Array Response Research Articles

Low-Complexity 2D-DOD and 2D-DOA Estimation in Bistatic MIMO Radar Systems: A Reduced-Dimension MUSIC Algorithm Approach.

This paper presents a new technique for estimating the two-dimensional direction of departure (2D-DOD) and direction of arrival (2D-DOA) in bistatic uniform planar array Multiple-Input Multiple-Output (MIMO) radar systems. The method is based on the reduced-dimension (RD) MUSIC algorithm, aiming to achieve improved precision and computational efficiency. Primarily, this pioneering approach efficiently transforms the four-dimensional (4D) estimation problem into two-dimensional (2D) searches, thus reducing the computational complexity typically associated with conventional MUSIC algorithms. Then, exploits the spatial diversity of array response vectors to construct a 4D spatial spectrum function, which is crucial in resolving the complex angular parameters of multiple simultaneous targets. Finally, the objective is to simplify the spatial spectrum to a 2D search within a 4D measurement space to achieve an optimal balance between efficiency and accuracy. Simulation results validate the effectiveness of our proposed algorithm compared to several existing approaches, demonstrating its robustness in accurately estimating 2D-DOD and 2D-DOA across various scenarios. The proposed technique shows significant computational savings and high-resolution estimations and maintains high precision, setting a new benchmark for future explorations in the field.

High-frequency magnetic response of superparamagnetic composites of spherical Fe and Fe3O4 nanoparticles

The response of arrays of magnetic nanoparticles (MNPs) of cubic anisotropy materials (magnetite or iron) to high-frequency (sub-GHz) field is investigated utilizing micromagnetic simulations. Composites of MNPs embedded in dielectric media are of interest as core materials for high-frequency power microconverters with low eddy-current losses. Going beyond the macrospin approximation for MNPs (including internal spin structure), we simulate the magnetization dynamics of arrays of spherical and periodically arranged MNPs under periodic boundary conditions and in the presence of thermal fluctuations of the magnetization within the stochastic thermal field. Analyzing the dependence of the dynamical response on the size of the MNPs, we find the size to be crucial for exciting regular magnetization oscillations at room temperature and reducing hysteresis loss. The efficiency of the dynamical response of composites of high-magnetization-metal (iron) MNPs is compared to that of magnetite nanocomposites. We find the sub-GHz susceptibility of magnetite-containing nanocomposite to be comparable to that of the iron MNPs despite the lower saturation magnetization of Fe3O4, (at the volumetric ratio of the magnetic phase of 0.13, susceptibility is χ≈1.6 for 5 nm Fe and ≈1.4 for 12 nm Fe3O4 MNPs at T=300 K and frequency of 0.1 GHz).

Shielding and wind direction effects on wind-induced response of cable-supported photovoltaic array

Recently, a new type of cable-supported photovoltaic system (CSPS) had been proposed. The new structure has light weight and large span, and is cost-effectiveness and adaptability to complex terrains. At the same time, as a large span flexible structure, wind-induced vibration (WIV) is the most important controlling factor for the new structure. To date, the response characteristics of the WIVs of new structures are still not well understood. In this study, the shielding and wind direction effects on the WIV of the new structure were investigated through wind tunnel tests. The experimental results show that the WIV of the new structure is close to buffeting. The vibration amplitude quadratically increases with increasing wind speed. The WIVs of the photovoltaic (PV) modules at central and downwind region were much weaker than those at upwind region. The upwind PV modules protect the downwind PV modules in the array because of the shielding effects. The wind direction of the incoming wind also has a significant effect on the WIVs of the new structure. The strongest WIVs were observed in the crosswind cases (Cases 0° and 180°), which are the most dangerous cases. The vibration amplitude decreases almost linearly when the wind direction deviates from the cross-winds. In addition, the wind vibration coefficient (WVC) of the new CSPS is recommended as 1.6, according to the experimental results.

Tuning the plasmonic response of periodic gold nanodisk arrays for urea sensing

Tuning the plasmonic response of periodic gold nanodisk arrays for urea sensing

SSA2py: A High-Performance Python Implementation of the Source-Scanning Algorithm for Spatiotemporal Seismic Source Imaging

Abstract This article introduces the first version of SSA2py (v.1.0)—an open-source package designed to implement the source-scanning algorithm (SSA). SSA2py is a Python-based, high-performance-oriented package that incorporates the SSA method, which has been effectively applied to numerous earthquakes for imaging the spatiotemporal behavior of the seismic source. The software supports a wide range of data and metadata resources. These include the International Federation of Digital Seismograph Networks Web Services, the SeedLink protocol, and others, ensuring optimal access to waveforms and station metadata. Furthermore, the code may evaluate the quality of accessible waveforms using signal analysis methods, allowing for the most appropriate data selection. The SSA method has been computationally optimized using multiprocessing techniques for efficient central processing unit and graphic processing units executions, enabling considerably accelerated computational processes even for large-scale grid searches. The program is also designed to provide statistical and methodological uncertainties for the executed cases through jackknife, bootstrap, and backprojection array response function tests. After appropriate tuning by the user, SSA2py can be used for detailed earthquake source studies that backprojection technique typically serves as a complementary output to the source inversion result or as a near-real-time tool for successful and quick identification of the style and complexity of the earthquake rupture. With a wide and flexible configuration, the user has complete control over all calculating aspects of SSA2py. This article provides a detailed description of the structure and capabilities of this new package, and its reliability is demonstrated through targeted applications to the 2004 Mw 6.0 Parkfield and 2019 Mw 7.1 Ridgecrest earthquakes. Furthermore, the computational efficiency of SSA2py is validated through rigorous performance tests.

Optimization of Photoelectrochemical Response on TiO2 Nanotube Arrays Treated by H3PO4 and Mechanism Analysis of the Slowing Down Effect during Preparation.

The process control of anodization has been a hot topic for a long time. In this study, the addition of phosphoric acid to the traditional electrolyte changed the ion distribution on the reaction interface and the composition of the anion contamination layer so as to achieve the slowing down effect on anodization, the mechanism and theoretical model of which are also given in this paper. TiO2 is a common material in photoelectrocatalysis, but there are few studies on the photoelectrochemical performance of TiO2 nanotube arrays. The stability and rapidity of the photoelectrochemical response of TiO2 nanotube arrays prepared in phosphoric acid containing an electrolyte were effectively optimized in this study.

A novel design of hard-magnetic soft switch array for planar and curved surface applications

This paper proposes an array structure with multidirectional remanent magnetization based on hard-magnetic soft materials, which can be used as a soft switch array on planar and curved surfaces. We firstly investigate the displacement response of a hard-magnetic soft switch which is excited by a magnetic field, and related to the magnitude and direction of the magnetic field. When the remanent magnetization direction of the soft switch is opposite to the horizontal component of the magnetic field, the displacement response is greater than that of the driving magnetic field in other directions. The maximum displacement of the soft switch can reach 4.5 mm under a 6 V driving voltage applied to the Helmholtz coil. We further design 2 × 2 and 3 × 3 switch arrays and the circuit structures of the switch arrays. The switch arrays are fabricated, and the displacement responses of the switch arrays under different driving magnetic fields on planar and curved surfaces are finally demonstrated. When the Z-axis displacement of the device reaches more than 3 mm, the LED light can be switched on. The hard-magnetic soft switch array structure designed in this paper can enable the application of soft switches in curved environments, verifying the feasibility of the application of hard-magnetic soft switch arrays. It is expected to provide a guidance for the design and manufacturing of multi-functional hard-magnetic soft switches in the future and the application of hard-magnetic soft switch arrays in planar and curved environments.

Ultrafast All‐Optical Control of Light Chirality with Nanostructured Graphene

AbstractUltrafast nanophotonics is a rapidly growing area of study focused on creating nanodevices that can modulate the properties of light at, to this date, unparalleled speed. To facilitate the growth of this field, there is a growing need for compact metamaterial designs for the manipulation of the amplitude, phase, and polarization of light. One promising strategy involves leveraging the optical nonlinearity of nanostructured materials to alter their permittivity by interacting with high‐intensity ultrashort laser pulses. This study showcases how such requirements can be met through the utilization of 2D materials, particularly graphene. The nonlinear optical response of a graphene nanorectangle array is theoretically modeled to achieve all‐optical, fully reversible, broadband, and ultrafast dynamic control of light chirality. This is achieved by taking advantage of the energy relaxation dynamics of coherently excited localized plasmons supported by the metasurface, and the transient increase in electron temperature in graphene. Using finite‐difference time‐domain simulations, ultrafast dynamic tuning between circular and linearly polarized light is demonstrated. The proposed platform gives promise for ultrathin, CMOS‐compatible nanophotonic systems that can provide high‐speed, room‐temperature modulation of light polarization.

Tracing the geographic origin of CTC black tea based on colorimetric sensor array response to taste substances combined with chemometrics

The quality of crush–tear–curl black tea (CTC-BT) varies greatly by geographic origin. Origin traceability is crucial for consumer interest protection, market order regulation, and food safety monitoring. This paper proposes a fast and accurate method for qualitative discrimination of CTC-BT origins and quantitative detection of its key taste-presenting substances. The method involves a simple colorimetric sensor array and ultraviolet–visible spectroscopy. The effects of various variable screening methods on modeling results were compared. A particle swarm optimization–based support vector machine achieved the highest performance in qualitative discrimination, with a correct classification rate of 99.48%. Based on their origin-distinguishing contributions and dose-over-thresholds, seven key taste-presenting substances were screened, namely, theaflavin, caffine, vitexin-2-O-rhamnoside, rutin, epigallocatechin gallate, epicatechin gallate, gallic acid. A least squares-support vector regression model achieved accurate quantification of the seven aforementioned compounds (square root of determination coefficient of prediction >0.9698, residual prediction deviation >2).

Probing Temperature-Induced Plasmonic Nonlinearity: Unveiling Opto-Thermal Effects on Light Absorption and Near-Field Enhancement.

Precise measurement and control of local heating in plasmonic nanostructures are vital for diverse nanophotonic devices. Despite significant efforts, challenges in understanding temperature-induced plasmonic nonlinearity persist, particularly in light absorption and near-field enhancement due to the absence of suitable measurement techniques. This study presents an approach allowing simultaneous measurements of light absorption and near-field enhancement through angle-resolved near-field scanning optical microscopy with iterative opto-thermal analysis. We revealed gold thin films exhibit sublinear nonlinearity in near-field enhancement due to nonlinear opto-thermal effects, while light absorption shows both sublinear and superlinear behaviors at varying thicknesses. These observations align with predictions from a simple harmonic oscillation model, in which changes in damping parameters affect light absorption and field enhancement differently. The sensitivity of our method was experimentally examined by measuring the opto-thermal responses of three-dimensional nanostructure arrays. Our findings have direct implications for advancing plasmonic applications, including photocatalysis, photovoltaics, photothermal effects, and surface-enhanced Raman spectroscopy.

Influence of Exposure to a Wet Atmosphere on the UV-Sensing Characteristics of ZnO Nanorod Arrays.

Zinc oxide is a promising material for the creation of various types of sensors, in particular UV detectors. In this work, arrays of ordered nanorods were grown by chemical vapor deposition. The effect of environmental humidity on the sensing properties of zinc oxide nanorod arrays was investigated, and a prototype UV sensor using indium as an ohmic contact was developed. UV photoresponses were measured for the samples stored in dry and wet atmospheres. The increase in sensitivity and response of the ZnO nanorod arrays was observed after prolonged exposure to a wet atmosphere. A model was proposed to explain this effect. This is due to the formation of hydroxyl groups on the surface of zinc oxide nanorods, which is confirmed by FTIR spectroscopy data. For the first time, it has been shown that after storage in a wet atmosphere, the sensory properties of the structure remain stable regardless of the ambient humidity.

An Artificial Olfactory Chemical‐Resistant Synapse for Training‐Free Gas Recognition

AbstractTransferring the concept of chemical‐driven responses into artificial intelligence technology holds the key to mimicking olfactory for neuromorphic computing of chemical recognition. Currently, artificial olfactory systems are designed based on chemical sensor arrays. Time‐dependent responses of the sensor arrays are processed by artificial neural networks for recognition. However, the sensors generate instantly volatile responses, and algorithms for the processing of the time‐dependent responses have not been involved. The recognition accuracy and speed are severely impeded. A sensor array can only achieve an accuracy of 90% after at least 5 training epochs. Herein an artificial olfactory chemical‐resistant synapse consisting of 3D hierarchical WO3@WO3 nanofibers are demonstrated. The nanofibers exhibit persistent resistance responses through chemical exposures due to the strong chemisorption of water molecules. Typical synaptic behaviors including paired‐pulse facilitation, long‐term −1 short‐term memory, and learning experience have been achieved. Next, a recurrent neural network that is committed to processing the time‐dependent data is used to identify gas‐phase chemicals of 3‐hydroxy‐2‐butanone, triethylamine, and trimethylamine. Training‐free gas recognition has been realized by a WO3@WO3 nanofiber synapse only, in which the accuracy is above 90% at the first epoch. The results have great potential to satisfy stringent performance requirements on artificial perception systems.

Perceptual transitions between object rigidity and non-rigidity: Competition and cooperation among motion energy, feature tracking, and shape-based priors.

Why do moving objects appear rigid when projected retinal images are deformed non-rigidly? We used rotating rigid objects that can appear rigid or non-rigid to test whether shape features contribute to rigidity perception. When two circular rings were rigidly linked at an angle and jointly rotated at moderate speeds, observers reported that the rings wobbled and were not linked rigidly, but rigid rotation was reported at slow speeds. When gaps, paint, or vertices were added, the rings appeared rigidly rotating even at moderate speeds. At high speeds, all configurations appeared non-rigid. Salient features thus contribute to rigidity at slow and moderate speeds but not at high speeds. Simulated responses of arrays of motion-energy cells showed that motion flow vectors are predominantly orthogonal to the contours of the rings, not parallel to the rotation direction. A convolutional neural network trained to distinguish flow patterns for wobbling versus rotation gave a high probability of wobbling for the motion-energy flows. However, the convolutional neural network gave high probabilities of rotation for motion flows generated by tracking features with arrays of MT pattern-motion cells and corner detectors. In addition, circular rings can appear to spin and roll despite the absence of any sensory evidence, and this illusion is prevented by vertices, gaps, and painted segments, showing the effects of rotational symmetry and shape. Combining convolutional neural network outputs that give greater weight to motion energy at fast speeds and to feature tracking at slow speeds, with the shape-based priors for wobbling and rolling, explained rigid and non-rigid percepts across shapes and speeds (R2 = 0.95). The results demonstrate how cooperation and competition between different neuronal classes lead to specific states of visual perception and to transitions between the states.

Resolvability of Multiple Microseismic P-Wave Source Regions with Two Large Seismic Arrays in China and the United States

Abstract P-wave microseisms are useful for understanding ocean waves. Resolving and locating multiple P-wave source regions using seismic data can provide valuable information about ocean waves. The resolvability of multiple microseismic P-wave source regions depends on the location accuracy and resolution, which can be improved using multiple large seismic arrays. In this article, we investigate the source locations of P-wave microseisms at the period of 5–10 s by combining the backprojection results from two large dense seismic arrays located in China (ChinArray) and the United States (USArray). We independently process data recorded by ChinArray and USArray during a two-year period (2014–2015) that border both the North Pacific and North Atlantic. Then the results are normalized and summed or intersected in the source region to improve the accuracy of the P-wave microseism source locations by reducing the deviation from the velocity structure model and the array response function. The results show that we can resolve two to three sources with a scale of ∼500–1000 km within one large P-wave source region. We also investigate how array parameters such as aperture, interstation spacing, and geographic position affect the detectability and accuracy of the P-wave microseism sources. The discrepancy in P-wave microseism source locations between backprojection observation and ocean model predictions in source number, source scale, and source region scope imply that the ocean model needs to be improved.

Three-dimensional Force Detection and Decoupling of a Flexible Tactile Sensor Array based on Porous Composite Piezoresistive Materials

Abstract Flexible piezoresistive sensor array has broad application prospects in human-computer interaction. However, due to the complexity of reality, it is difficult to balance flexibility and perceptual ability in the process of tactile perception. Presented herein is a 4 × 4 matrix of a piezoresistive tactile sensor (TS) that is both pliable and composed of a porous blend of multi-walled carbon nanotubes (MWCNTs) and polydimethylsiloxane (PDMS). This sensor matrix is endowed with characteristics like pliability, consistency, and acute sensitivity, which facilitate its adherence to various shaped surface profiles. It boasts a peak sensitivity of 0.6 kPa−1 and is capable of detecting pressures within a broad spectrum from 0 to 640 kPa. An in-depth examination has been undertaken to assess the TS array's response to pressure, encompassing aspects such as hysteresis and repeatability. In addition to this, a scanning system for the array has been constructed to promptly detect, digitize, and present the pressure applied. A neural network model for three-dimensional force decoupling has been established to analyze the real-time data emanating from the sensor matrix, thereby enabling the precise forecasting of the three-dimensional force exerted upon the array.

DETERMINATION OF LAKEBED SEDIMENT DISTRIBUTION BASED ON UNDERWATER ELECTRICAL RESISTIVITY TOMOGRAPHY DATA

Electrical resistivity tomography (ERT) in an aquatic environment is usually measured using two basic systems. One system uses floating electrodes, which is usually applied in shallow water, and the other uses underwater cables with integrated electrodes, which is often carried out as a mobile system. The aim of this research was to test an underwater ERT measurement with floating cables on the water surface, but with electrodes submerged at the water bottom. This type of cable spread makes it possible to lay all the electrodes vertically to the bottom without the distance between them being reduced by the uneven topography and various underwater obstacles. Prior to the field survey that was conducted in a 40 m – deep lake, the response of common electrode arrays was tested using synthetic models. Two models were used that correspond to the geological condition in the field, higher resistivity bodies in a lower resistivity environment and a model with inverse relationship of resistivity to the first one. The Wenner Schlumberger and dipole-dipole arrays resolved the resistivity range, size and shape of the bodies very well and were therefore used in the field. The field data quality was very good and it was shown that ERT measurements in freshwater depths of more than 40 metres can provide very good results. As expected from the modelling, the dipole-dipole array led to a high-resolution resistivity model that enabled the characterisation of the lakebed sediments.

Ensuring food safety by artificial intelligence-enhanced nanosensor arrays.

Current analytical methods utilized for food safety inspection requires improvement in terms of their cost-efficiency, speed of detection, and ease of use. Sensor array technology has emerged as a food safety assessment method that applies multiple cross-reactive sensors to identify specific targets via pattern recognition. When the sensor arrays are fabricated with nanomaterials, the binding affinity of analytes to the sensors and the response of sensor arrays can be remarkably enhanced, thereby making the detection process more rapid, sensitive, and accurate. Data analysis is vital in converting the signals from sensor arrays into meaningful information regarding the analytes. As the sensor arrays can generate complex, high-dimensional data in response to analytes, they require the use of machine learning algorithms to reduce the dimensionality of the data to gain more reliable outcomes. Moreover, the advances in handheld smart devices have made it easier to read and analyze the sensor array signals, with the advantages of convenience, portability, and efficiency. While facing some challenges, the integration of artificial intelligence with nanosensor arrays holds promise for enhancing food safety monitoring.

Evaluation of 2D ion chamber arrays for patient specific quality assurance using a static phantom at a 0.35 T MR-Linac

IntroductionPatient specific quality assurance (QA) in MR-Linacs can be performed with MR-compatible ion chamber arrays. However, the presence of a static magnetic field can alter the angular response of such arrays substantially. This works investigates the suitability of two ion chamber arrays, an air-filled and a liquid-filled array, for patient specific QA at a 0.35 T MR-Linac using a static phantom. MethodsIn order to study the angular response, the two arrays were placed in a static, solid phantom and irradiated with 9.96 × 9.96 cm2 fields every 10° beam angle at a 0.35 T MR-Linac. Measurements were compared to the TPS calculated dose in terms of gamma passing rate and relative dose to the central chamber. 20 patient specific quality assurance plans were measured using the liquid-filled array. ResultsThe air-filled array showed asymmetric angular response changes of central chamber dose of up to 18% and down to local 3 mm / 3% gamma rates of 20%, while only minor differences within 3% (excluding parallel irradiation and beams through the couch edges) were found for the liquid-filled ion chamber array without rotating the phantom. Patient plan QA using the liquid-filled array yielded a median local 3 mm / 3% 3D gamma passing rate of 99.8% (range 96.9%–100%) ConclusionA liquid-filled ionization chamber array in combination with a static phantom can be used for efficient patient specific plan QA in a single measurement set-up in a 0.35 T MR-Linac, while the air-filled ion chamber array phantom shows large angular response changes and has its limitations regarding patient specific QA measurements

Characteristics of a two-dimensional periodic wave energy converter array

This study concentrates on the hydrodynamics of wave energy converters (WECs) consisting of an array of periodic buoys. The interaction between the bodies and waves was solved by a precise analytical method. The intrinsic relationships between wave propagation, energy capture, and array response are analyzed. Bragg resonance was found not only in scattering waves but also in radiation waves. The radiation wave is affected by different power take-off (PTO) damping, which could lead to incoming waves travelling freely through the array or being prevented through the array. The results show that Bragg resonance reduces the extraction efficiency significantly, and each device is affected to a different degree. In addition, this study reveals that there is collective behavior in the periodic WECs, all bodies in the array oscillate with identical amplitude at the Bragg resonance frequencies. Furthermore, the parametric effects on the hydrodynamic performance are investigated. The result of the study may provide useful guidance for the practical design of the WEC array.

Inertia Modulated Meta-Structure With Time-Varying Inertia Amplification

Abstract In this work, a new inertia modulated meta-structure is proposed to enable time-dependent inertia parameters, and thereby realize non-reciprocal wave propagation via spatiotemporal modulation. The designed cell structure is composed of an oscillatory disk and a mass that slides in a guide embedded in the disk frictionlessly with prescribed motion. Effective moment of inertia and damping coefficients of the rocking motion of the cell structure are rendered time-dependent due to the inertia and Coriolis forces of the periodically sliding mass, which allows us to implement the expected spatiotemporal modulation upon a super-cell. Non-reciprocal propagation behavior of the proposed meta-structure is verified via the theoretical solution of the dispersion relation as well as the dynamic response of a finite array. Effects of modulation parameters, including the frequency, amplitude, and phase, on the unidirectional propagation characteristic are thoroughly investigated.