Near-field Data Research Articles

Uniqueness in Inverse Diffraction Grating Problems With Infinitely Many Plane Waves at a Fixed Frequency

This paper is concerned with uniqueness of solution of the inverse diffraction by problems by a periodic curve with Dirichlet boundary condition in two dimensions. It is proved that the periodic curve can be uniquely determined by the near-field measurement data corresponding to infinitely many incident plane waves with distinct directions at a fixed frequency. Our proof is based on Schiffer’s idea which consists of two ingredients: (i) the total fields for incident plane waves with distinct directions are linearly independent, and (ii) for a fixed wave number there exist only finitely many linearly independent Dirichlet eigenfunctions in a bounded domain or in a closed waveguide under additional assumptions on the waveguide boundary. Based on the Rayleigh expansion, we prove that the phased near-field data can be uniquely determined by the phaseless near-field data in a bounded domain, with the exception of a finite set of incident angles. Such a phase retrieval result leads to a new uniqueness result for the inverse grating diffraction problem with phaseless near-field data at a fixed frequency. Since the incident direction determines the quasi-periodicity of the boundary value problem, our inverse issues are different from the existing results of [F. Hettlich and A. Kirsch, Inverse Problems, 13 (1997), pp. 351–361], where fixed-direction plane waves at multiple frequencies were considered.

Research on the Method of Near-Field Measurement and Modeling of Powerful Electromagnetic Equipment Radiation Based on Field Distribution Characteristics

With the wide application of power equipment consisting of high switching frequencies and large current switching devices in the integrated power system on ships, the low-frequency radiation interference caused by the powerful electromagnetic equipment becomes more and more serious. Establishing an equivalent model of radiation interference based on the near-field measurement data is the key to subsequent electromagnetic compatibility design. Due to the large size of the equipment, there will be many measurement points in the near-field measurement area, which leads to long testing times and low modeling efficiency. To solve the above problems, this article first proposes a method of near-field measurement and a modeling method of powerful electromagnetic equipment radiation based on field distribution characteristics. Firstly, the near-field measurement data are obtained by the sparse and uniform sampling of the near-field measurement plane at large sampling intervals. Then, the near-field measuring plane is separated into several regions by the magnetic field’s distribution characteristics. The near-field measurement data required for modeling are obtained by further sampling in the region with a large magnetic field amplitude. Finally, the equivalent radiation model is obtained by the equivalent dipole method. Simulations and experiments show that the method can significantly reduce the amount of measurement data and testing time while improving the efficiency of equivalent radiation modeling and maintaining the accuracy of the modeling.

A Potential Earthquake with Magnitude Mw 7.2 on the Northern Xiaojiang Fault Revealed by GNSS Measurement

We used near-field and regional GNSS (Global Navigation Satellite System) data to quantify the deformation and locking ratio of the Xiaojiang fault (XJF) in southeastern Tibet. The inversion based on the dislocation model shows that the slip rate of the XJF is 9–11 mm/a; the locking depths of the northern, central, and southern segments are 25.5 km, 12 km, and 22.5 km, respectively. The inversion with DEFNODE program shows that the locking of the northern segment is the strongest above a depth of 20 km, while the locking between 20 km and 26 km is intermediate, and the weakest locking is found below 26 km. In the central segment, the depths of the interface are 6 km and 12 km. Additionally, a locked asperity that has the potential of generating an Mw 7.2 earthquake along the northern segment is delineated. The asperity and the shallow locking zone are basically consistent with the rupture area of the 1733 M 7.8 Dongchuan earthquake and the 1833 M 8 Songming earthquake, respectively. Both the activity of the historical strong earthquakes and the seismicity of the microearthquakes recorded over recent years seem to suggest that a potential earthquake is imminent.

Measurement Method for the Dispersion Curves of a Spoof SPP Transmission Line Using a Single Sample

Research works on spoof surface plasmon polariton (SPP) transmission lines (TLs) have been carried out toward the goal of achieving flexible control of dispersion. The existing measurement methods for the dispersion of the spoof SPPs require two SPP TL samples with different numbers of units and transition structures, which makes the process more difficult and expensive. This work proposes a new approach for measuring the dispersion curve of a spoof SPP TL by using experimental near-field data. A mathematical model is presented to describe the relation between the wavenumber <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> and the near-field data by considering the presence of reflected waves. The high efficiency and accuracy of this method are verified by the good agreement obtained between the measured dispersion curve and the eigenmode simulation result for a typical spoof SPP TL. Hence, the proposed method makes it possible to measure the dispersion curve of a spoof SPP TL based on a single sample, providing significant progress toward decreasing testing error and cost.

Data-Driven Multiobjective Optimization of Wave-Packets for Near-Field Subsonic Jet Noise

Aeroacoustics of innovative aircraft cannot disregard the development of low-order models for the jet noise source, which are essential to assess the propulsion–airframe interactions from the conceptual design stage. The main scope of this work is to provide a noise source model that can be coupled with relatively low computational cost methods for aeroacoustic scattering. To this end, this paper presents for the first time a multiobjective optimization of the zeroth-mode wave-packet in the jet near field. The importance of calibrating the model with near-field pressure data stems from the fact that in new aircraft, the engine nacelles are typically positioned at a few diameters from the wing or fuselage. In this work, the near field of a high subsonic jet at a Mach number of 0.9 is represented as a cylindrical surface radiating the pressure disturbances of a wave-packet source, which is optimized using large-eddy simulation data from three lines at different radial distances. The optimized model has been tested at Strouhal numbers between 0.25 and one, and the optimized solutions have been chosen using a Pareto-ranking criterion considering the wave-packet prediction over an extra line. A good agreement is achieved between the reference data and model predictions for multiple near-field radial distances.

Pattern Reconstruction from Near-Field Data Affected by 3D Probe Positioning Errors Collected via Planar-Wide Mesh Scanning

An effective procedure to correct known 3D probe positioning errors affecting the near-field–far-field transformation (NF–FF) with non-conventional plane rectangular scanning, named planar wide-mesh scanning (PWMS), is developed in this paper. It relies on the non-redundant sampling representations of electromagnetic fields and related optimal sampling interpolation (OSI) expansions and has been devised when a quasi-planar antenna under test is considered as suitably modelled by either a double bowl or an oblate spheroid. Such an algorithm first makes use of the so-called k-correction to compensate for the errors occurring when the actual sampling points deviate from the acquisition plane and then adopts an iterative procedure to restore the NF samples at the points specified by the used non-redundant sampling representation from those obtained at the previous step and affected by 2D positioning errors. Finally, once the regularly arranged PWMS samples have been calculated, the NF data required to compute the classic plane-rectangular NF–FF transformation are accurately evaluated by using an effective 2D OSI algorithm. Several numerical results are presented in order to assess the effectiveness of the devised approach.

Cosmic coding and transfer for ultra high security near-field communications

By using true random number (TRN) generators, encoding with the highest security can be realized. However, a completely secure strategy to transfer these TRNs has not yet been devised. Quantum key distribution (QKD) has attempted to establish secure key distribution methodology of this kind; however, several quantum cracking strategies have been predicted and experimentally demonstrated. In this work, COSMOCAT was invented as a solution for next-generation ultrahigh security near-field communications. With COSMOCAT, TRNs are generated from naturally occurring and ubiquitous cosmic-ray muons and the generated cosmic keys are distributed by these muons with an unprecedented level of security. The successful results of this experiment indicate that our prototype and the new key-generation-and-distribution standard can be utilized for practical encoding and near-field data transfer at rates of 10-100 Mbps. It is anticipated that COSMOCAT will be one of key techniques for future high security, near-field communication management.

Fast Antenna Characterization With Numerical Expansion Functions Built With Partial Knowledge of the Antenna and Accelerated Asymptotic Methods

We describe a method to use numerical simulations concurrently with measurements (near-field data) to characterize the radiation properties of an antenna (far-field) with a strongly reduced number of samples. Both the simulations and experimental data are dealt with as sources of information toward obtaining the desired characterization. Simulations compensate for data scarceness, allowing to obtain an accurate characterization with fewer data than with measurements only, and the few measured data allow the comprehensive numerical proxy to get tuned to the true antenna under test (AUT). The method uses partial knowledge of the antenna and leverages accelerated asymptotic numerical methods to perform the numerical simulations needed by the algorithm. We report experimental tests of performance, both in terms of accuracy and speed-up with respect to the classical methods, with reflector antennas up to 27 wavelength. It is important to note that good results are obtained both when samples are taken on irregular optimized grids and on regular grids usually resulting from the conventional measurement rigs.

Application of neural networks to inverse elastic scattering problems with near-field measurements

&lt;abstract&gt;&lt;p&gt;This paper is concerned with the application of a machine learning approach to inverse elastic scattering problems via neural networks. In the forward problem, the displacements are approximated by linear combinations of the fundamental tensors of the Cauchy-Navier equations of elasticity, which are expressed in terms of sources placed inside the elastic solid. From the near-field measurement data, a two-layer neural network method consisting of a gated recurrent unit to gate recurrent unit has been used to reconstruct the shape of an unknown elastic body. Moreover, the convergence of the method is proved. Finally, the feasibility and effectiveness of the presented method are examined through numerical examples.&lt;/p&gt;&lt;/abstract&gt;

Technical Theme Topics

Electromagnetic near-field scanning has been receiving great attention from EMC engineers as it enables understanding of the electromagnetic behavior of electronic components and sub-systems. The technique allows for intra- and inter-system assessment of EMC characteristics even at the early design stage of the product without requiring expensive test facilities, such as semi-anechoic chambers. Also, the acquired near-field data can be post-processed with the objective to obtain equivalent radiation source distributions to be used to predict far-field radiation. Data acquisition and post-processing usually take advantage of advanced machine learning algorithms, whose exploitation allows optimizing the process in terms of time, computational burden, and prediction accuracy.

Распределенный реестр истории эксплуатации транспортного средства на основе блокчейн-платформы Hyperledger Fabric

Due to the rapid development of various transport platforms, including those using unmanned technologies, systems that provide storage of vehicle operating history throughout its lifecycle are becoming increasingly relevant. Purpose: the purpose and functionality of the developed system for storing such information are defined. The main purpose of the system is to maintain a single source of reliable and unchangeable information about the operating history of the vehicle. Such a system can increase the transparency of business processes that arise between participants in the automotive industry: manufacturers and owners of vehicles, service stations, insurance companies and other industry participants. Methods: Blockchain technology, smart contracts and various methods of transaction processing were used. Results: the system was designed based on a distributed platform, based on the criteria defined in the work, Hyperledger Fabric was chosen as the platform. Communication network and information system architecture were designed and developed based on the distributed registry technology. The paper describes the process of creating the Hyperledger Fabric network, which is supported by the member organizations of the automotive industry. A description of the basic elements of the system is presented, as well as the mechanisms that maintain and harmonize the distributed registry, transaction processing, execution of smart contracts and interaction of the connected system participants. The hardware was designed in the form of a plug-in unit, which implements the functions of collection and pre-preparation of data collected from the nodes, units, sensors of the vehicle, as well as additional sensors built into the hardware unit. The collected data are transmitted from the block to the storages, the maintenance of which is carried out by the system participants interested in such data. The fact of data transfer and data source identifier is recorded in a distributed registry in the form of a transaction, placed in the block. Practical relevance: On the basis of smart contract technology the issues of forming reports on the history of vehicle operation are considered. The system is scalable and allows the deployment of new smart contracts, which provides the ability to create new scenarios for its use. Discussion Possible variants of further development and use of the system are considered: the solution of scaling the system by local zones is proposed, and a brief overview of the approach of dynamic channel definition Hyperledger Fabric using dedicated near-field data communication is presented.

A hybrid equivalent source—particle swarm optimization model for accurate near-field to far-field conversion

This paper proposes an improved equivalent source (ES) model based on particle swarm optimization (PSO) to predict the radiated emissions of a 2.4 GHz ISM band patch antenna. The proposed model uses near-field data to extract an equivalent set of infinitesimal electric dipoles representation. Characterized by their positions, orientations, and currents, these dipoles can reproduce the same field distribution as the target device under test (DUT). To build an accurate equivalent dipole model, a numerical experiment is performed and presented in this paper, where many variable selections of observation points and dipole numbers and locations of the dipole plane are examined, with the aspiration of determining a suitable conversion problem. Based on the proper combination of the two methods (ES-PSO), the complete modeling procedure consists of the application of the pseudo-inverse method to find the minimum norm solution to the least-square problem. Then, the obtained solution is provided to the PSO algorithm to initialize the search for the best-fit dipole parameters. The PSO method can further enhance the stability of the obtained dipole solution and improve the accuracy of the far field prediction. Promising and encouraging results in terms of field prediction at higher planes above the DUT are obtained.

Rupture process and aftershock focal mechanisms of the 2022 M6.8 Luding earthquake in Sichuan

According to the China Earthquake Networks Center, a strong earthquake of M6.8 occurred in Luding County, Ganzi Tibetan Autonomous Prefecture, Sichuan Province, China (102.08°E, 29.59°N), on September 5, 2022, with a focal depth of 16 km. Rapid determination of the source parameters of the earthquake sequence is vital for post-earthquake rescue, disaster assessment, and scientific research. Near-field seismic observations play a key role in the fast and reliable determination of earthquake source parameters. The numerous broadband seismic stations and strong-motion stations recently deployed by the National Earthquake Intensity Rapid Report and Early Warning project have provided valuable real-time near-field observation data. Using these near-field observations and conventional mid- and far-field seismic waveform records, we obtained the focal mechanism solutions of the mainshock and M ≥ 3.0 aftershocks through the waveform fitting method. We were further able to rapidly invert the rupture process of the mainshock. Based on the evaluation of the focal mechanism solution of the mainshock and the regional tectonic setting, we speculate that the Xianshuihe fault formed the seismogenic structure of the M6.8 strong earthquake. The aftershocks formed three spatially separated clusters with distinctly different focal mechanisms, reflecting the segmented nature of the Xianshuihe fault. As more high-frequency information has been applied in this study, the absolute location of the fault rupture is better constrained by the near-field strong-motion data. The rupture process of the mainshock correlates well with the spatial distribution of aftershocks, i.e., aftershock activities were relatively weak in the maximum slip area, and strong aftershock activities were distributed in the peripheral regions.

A CNN Based Approach for the Point-Light Photometric Stereo Problem

Reconstructing the 3D shape of an object using several images under different light sources is a very challenging task, especially when realistic assumptions such as light propagation and attenuation, perspective viewing geometry and specular light reflection are considered. Many of works tackling Photometric Stereo (PS) problems often relax most of the aforementioned assumptions. Especially they ignore specular reflection and global illumination effects. In this work, we propose a CNN-based approach capable of handling these realistic assumptions by leveraging recent improvements of deep neural networks for far-field Photometric Stereo and adapt them to the point light setup. We achieve this by employing an iterative procedure of point-light PS for shape estimation which has two main steps. Firstly we train a per-pixel CNN to predict surface normals from reflectance samples. Secondly, we compute the depth by integrating the normal field in order to iteratively estimate light directions and attenuation which is used to compensate the input images to compute reflectance samples for the next iteration. Our approach sigificantly outperforms the state-of-the-art on the DiLiGenT real world dataset. Furthermore, in order to measure the performance of our approach for near-field point-light source PS data, we introduce LUCES the first real-world 'dataset for near-fieLd point light soUrCe photomEtric Stereo' of 14 objects of different materials were the effects of point light sources and perspective viewing are a lot more significant. Our approach also outperforms the competition on this dataset as well. Data and test code are available at the project page.

Implementing a heuristic method to correct ground reflection effects observed in full-scale tactical aircraft noise measurements

In a recent study of noise from a T-7A-installed GE F404 engine, microphones along 38 and 76 m (125 and 250 ft) arcs were mounted 1.5 m (5 ft) above the ground to quantify human impact. While helpful for this purpose, the resulting multipath effects pose challenges for other acoustical analyses. For jet noise runup measurements, these effects are complicated by the fact that the noise source is extended and partially correlated and its spatial properties are frequency dependent. Furthermore, a finite-impedance ground surface and atmospheric turbulence affect interference nulls. This study applies a ground-reflection method developed previously [Gee et al., Proc. Mtgs. Acoust. 22, 040001 (2014)] for rocket noise measurements. The model accounts for finite ground impedance, atmospheric turbulence, and extended source models that are treated as coherent and incoherent arrays of monopoles. Application to the ground runup data to correct the 38 and 76 m spectra at a range of angles suggests the incoherent line source model is more appropriate at sideline angles whereas the coherent source model is more appropriate for upstream and downstream propagation. Comparisons with near-field data and similarity spectra show that, while imperfect, this method represents an advancement in correcting jet noise spectra for ground reflection effects. [Work supported by ONR Grant No. N00014-21-1-2069.]

Estimation of Equivalent Current Distribution Using Fourier Transform and Eigenmode Currents

The estimation of the equivalent current distribution is a challenge when the precise geometry of the real source is unknown. In this study, a novel estimation method for the equivalent current distribution is proposed. The proposed method is a hybrid of the Fourier transform and eigenmode currents of equivalent sources. The equivalent current distribution is estimated using the proposed method as follows. First, the Fourier transform is applied to an electric field integral equation, and the initial equivalent current distribution on a specific estimation plane is estimated from the near-field data of the real source. Utilizing the initial equivalent current distribution, the equivalent sources that are uniformly arranged over the estimation plane are thinned. Subsequently, the equivalent current distribution is estimated using a matrix equation and the eigenmode currents of the remaining equivalent sources. The advantages of the proposed method are as follows. First, the precise geometry of the real source is not needed during estimation. Second, the number of equivalent sources is reduced, and the estimation of the equivalent current distribution is well conditioned. The performance of the proposed method is validated both numerically and experimentally. Empirical guidelines for threshold values for thinning equivalent sources are provided.

Simulation and Regression Modeling of NASA’s X-59 Low-Boom Carpets Across America

NASA’s X-59 aircraft is predicted to produce a significantly quieter cruise sonic boom than traditional -wave-producing aircraft. A propagation simulation study was undertaken to quantify loudness levels, exposure size, and variability of the X-59’s low-boom carpet using realistic atmospheric profiles across the contiguous United States of America (CONUS). Near-field pressure data of the X-59 in supersonic cruise from NASA’s fully unstructured Navier–Stokes three-dimensional (known as FUN3D) computational fluid dynamics code were propagated using NASA’s PCBoom code, which solves an enhanced Burgers equation along acoustic rays. Atmospheric profiles from the National Oceanic and Atmospheric Administration’s Climate Forecast System Version 2 database were used for propagation at 138 locations across the CONUS. Carpets at each location were generated for aircraft headings in the four cardinal directions. Over one million X-59 carpets were generated in total. The effects of the heading, season, geography, and climate zone on boom levels and exposure size are presented. Multiple linear regression models were developed to estimate carpet width and loudness metrics across the CONUS. These results inform regulators and mission planners on expected variations in boom levels and carpet extent from atmospheric variations. Understanding potential carpet variability is important when planning community noise surveys using the X-59.

Source localization of ictal SEEG to predict postoperative seizure outcome

ObjectiveStereo-electroencephalography (SEEG) is inherently-three-dimensional and can be modeled using source localization. This study aimed to assess the validity of ictal SEEG source localization. MethodsThe dominant frequency at ictal onset was used for source localization in the time and frequency domains using rotating dipoles and current density maps. Validity was assessed by concordance with the epileptologist-defined seizure onset zone (conventional SOZ) and the surgical treatment volume (TV) of seizure-free versus non-seizure-free patients. ResultsSource localization was performed on 68 seizures from 27 patients. Median distance to nearest contact in the conventional SOZ was 7 (IQR 6–12) mm for time-domain dipoles. Current density predicted ictal activity with up to 86 % (60–87 %) accuracy. Distance from time-domain dipoles to the TV was smaller (P = 0.045) in seizure-free (2 [0–4] mm) versus non-seizure-free (12 [2–17] mm) patients, and predicted surgical outcome with 91 % sensitivity and 63 % specificity. Removing near-field data from contacts within the TV negated outcome prediction (P = 0.51). ConclusionsSource localization of SEEG accurately mapped ictal onset compared with conventional interpretation. Proximity of dipoles to the TV predicted seizure outcome when near-field recordings were analyzed. SignificanceIctal SEEG source localization is useful in corroborating the epileptogenic zone, assuming near-field recordings are obtained.

Anisotropic Turbulent Kinetic Energy Budgets in Compressible Rectangular Jets

Turbulence is governed by various mechanisms, such as production, dissipation, diffusion, dilatation and convection, which lead to its evolution and decay. In high-speed flows, turbulence becomes complicated due to compressibility effects. Therefore, the goal of the current work is to characterize these mechanisms in rectangular supersonic jets by directly evaluating their contributions in turbulent kinetic energy (TKE) budget equation. The budgets are obtained using high-fidelity Large Eddy Simulations that employ WALE subgrid-scale model. Jet nearfield data are validated with PIV experimental measurements, available from the literature, which include mean flow and second-order statistics. To ensure spatial resolution and temporal convergence of higher-order statistics, qualitative performance metrics are presented. The results indicate that TKE production is the major source term, while pressure-dilatation term acts as a sink throughout the development of the jet. The diffusion term has the highest contribution from triple-velocity correlations, followed by pressure diffusion and molecular diffusion. Subgrid-scale diffusion and dissipation are also evaluated and their contributions are minimal. Each term is presented on both minor and major axis plane and reveals asymmetry in the statistics. A detailed explanation of budget contributions is provided, leading to the mechanisms responsible for the anisotropy of TKE.

Recovery of an infinite rough surface by a nonlinear integral equation method from phaseless near-field data

Abstract This paper is concerned with the two-dimensional inverse acoustic scattering by an unbounded, sound-soft rough surface. We propose a nonlinear integral equation method using multi-frequency phaseless near-field data associated with point sources to reconstruct the shape and location of the rough surface, yielding a fast imaging algorithm. Numerical examples are presented to show the effectiveness of the inverse algorithm.