Showing papers on "Near and far field published in 2009"

Surface phonon polaritons mediated energy transfer between nanoscale gaps.

Abstract: Surface phonon polaritons are electromagnetic waves that propagate along the interfaces of polar dielectrics and exhibit a large local-field enhancement near the interfaces at infrared frequencies. Theoretical calculations show that such surface waves can lead to breakdown of the Planck’s blackbody radiation law in the near field. Here, we experimentally demonstrate that surface phonon polaritons dramatically enhance energy transfer between two surfaces at small gaps by measuring radiation heat transfer between a microsphere and a flat surface down to 30 nm separation. The corresponding heat transfer coefficients at nanoscale gaps are 3 orders of magnitude larger than that of the blackbody radiation limit. The high energy flux can be exploited to develop new radiative cooling and thermophotovoltaic technologies.

Photon-induced near-field electron microscopy

Abstract: In materials science and biology, optical near-field microscopies enable spatial resolutions beyond the diffraction limit, but they cannot provide the atomic-scale imaging capabilities of electron microscopy. Given the nature of interactions between electrons and photons, and considering their connections through nanostructures, it should be possible to achieve imaging of evanescent electromagnetic fields with electron pulses when such fields are resolved in both space (nanometre and below) and time (femtosecond). Here we report the development of photon-induced near-field electron microscopy (PINEM), and the associated phenomena. We show that the precise spatiotemporal overlap of femtosecond single-electron packets with intense optical pulses at a nanostructure (individual carbon nanotube or silver nanowire in this instance) results in the direct absorption of integer multiples of photon quanta (nhomega) by the relativistic electrons accelerated to 200 keV. By energy-filtering only those electrons resulting from this absorption, it is possible to image directly in space the near-field electric field distribution, obtain the temporal behaviour of the field on the femtosecond timescale, and map its spatial polarization dependence. We believe that the observation of the photon-induced near-field effect in ultrafast electron microscopy demonstrates the potential for many applications, including those of direct space-time imaging of localized fields at interfaces and visualization of phenomena related to photonics, plasmonics and nanostructures.

Controlling the near-field oscillations of loaded plasmonic nanoantennas

Abstract: Optical and infrared antennas 1–6 enable a variety of cuttingedge applications ranging from nanoscale photodetectors 7 to highly sensitive biosensors 8 All these applications critically rely on the optical near-field interaction between the antenna and its ‘load’ (biomolecules or semiconductors) However, it is largely unexplored how antenna loading affects the near-field response Here, we use scattering-type near-field microscopy to monitor the evolution of the near-field oscillations of infrared gap antennas progressively loaded with metallic bridges of varying size Our results provide direct experimental evidence that the local near-field amplitude and phase can be controlled by antenna loading, in excellent agreement with numerical calculations By modelling the antenna loads as nanocapacitors and nanoinductors 9–11 , we show that the change of near-field patterns induced by the load can be understood within the framework of circuit theory Targeted antenna loading provides an excellent means of engineering complex antenna configurations in coherent control applications 12 , adaptive nano-optics 13 and metamaterials 14 Optical and infrared antennas based on metal nanostructures allow for efficient conversion of propagating light into nanoscale confined and strongly enhanced optical fields, and vice versa 1–5,15

Wireless power transmission for electronic devices

Abstract: Exemplary embodiments are directed to wireless power transfer. A wireless power receiver includes a receive antenna for coupling with a transmit antenna of transmitter generating a magnetic near field. The receive antenna receives wireless power from the magnetic near field and includes a resonant tank and a parasitic resonant tank wirelessly coupled to the resonant tank. A wireless power transmitter includes a transmit antenna for coupling with a receive antenna of a receiver. The transmit antenna generates a magnetic near field for transmission of wireless power and includes a resonant tank and a parasitic resonant tank coupled to the resonant tank.

Review of near-field thermal radiation and its application to energy conversion

Abstract: Understanding energy transfer via near-field thermal radiation is critical for the future advances of nanotechnology. Evanescent waves and photon tunneling are responsible for the near-field energy transfer being several orders of magnitude greater than that between two blackbodies. The enhanced energy transfer may be used for improving the performance of energy conversion devices, developing novel nanofabrication techniques, and imaging nanostructures with higher spatial resolution. Near-field heat transfer can be analyzed using fluctuational electrodynamics. This article reviews the fundamentals of near-field radiation and outlines the recent advances in this field. Important results are presented for near-field energy transfer between parallel plates and between multilayered structures. Application of near-field thermal radiation in near-field thermophotovoltaic devices is also discussed. Copyright © 2009 John Wiley & Sons, Ltd.

Plasmonic Lens Made of Multiple Concentric Metallic Rings under Radially Polarized Illumination

Abstract: Optimal plasmonic focusing can be achieved through matching the rotational symmetry of the plasmonic lens to the polarization symmetry of a radially polarized illumination. In this letter, we report the experimental confirmation of the focusing properties and field enhancement effect of plasmonic lens made of multiple concentric annular rings using a collection mode near field scanning optical microscope. Surface plasmons excited at all azimuthal directions propagate toward the geometric center and constructively interfere at the focus to create a strongly enhanced evanescent optical “needle” field that is substantially polarized vertically to the plasmonic lens surface. The field enhancement factor can be improved through adding more rings while maintaining the plasmonic focal spot size. Strategy for optimizing the field enhancement factor is studied with both analytical and numerical methods.

Confining light to deep subwavelength dimensions to enable optical nanopatterning.

Abstract: In the past, the formation of microscale patterns in the far field by light has been diffractively limited in resolution to roughly half the wavelength of the radiation used. Here, we demonstrate lines with an average width of 36 nanometers (nm), about one-tenth the illuminating wavelength lambda1 = 325 nm, made by applying a film of thermally stable photochromic molecules above the photoresist. Simultaneous irradiation of a second wavelength, lambda2 = 633 nm, renders the film opaque to the writing beam except at nodal sites, which let through a spatially constrained segment of incident lambda1 light, allowing subdiffractional patterning. The same experiment also demonstrates a patterning of periodic lines whose widths are about one-tenth their period, which is far smaller than what has been thought to be lithographically possible.

Solution of near-field thermal radiation in one-dimensional layered media using dyadic Green's functions and the scattering matrix method

Abstract: A general algorithm is introduced for the analysis of near-field radiative heat transfer in one-dimensional multi-layered structures. The method is based on the solution of dyadic Green's functions, where the amplitude of the fields in each layer is calculated via a scattering matrix approach. Several tests are presented where cubic boron nitride is used in the simulations. It is shown that a film emitter thicker than 1 μm provides the same spectral distribution of near-field radiative flux as obtained from a bulk emitter. Further simulations have pointed out that the presence of a body in close proximity to an emitter can alter the near-field spectrum emitted. This algorithm can be employed to study thermal one-dimensional layered media and photonic crystals in the near-field in order to design radiators optimizing the performances of nanoscale-gap thermophotovoltaic power generators.

Transmit power control for a wireless charging system

Abstract: Exemplary embodiment, the coupling in the near field of the transmission antennas to wireless power transmission, comprising generating an electromagnetic field to the resonance frequency of the transmitting antenna for generating the mode area. Coupling the receiving antenna disposed in the area mode is in resonance at a resonance frequency or in the vicinity. Receive antenna and extracts energy from coupling between the two antennas. A coupling rod to an amplifier for driving the transmitting antenna sensing circuit, it is possible in response to the energy extracted by the receiving antenna to detect the change in power consumed by the amplifier. Transmit antenna, one or more receivers coupled-mode region when present in and adjusted to the high-power charging mode, a coupling-mode region does not exist if the receiver is adjusted to the low power beacon mode.

Noncontact electric power receiving device, noncontact electric power transmitting device, noncontact electric power feeding system, and electrically powered vehicle

Abstract: A first shielding box is disposed so that its first surface can be opposite to an electric power feeding unit. The first surface has an opening and remaining five surfaces thereof reflect, during reception of electric power from the electric power feeding unit, a resonant electromagnetic field (near field) generated in the surroundings of the electric power receiving unit. The electric power receiving unit is provided in the first shielding box to receive the electric power from the electric power feeding unit via the opening (first surface) of the first shielding box. A second shielding box has a similar configuration, i.e., has a second surface with an opening and remaining five surfaces thereof reflect the resonant electromagnetic field (near field) generated in the surroundings of the electric power feeding unit.

Local density of states, spectrum, and far-field interference of surface plasmon polaritons probed by cathodoluminescence

Abstract: The surface plasmon polariton (SPP) field intensity in the vicinity of gratings patterned in an otherwise planar gold surface is spatially resolved using cathodoluminescence (CL). A detailed theoretical analysis is presented that successfully explains the measured CL signal based upon interference of transition radiation directly generated by electron impact and SPPs launched by the electron and outcoupled by the grating. The measured spectral dependence of the SPP yield per incoming electron is in excellent agreement with rigorous electromagnetic calculations. The CL emission is shown to be similar to that of a dipole oriented perpendicular to the surface and situated at the point of electron impact, which allows us to establish a solid connection between the CL signal and the photonic local density of states associated to the SPPs.

Near-field direct antenna modulation

Abstract: NFDAM systems provide a unique solution for transmitting highly secured direction-dependent data and hence preventing eavesdroppers from properly demodulating the signal. A 60-GHz proof-of-concept chip was designed and measured.

Synthetic spectra from particle-in-cell simulations of relativistic collisionless shocks

Abstract: We extract synthetic photon spectra from first-principles particle-in-cell simulations of relativistic shocks propagating in unmagnetized pair plasmas. The two basic ingredients for the radiation, namely accelerated particles and magnetic fields, are produced self-consistently as part of the shock evolution. We use the method of Hededal and Nordlund and compute the photon spectrum via Fourier transform of the electric far field from a large number of particles, sampled directly from the simulation. We find that the spectrum from relativistic collisionless shocks is entirely consistent with synchrotron radiation in the magnetic fields generated by Weibel instability. We can recover the so-called 'jitter' regime only if we artificially reduce the strength of the electromagnetic fields, such that the wiggler parameter K ident to qBlambda/mc {sup 2} becomes much smaller than unity (B and lambda are the strength and scale of the magnetic turbulence, respectively). These findings may place constraints on the origin of non-thermal emission in astrophysics, especially for the interpretation of the hard (harder than synchrotron) low-frequency spectrum of gamma-ray bursts.

Multiple aperture VCSEL EAMR heads

Abstract: A magnetic recording device comprises a multi-aperture vertical cavity surface emitting laser (VCSEL) operably coupled to a magnetic recording head and a plurality of waveguides disposed in the magnetic recording head. Each of the plurality of waveguides has a first end coupled to a different aperture of the multi-aperture VCSEL. The magnetic recording device further comprises a near field transducer disposed in the magnetic recording head. Each of the plurality of waveguides has a second end coupled to the near field transducer.

Split-ring-resonator-coupled enhanced transmission through a single subwavelength aperture

Abstract: We report the enhanced transmission of electromagnetic waves through a single subwavelength aperture by using a split-ring resonator (SRR) at microwave frequencies. By placing a single SRR at the near field of the aperture, strongly localized electromagnetic fields are effectively coupled to the aperture with a radius that is 20 times smaller than the resonance wavelength (r/lambda=0.05). We obtained 740-fold transmission enhancement by exciting the electric resonance of SRR. A different coupling mechanism, through the magnetic resonance of SRR, is also verified to lead to enhanced transmission.

Near-field polarization shaping by a near-resonant plasmonic cross antenna

Abstract: The optical phase in the feed gap of a plasmonic dipole antenna shows a transition from in-phase to counter-phase response, when its length is varied across the resonance length. We exploit this behavior in an asymmetric cross antenna structure, constituted of two perpendicular dipole antennas with different lengths, sharing the same feed gap, in order to shape the local polarization state. As an application of this concept, we propose a \ensuremath{\lambda}/4 nanowaveplate, able to shape and confine linearly polarized propagating waves into circularly polarized fields localized in the feed gap.

Controlling the optical near field of nanoantennas with spatial phase-shaped beams.

Abstract: We report on a novel approach, based on sub-wavelength spatial phase variations at the focus of high-order beams, to reconfigure the optical near field distribution near plasmonic nanostructures. We first show how the introduction of phase jumps in the incident field driving a gap nanoantenna strongly affects its near field response. Beyond, we demonstrate the feasibility of exploiting this approach to selectively switch on and off hot-spots sites within a complex antenna architecture.

Field enhancement in metallic subwavelength aperture arrays probed by erbium upconversion luminescence.

Abstract: Upconversion luminescence from erbium ions placed in the near field of subwavelength aperture arrays is used to investigate field enhancement of incident near-infrared light in such nanostructures. We study field enhancement due to the excitation of both propagating and localized surface plasmon resonances in arrays of square and annular apertures in a Au film. The conversion of 1480 nm excitation light to 980 nm emission is shown to be enhanced up to a factor 450 through a subwavelength hole array. The effects of array periodicity and aperture size are investigated. It is shown that a Fano model can describe both far-field transmission and near-field intensity. The upconversion enhancement reveals the wavelength and linewidth of the surface plasmon modes that are responsible for extraordinary transmission in such arrays. Angle-dependent measurements on annular aperture arrays prove that the field enhancement due to localized resonances is independent of the incident angle. These experiments provide insight in the mechanisms responsible for extraordinary transmission and are important for applications that aim to exploit near-field enhancement in nanostructured metal films.

A Note on Noise Generation by Large Scale Turbulent Structures in Subsonic and Supersonic Jets

Abstract: This paper describes a method to connect the measured spectral density in the acoustic far field with the wavenumber/frequency spectrum of the near field fluctuations that produce the noise. A relationship is first derived between the far field spectral density and the wavenumber/frequency spectrum of the pressure fluctuations on a cylindrical surface surrounding the jet in the near field. Measurements of the far field spectral density are then decomposed into contributions from the Large Scale Similarity (LSS) and Fine Scale Similarity (FSS) spectra. The near field wavenumber/frequency spectrum associated with the LSS spectral density alone is then determined. It is shown to have a very similar form for a range of jet operating conditions and Strouhal numbers. This form is consistent with an instability wave or wave packet model. Since both subsonic and supersonic jet exit conditions are examined, it is argued that the noise radiation in the peak radiation directions is controlled by the axial evolution ...

Segmented loop antenna for UHF near-field RFID applications

Abstract: A segmented loop antenna is presented for ultra-high frequency (UHF) near-field radio frequency identification (RFID) applications. The proposed segmented configuration makes the current along the loop remain in-phase even though the perimeter of the loop is comparable to the operating wavelength, so that a strong and uniform magnetic field is generated in the region surrounding the antenna. The antenna printed on a FR4 printed circuit board (PCB) with an overall size of 160 times 180 times 0.5 mm achieves good impedance matching and uniform magnetic field distribution over an operating bandwidth of 800-1040 MHz, which is desirable for UHF near-field RFID reader applications.

Binary black holes' effects on electromagnetic fields.

Abstract: In addition to producing gravitational waves, the dynamics of a binary black hole system could induce emission of electromagnetic radiation by affecting the behavior of plasmas and electromagnetic fields in their vicinity. We here study how the electromagnetic fields are affected by a pair of orbiting black holes through the merger. In particular, we show how the binary's dynamics induce a variability in possible electromagnetically induced emissions as well as a possible enhancement of electromagnetic fields during the late-merge and merger epochs. These time dependent features will likely leave their imprint in processes generating detectable emissions and can be exploited in the detection of electromagnetic counterparts of gravitational waves.

Langevin acoustic radiation force of a high-order bessel beam on a rigid sphere

Abstract: The acoustic radiation force of Langevin type resulting from the interaction of a high-order Bessel beam with a rigid immovable sphere in an ideal fluid is theoretically investigated. The analysis is based on applying the generalized Rayleigh series used in the near-field acoustic scattering problem to calculate the force. With appropriate selection of specific Bessel beam parameters, results for the rigid sphere unexpectedly reveal a negative radiation force caused by the Lagrangean energy density. Specifically, the negative force on the rigid sphere arises when the kinematic energy density is larger than the potential energy density. This condition provides an impetus for further designing acoustic tweezers operating with high-order Bessel beams of progressive waves for potential applications in particle entrapment and manipulation.

Focused Microstrip Array Antenna Using a Dolph-Chebyshev Near-Field Design

Abstract: A new concept in designing large array antennas to focus the microwave power in the radiation near-field region is presented A small focused array antenna using microstrip patch elements to achieve the desired sidelobes levels in the Fresnel region based on Dolph-Chebyshev design is implemented This array is built to verify the concept, and then the measured and computed near fields are compared to verify the accuracy of the design Larger arrays are designed by using the knowledge of the mutual admittances between the elements of smaller arrays Several computed examples are presented in order to show some properties of focusing arrays It is shown that the maximum intensity of the electric field along the axial direction is displaced from the focal point towards the antenna aperture This displacement decreases as the aperture size increases

Magnetic field strength of active region filaments

Abstract: Aims. We study the vector magnetic field of a filament observed over a compact active region neutral line.Methods. Spectropolarimetric data acquired with TIP-II (VTT, Tenerife, Spain) of the 10 830 A spectral region provide full Stokes vectors that were analyzed using three different methods: magnetograph analysis, Milne-Eddington inversions, and PCA-based atomic polarization inversions.Results. The inferred magnetic field strengths in the filament are around 600–700 G by all these three methods. Longitudinal fields are found in the range of 100–200 G whereas the transverse components become dominant, with fields as high as 500–600 G. We find strong transverse fields near the neutral line also at photospheric levels.Conclusions. Our analysis indicates that strong (higher than 500 G, but below kG) transverse magnetic fields are present in active region filaments. This corresponds to the highest field strengths reliably measured in these structures. The profiles of the helium 10 830 A lines observed in this active region filament are dominated by the Zeeman effect.

Femtosecond laser near field ablation

Abstract: The high field strength of femtosecond laser pulses leads to nonlinear effects during the interaction with condensed matter. One such effect is the ablation process, which can be initiated below the threshold of common thermal ablation if the excitation pulses are sufficiently short. This effect leads to structure formation, which is anisotropic because of the polarization properties of the near field and can result in pattern sizes below the resolution limit of light. These effects are explored by temporally resolved scattering methods and by post-mortem analysis to show the non-thermal and anisotropic nature of this process. The near-field distribution of plasmon modes can be tailored to a large extent in order to obtain control of the pattern formation.

Maximum energy transfer in near-field thermal radiation at nanometer distances

Abstract: Radiative energy transfer at nanoscale distances can exceed that of blackbody radiation by several orders of magnitude due to photon tunneling and the excitation of surface polaritons. While significant progress has been made recently in understanding near-field thermal radiation, an outstanding question remains as whether there exists an upper limit of near-field radiation for arbitrarily selected material properties at finite separation distances. We investigate the maximum achievable radiative heat flux between two parallel plates separated by a vacuum gap from 0.1 to 100 nm. By assuming a frequency-independent dielectric function and introducing a cutoff parallel wavevector component, we find that the ideal dielectric function for the two media that will maximize the near-field radiative transfer is −1+iδ, where δ is the imaginary part. For vacuum gaps greater than 1 nm, the near-field heat transfer peaks when δ⪡1, while at subnanometer gaps, the peak in the energy transfer shifts toward larger values...

Near-field plane-wave-like beam emitting antenna fabricated by anisotropic metamaterial

Abstract: In this work, the authors showed that the directivity and efficiency of an electromagnetic (EM) emission could be greatly improved by embedding the source in an anisotropic matrix with one component of the physical parameters near zero This unique property led us to design a slab-shaped rectangular antenna that could emit a monopolarized planar wave beam into the near field This greatly reduced the spatial and anechoic requirements needed for polarization-relevant EM characterizations The practical feasibility of building such a device was numerically discussed by engineering a real anisotropic embedding matrix made of metamaterial

Feasibility of estimating the degree of coherence of waves at the near field.

Abstract: Information on the degree of coherence of electromagnetic optical waves that is contained both in intensity modulation and in spatial polarization modulation of the resulting distribution of superposing waves is considered. Such an experimental situation is often realized in near-field optics. The possibility of experimental estimation of the degree of mutual coherence of waves polarized at the incidence plane is shown.