Near-field Method Research Articles

Single Far-Field or Near-Field Source Localization With Sparse or Uniform Cross Array

Existing works for 3-D source localization are based on uniform cross arrays. In this correspondence, we propose a single far-field (FF) or near-field (NF) source localization method based on uniform cross arrays and then generalize it to the symmetric sparse cross arrays where each linear array is a symmetric sparse one. We utilize the cross-covariance matrix to exploit the full array aperture and employ the atomic norm minimization technique to retrieve the angle information without discretization. The range is estimated by MUSIC-like method. Our method is superior to traditional methods and exhibits enormous advantages in low signal-to-noise ratio (SNR) and small number of snapshots regions. Numerical simulations are carried out to verify the effectiveness of our method.

Instantaneous radiation from time-varying electric and magnetic dipoles

Radiation from magnetic and electric dipole moments is a key subject in theory of electrodynamics. Although people treat the problem thoroughly in the context of frequency domain, the problem is still not well understood in the context of time domain, especially if dipole moments arbitrarily vary in time under action of external forces. Here, we scrutinize the instantaneous power radiated by magnetic and electric dipole moments, and report findings that are different from the conventional understanding of their instantaneous radiation found in textbooks. In contrast to the traditional far-field approach based on the Poynting vector, our analysis employs a near-field method based on the induced electromotive force, leading to corrective terms that are found to be consistent with time-domain numerical simulations, unlike previously reported expressions. Beyond its theoretical value, this work may also have significant impact in the field of time-varying metamaterials, especially in the study of radiation from subwavelength meta-atoms, scatterers and emitters that are temporally modulated.

Research on patch near-field acoustic holography based on two-level iteration

In order to solve the “window effect” and “aperture repetition effect” caused by limited measurement aperture, a patch near-field acoustic holography method based on two-level iteration is proposed. After analyzing the principle and process of patch near-field acoustical holography based on orthogonal spherical wave, a patch near-field acoustical holography method based on two-level iteration is proposed. The validity of the method is verified by simulation and experiment. Compared with the reconstruction results of patch near-field acoustical holography based on orthogonal spherical wave, it shows the superiority of patch near-field acoustical holography based on two-level iteration.

Aerodynamic Design and Shape Optimization with the Far-Field Drag Decomposition Approach

In the aerodynamic shape design, the drag prediction has always been an extremely challenging mission for the exploration of a configuration. As for the more complex configurations, it is especially desired to the availability of a highly accurate and reliable aerodynamic numerical solution. For improving the drag prediction accuracy and promoting the aerodynamic shape designs, firstly, the characteristics of drag prediction based on far-field drag method and near-field drag method is analyzed and compared. Also, the merits and demerits of defining axial velocity defect with the current main far-field drag prediction approaches is summarized, which promotes the building of the improved method of axial velocity defect and the improved far-field drag prediction and decomposition approach. Moreover, during the establishment of the drag decomposition method, it is necessary to judge and decide on the selection of the drag region. Therefore, the discussions on the sensitivity of the relevant parameters are fulfilled. Furthermore, based on the far-field drag prediction and decomposition method constructed, the aerodynamic performance research of Common Research Model wing-body configuration is launched. The results show that it can effectively observe and analyze the changes in drag components, their impact on the total drag and the contribution percentage. Finally, combining the far-field drag prediction and decomposition method proposed in this paper with a gradient-based aerodynamic shape optimization design system, the aerodynamic shape optimization designs are studied with CRM wing-body configuration. The results can not only directly analyze the detailed change of the visualized drag region, but also can obtain the more accurate total drag and lift-to-drag ratio of the optimized configuration by removing the spurious drag.

Magnetic Dipole Moment Determination Using Near-Field Magnetic Gradient Tensor Data

Determination of the magnetic dipole moment of a spacecraft is a key issue for magnetic cleanliness and attitude control of various space scientific spacecraft. Two main methods, namely the multiple magnetic dipole modeling method and near-field analysis, have been used with good results inside a coil facility for prelaunch magnetic testing of a spacecraft. When field-canceling coil sets are unavailable, or coil feedback controls are inadequate to compensate for time-varying geomagnetic fields, determination of the magnetic signature of a spacecraft from measurements of field components is compromised. Therefore, we propose a magnetic dipole moment determination method using magnetic gradient tensor data without any coil facility, which is based on the fact that the time variation of the gradient tensor of the geomagnetic field is very small compared with that of field. We improve the near-field analysis method by expanding the magnetic gradient tensor in a series of spherical harmonics, obtain sets of near-field equations using Fourier analysis, and solve these equations to determine the dipole-moment components. The proposed tensor method can effectively suppress the interference from time variations of ambient magnetic fields. Simulations and experiments have been conducted to prove the validity, robustness, and accuracy of the tensor method.

Framework for estimation of nacelle drag on isolated aero-engines with separate jets

Typically, the evaluation of nacelle drag in preliminary design is required to find an overall optimum engine cycle and flight trajectory. This work focuses on the drag characteristics of aero-engine nacelles with separate jet exhausts. The main body of analysis comes from 3D numerical simulations. A new near-field method to compute the post-exit force of a nacelle is presented and evaluated. The effects of the engine size, Mach number, mass flow capture ratio and angle of attack are assessed. The results obtained from the numerical assessments were used to evaluate conventional reduced-order models for the estimation of nacelle drag. Within this context, the effect of the engine size is typically estimated by the scaling ratio between the maximum areas and Reynolds numbers. The effect of the angle of attack on nacelle drag is mostly a function of the nacelle geometry and angle of attack. In general, typical low-order models based on skin friction and form factor can underestimate the friction drag by up to 15% at cruise operating point. Similarly, reduced-order models based solely on Reynolds number, and Mach number can underestimate the overall nacelle drag by up to 74% for free stream Mach number larger than the drag rise Mach number.

Study on Wave Added Resistance of a Deep-V Hybrid Monohull Based on Panel Method

In this paper, a panel method based on three dimensional potential flow theory is used to study the problem of wave added resistance. The time-domain motion response of Wigely III ship in head waves is calculated by AQWA, and then the wave added resistance of ship is obtained by near-field pressure integration method. By comparing the calculated results with the experimental data in literature, it is shown that the variation trend and peak value are in good agreement, and the accuracy and efficiency meet the research requirements. Based on the above mentioned method, the wave added resistance of a deep-V hybrid monohull in head waves is studied. The motions and wave added resistances of the deep-V hybrid monohull and the deep-V original ship advancing in head waves with various forward speed and wave frequencies are calculated and analyzed. The results show that the longitudinal motion response of the deep-V hybrid monohull is effectively suppressed and the wave added resistance is obviously reduced, the new type of ship has good engineering application prospects. The present method provides an approach of satisfactory accuracy and efficiency to predict wave added resistance of ships voyaging in waves.

Near-Field Remote Sensing of Surface Velocity and River Discharge Using Radars and the Probability Concept at 10 U.S. Geological Survey Streamgages

Near-field remote sensing of surface velocity and river discharge (discharge) were measured using coherent, continuous wave Doppler and pulsed radars. Traditional streamgaging requires sensors be deployed in the water column; however, near-field remote sensing has the potential to transform streamgaging operations through non-contact methods in the U.S. Geological Survey (USGS) and other agencies around the world. To differentiate from satellite or high-altitude platforms, near-field remote sensing is conducted from fixed platforms such as bridges and cable stays. Radar gages were collocated with 10 USGS streamgages in river reaches of varying hydrologic and hydraulic characteristics, where basin size ranged from 381 to 66,200 square kilometers. Radar-derived mean-channel (mean) velocity and discharge were computed using the probability concept and were compared to conventional instantaneous measurements and time series. To test the efficacy of near-field methods, radars were deployed for extended periods of time to capture a range of hydraulic conditions and environmental factors. During the operational phase, continuous time series of surface velocity, radar-derived discharge, and stage-discharge were recorded, computed, and transmitted contemporaneously and continuously in real time every 5 to 15 min. Minimum and maximum surface velocities ranged from 0.30 to 3.84 m per second (m/s); minimum and maximum radar-derived discharges ranged from 0.17 to 4890 cubic meters per second (m3/s); and minimum and maximum stage-discharge ranged from 0.12 to 4950 m3/s. Comparisons between radar and stage-discharge time series were evaluated using goodness-of-fit statistics, which provided a measure of the utility of the probability concept to compute discharge from a singular surface velocity and cross-sectional area relative to conventional methods. Mean velocity and discharge data indicate that velocity radars are highly correlated with conventional methods and are a viable near-field remote sensing technology that can be operationalized to deliver real-time surface velocity, mean velocity, and discharge.

Measurement of optical fiber geometry parameters by gray distribution fitting with Gaussian function

The geometry parameters of optical fiber affect the optical transmission and mechanical properties, which are the important indexes to measure the quality of fiber. Near-field light distribution method is recommended in GB15972.20-2008 for the measurement of geometry parameters. In order to distinguish the boundary between fiber core and cladding, the method needs to illuminate the fiber. The end face of the fiber core is a bright spot with unclear edge, so the true edge of the core and cladding cannot be accurately judged. In this paper, the distribution of mode field in optical fiber is analyzed. Theoretically, the solution of electromagnetic vector of mode field satisfies Bessel function, but Gaussian function can also be used under approximate conditions. Therefore, Gaussian function is used to fit the distribution of the fiber core in this paper, and the real edge of the fiber core and cladding can be obtained from the Gaussian function after fitting. This method is a further improvement on the measurement method of GB15972.20-2008. The experimental results show that when the cutting effect of the fiber is not good or the imaging quality is poor, the Gaussian function method fitting with mode distribution can still ensure the repeatability of the measurement and the stability of the measured data.

Harmonic surface mapping algorithm for molecular dynamics simulations of particle systems with planar dielectric interfaces.

We have developed an accurate and efficient method for molecular dynamics simulations of charged particles confined by planar dielectric interfaces. The algorithm combines the image-charge method for near field with the harmonic surface mapping, which converts the contribution of infinite far-field charges into a finite number of charges on an auxiliary spherical surface. We approximate the electrostatic potential of far-field charges via spherical harmonic expansion and determine the coefficients by fitting the Dirichlet-to-Neumann boundary condition, which only requires the potential within the simulation cell. Instead of performing the direct evaluation of spherical harmonic series expansion, we use Green's second identity to transform the series expansion into a spherical integral, which can be accurately represented by discrete charges on the sphere. Therefore, the fast multipole method can be readily employed to sum over all charges within and on the sphere, achieving truly linear O(N) complexity. Our algorithm can be applied to a broad range of charged complex fluids under dielectric confinement.

Fast extreme ultraviolet lithography mask near-field calculation method based on machine learning.

Near-field calculation for a three-dimensional (3D) mask is a fundamental task in extreme ultraviolet (EUV) lithography simulations. This paper develops a fast 3D mask near-field calculation method based on machine learning for EUV lithography. First, the training libraries of rigorous mask near fields are built based on a set of representative mask samples and reference source points. In the testing stage, the mask under consideration is first segmented into a set of non-overlapped patches. Then the local near field of each patch is calculated based on the non-parametric regression and data fusion techniques. Finally, the entire mask near field is synthesized based on the image stitching and data fitting methods. The proposed method is shown to achieve higher accuracy compared to the traditional domain decomposition method. In addition, the computational efficiency is improved up to an order of magnitude compared to the rigorous electromagnetic field simulator.

Near-real time tsunami inundation forecast for Central America : case study of the 1992 Nicaragua tsunami earthquake

ABSTRACT A near-field tsunami inundation forecast method (NearTIF) for the Pacific coast of Central America is developed and tested on the basis of the 1992 Nicaragua tsunami earthquake case. The appropriate source model of the 1992 Nicaragua earthquake, estimated using the W-phase inversion with a depth dependent rigidity curve from a previous study, is used as a reference model to test the proposed NearTIF method. The tsunami inundation along the Pacific coast of Nicaragua is computed from the reference model of the 1992 Nicaragua earthquake. The tsunami inundation obtained using the NearTIF method matches the tsunami inundations computed from the reference model. The tsunami heights and the tsunami inundation of the 1992 Nicaragua tsunami surveyed by a previous study are roughly matched by the tsunami inundations obtained using the NearTIF method in this study. Although the computational time for the tsunami inundation from the reference source model is about 95 min, the computational time plus the database search time for the NearTIF method is approximately 2–4 min. The method presented in this study can be used as a near-real time tsunami inundation forecast method for the Pacific coast of Central America.

Effects of different methods on drying root canal by near-field microwave detection system

OBJECTIVE To set up near-field microwave detection system, to evaluate the accuracy of measuring water and to compare the effects of different methods on drying root canal. METHODS Known and quantitative distilled water in Eppendorf tube and root canal was detected by near-field microwave detection system which was set up first. The microwave reflection coefficient was recorded so as to evaluate the accuracy of the measuring water. 12 single-rooted mandibular premolar teeth with apical matureness and a curvature less than 10° were decoronated, leaving roots 14 mm in length. After instrumentation to F3, the root canals were air-dried and injected with 10 μL distilled water each. Then all the root canals were assigned to 4 groups (n=12) according to different methods on root canal drying. Near-field microwave detection system was used to detect the change of water after air-drying and root canal drying so as to evaluate the effects of different root canal drying methods: (1) negative control group, the canals were injected with 10 μL distilled water and no root canal drying method was performed; (2) paper points drying experimental group, four #60 paper points were used to blot-dry the middle and upper part of the canal, followed by #40 paper points blot-drying the apical area. The above step was repeated with the tip of paper point that appeared with no water under microscope as finished; (3) 95% (volume fraction) ethanol drying experimental group, after the distilled water was removed with paper points (similar to paper points experimental group), 10 μL 95% ethanol was injected into the canal and was left in place for 10 s, then paper points were used to dry the canal; (4) 70% (volume fraction) isopropyl alcohol drying experimental group, after the distilled water was removed with paper points (similar to paper points experimental group), 10 μL 70% isopropyl alcohol was injected into the canal and was left in place for 10 s, then paper points were used to dry the canal. The linear correlation analysis was used to test the accuracy of the measuring water by near-field microwave detection method and physical measurement. The Pearson correlation coefficient was calculated based on the data. The effects of different methods on drying root canal were analyzed by Chi square test. RESULTS The R2 for the microwave reflection coefficient and the physical measurement of the water in Eppendorf tube and root canal were 0.991 and 0.970. The microwave reflection coefficient in all the experimental groups showed significant difference (P<0.05). After drying with paper points, the residual water was the most, and the microwave reflection coefficient was the highest: 0.023. While after 70% isopropyl alcohol drying root canal, the residual water was the least with the microwave reflection coefficient 0.006, showing that the effect of drying was the best. CONCLUSION Near-field microwave detection system could detect the change of water in root canal. The effect of root canal drying by 70% isopropyl alcohol was superior to 95% ethanol and paper points.

Study on steady flow approximation in turning simulation of ship in waves

This study considers the effects of steady flow approximation in the analysis of ship maneuvering in waves. To this end, the ship motion due to waves is analyzed using the three-dimensional time-domain Rankine panel method, and the wave drift forces acting on a ship are calculated by applying the near-field method to directly integrate the pressure on the hull surface. In this seakeeping analysis, the steady flow induced by the operation velocity of the ship is approximated by a uniform flow or double-body flow. The ship maneuvering in waves not only advances forward but also drifts and rotates; hence, it can be regarded as a lifting body. Therefore, the vortex flow generated at the sharp end of the hull is also modeled and reflected in the steady-flow approximation. In order to investigate how the seakeeping performance is determined according to the approximation method, ship motions and drift forces induced by waves are computed for the ship moving forward or obliquely. Lastly, the numerical simulation for the turning test in a regular wave is performed based on the time-domain direct coupling method. Based on the accuracies of computation results compared with existing experimental data, the steady-flow induced coupling effects between seakeeping and maneuvering quantities are discussed.

Nearfield acoustic holography-based methods for far field prediction

The paper is intended to explore the possibility of using near-field acoustic holography methods for determining the far field radiation profile of a sound source. An experiment was carried out in an anechoic chamber for this purpose. First, the acoustic pressures on a plane in the near-field of a source were recorded as a profile. The measured signals were then used to reconstruct the far field profile using the said algorithms, respectively. Second, the acoustic pressures in the far field were directly measured and the results were compared with the predicted ones. Of the four methods used in the study, the one that yields the best result was the so-called “Far plane series” method, yielding 12% error upon comparison with the directly measured values. In addition to that a research on possible reduction of the microphone array size was carried out. A significant reduction of the measurement facility was realized with the use of a linear array instead of the planar array that was made possible using the studied far-field prediction algorithms.

Indoor Occupancy Awareness and Localization Using Passive Electric Field Sensing

This paper introduces sparse low-power sensor networks using passive electric potential sensors for crowd-aware smart buildings. The proposed networks can detect human presence, track their positions, and estimate room occupancy by measuring the electric field disturbances caused by human movement. In addition, the proposed passive sensing system can remotely monitor human physiological signals of nearby stationary occupants (standoff ~1.5 m) when the ambient 60-Hz fields are filtered out. Based on an experimentally calibrated source range model, we further propose an improved multiple-occupant near-field indoor localization method using a maximum likelihood algorithm combined with dividing rectangular search. The tradeoff between search efficiency and localization accuracy is also discussed. Experimental results in two different rooms for 1 week duration show the effectiveness of our proposed sensing system: human identification with an accuracy of 98.3% on six participants, occupant localization methods with room occupancy estimation accuracy of 89.03%, and average localization error less than 0.3 m. These results open up new possibilities in security, indoor navigation or positioning systems, human–machine interfaces, and tele-health applications.

Terahertz field confinement and enhancement in various sub-wavelength structures

Terahertz plasmonics is one of the fascinating research fields that includes diverse applications in nonlinear terahertz optics and nano-optics, as well as studies about strong localization and enhancement of millimeter waves. Recent advanced lithography techniques enable one to reach the confinement scale of electromagnetic waves down to subnanometer, which corresponds to wavelength/10 000 000. In particular, the strong electric-field enhancement in metal gaps can produce atomically strong field exceeding ∼10 MV/cm in a picosecond time scale. In this article, we review the strong localization and enhancement of electromagnetic waves in terahertz frequency ranges achieved by subwavelength metal structures. Based on understanding the underlying capacitive coupling and antenna effects, we focus on the field confinement and enhancement of various metal structures such as slit, slot antenna, and dipole antenna. We also give a brief introduction about near-field detection methods.

Fabrication of flexible organic electronic microcircuit pattern using near-field electrohydrodynamic direct-writing method

Inorganic materials face enormous challenges in designing and processing flexible devices that can be stretchable, crimped and folded. Organic materials have attracted wide attention because of their flexible properties and advantages in manufacturing flexible electronic devices. In this study, the flexible organic microcircuit pattern of poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) material was fabricated by using the near-field electrohydrodynamic direct -writing method, the experimental results show that the bending deformation of the flexible substrate with different curvatures has no effect on the conductivity of the microcircuit pattern deposited on the flexible substrate, which has no effect on the performance of the flexible microcircuit pattern. In order to improve the conductivity of the flexible organic electronic microcircuit, the multi-layer microcircuit pattern was fabricated by using the near-field electrohydrodynamic direct-writing method. With the increase of the number of the direct-writing micro-pattern layer, the conductivity of the microcircuit patterns sintered at 105 °C for 10 min increase from 168.32 to 313.05 S/cm. Atomic force microscope was used to observe the morphology of the direct-writing microcircuit patterns. With the increase of the layer number of the microcircuit pattern, the internal density of the microcircuit pattern increases, and the microcircuit-pattern morphology becomes smoother. The experimental results show that the multi-layer direct- writing method can effectively improve the conductivity of the flexible organic electronic microcircuit pattern. This study provides a new method to fabricate the flexible organic microcircuit pattern with high conductivity by a non-contact and low-cost mode.

Peculiarities of the Nonlinear Response of a Superconductor–Normal Metal Structure with a Large Ratio of Resistivities

Using the near-field microwave microscopy method, the temperature dependence of third harmonics power P3ω(T) of the MoN/Al superconductor–normal metal structures with the proximity effect is studied. The presence of a secondary (low-temperature) maximum and zeroings is detected in the P3ω(T) dependence of the MoN/Al structure, which disappear upon applying a weak magnetic field perpendicular to the plane of the structure.

Characterization of thin-film optical properties by THz near-field imaging method

We present a new method to characterize thin-film electro-optic materials. The method is based on resolving the electric and/or magnetic field distributions in the near-field region of a split-ring resonator (SRR) designed for the terahertz (THz) frequency range. We experimentally validate our simulations by THz near-field imaging of SRRs directly patterned in contact with a thin-film lithium niobate crystal as a sensor. Furthermore, we analytically study the effect of the different applied electric field polarizations and calculate the sensitivity of the sensor via various polarizations of probe beams.