Near-field Effects Research Articles

The confined stresslet for suspensions in a spherical cavity. Part 1. Traceless elements

The confined Stokesian dynamics (CSD) algorithm recently reported equilibrium properties but was missing hydrodynamic functions required for suspension stress and non-equilibrium properties. In this first of a two-part series, we expand the CSD algorithm to model the traceless part of the stress tensor. To obtain quantities needed to solve the integral expressions for the stress, we developed a general method to solve Stokes’ equations in bispherical coordinates. We calculate the traceless stress tensor for arbitrary particle-to-enclosure size ratio. We next compute rheology of a confined suspension by implementing the stresslet hydrodynamic coefficients into CSD, yielding the deviatoric part of the many-body hydrodynamic stresslet. We employed energy methods to relate this stresslet to the high-frequency viscosity of the confined suspension, finding an increase in viscous dissipation with crowding and confinement well beyond the unconfined value. We show that confinement effects on viscosity are dominated by near-field interactions between the particles that reside very near the cavity wall (rather than particle–wall interactions). Surprisingly, this near-field effect is stronger than the viscosity of an unconfined suspension, showing that entropic exclusion driven by the wall sets up many lubrication interactions that then generate strong viscous dissipation. The limiting case of a particle near a flat wall reveals a correction to prior literature. The theory presented in this work can be expanded to study the Brownian contribution to the viscosity of confined suspensions in and away from equilibrium. In part 2, we report the osmotic pressure, via the trace of the stress tensor.

Deep learning-based near-field effect correction method for Controlled Source Electromagnetic Method and application.

Addressing the impact of near-field effects in the Controlled Source Electromagnetic Method(CSEM) has long been a focal point in the realm of geophysical exploration. Therefore, we propose a deep learning-based near-field correction method for controlled-source electromagnetic methods. Initially, diverse datasets for a layered geologic model are generated through forward simulation. Building upon the characteristics of near-field effects, a deep learning network utilizing LSTM-CNN is meticulously constructed. Multiple experiments are executed to scrutinize the network's effectiveness in mitigating near-field effects and its resilience against noise. Following this, the proposed method is applied to actual CSEM data to validate its applicability in practice. The method is subsequently tested on measured CSEM data, confirming its practical efficacy. Results from experiments indicate that, for theoretical data, the LSTM-CNN network-trained data closely aligns with simulated data, showcasing a significant improvement. Moreover, when applied to measured data, the method eradicates false high-resistance anomalies at lower frequencies. In conclusion, this deep learning-based correction method proficiently eliminates the influence of near-field effects in the CSEM, delivering practical application benefits that more accurately reflect the authentic geologic structure.

Direct combustion noise: Nearfield and non-compactness influences on pressure–heat release coherence

There are several mechanisms through which turbulent flames produce sound. In low Mach number, unconfined flows, direct combustion noise – i.e., unsteady gas expansion generated by heat release fluctuations – is known to be a dominant contributor. This study is motivated by the fact that in the farfield, the coherence between spatially integrated heat release fluctuations from acoustically compact flames and direct combustion noise is unity. This suggests that the role of direct combustion noise relative to other sources can be ascertained from the value of the coherence. However, in practice it is difficult to fully satisfy the requirements to achieve a unity coherence, even in cases where direct combustion noise is the dominant noise source. This paper explores the contribution of noncompactness and nearfield effects on coherence. For the noncompactness part, while it is often the case that flames are small relative to a wavelength, they are never infinitesimally small. For the nearfield aspect, it is often not possible or practical to obtain farfield measurements, particularly in confined environments. This paper presents calculations that quantify how these noncompactness and nearfield effects influence coherence values. These calculations provide guidance on frequency ranges over which direct combustion noise will lead to near-unity coherence values, as well as required distances and optimal angles for acoustic instrumentation.Novelty and significance statementThis study presents a theoretical study on the coherence between heat release rate and acoustic pressure fluctuations, which has been mostly overlooked in prior literature. To the extent of the author’s knowledge, this is the first attempt that identify and investigate the inconsistencies between traditional theory and experimental literature on coherence. Results have implications for our previous understanding of the relationship between the heat release rate fluctuations and direct noise, aiding in future studies on combustion noise.

Optimized Kretschmann–Raether configuration for maximized electromagnetic near-field enhancement

This work focuses on maximizing the near-field enhancement effect of a Kretschmann–Raether configuration. Through theoretical calculation and numerical simulation, we demonstrate that a global optimization of excitation parameters provides 36 times more near-field intensity enhancement. This maximum near-field enhancement at the transmitted side of a metal surface occurs at the coalescence of the transmission coefficient’s pole and the reflection coefficient’s zero. The additional enhancement is possible by tuning the excitation wavelength, incident angle, and metal layer thickness synergistically. This work paves the way for further enhancing light-matter interaction in a broad application using layered structures.

Edge-based near-field photolithography optical proximity effect correction technique

Edge-based near-field photolithography optical proximity effect correction technique

Impact of Air Gaps Between Microstrip Line and Magnetic Sheet on Near-Field Magnetic Shielding

This study experimentally analyzed the impact of air gaps between a magnetic sheet and a test board with a microstrip line, which is used to measure the near-field magnetic shielding effectiveness (NSE) of magnetic sheets made of metallic powder. To conduct the measurements, a material fixture equipped with a microstrip line to generate the near magnetic field, a rectangular loop probe, and an automatic probe positioning system capable of moving the loop probe along three axes were designed and fabricated. In addition, to systematically vary the thickness of the gaps, three paper spacers with a thickness of 0.11 mm per paper were used, and a 1.0 mm thick acrylic sheet, along with a specially designed material fixture, was used to press down the magnetic sheets during measurement. The magnetic shielding properties were measured and compared under various air gap conditions using a near-field magnetic loop probe. The effect of the gaps on the shielding performance of the magnetic sheets was quantitatively evaluated for three different magnetic sheets. The experimental results showed that as the gap thickness increased, NSE tended to improve up to a frequency around 1 GHz, while in the higher frequency range of a few GHz, NSE tended to decrease. The physical background of this phenomenon was explained using an equivalent magnetic circuit represented by reluctances for the structure, where the magnetic sheet is placed above the microstrip line with an air gap. This model helps to elucidate how the presence of the air gap affects the near-field magnetic shielding performance.

Controlling directional emission of ions attached on the surface of nanoparticles

Abstract The interaction between lasers and nanoparticles holds significant theoretical and practical importance. Here, we investigate the near-field enhancement effects on silver nanotriangles and nanodiscs under ultrafast laser pulses, as well as the dynamics of protons and ions attached to the nanoparticle surfaces. By adjusting the size parameters of the nanoparticles, we explore the near-field enhancement effects and proton emission dynamics at different laser wavelengths. The results demonstrate that nanoparticles with varying morphologies substantially impact the proton momentum spectrum. The directional proton emission of nanotriangle structures is more pronounced compared to that of nanodiscs, and this effect can be further enhanced by adjusting the laser wavelength. Additionally, manipulating the thickness of particles also controls the Mie scattering phenomenon of light. Finally, we qualitatively discuss the emission processes of alpha particles and 9C6+ heavy ions. This research has important implications for proton and heavy ion radiotherapy in cancer treatment and targeted drug delivery, while providing theoretical foundations for understanding, characterizing, and controlling experimental studies of nanosystems with significant potential for expanding research into microdynamic behavior in complex nanomaterial superstructures.

Acoustic near field effects in distribution transformer noise measurement

This paper examines the near field effect, including the active and reactive acoustic field around a liquid-filled distribution transformer with heat-dissipating corrugated fins on the tank walls. The analysis was carried out on the basis of measurements of sound pressure and sound intensity levels along with acoustic maps including the phase correlation of acoustic waves. The acoustic field around the transformer was evaluated in the measurement planes showing normal direction radiation of up to 1,0 m distance. Discrete point measurements made with the PU (pressure - velocity) probe was used to obtain parameters such as particle velocity, active and reactive sound intensity as well as the transfer function associated with the reference microphone. The last parameter, the transfer function, allows to show the phase correlation between acoustic wave propagation, which contributes to a better understanding of acoustic near-field effects where energy circulates, creating a sound field that can have overestimated sound pressure and intensity levels.

Reverberation room design optimisation for low-frequency diffuse sound absorption testing

The reproducibility of sound absorption testing with the reverberation room method is a long-standing concern. Absorptive samples induce directionality in the nearfield, while the farfield depends on the room geometry below the Schroeder frequency. Nevertheless, when properly accounting for nearfield effects, the theoretical diffuse absorption coefficient of a sample still represents its average performance across an ensemble of different rooms, even at very low frequencies. Recent research found that particular reverberation room designs allow for an accurate measurement of the diffuse sound absorption coefficient of highly absorptive samples at low frequencies. Pinpointing such designs hence opens up a possibility to sustainably improve the low-frequency reproducibility of sound absorption testing in reverberation rooms. The present paper introduces a numerical optimisation framework that serves this purpose. Specific room shapes are parametrised and the geometrical room parameters are optimised so as to minimise the difference between the measured and the diffuse absorption coefficient under appropriate constraints. The sound absorption testing of a sample in a particular reverberation room is numerically simulated using a method that is both accurate and computationally efficient at low frequencies. The diffuse absorption is computed with a hybrid deterministic-statistical energy analysis approach that accounts for the detailed absorber properties, geometry, and boundary conditions, as well as the nearfield effects. The methodology is applied to both cuboidal and hexahedral room shapes. Certain optimised designs are found not only to provide an excellent match for the absorber that was used during the optimisation, but they also maintain their performance across a range of absorptive samples. Additionally, potential geometrical deviations are found to be well tolerated by these reverberation room designs.

Au Nanorings/TiO2 NPs@MXene-Based Metasurfaces with a Magnetic Mirror-Modulated ECL Strategy for Extracellular Vesicle Detection.

A metasurface as an artificial electromagnetic structure can concentrate optical energy into nanometric volumes to strongly enhance the light-matter interaction, which has been becoming a powerful platform for optical sensing, nonlinear effects, and quantum optics. Herein, we developed a novel hybrid plasmonic-dielectric metasurface consisting of Au nanorings (Au NRs) and TiO2 nanoparticles derived from MXene (TiO2 NPs@MXene). The hybrid metasurface simultaneously benefited from the high near-field enhancement effect of plasmonic materials and the low loss of dielectric materials. Furthermore, the optical modulation efficiency of the hybrid metasurface can be regulated by a magnetic mirror configuration. The magnetic mirror acted like a mirror, confining the electrons to a limited region and increasing the density of the surface plasmon. Moreover, the electrochemiluminescence (ECL) of the Cu2BDC metal-organic framework (Cu2BDC-MOF) served as a light source for the Au NRs/TiO2 NPs@MXene metasurface. Due to the exceptional light manipulation capability of the hybrid metasurface and the coordination of the magnetic mirror, the isotropic ECL signal can be dynamically amplified and converted into polarized emission. Finally, a metasurface-regulated ECL (MECL)-based biosensor with a dual-positive membrane protein recognition strategy was developed for the accurate identification of gastric cancer-derived extracellular vesicles. The novel MECL research opened up a new route in the realization of dynamically tunable metasurfaces for optical sensing and novel nanophotonic devices.

Dual-Functional Cross-Meandering Resonator for Power Frequency Electromagnetic Shielding and Wireless Sensing Communication.

The research on MEMS wireless sensing technology adapted to strong power frequency electromagnetic field environments is of great significance to our energy security, economic society, and even national security. Here, we propose a subwavelength cross-meandering resonator (0.49λ0 × 0.49λ0) to simultaneously achieve power frequency electromagnetic field shielding and wireless communication signal transmission. The element size of the resonator is only λ0/11, which is much smaller than that of previous works. In the resonator, a resonance mode with the significant near-field enhancement effect (about 180 times that at f = 1 GHz) is supported. Based on the self-made shielding box experimental setup, the measured shielding effectiveness of the resonator sample can reach more than 33 dB. Moreover, by integrating the cross-meandering resonator with the MEMS sensor, a wireless communication signal can be successfully transmitted. A dual-function cross-meandering resonator integrated with sensors may find potential applications in many military and civilian industries associated with strong power frequency electromagnetic fields.

Near-Field Effects at the Nodes of a Gold Nanonetwork Grown by Laser Ablation in Superfluid Helium: Crossover between “Tip and Gap Hot Spots”

Near-Field Effects at the Nodes of a Gold Nanonetwork Grown by Laser Ablation in Superfluid Helium: Crossover between “Tip and Gap Hot Spots”

Hybrid Twins Modeling of a High-Level Radioactive Waste Cell Demonstrator for Long-Term Temperature Monitoring and Forecasting.

Monitoring a deep geological repository for radioactive waste during the operational phases relies on a combination of fit-for-purpose numerical simulations and online sensor measurements, both producing complementary massive data, which can then be compared to predict reliable and integrated information (e.g., in a digital twin) reflecting the actual physical evolution of the installation over the long term (i.e., a century), the ultimate objective being to assess that the repository components/processes are effectively following the expected trajectory towards the closure phase. Data prediction involves using historical data and statistical methods to forecast future outcomes, but it faces challenges such as data quality issues, the complexity of real-world data, and the difficulty in balancing model complexity. Feature selection, overfitting, and the interpretability of complex models further contribute to the complexity. Data reconciliation involves aligning model with in situ data, but a major challenge is to create models capturing all the complexity of the real world, encompassing dynamic variables, as well as the residual and complex near-field effects on measurements (e.g., sensors coupling). This difficulty can result in residual discrepancies between simulated and real data, highlighting the challenge of accurately estimating real-world intricacies within predictive models during the reconciliation process. The paper delves into these challenges for complex and instrumented systems (multi-scale, multi-physics, and multi-media), discussing practical applications of machine and deep learning methods in the case study of thermal loading monitoring of a high-level waste (HLW) cell demonstrator (called ALC1605) implemented at Andra's underground research laboratory.

Simulations of Femtosecond-Laser Near-Field Ablation Using Nanosphere under Dynamic Excitation.

Femtosecond lasers have garnered widespread attention owing to their subdiffraction processing capabilities. However, their intricate natures, involving intrapulse feedbacks between transient material excitation and laser propagation, often present significant challenges for near-field ablation predictions and simulations. To address these challenges, the current study introduces an improved finite-difference time-domain method (FDTD)-plasma model (plasma)-two-temperature model (TTM) framework for simulating the ablation processes of various nanospheres on diverse substrates, particularly in scenarios wherein dynamic and heterogeneous excitations significantly influence optical-field distributions. Initially, FDTD simulations of a single Au nanosphere on a Si substrate reveal that, with transitions in the excitation states of the substrate, the field-intensity distribution transforms from a profile with a single central peak to a bimodal structure, consistent with experimental reports. Subsequently, simulations of a polystyrene nanosphere array on a SiO2 substrate reveal that different excitation states of the nanospheres yield two distinct modes, namely near-field enhancement and masking. These modes cannot be adequately modeled in the FDTD simulations. Our combined model also considers the intrapulse feedback between the electromagnetic-field distribution resulting from near-field effects and material excitations. Furthermore, the model can quantitatively analyze subsequent electron-phonon coupling and material removal processes resulting from thermal-phase transitions. Consequently, our model facilitates predictions of the femtosecond-laser ablation of single nanospheres or nanosphere arrays with varying sizes and materials placed on substrates subjected to near-field effects.

Small-strain stiffness of selected anthropogenic aggregates from bender element tests

Abstract This article presents a study on the stiffness of mixtures of anthropogenic materials derived from construction or demolition waste, specifically fine recycled concrete aggregates (fRCAs) with different fine fraction (FF) contents. The study investigated small-strain shear moduli via various signal interpretation methods, examining, above all, the time domain approaches and considering the influence of FF content. However, the inconclusive results from the bender element (BE) tests highlight the complexity of factors affecting shear wave velocity, which requires further research to refine the methodology and assess long-term performance in geotechnical applications. Selecting the correct test frequency and interpretation method is crucial to obtain accurate results. The BE test method should consider all relevant factors. At low input frequencies (≤5 kHz), the near-field effect affected the received signal for fRCA mixtures. At higher frequencies (around 14 kHz), the noise levels increased, thereby interfering with the S-wave travel time determination. Intermediate input frequencies (10.0 and 12.5 kHz) provided the representative shear modulus (G) values. The small-strain shear modulus (G max) of the fRCA compounds from the resonant column and BE tests was found to be in good agreement, despite differences in the test procedures themselves.

Scenario-based seismic hazard for horizontal and vertical ground motions in central Italy

We propose an innovative methodology for seismic emergency planning and earthquake risk mitigation in central Italy by integrating three prototypal earthquake scenarios. The different scenarios derive maximum earthquake magnitudes from different input data. The first scenario utilizes local rheological, geological, and geophysical conditions; the second scenario considers the study area fault characteristics, while the third scenario relies on the cluster analysis of historical and instrumental earthquake records. The magnitudes and related uncertainties are combined using a conflation method to derive the expected ground motions for a grid of sites in central Italy. The resulting scenarios include peak ground acceleration and spectral ordinates, presented as maps and spectra for two selected localities. The vertical component of ground motion is also presented, because it is essential for accurately assessing the response of short-period structures. Our methodology complements the more classic seismic hazard analyses, offering additional insights for earthquake contingency planning and loss analysis. The proposed methodology is flexible; multiple models and ongoing advancements in scenario practice (near-field effects, vertical ground motion, and the choice of ground motion models) can be easily incorporated, increasing the effectiveness of seismic scenario modeling in seismic emergency planning and risk mitigation.

Dependent scattering and plasmon coupling in concentrated suspensions of optically hard nanoparticles

This study establishes the accuracy and efficacy of the recently developed radiative transfer with reciprocal transactions (R2T2) method for quickly simulating radiation transfer through concentrated thick suspensions of optically hard nanoparticles featuring a large mismatch in refractive and/or absorption indices compared with their surrounding medium. Concentrated suspensions of optically hard nanoparticles exhibit strong light scattering and dependent scattering effects including both near-field interactions among particles and interferences of scattered waves in the far-field. Concentrated suspensions of metallic nanoparticles also exhibit plasmon coupling effect that leads to widening of absorption peak and red-shift in the peak surface plasmon resonance wavelength. However, predicting these complex interactions between EM waves and particles in thick and concentrated suspensions by explicitly solving Maxwell's equations is computationally intensive, if not impossible. Conventional solutions like Lorenz–Mie theory combined with independent scattering approximation do not account for dependent scattering and plasmon coupling. Furthermore, the dense medium radiative transfer theory is a far-field approximation that does not account for near-field effects, leading to significant errors in predictions, as illustrated in this study. By contrast, the R2T2 method's predictions showed excellent agreement with the solutions of Maxwell's equations obtained using the superposition T-matrix method for thin films containing optically hard particles. The method also rigorously accounted for multiple scattering as well as plasmon coupling in thick concentrated suspensions. These results could facilitate the design of plasmonic suspensions used in various energy and environmental applications.

Combined Effect of A-Priori Information and Varying Source Offset in Minimizing Propagation of Near-Field Effects in MASW Testing and Subsequent Site Response Analysis

Combined Effect of A-Priori Information and Varying Source Offset in Minimizing Propagation of Near-Field Effects in MASW Testing and Subsequent Site Response Analysis

Quantitative measurement of spatial distribution of effective refractive index induced by local electron concentration at a nano slit

Abstract Surface plasmon polaritons (SPPs) have found their key applications in high-sensitivity biomolecular detection and integrated photonic devices for optical communication via light manipulation at nanostructures. Despite their broad utility, SPPs are known to be accompanied by other complex near-field propagation modes, such as quasi-cylindrical waves (QCWs) and composite diffracted evanescent waves (CDEWs), whose electromagnetic and quantum propagation effects have not been comprehensively understood especially regarding their mutual interaction with SPPs. In this study, we addressed this complexity by employing a nano groove structure and a high-stability broadband femtosecond laser as a light source, the spatial phase distribution around the nano slit edge was measured with relative stability of a 4.6 × 10−11 at an averaging time of 0.01 s. Through this spatial phase spectrum, we precisely measured the nonlinear distribution of effective refractive index changes with an amplitude of 10−2 refractive index units at the edge of the nano slit–groove structure. These results reveal that the near-field effects on local electron concentration induced by nanostructure’s discontinuity can be quantitatively measured, which can contribute to a deeper understanding of SPP phenomena in nanostructures for the optimal design and utilization of the SPP effects in diverse nano-plasmonic applications.

A Gaussian-plume based Monte Carlo method for calculating radiation dose in the near field of buildings

A Monte Carlo (MC) programme was written using the dose point kernel method to calculate doses in the roof zone of a building from nearby releases of radioactive gases. A Gaussian Plume Model (GPM) was parameterised to account for near-field building effects on plume spread and reflection from the roof. Rooftop recirculation zones and building-generated plume spread effects were accounted in a novel Dual Gaussian Plume (DGP) formulation used with the MC model, which allowed for the selection of angle of approach flow, plume release height in relation to the building and position of the release point in relation to the leading edge of the building. Three-dimensional wind tunnel concentration field data were used for the parameterisation. The MC code used the parameterised concentration field to calculate the contributions to effective dose from inhalation, cloud immersion from positron/beta particles, and gamma-ray dose for a wide range of receptor dose positions in the roof zone, including receptor positions at different heights above the roof. Broad trends in predicted radiation dose with angle of approach flow, release position in relation to the building and release height are shown. Alternative approaches for the derivation of the concentration field are discussed.