likelihood estimation framework allows joint high-resolution in all dimensions. The prerequisite for this is an appropriate parametric data model that represents the multipath propagation correctly. At the same time, a device data model is necessary that typically results from calibration measurements. The used model should be as simple as possible since its structure has a considerable effect on the estimation effort. For instance, the inherent effort in parameter search is reduced if the influence of the parameters is kept independent. Therefore, the data model is characterized by several approximations. The most important is the “narrowband assumption” which assumes a low relative bandwidth and also avoids considering any frequency response in magnitude and phase. We extend the well-known multidimensional RIMAX parameter estimation framework by including proper frequency responses. The advantage reveals itself with high bandwidth in the mmWave and sub-THz range. It allows for a more realistic modeling of antenna arrays, it breaks with the usual narrowband model and allows a better modeling of mutual coupling and time delay effects. If the interacting object extends over several delay bins (hence an extended target in radar terminology) we propose a model that assigns a short delay spread, respectively a frequency response to the propagation path that associates it to the respective object. We verify the validity of the device model by numerical experiments on simulated and measured antenna data and compare it to RIMAX. Additionally, we use synthetic data based on ray-tracing results and measurements both ranging from 27.0GHz to 33.0GHz with known ground truth information and show that the proposed estimator delivers better performance for higher relative bandwidths than the conventional RIMAX implementation.

Analysis of the cylindrical plasma antenna system modes in a wide frequency range

Plasma antennas have promising prospects for practical use with quick changes in their parameters in a wide frequency range. In this work, the radiation pattern of a plasma antenna system, which consists of a short linear antenna surrounded by fluorescent lamps, is analyzed in a frequency range of 0.5–1.5 GHz. In numerical simulation, the parameters of the gas-discharge plasma were used, which were obtained using the drift theory. In addition, an analysis of the radiation patterns using a simple and intuitive ring antenna array model was carried out, and the limit of its applicability was demonstrated. The experimental data were compared with those of simulation and theoretical analysis. Finally, a simulation was performed to compare the plasma antenna system with its metal counterpart. The results obtained are important for a whole class of nested antenna systems.

An equivalent lattice-modified model of interfering Bragg bandgaps and Locally Resonant Stop Bands for phononic crystal made from Locally Resonant elements

The design and development of advanced devices based on metamaterials to control the transmission of acoustic waves is a hot topic. An important class of these metamaterials is based on phononic crystals with Locally Resonant Structure, included in those commonly known as Locally Resonant Sonic Materials. In these metamaterials, wave control is basically performed by two mechanisms: internal (or local) resonances in the scatterers that form the phononic crystal, and Bragg bandgaps due to structural periodicity. Their main control feature is the resonance peaks forming additional stop-bands away from the Bragg frequency, mainly in the low frequency regime. For some applications, coupling of the two phenomena is necessary to create a broad transmission gap. However, when both are located in close frequency ranges, some destructive interferences can occur. In this paper, the authors develop a comprehensive numerical model of periodic arrays of Hemholtz resonators, which explains in detail the physical mechanisms of this destructive interference and, simultaneously, allows the reproduction of the consequences of the interference. The numerical results are supported by experimental tests.

Comment on “Deep reinforcement learning approach for MPPT control of partially shaded PV systems in Smart Grids”

In a recent work, (Avila et al., 2020), an environment was developed and reported for partial shading conditions (PSC) in the open-source OpenAI Gym platform. This work presented deep reinforcement learning (DRL) techniques to address the maximum power point tracking (MPPT) problem of a photovoltaic (PV) array under PSC. Two DRL algorithms, namely, Deep Deterministic Policy Gradient (DDPG) and Twin Delayed DDPG (TD3) were investigated. A deviation of less than 1%, compared to the theoretical maximum power, was claimed for the DDPG algorithm. Based on the presented fact-based investigations, this comment highlights the issues in the reported approach. The main issues are found to be the approximate PV array modeling, erroneous performance metric and erroneous choice of DRL algorithms. Of the presented PSCs, the proposed technique in Avila et al. (2020) always attained the very first peak of the PV characteristic of the PV system. It may be noted that the first peak may not always be the global maximum power point. Overall, based on the presented investigations this comment demonstrates that the DDPG technique used in Avila et al. (2020) is not able to effectively address the MPPT problem in PV array under PSC.