Near-field Sources Research Articles

Gold Nanoparticle 2D-Arrays Chemically Immobilized as Large-Area Near-Field Light Source

Near-field light sources made it possible to go beyond the diffraction limit. Innovative nanophotonics offers potential throughout the field of photonics, including industrial applications such as high-efficiency solar cells. These applications require a novel technique for generating not a nanometer-scale point but a large-area (mm2-m2) near-field light source. Here, we report the first large-area near-field light source that is densely constructed of uniform-size gold nanoparticles (AuNPs) two-dimensionally arrayed with regular interparticle gaps, which eventually has tunable localized surface plasmon resonance (LSPR) bands (600-1100 nm). The light source is attached by means of chemical coating on 1×1-cm2 substrates, but there is no limitation on the size.

Combining near‐ and far‐field exposure for an organ‐specific and whole‐body RF‐EMF proxy for epidemiological research: A reference case

A framework for the combination of near-field (NF) and far-field (FF) radio frequency electromagnetic exposure sources to the average organ and whole-body specific absorption rates (SARs) is presented. As a reference case, values based on numerically derived SARs for whole-body and individual organs and tissues are combined with realistic exposure data, which have been collected using personal exposure meters during the Swiss Qualifex study. The framework presented can be applied to any study region where exposure data is collected by appropriate measurement equipment. Based on results derived from the data for the region of Basel, Switzerland, the relative importance of NF and FF sources to the personal exposure is examined for three different study groups. The results show that a 24-h whole-body averaged exposure of a typical mobile phone user is dominated by the use of his or her own mobile phone when a Global System for Mobile Communications (GSM) 900 or GSM 1800 phone is used. If only Universal Mobile Telecommunications System (UMTS) phones are used, the user would experience a lower exposure level on average caused by the lower average output power of UMTS phones. Data presented clearly indicate the necessity of collecting band-selective exposure data in epidemiological studies related to electromagnetic fields.

Efficient Method of Passive Localization for Mixed Far-Field and Near-Field Sources

An effective second-order statistics (SOS)-based algorithm is addressed for scenarios where both far-field and near-field narrowband sources may exist simultaneously. After estimating the direction-of-arrivals (DOAs) and powers of far-field signals, the related far-field components can be eliminated from the signal subspace. Then, based on the symmetric property of the uniform linear array geometry, a near-field estimator without two-dimensional search or parameter pairing is performed. Compared to the previous SOS based method, the resultant algorithm can provide an improved estimation accuracy, as well as realize a more reasonable classification of the signal types. Simulation results are carried out to demonstrate the performance of the proposed algorithm.

Passive Localization of 3D Near-Field Cyclostationary Sources Using Parallel Factor Analysis

By exploiting favorable characteristics of a uniform cross-array, a passive localization algorithm of narrowband cyclostationary sources in the spherical coordinates (azimuth, elevation, and range) is proposed. Firstly, we construct a parallel factor (PARAFAC) analysis model by computing the third-order cyclic moment matrices of the properly chosen sensor outputs. Then, we analyze the uniqueness of the constructed model and obtain three-dimensional (3D) near-field parameters via trilinear alternating least squares regression (TALS). The investigated algorithm is well suitable for the localization of the near-field cyclostationary sources. In addition, it avoids the multidimensional search and pairing parameters. Results of computer simulations are carried out to confirm the satisfactory performance of the proposed method.

Platform for dynamic virtual auditory environment real-time rendering system

This paper reports the recent works and progress on a PC and C++ language-based virtual auditory environment (VAE) system platform. By tracing the temporary location and orientation of listener’s head and dynamically simulating the acoustic propagation from sound source to two ears, the system is capable of recreating free-field virtual sources at various directions and distances as well as auditory perception in reflective environment via headphone presentation. Schemes for improving VAE performance, including PCA-based (principal components analysis) near-field virtual source synthesis, simulating six degrees of freedom of head movement, are proposed. Especially, the PCA-based scheme greatly reduces the computational cost of multiple virtual sources synthesis. Test demonstrates that the system exhibits improved performances as compared with some existing systems. It is able to simultaneously render up to 280 virtual sources using conventional scheme, and 4500 virtual sources using the PCA-based scheme. A set of psychoacoustic experiments also validate the performance of the system, and at the same time, provide some preliminary results on the research of binaural hearing. The functions of the VAE system is being extended and the system serves as a flexible and powerful platform for future binaural hearing researches and virtual reality applications.

Direction-of-Arrival Estimation for Near-Field Sources with Multiple Symmetric Subarrays

Direction-of-Arrival Estimation for Near-Field Sources with Multiple Symmetric Subarrays

Near-field time-frequency localization method using sparse representation

This paper presents a novel near-field source localization method based on the time-frequency sparse model. Firstly, the method converts the time domain data of array output into time-frequency domain by time-frequency transform; then constructs sparse localization model by utilizing the specially selected time-frequency points, and finally the greedy algorithms are chosen to solve the sparse problem to localize the source. When the coherent sources exist, we propose an additional iterative selection procedure to improve the estimation performance. The proposed method is suitable for uncorrelated and coherent sources, moreover, the improved estimation accuracy and the robustness to low signal to noise ratio (SNR) are achieved. Simulations results verify the efficiency of the proposed algorithm.

Line-source excitation of realistic conformal metasurface cloaks

Following our recently introduced analytical tools to model and design conformal mantle cloaks based on metasurfaces [Padooru et al., J. Appl. Phys. 112, 034907 (2012)], we investigate their performance and physical properties when excited by an electric line source placed in their close proximity. We consider metasurfaces formed by 2-D arrays of slotted (meshes and Jerusalem cross slots) and printed (patches and Jerusalem crosses) sub-wavelength elements. The electromagnetic scattering analysis is carried out using a rigorous analytical model, which utilizes the two-sided impedance boundary conditions at the interface of the sub-wavelength elements. It is shown that the homogenized grid-impedance expressions, originally derived for planar arrays of sub-wavelength elements and plane-wave excitation, may be successfully used to model and tailor the surface reactance of cylindrical conformal mantle cloaks illuminated by near-field sources. Our closed-form analytical results are in good agreement with full-wave numerical simulations, up to sub-wavelength distances from the metasurface, confirming that mantle cloaks may be very effective to suppress the scattering of moderately sized objects, independent of the type of excitation and point of observation. We also discuss the dual functionality of these metasurfaces to boost radiation efficiency and directivity from confined near-field sources.

Bearing and Range Estimation for Multiple Near-Field Sources based on Ambiguity Function

Abstract AD-MUSIC is introduced to near-field to investigate the bearing and range estimation for the mixed source localization of sinusoidal signal and LFM signal. Firstly, a near-field two-dimensional MUSIC method based on ambiguity function distribution is put forward. Further, a novel Root-MUSIC method which constructs two ambiguity function distribution matrices is proposed for near-field source localization. The simulation results show that the two ambiguity function based methods have higher accuracy and resolution for the position estimation of the mixed-source signals compared with WVD based methods and conventional algorithms, even when the signal-to-noise ratio is low.

A Decoupled Approach for Near-Field Source Localization Using a Single Acoustic Vector Sensor

This paper considers the problem of three-dimensional (3-D, azimuth, elevation, and range) localization of a single source in the near-field using a single acoustic vector sensor (AVS). The existing multiple signal classification (MUSIC) or maximum likelihood estimation (MLE) methods, which require a 3-D search over the location parameter space, are computationally very expensive. A computationally simple method previously developed by Wu and Wong (IEEE Trans. Aerosp. Electron. Syst. 48(1):159–169, 2012), which we refer to as Eigen-value decomposition and Received Signal strength Indicator-based method (Eigen-RSSI), was able to estimate 3-D location parameters of a single source efficiently. However, it can only be applied to an extended AVS which consists of a pressure sensor separated from the velocity sensors by a certain distance. In this paper, we propose a uni-AVS MUSIC (U-MUSIC) approach for 3-D location parameter estimation based on a compact AVS structure. We decouple the 3-D localization problem into step-by-step estimation of azimuth, elevation, and range and derive closed-form solutions for these parameter estimates by which a complex 3-D search for the parameters can be avoided. We show that the proposed approach outperforms the existing Eigen-RSSI method when the sensor system is required to be mounted in a confined space.

Numerical Study of Mach Number and Thermal Effects on Sound Radiation by a Mixing Layer

Mach number and thermal effects on the mechanisms of sound generation and propagation are investigated in spatially evolving two-dimensional isothermal and non-isothermal mixing layers at Mach number ranging from 0.2 to 0.4 and Reynolds number of 400. A characteristic-based formulation is used to solve by direct numerical simulation the compressible Navier-Stokes equations using high-order schemes. The radiated sound is directly computed in a domain that includes both the near-field aerodynamic source region and the far-field sound propagation. In the isothermal mixing layer, Mach number effects may be identified in the acoustic field through an increase of the directivity associated with the non-compactness of the acoustic sources. Baroclinic instability effects may be recognized in the non-isothermal mixing layer, as the presence of counter-rotating vorticity layers, the resulting acoustic sources being found less efficient. An analysis based on the acoustic analogy shows that the directivity increase with the Mach number can be associated with the emergence of density fluctuations of weak amplitude but very efficient in terms of noise generation at shallow angle. This influence, combined with convection and refraction effects, is found to shape the acoustic wavefront pattern depending on the Mach number.

Properties of the Far-Field Pressure Signatures of Individual Jet Noise Sources

The detection of intermittent near-field noise sources is achieved by continuous wavelet transform of far-field acoustic data. The similarities between signals from three far-field microphones in the annular cone of acoustic radiation from coherent sources in a Ma = 0.6 cold jet are used to identify some of the loudest events. Cross-correlation of relevant band-passed excerpts identifies the most reliable matches, which occur at the rate of one every 20 dimensionless time units on average, and are intermittent in both time and frequency with no obvious pattern. Processing our database produced a catalog of over 9500 individual events with quantitative properties including the magnitude, frequency and time of detection at each microphone. The differences in detection times (lags) are distributed smoothly around the peak of cross-correlations for the raw data. We show how source magnitude and frequency depends on lags, and relate the lags to their relative source location.

Modeling the generation of infrasound from earthquakes

Earthquakes can generate complex seismo-acoustic wavefields, consisting of seismic waves, epicenter-coupled infrasound, and secondary infrasound. We report on the development of a numerical seismo-acoustic model for the generation of infrasound from earthquakes. We model the generation of seismic waves using a 3D finite difference algorithm that accounts for the earthquake moment tensor, source time function, depth, and local geology. The resultant acceleration-time histories (on a 2D grid at the surface) provide the initial conditions for modeling the near-field infrasonic pressure wave using the Rayleigh integral. Finally, we propagate the near-field source pressure through the Ground-to-Space atmospheric model using a time-domain parabolic equation technique. The modeling is applied to an earthquake of MW 4.6, that occurred on January 3, 2011 in Circleville, Utah; the ensuing predictions are in good agreement with observations made at the Utah network of infrasonic arrays, which are unique and indicate that the signals recorded at 6 arrays are from the epicentral region. These results suggest that measured infrasound from the Circleville earthquake is consistent with the generation of infrasound from body waves in the epicentral region.

Dark-field hyperlens exploiting a planar fan of tips

Metallo-dielectric superlenses transfer subwavelength-scale information without magnification. The so-called hyperlenses additionally magnify, transferring images into traditional far-field optics. We target hyperlenses based on the “canalization” phenomenon in an array of wires, modified to form an open fan, also called “endoscope.” We use an integrated optics design with silicon wires, fed for instance by grating couplers, accessing gold wire fans. This alleviates the need to care for wire length. We explore a regime where we do not only image a near-field source, but where we image illuminated nano-objects, as done in microscopy, light being fed by a second fan before the object plane. In order to counter the low contrast from illuminated nano-objects, we propose here a dark-field hyperlens concept: We show that the illumination fan can be fed so as to get a dark output for a “void” object field, as occurs in the eponym microscopy method. We obtain, at a wavelength as large as 1200 nm, a well-resolved imaging capability for a scene of two 30 nm silicon particles.

Cramér–Rao bounds of direction-of-arrival and distance estimation of a near-field incident source for an acoustic vector sensor: Gaussian source and polynomial-phase source

The near-field array manifold of the acoustic vector sensor was recently derived by Wu et al [see `the acoustic vector sensor`s near-field array manifold` in IEEE Trans. Signal Process. ]. The CramerRao bounds (CRBs) of direction-of-arrival and distance estimation with a single pure tone were also derived therein. This study aims to investigate the estimation accuracy of the acoustic vector sensor in the near-field, through the CRBs analysis, by modelling the incident source as: (i) a Gaussian distributed random sequence, and (ii) a polynomial-phase signal. All the four different compositions of the acoustic vector sensor in the near-field are considered, and their closed-form CRBs are derived.

Mixed Sources Localization Based on Sparse Signal Reconstruction

In this letter, a novel mixed sources localization method based on sparse signal reconstruction is presented, which can efficiently estimate direction-of-arrival (DOA) and range parameters of near-field and far-field sources. By constructing the cumulant domain data of array which is only related to DOA parameters of mixed sources, we obtain DOA estimation of all sources using the weighted l1-norm minimization. And then, a mixed overcomplete matrix on the basis of DOA estimation is introduced in the sparse signal representation framework to estimate range parameters and distinguish far-field sources from mixed sources. Compared with the two-stage MUSIC algorithm, the proposed method can provide improved accuracy and resolve closely spaced sources. The simulation results show the effectiveness of our method.

Gold Nanoparticle 2D-Arrays Chemically Immobilized as Large-Area Near-Field Light Source

not Available.

Efficient Application of MUSIC Algorithm Under the Coexistence of Far-Field and Near-Field Sources

This correspondence is concerned with source localization and classification for scenarios where both the far-field and near-field narrowband sources may coexist. We propose an efficient MUSIC-based solution that requires neither a multidimensional search nor high-order statistics (HOS). We also derive the stochastic Cramer-Rao bound (CRB) for the problem under consideration. The performance of the proposed method is compared with an existing method and with the CRB.

Lessons learned for implementing near-field active control systems to achieve global control of fan noise

Work has been ongoing for a number of years to develop compact active noise control systems that can effectively achieve global attenuation of radiated fan noise associated with information technology (IT) equipment. Both axial and centrifugal fans are used in IT applications, and both types of fans have been studied. An approach has been developed that can guide the user to properly implement near-field sources and sensors to achieve significant global attenuation of the fan noise. These concepts have been investigated experimentally in numerous configurations to verify the effectiveness of the approach. Both narrowband and broadband noise components have been targeted, and limitations on the attenuation that can be achieved have been established. The sensitivity of various configurations has also been studied, and it has been found that some implementations may be able to achieve greater attenuation, but are also much more sensitive to placement errors of the sources and sensors. This paper will overview the research to date and provide an overview of lessons that have been learned for effective implementation of near-field control techniques in order to achieve global attenuation.

A seismoacoustic study of the 2011 January 3 Circleville earthquake

SUMMARY Wereportonauniquesetofinfrasoundobservationsfromasingleearthquake,the2011January 3Circlevilleearthquake(Mw 4.7,depthof8km),whichwasrecordedbynineinfrasoundarrays inUtah.Basedonananalysisofthesignalarrivaltimesandbackazimuthsateacharray,wefind thattheinfrasoundarrivalsatsixarrayscanbeassociatedtothesamesourceandthatthesource location is consistent with the earthquake epicentre. Results of propagation modelling indicate that the lack of associated arrivals at the remaining three arrays is due to path effects. Based on these findings we form the working hypothesis that the infrasound is generated by body waves causing the epicentral region to pump the atmosphere, akin to a baffled piston. To test this hypothesis, we have developed a numerical seismoacoustic model to simulate the generation of epicentral infrasound from earthquakes. We model the generation of seismic waves using a 3-D finite difference algorithm that accounts for the earthquake moment tensor, source time function, depth and local geology. The resultant acceleration–time histories on a 2-D grid at the surface then provide the initial conditions for modelling the near-field infrasonic pressure wave using the Rayleigh integral. Finally, we propagate the near-field source pressure through the Ground-to-Space atmospheric model using a time-domain Parabolic Equation technique. By comparing the resultant predictions with the six epicentral infrasound observations from the 2011 January 3, Circleville earthquake, we show that the observations agree well with our predictions. The predicted and observed amplitudes are within a factor of 2 (on average, the synthetic amplitudes are a factor of 1.6 larger than the observed amplitudes). In addition, arrivalsarepredictedatallsixarrayswheresignalsareobserved,andimportantlynotpredicted at the remaining three arrays. Durations are typically predicted to within a factor of 2, and in some cases much better. These results suggest that measured infrasound from the Circleville earthquake is consistent with the generation of infrasound from body waves in the epicentral region.