near-to-far field transformation model

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Near-field measurement of continuously modulated fields employing the time-harmonic near- to far-field transformation

Near-field measurement of continuously modulated fields employing the time-harmonic near- to far-field transformation

equivalent sources, e.g., equivalent surface current densities on a surface enclosing the AUT, plane wave spectra or spher- ical multipoles, are to be retrieved. Solving this inverse prob- lem, an equivalent source model is attained that reconstructs the measured NF and from which the FF is calculated. State- of-the-art algorithms for time-harmonic signals work in the spectral domain, i.e., for single-frequency signals. For modu- lated signals, the single-frequency assumption does not hold any more. Even if there are NFFFT algorithms that work in the time domain and can deal with modulated fields (Oet- ting and Klinkenbusch, 2005), most NFFFTs deal with time- harmonic fields and work in the frequency domain. Further, frequency domain NFFFTs are usually faster and more effi- cient than their time-domain counterparts. To overcome this problem, we present two methods to measure or process the time-varying electromagnetic fields in a way that they can be used in a time-harmonic NFFFT algorithm. Still, the applica- tion we have in mind are UAV-based in-situ measurements of modulated signals. Worth mentioning is a certain drawback of UAVs which are normally not able to hover at a specific position for a longer time. This leads to errors due to some uncertainty in the position of the NF measurements which depends on the measurement time. Therefore, the measure- ment time must be kept as short as possible in UAV-based measurement setups.
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NUFFT-Accelerated Plane-Polar (Also Phaseless) Near-Field/Far-Field Transformation

NUFFT-Accelerated Plane-Polar (Also Phaseless) Near-Field/Far-Field Transformation

The results regard a horn antenna (NARDA model No. 639), having an aperture of 57 mm × 43 mm, working in the Ku band, and characterized at 15 GHz from measurements performed on a planar scanning surface set at 6.5λ for the complex case and on two planar scanning surfaces set at 6.5λ and 14λ for the phaseless case. A domain D with radius equal to 15λ has been chosen in both the cases.

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Far Field Pattern Reconstruction from Positioning Errors Affected Near Field Data Acquired via Helicoidal Scanning

Far Field Pattern Reconstruction from Positioning Errors Affected Near Field Data Acquired via Helicoidal Scanning

half-spheres to model an electrically long antenna has been here proposed. In particular, the helicoidal NF data at the points fixed by the sampling representation are efficiently reconstructed from the acquired irregularly spaced ones, whose positions are known. Once the heli- coidal data have been retrieved, those needed by a clas- sical NF-FF transformation with cylindrical scanning are efficiently evaluated via the two-dimensional OSI algo- rithm. The effectiveness of the approach has been as- sessed both numerically and experimentally.

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Near-Field-Far-Field Transformation Technique with Helicoidal Scanning for Elongated Antennas

Near-Field-Far-Field Transformation Technique with Helicoidal Scanning for Elongated Antennas

Abstract—A fast and accurate near-field — far-field transformation technique with helicoidal scanning is proposed in this paper. It is tailored for elongated antennas, since a prolate ellipsoid instead of a sphere is considered as surface enclosing the antenna under test. Such an ellipsoidal modelling allows one to consider measurement cylinders with a diameter smaller than the antenna height, thus reducing the error related to the truncation of the scanning surface. Moreover, it is quite general, containing the spherical modelling as particular case, and allows a significant reduction of the number of the required near- field data when dealing with elongated antennas. Numerical tests are reported for demonstrating the accuracy of the far-field reconstruction process and its stability with respect to random errors affecting the data.
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Performance of Intez Tank Under Near Fault And Far Field Earthquake Motion

Performance of Intez Tank Under Near Fault And Far Field Earthquake Motion

Tavakoli. H. R, Naeej. M, and Salari. A (2011) [7]Their objective for study was to investigate the effect of near fault and far fault earthquake motions on the response of reinforced concrete structures considering soilstructureinteraction. For this purpose, a series of linear time-history analysis wascarried out for three example buildings.For all buildings time-history analysis were performed under 3 example earthquake motions: Tabbas, Kobe and Loma Prieta. The main evaluated parameters were period of structure, base shear.

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Near  and far field aerodynamics in insect hovering flight: an integrated computational study

Near and far field aerodynamics in insect hovering flight: an integrated computational study

We present the first integrative computational fluid dynamics (CFD) study of near- and far-field aerodynamics in insect hovering flight using a biology-inspired, dynamic flight simulator. This simulator, which has been built to encompass multiple mechanisms and principles related to insect flight, is capable of ʻflyingʼ an insect on the basis of realistic wing–body morphologies and kinematics. Our CFD study integrates near- and far-field wake dynamics and shows the detailed three-dimensional (3D) near- and far-field vortex flows: a horseshoe-shaped vortex is generated and wraps around the wing in the early down- and upstroke; subsequently, the horseshoe-shaped vortex grows into a doughnut-shaped vortex ring, with an intense jet-stream present in its core, forming the downwash; and eventually, the doughnut-shaped vortex rings of the wing pair break up into two circular vortex rings in the wake. The computed aerodynamic forces show reasonable agreement with experimental results in terms of both the mean force (vertical, horizontal and sideslip forces) and the time course over one stroke cycle (lift and drag forces). A large amount of lift force (approximately 62% of total lift force generated over a full wingbeat cycle) is generated during the upstroke, most likely due to the presence of intensive and stable, leading-edge vortices (LEVs) and wing tip vortices (TVs); and correspondingly, a much stronger downwash is observed compared to the downstroke. We also estimated hovering energetics based on the computed aerodynamic and inertial torques, and powers.
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Efficient Localization Algorithm of Mixed Far-Field and Near-Field Sources Using Uniform Circular Array

Efficient Localization Algorithm of Mixed Far-Field and Near-Field Sources Using Uniform Circular Array

There has been considerable interest in the passive sources localization with an array of spatially separated sensors, which has many important application areas such as radar, guidance systems and sonar [1]. Various high performance algorithms such as MUSIC [2] and ESPRIT [3] have been used to deal with the DOA estimation of the FFSs. However, the both DOA and range of the source that is localized at the Fresnel region of the array aperture need be considered in some practical applications like lightening localization and speaker guidance systems [4], each source may be in the near field or the far field of the sensor position. Hence, when the classical algorithms may fail in such scenarios, several solutions are available to process the mixed sources localization. Using two high dimensional cumulant matrices of the sensor outputs, Liang and Liu [4] provided a two-stage MUSIC algorithm to solve the mix sources localization problem of the high resolution, which has high computational complexity and cannot classify the FFSs and NFSs in similar DOA. Wang et al. [5] used the mixed-order MUSIC algorithm to decline the computational complexity and improved the accuracy. Jiang et al. [6] gave an algorithm that estimates DOAs of all FFSs and NFSs by ESPRIT, distinguishes the FFSs and NFSs and estimates the range of NFSs by MUSIC. Liu and Sun [7] used the spatial differencing technique to classify the NFSs from the mixed sources after the estimations of FFSs, which has the higher accuracy, classify the mixed signals successfully and lower computational load. The algorithm in [8] built the optimization problem to get the estimation function used to obtain the DOA and estimated the range of the source by the minimum variance distortionless response (MVDR). Yet, the aforementioned high resolution algorithms are all aimed at two dimensional localization (elevation DOA and range). For some three dimensional problems (azimuth angle, elevation angle and range), they may fail in mixed sources localization so that we need to have an increase for the performances.
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Fast near-field far-field transformation for phaseless and irregular antenna measurement data

Fast near-field far-field transformation for phaseless and irregular antenna measurement data

mal solution. If an initial solution candidate can be provided which lies in the attraction region of the desired solution, the iterative algorithm computes the correct result. For exam- ple, consider a scenario where the measurement equipment provides accurate amplitude information but the phase infor- mation is erroneous due to small phase uncertainties. In this case, an approximate solution can be computed by the linear transformation using the inaccurate phase information and subsequently could be used to initialize the nonlinear trans- formation. The correct result will be obtained if the approx- imate solution belongs to the attraction region of the desired result which is the case if the phase errors are small enough. In order to achieve convergence to the globally optimal solu- tion, a global optimization scheme is required.
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Jrdf Algorithm for Joint Range-DOA-Frequency Estimation of Mixed Near-Field and Far-Field Sources

Jrdf Algorithm for Joint Range-DOA-Frequency Estimation of Mixed Near-Field and Far-Field Sources

Source localization from noisy observations is one of the fundamental problems in array signal processing, such as sonar, radar, seismic exploration system and microphone arrays [1]. Therefore, it has received a significant amount of attention, and a number of algorithms have been developed to deal with far- field sources (FFSs) [2–5] or near-field sources (NFSs) [6–9]. For FFSs (beyond Fresnel zone) scenario, the wavefronts are usually approximated as planar, thus only DOA parameter needs to be estimated when the carrier frequency is known. Otherwise, for the NFSs (in Fresnel zone), as the wavefronts are spherical, both DOA and range parameters should be estimated when the carrier frequency is known as a priori. In some practical applications, the signals received at an array may be the mixture of NFSs and FFSs, for example, when using microphone arrays to localize speakers’ localizations, each speaker may be in near-field (NF) or far-field (FF) since speakers’ positions keep changing. So the pure NF source localization and pure FF source localization algorithm may encounter problems in localizing mixed NFSs and FFSs.
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Electronic and Satellite Navigation

Electronic and Satellite Navigation

Ez plane of far field,of radiation pattern The plane wave excitation is observed in magnetic field from the near field of matlab simulation of the electronic and satellite na[r]

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Reconstruction of radiating sources

Reconstruction of radiating sources

relationship between the aperture distribution of an aI1.tenna and its far-field radiation pattern, they are not directly applicable to near-field pattern measurements... It is shown.[r]

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Identification of Near-Field and Far-Field Using Confocal Microscopy Setup for Optical Sensing Applications

Identification of Near-Field and Far-Field Using Confocal Microscopy Setup for Optical Sensing Applications

Besides the application of optical fibre probe, the near- field can also be created by employing a confocal microscopy setup which is less costly and much simpler than probe’s fabrication. Confocal microscopy is a technique that is applied in the scientific discipline by irradiates the targeted sample with focused light originating from a source and directs the response from the sample onto a pinhole (Novotny & Hecht 2006). Light from a laser source is spatially filtered by sending it through an aperture. After propagating through the aperture, light is collimated by a lens, as shown in Figure 1. Size of aperture plays a significant role in yielding the near-field or far-field. The existence of near-field indicates the presence of evanescent waves which is one of the important criteria in optical sensing (Eleftheriades et al., 2008; Maliakal et al., 2016; Ton et al., 2015). As the targeted sample or analyte is located in the near-field region, the detector will detect the change in refractive index sensing properties of the optical system.
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Exploring surface wave interaction with angled defects in the near and far field

Exploring surface wave interaction with angled defects in the near and far field

We first explore the effect of crack angle and length on Rayleigh reflection and transmission coefficients, using both model and experimental data. OP reflection coefficients were calculated from A-Scan data as the amplitude ratio of reflected Rayleigh over incident Rayleigh wave. Figure 2(a) shows the model (line and open squares) and experimental (filled squares) reflection coefficients for a crack length to central wavelength ratio of d/λ = 1.11, where λ is the central wavelength of the broadband incident pulse, showing very good agreement. The same figure also shows reflection coefficients for smaller d/λ of 0.55, 0.28 and 0.14, showing a progressive decrease of amplitude, as expected when considering the broadband nature of the pulse and the fact that the majority of the energy in the Rayleigh wave is contained within one wavelength of the sample surface. Corresponding calculations were performed for the transmission coefficients using model and experimental data, with the coefficient also measured more than three wavelengths past the crack opening. Figure 2(b) shows the model and experimental transmission coefficients for d/λ = 1.11, showing very good agreement.
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Multilayer Dielectric Resonator Antenna Transmitarray for Near-Field and Far-Field Fixed RFID Reader

Multilayer Dielectric Resonator Antenna Transmitarray for Near-Field and Far-Field Fixed RFID Reader

Recently, a reader phased array antenna exhibiting a near-field (NF) focused radiation, which is able to maximize the field amplitude in a size-limited spot within the antenna near-field region, while not affecting the field strength far from the antenna (far-field region) is introduced [7]. NF-focusing radiation is used in RFID reader to increase the field incident on the tags at allowed effective isotropic radiated power. Phased array antennas suffer from complicated beam- forming networks, complex feeding circuit and relatively high power loss. Phased array problems are overcome using reflectarray introduced in [7, 8]. Some of the phased array limitations have been overcome using reflectarray in [9, 10] for RFID reader. The advantages of reflectarray are easy to fabricate, low profile and has no insertion loss. But, the reflectarray requires an offset feed to avoid blockage losses. This offset feed increases the angle of incidence to the individual elements, thus reducing the reflectarray gain and complicating the design [11, 12]. Transmitarray is similar to the reflectarray, but the incident wave is not reflected, but passes through the antenna structure as it is collimated into a plane wave [13, 14]. Thus the feed horn is positioned directly in front of the array, cannot interfere with the transmitted and received waves, and there is no blockage loss. Dielectric resonator antennas (DRA) have many applications in wireless communication systems over a wide frequency range from 1.3– 40 GHz. DRAs offer many advantages such as low profile, low cost, ease of excitation and high radiation efficiency [15]. The DRA have been applied in RFID applications at 5.8 GHz for portable reader [3] and fixed reader [7]. The DRA offer wide bandwidth with reduced size compared with conventional printed antennas.
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Cosmic Wireless Power Transfer System and the Equation for Everything E=mc2=vc2/60=a3/T=G(M1+ M2)/4π2=(KE+PE)/1 0E15=Q=PA/F=λ/hc=1/2q=VI=1/2LI2=1/2CV=I2R=…

Cosmic Wireless Power Transfer System and the Equation for Everything E=mc2=vc2/60=a3/T=G(M1+ M2)/4π2=(KE+PE)/1 0E15=Q=PA/F=λ/hc=1/2q=VI=1/2LI2=1/2CV=I2R=…

By representing the Earth as a rotating spherical antenna several historic and scientific breakthroughs are achieved. Visualizing the Sun as a transmitter and the planets as receivers the solar system can be represented as a long wave ra- dio system operating at Tremendously Low Frequency (TLF). Results again confirm that the “near-field” is Tesla’s “ dynamic gravity ”, better known to en- gineers as dynamic braking or to physicists as centripetal acceleration, or simply (g). Timewave theory is invented, and the relationship of reflected timewaves and time travel explored. A new law of the Sun is proposed as well as the merging of Einstein’s equation with acoustics and cosmic superstring theory. A new law of cosmic efficiency is also proposed that equates vibratory force and pressure with volume acceleration of the solar system. Lorentz force is broken down into centripetal and gravitational waves. Ten-dimensional cosmic superstring theory is espoused versus the aging three-dimensional Maxwellian model. Spherical antenna patterns for planets are presented and flux transfer frequency is calculated using distance to planets as wavelengths. The galactic grid operates at a Schumann Resonance of 7.83 Hz, which is de- rived from the science of dark energy and dark matter. The Sun and the pla- nets are tuned to transmit and receive electrical power like resonating Tesla coils. The Earth’s stator winding has been modeled as a toroid tesla coil and the armature as a spherical armature. The equation for everything is born. How to cite this paper: Poole, G. (2018)
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Influence of Passive Isolator Parameters on Seismic Response Control of Multi-Span Bridges

Influence of Passive Isolator Parameters on Seismic Response Control of Multi-Span Bridges

In the present study a three span continuous bridge is selected from the literature [18] and a lumped mass model of the bridge is numerically modeled using Matlab. The properties of the three-span bridge taken from Ref. [18] are: deck mass = 771.12×10 3 kg; mass of each pier = 39.26 × 10 3 kg; moment of inertia of piers = 0.64 m 4 ; Young’s modules of elasticity = 20.67 × 10 9 (N/m 2 ); pier height = 8 m; and total length of bridge = 90 m. These properties correspond to the bridge studied by Wang et al [18] using the sliding isolation system. The numerical modeling of the isolated bridge is done by considering the lumped mass model and the performance of the bridge is studied by subjecting it to different near-field and far-field earthquake ground motions.
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Anthropogenic noise and the bioacoustics of terrestrial invertebrates

Anthropogenic noise and the bioacoustics of terrestrial invertebrates

First, near-field communication may take place at much longer distances than once suspected. Previous physical modeling and measurements suggested that near-field communication could only occur across small distances (1 – 70 cm), such as when animals are flying next to each other in a swarm (Aldersley et al., 2017) or interacting at close distances (Tauber and Eberl, 2003; Santer and Hebets, 2008). However, Shamble et al. (2016) demonstrated with behavioral and physiological data that jumping spiders can detect acoustic energy at distances of at least 3 m using near-field receptors. Similarly, Menda et al. (2019) demonstrated that mosquitoes can detect sound up to 10 m away using their antennae. Furthermore, Zhou and Miles (2017) presented models showing that small fibers (>1 μ m), such as those used as near-field receptors, move with the surrounding medium. This scenario suggests that thin hairs will move in response to a large range of stimuli, even those produced at long distances. Additionally, some invertebrates, such as mosquitoes and flies, employ near-field receptor organs that actively amplify quiet signals and provide directional sensitivity (Göpfert and Robert, 2001; Gopfert et al., 2005; Morley et al., 2018). Together, these pieces of evidence extend the effective range of anthropogenic near-field noise to at least 10 m and potentially much further.
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An Analytic Expression for Near-Field Angular Glint Prediction of Radar Sensor Using Far-Field Scattering Centers Models

An Analytic Expression for Near-Field Angular Glint Prediction of Radar Sensor Using Far-Field Scattering Centers Models

In this paper, we focus on the calculation of angle glint at near field. Based on the phase gradient method, we derive the exact expression of angle glint, which is applicable for the far-field angle glint. Theoretical analysis shows that the angle glint expression in [1] is just the far-field approximation of the derived expression under specified polarization. Combined with the terminal guidance, we demonstrate that in the range of considered distance, the amplitude impact on the phase gradient can be ignored, and gives the responding approximate expression. Eventually, we analyze the effect of each factor on angle glint by simulation, and the approximate error between the simplified and exact expressions. The relative results obtained in this study could be adopted as some theoretical basis for the estimation and investigation of the near-field angle glint.
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Small Electrical Loop Analytical Calculation

Small Electrical Loop Analytical Calculation

Abstract The article deals with vector potential calculation of the small electrical loop. The method of integral analytical expression solves the problem in the details. This type of integral is the same as in the theory of antenna. This method is simpler than standard method and it makes some connection between radiation theories of point source at the far field and loop at the near field.

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Comparison of a coupled near- and far-wake model with a free-wake vortex code

Comparison of a coupled near- and far-wake model with a free-wake vortex code

Abstract. This paper presents the integration of a near-wake model for trailing vorticity, which is based on a prescribed-wake lifting-line model proposed by Beddoes (1987), with a blade element momentum (BEM)- based far-wake model and a 2-D shed vorticity model. The resulting coupled aerodynamics model is validated against lifting-surface computations performed using a free-wake panel code. The focus of the description of the aerodynamics model is on the numerical stability, the computation speed and the accuracy of unsteady simula- tions. To stabilize the near-wake model, it has to be iterated to convergence, using a relaxation factor that has to be updated during the computation. Further, the effect of simplifying the exponential function approximation of the near-wake model to increase the computation speed is investigated in this work. A modification of the dynamic inflow weighting factors of the far-wake model is presented that ensures good induction modeling at slow timescales. Finally, the unsteady airfoil aerodynamics model is extended to provide the unsteady bound circulation for the near-wake model and to improve the modeling of the unsteady behavior of cambered air- foils. The model comparison with results from a free-wake panel code and a BEM model is centered around the NREL 5 MW reference turbine. The response to pitch steps at different pitching speeds is compared. By means of prescribed vibration cases, the effect of the aerodynamic model on the predictions of the aerodynamic work is investigated. The validation shows that a BEM model can be improved by adding near-wake trailed vorticity computation. For all prescribed vibration cases with high aerodynamic damping, results similar to those obtained by the free-wake model can be achieved in a small fraction of computation time with the proposed model. In the cases with low aerodynamic damping, the addition of trailed vorticity modeling shifts the results closer to those obtained by using the free-wake code, but differences remain.
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