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Showing papers on "Near and far field published in 2016"


Journal ArticleDOI
TL;DR: In this paper, a novel metamaterial absorber integrated microfluidic (MAIM) sensor is proposed and demonstrated in terahertz (THz) range, where the dielectric layer of the MDM structure is hollow and acts as the microfluideic channel, and greatly confined electromagnetic fields can be obtained in the channel resulting in significantly enhanced interaction between the analytes and the THz wave.
Abstract: Spatial overlap between the electromagnetic fields and the analytes is a key factor for strong light-matter interaction leading to high sensitivity for label-free refractive index sensing Usually, the overlap and therefore the sensitivity are limited by either the localized near field of plasmonic antennas or the decayed resonant mode outside the cavity applied to monitor the refractive index variation In this paper, by constructing a metal microstructure array-dielectric-metal (MDM) structure, a novel metamaterial absorber integrated microfluidic (MAIM) sensor is proposed and demonstrated in terahertz (THz) range, where the dielectric layer of the MDM structure is hollow and acts as the microfluidic channel Tuning the electromagnetic parameters of metamaterial absorber, greatly confined electromagnetic fields can be obtained in the channel resulting in significantly enhanced interaction between the analytes and the THz wave A high sensitivity of 35 THz/RIU is predicted The experimental results of devices working around 1 THz agree with the simulation ones well The proposed idea to integrate metamaterial and microfluid with a large light-matter interaction can be extended to other frequency regions and has promising applications in matter detection and biosensing

193 citations


Journal ArticleDOI
TL;DR: It is shown via the quantum Cramér-Rao bound that, contrary to the Rayleigh limit in conventional direct imaging, quantum mechanics does not mandate any loss of precision in estimating even deep sub-Rayleigh separations.
Abstract: We obtain the ultimate quantum limit for estimating the transverse separation of two thermal point sources using a given imaging system with limited spatial bandwidth. We show via the quantum Cramer-Rao bound that, contrary to the Rayleigh limit in conventional direct imaging, quantum mechanics does not mandate any loss of precision in estimating even deep sub-Rayleigh separations. We propose two coherent measurement techniques, easily implementable using current linear-optics technology, that approach the quantum limit over an arbitrarily large range of separations. Our bound is valid for arbitrary source strengths, all regions of the electromagnetic spectrum, and for any imaging system with an inversion-symmetric point-spread function. The measurement schemes can be applied to microscopy, optical sensing, and astrometry at all wavelengths.

167 citations


Journal ArticleDOI
20 Oct 2016
TL;DR: In this paper, optical heterodyne detection in higher-order transverse electromagnetic modes (TEMs) can help in achieving sub-Rayleigh precision for a variety of microscopy-related tasks.
Abstract: The Rayleigh limit has so far applied to all microscopy techniques that rely on linear optical interaction and detection in the far field. Here we demonstrate that detecting the light emitted by an object in higher-order transverse electromagnetic modes (TEMs) can help in achieving sub-Rayleigh precision for a variety of microscopy-related tasks. Using optical heterodyne detection in TEM01, we measure the position of coherently and incoherently emitting objects to within 0.0015 and 0.012 of the Rayleigh limit, respectively, and determine the distance between two incoherently emitting objects positioned within 0.28 of the Rayleigh limit with a precision of 0.019 of the Rayleigh limit. Heterodyne detection in multiple higher-order TEMs enables full imaging with a resolution significantly below the Rayleigh limit in a way that is reminiscent of quantum tomography of optical states.

131 citations


Journal ArticleDOI
TL;DR: In this article, the time-averaged conservation law of optical chirality in lossy dispersive media was formulated and identified as an ideal far-field observable for characterizing chiral optical near fields.
Abstract: To optimize the interaction between chiral matter and highly twisted light, quantities that can help characterize chiral electromagnetic fields near nanostructures are needed. Here, by analogy with Poynting’s theorem, we formulate the time-averaged conservation law of optical chirality in lossy dispersive media and identify the optical chirality flux as an ideal far-field observable for characterizing chiral optical near fields. Bounded by the conservation law, we show that it provides precise information, unavailable from circular dichroism spectroscopy, on the magnitude and handedness of highly twisted fields near nanostructures.

99 citations


Journal ArticleDOI
TL;DR: In this paper, a method based on Lorentz reciprocity theorem is proposed to calculate the free-space and guided radiation diagrams with a high accuracy from the sole knowledge of the near-field around the emitters or scatterers.
Abstract: Light emitters or scatterers embedded in stratified media may couple energy to both free-space modes and guided modes of the stratified structure. For a comprehensive analysis, it is important to evaluate the angular intensity distribution of both the free-space modes and guided modes excited in such systems. In the present work, we propose an original method based on Lorentz reciprocity theorem to efficiently calculate the free-space and guided radiation diagrams with a high accuracy from the sole knowledge of the near-field around the emitters or scatterers. Compared to conventional near-to-far field transformation techniques, the proposal allows one to easily evaluate the guided-mode radiation diagrams, even if material dissipation is present in the stack, and thus to simultaneously track the coupling of light to all channels (i.e., free-space and guided ones). We also provide an open-source code that may be used with essentially any Maxwell’s equation solver. The numerical tool may help to engineer va...

88 citations


Journal ArticleDOI
TL;DR: In this paper, experimental and theoretical studies on ratchet effects in graphene with a lateral superlattice excited by alternating electric fields of terahertz frequency range are presented, including the Seebeck thermoratchet effect as well as the effects of "linear" and "circular" ratchets, sensitive to the corresponding polarization of the driving electromagnetic force.
Abstract: Experimental and theoretical studies on ratchet effects in graphene with a lateral superlattice excited by alternating electric fields of terahertz frequency range are presented. A lateral superlattice deposited on top of monolayer graphene is formed either by periodically repeated metal stripes having different widths and spacings or by interdigitated comblike dual-grating-gate (DGG) structures. We show that the ratchet photocurrent excited by terahertz radiation and sensitive to the radiation polarization state can be efficiently controlled by the back gate driving the system through the Dirac point as well as by the lateral asymmetry varied by applying unequal voltages to the DGG subgratings. The ratchet photocurrent includes the Seebeck thermoratchet effect as well as the effects of "linear" and "circular" ratchets, sensitive to the corresponding polarization of the driving electromagnetic force. The experimental data are analyzed for the electronic and plasmonic ratchets taking into account the calculated potential profile and the near field acting on carriers in graphene. We show that the photocurrent generation is based on a combined action of a spatially periodic in-plane potential and the spatially modulated light due to the near-field effects of the light diffraction.

78 citations


Journal ArticleDOI
TL;DR: In this article, a miniature magnetic-field probe for near-field measurements in 9-kHz-20-GHz bandwidth, which is applied to high-speed circuits, has been proposed and manufactured.
Abstract: A simple miniature magnetic-field probe for near-field measurements in 9-kHz–20-GHz bandwidth, which is applied to high-speed circuits, has been proposed and manufactured. The magnetic-field probe is built on a four-layer printed circuit board (PCB) using high-performance and low-loss Rogers material ( $\varepsilon _{r}= 3.48$ and tan $\delta = 0.0037$ ). Electric field coupling can be suppressed by PCB shielding structure of the magnetic-field probe. Coax-thru-hole via array technique is used to achieve impedance match. The resonance in working frequency band is suppressed through via fence, making $\vert S_{21}\vert $ rather smooth in the operation band. Experimental results show that the working frequency band is up to 9 kHz–20 GHz.

71 citations


Journal ArticleDOI
TL;DR: In this article, a multijunction system that laterally splits the solar spectrum onto a planar array of single-junction cells with different band gaps is proposed, which achieves an average splitting ratio of 69.5% between visible and near-infrared light over the 380-970 nm range at normal incidence.
Abstract: The greatest source of loss in conventional single-junction photovoltaic cells is their inefficient utilization of the energy contained in the full spectrum of sunlight. To overcome this deficiency, we propose a multijunction system that laterally splits the solar spectrum onto a planar array of single-junction cells with different band gaps. As a first demonstration, we designed, fabricated, and characterized dispersive diffractive optics that spatially separated the visible (360–760 nm) and near-infrared (760–1100 nm) bands of sunlight in the far field. Inverse electromagnetic design was used to optimize the surface texture of the thin diffractive phase element. An optimized thin film fabricated by femtosecond two-photon absorption 3D direct laser writing shows an average splitting ratio of 69.5% between the visible and near-infrared light over the 380–970 nm range at normal incidence. The splitting efficiency is predicted to be 80.4% assuming a structure without fabrication errors. Spectral-splitting a...

70 citations


Journal ArticleDOI
TL;DR: In this paper, the time-averaged conservation law of optical chirality in lossy dispersive media was formulated and identified as an ideal far-field observable for characterizing chiral optical near fields.
Abstract: To optimize the interaction between chiral matter and highly twisted light, quantities that can help characterize chiral electromagnetic fields near nanostructures are needed. Here, by analogy with Poynting's theorem, we formulate the time-averaged conservation law of optical chirality in lossy dispersive media and identify the optical chirality flux as an ideal far-field observable for characterizing chiral optical near fields. Bounded by the conservation law, we show that it provides precise information, unavailable from circular dichroism spectroscopy, on the magnitude and handedness of highly twisted fields near nanostructures.

66 citations


Journal ArticleDOI
TL;DR: It is demonstrated that the polarization dependent scattering radiation of the film-coupled nanosphere dimer can be used to optically distinguish from monomers and concurrently determine the spatial orientation of the dimer with significantly improved accuracy at the single-particle level, illustrating a simple yet highly sensitive plasmon resonance based nanometrology method.
Abstract: Plasmonic gap modes sustained by metal film-coupled nanostructures have recently attracted extensive research attention due to flexible control over their spectral response and significantly enhanced field intensities at the particle-film junction. In this work, by adopting an improved dark field spectroscopy methodology - polarization resolved spectral decomposition and colour decoding - we are able to "visualize" and distinguish unambiguously the spectral and far field radiation properties of the complex plasmonic gap modes in metal film-coupled nanosphere monomers and dimers. Together with full-wave numerical simulation results, it is found that while the monomer-film system supports two hybridized dipole-like plasmon modes having different oscillating orientations and resonance strengths, the scattering spectrum of the dimer-film system features two additional peaks, one strong yet narrow resonant mode corresponding to a bonding dipolar moment and one hybridized higher order resonant mode, both polarized along the dimer axis. In particular, we demonstrate that the polarization dependent scattering radiation of the film-coupled nanosphere dimer can be used to optically distinguish from monomers and concurrently determine the spatial orientation of the dimer with significantly improved accuracy at the single-particle level, illustrating a simple yet highly sensitive plasmon resonance based nanometrology method.

64 citations


Journal ArticleDOI
TL;DR: In this article, the authors theoretically investigate the performance of a near-field thermophotovoltaic (TPV) energy conversion system in which a W/SiO2-multilayer-based HMM serves as the emitter at 1000 K and InAs works as the TPV cell at 300 K.
Abstract: Artificially designed hyperbolic metamaterial (HMM) possesses extraordinary electromagnetic features different from those of naturally existing materials. In particular, the dispersion relation of waves existing inside the HMM is hyperbolic rather than elliptical; thus, waves that are evanescent in isotropic media become propagating in the HMM. This characteristic of HMMs opens a novel way to spectrally control the near-field thermal radiation in which evanescent waves in the vacuum gap play a critical role. In this paper, we theoretically investigate the performance of a near-field thermophotovoltaic (TPV) energy conversion system in which a W/SiO2-multilayer-based HMM serves as the emitter at 1000 K and InAs works as the TPV cell at 300 K. By carefully designing the thickness of constituent materials of the HMM emitter, the electric power of the near-field TPV devices can be increased by about 6 times at 100-nm vacuum gap as compared to the case of the plain W emitter. Alternatively, in regards to the electric power generation, HMM emitter at experimentally achievable 100-nm vacuum gap performs equivalently to the plain W emitter at 18-nm vacuum gap. We show that the enhancement mechanism of the HMM emitter is due to the coupled surface plasmon modes at multiple metal-dielectric interfaces inside the HMM emitter. With the minority carrier transport model, the optimal p-n junction depth of the TPV cell has also been determined at various vacuum gaps.

Journal ArticleDOI
TL;DR: Three methods that jointly estimate the range and bearing of multiple sources in the spherical array framework are proposed and formulated and the near-field data model is developed in spherical harmonics domain.
Abstract: In this paper, we address the issue of near-field source localization using spherical microphone array. The spherical array has been widely used for far-field source localization due to ease of array processing in spherical harmonics domain. Various methods for far-field source localization has been reformulated in spherical harmonics domain. However, near-field source localization that involves joint estimation of range and bearing of the sources has hitherto not been investigated. In this paper, the near-field data model is developed in spherical harmonics domain. In particular, three methods that jointly estimate the range and bearing of multiple sources in the spherical array framework are proposed. Two subspace-based methods called the Spherical Harmonic MUltiple SIgnal Classification (SH-MUSIC) and the Spherical Harmonics MUSIC-Group Delay (SH-MGD) for near-field source localization are first presented. In addition, a method for near-field source localization and beamforming using Spherical Harmonic MVDR (SH-MVDR) is also formulated. Formulation and analysis of Cramer–Rao bound for near-field sources is presented in spherical harmonics domain. Various source localization experiments were conducted on simulated and signal acquired over spherical microphone array in an anechoic chamber. Root-mean-square error and probability of resolution are utilized as measures to evaluate the proposed methods. The significance and practical application of the proposed methods is discussed using experiment on interference suppression. The near-field SH-MVDR beamforming is utilized in this context.

Journal ArticleDOI
TL;DR: In this paper, the Kapitza-Dirac effect was used to predict a new type of interaction between electrons and the electromagnetic field, opening up new possibilities for the manipulation of electron beams.
Abstract: The properties of an electron beam can be manipulated by electromagnetic fields in vacuum via the ponderomotive force. Such an interaction is also at the core of the Kapitza-Dirac effect, which describes the diffraction of electrons by an optical standing wave. Here, the authors predict a new type of interaction between electrons and the electromagnetic field, opening up new possibilities for the manipulation of electron beams. If surface plasmon polaritons are tailored to interfere forming a periodic field pattern, it becomes possible to diffract electrons from such near field. With the proper manipulation of the plasmonic fields, orbital angular momentum can be imparted to the electrons, and even the phase of their wave functions can be manipulated. An additional degree of freedom is provided by the possibility to tailor the spatial properties of the light and the materials supporting the surface plasmons. This arbitrary control can be extended to different substrates such as graphene or layered systems and may open up a viable route to create tunable phase plates for electron microscopes.

Journal ArticleDOI
TL;DR: In this article, a tunable optical technique was developed to probe the near-field resonances within individual plasmonic nanostructures that can be directly compared to the corresponding far-field response.
Abstract: The near-field and far-field spectral response of plasmonic systems are often assumed to be identical, due to the lack of methods that can directly compare and correlate both responses under similar environmental conditions. We develop a widely tunable optical technique to probe the near-field resonances within individual plasmonic nanostructures that can be directly compared to the corresponding far-field response. In tightly coupled nanoparticle-on-mirror constructs with nanometer-sized gaps we find >40 meV blue-shifts of the near-field compared to the dark-field scattering peak, which agrees with full electromagnetic simulations. Using a transformation optics approach, we show such shifts arise from the different spectral interference between different gap modes in the near- and far-field. The control and tuning of near-field and far-field responses demonstrated here is of paramount importance in the design of optical nanostructures for field-enhanced spectroscopy, as well as to control near-field acti...

Journal ArticleDOI
TL;DR: Temperature sensing without electronics is demonstrated through wireless interrogation of passive antenna-sensors using an ultra-wide-band microstrip antenna as the transmitting/receiving antenna and a microstrip patch antenna serving as the temperature-sensing element.
Abstract: Temperature sensing without electronics is demonstrated through wireless interrogation of passive antenna-sensors. The sensor node is equipped with an ultra-wide-band microstrip antenna as the transmitting/receiving (Tx/Rx) antenna and a microstrip patch antenna serving as the temperature-sensing element. A microstrip transmission line connecting the Tx/Rx antenna and the antenna-sensor delays the signal reflected from the sensing element and thus separated it from the background clutter. The operation principle of the wireless sensing scheme is first discussed, followed by the design and simulations of the sensor node circuitry. A digital signal processing algorithm that extracts the antenna resonant frequency from the wirelessly received signal is also described. Temperature tests were conducted to validate the performance of the wireless antenna sensor inside an oven.

Journal ArticleDOI
TL;DR: In this paper, the interaction between a sub-wavelength particle (the probe) and a material surface (the sample) is studied theoretically, and the interaction is governed by a series of resonances corresponding to surface polariton modes localized near the probe.
Abstract: Electromagnetic interaction between a sub-wavelength particle (the “probe”) and a material surface (the “sample”) is studied theoretically. The interaction is shown to be governed by a series of resonances corresponding to surface polariton modes localized near the probe. The resonance parameters depend on the dielectric function and geometry of the probe as well as on the surface reflectivity of the material. Calculation of such resonances is carried out for several types of axisymmetric probes: spherical, spheroidal, and pear-shaped. For spheroids, an efficient numerical method is developed, capable of handling cases of large or strongly momentum-dependent surface reflectivity. Application of the method to highly resonant materials, such as aluminum oxide (by itself or covered with graphene), reveals a rich structure of multi-peak spectra and nonmonotonic approach curves, i.e., the probe-sample distance dependence. These features also strongly depend on the probe shape and optical constants of the model. For less resonant materials such as silicon oxide, the dependence is weak, so that the spheroidal model is reliable. The calculations are done within the quasistatic approximation with radiative damping included perturbatively.

Journal ArticleDOI
TL;DR: In this paper, a fluctuational electrodynamics-based formalism for calculating near-field radiative heat transfer between objects of arbitrary size and shape and an infinite surface is presented.
Abstract: A fluctuational electrodynamics-based formalism for calculating near-field radiative heat transfer between objects of arbitrary size and shape and an infinite surface is presented. The surface interactions are treated analytically via Sommerfeld's theory of electric dipole radiation above an infinite plane. The volume integral equation for the electric field is discretized using the thermal discrete dipole approximation (T-DDA). The framework is verified against exact results in the sphere-surface configuration and is applied to analyze near-field radiative heat transfer between a complex-shaped probe and an infinite plane, both made of silica. It is found that, when the probe tip size is approximately equal to or smaller than the gap $d$ separating the probe and the surface, coupled localized surface phonon (LSPh)-surface phonon-polariton (SPhP) mediated heat transfer occurs. In this regime, the net spectral heat rate exhibits four resonant modes due to LSPhs along the minor axis of the probe, while the net total heat rate in the near field follows a ${d}^{\ensuremath{-}0.3}$ power law. Conversely, when the probe tip size is much larger than the separation gap $d$, heat transfer is mediated by SPhPs, resulting in two resonant modes in the net spectral heat rate, corresponding to those of a single emitting silica surface, while the net total heat rate approaches a ${d}^{\ensuremath{-}2}$ power law. It is also demonstrated that a complex-shaped probe can be approximated by a prolate spheroidal electric dipole when the thermal wavelength is larger than the major axis of the spheroidal dipole and when the separation gap $d$ is much larger than the radius of curvature of the dipole tip facing the surface.

Journal ArticleDOI
TL;DR: A novel method realizing multi-input-multi-output (MIMO) transmission in near-field magnetic induction (NFMI) communication for increasing channel capacity where limited capacity is a major bottleneck problem in magnetic communication systems is proposed.
Abstract: In this paper, we propose a novel method realizing multi-input–multi-output (MIMO) transmission in near-field magnetic induction (NFMI) communication for increasing channel capacity where limited capacity is a major bottleneck problem in magnetic communication systems. Since conventional magnetic communication systems using the same antenna patterns cannot easily implement MIMO transmission due to strong crosstalk between transmitters, we propose heterogeneous antenna arrays with multipole antennas, enabling crosstalk cancellation. We confirm the crosstalk cancellation of the proposed antenna array through numerical simulations and experiments, and verify the capacity enhancement of the proposed NFMI communication system over conventional NFMI communication schemes.

Journal ArticleDOI
TL;DR: Wilson et al. as mentioned in this paper proposed a single-chip optonanomechanical transducer based on a high-stress Si3N4 nanobeam monolithically integrated into the evanescent near field of SiO2 microdisk cavity.
Abstract: Placing a nanomechanical object in the evanescent near field of a high-Q optical microcavity gives access to strong gradient forces and quantum-limited displacement readout, offering an attractive platform for both precision sensing technology and basic quantum optics research. Robustly implementing this platform is challenging, however, as it requires integrating optically smooth surfaces separated by less than or similar to lambda/10. Here we describe an exceptionally high-cooperativity, single-chip optonanomechanical transducer based on a high-stress Si3N4 nanobeam monolithically integrated into the evanescent near field of SiO2 microdisk cavity. Employing a vertical integration technique based on planarized sacrificial layers, we realize beam-disk gaps as little as 25 nm while maintaining mechanical Qf > 10(12) Hz and intrinsic optical Q similar to 10(7). The combination of low loss, small gap, and parallel-plane geometry results in radio-frequency flexural modes with vacuum optomechanical coupling rates of 100 kHz, single-photon cooperativities in excess of unity, and large zero-point frequency (displacement) noise amplitudes of 10 kHz (fm) / root Hz. In conjunction with the high power-handling capacity of SiO2 and low extraneous substrate noise, the transducer performs particularly well as a sensor, with recent deployment in a 4-K cryostat realizing a displacement imprecision 40 dB below that at the standard quantum limit (SQL) and an imprecision-backaction product < 5h [Wilson et al., Nature (London) 524, 325 (2015)]. In this report, we provide a comprehensive description of device design, fabrication, and characterization, with an emphasis on extending Heisenberg-limited readout to room temperature. Towards this end, we describe a roomtemperature experiment in which a displacement imprecision 32 dB below that at the SQL and an imprecision-backaction product < 60h is achieved. Our results extend the outlook for measurement-based quantum control of nanomechanical oscillators and suggest an alternative platform for functionally integrated "hybrid" quantum optomechanics.

Book ChapterDOI
01 Jan 2016
TL;DR: In this paper, a complete description of the near-field antennameasurement techniques is provided, by also providing some analytical details on the wave expansions commonly adopted to represent the antenna radiated field.
Abstract: A complete description of the near-field antennameasurement techniques is provided in this chapter. After a discussion of the state of the art, the key steps of the classical near-field–far-field (NF-FF) transformations with plane-rectangular, cylindrical, and spherical scannings, in their probe-uncompensated and probe-compensated versions, are summarized, by also providing some analytical details on the wave expansions commonly adopted to represent the antenna radiated field. The nonredundant sampling representations of electromagnetic field are then introduced and applied to drastically reduce the number of required NF data and related measurement time with respect to the classical NF-FF transformations. At last, the NF-FF transformations with innovative spiral scannings, allowing a further measurement time saving, are described.

Journal ArticleDOI
TL;DR: In this article, the emergence of polarization singularities in the scattered fields of optical resonators excited by linearly polarized plane waves was studied, and it was shown that high refractive index spherical resonators present such topologically protected features.
Abstract: In this article, we study the emergence of polarization singularities in the scattered fields of optical resonators excited by linearly polarized plane waves. First, we prove analytically that combinations of isotropic electric and magnetic dipoles can sustain L surfaces, and C lines that propagate from the near-field to the far field. Moreover, based on these analytical results, we derive anomalous scattering Kerker conditions trough singular optics arguments. Secondly, through exact full-field calculations, we demonstrate that high refractive index spherical resonators present such topologically protected features. Furthermore, we calculate the polarization structure of light around the generated C lines, unveiling a Mobius strip structure in the main axis of the polarization ellipse. These results prove that high-index nanoparticles are excellent candidates for the generation and control of polarization singularities and that they may lead to new platforms for the experimental study of the topology of light fields around optical antennas.

Posted Content
TL;DR: In this paper, a widely-tuneable optical technique was developed to probe the near-field resonances within individual plasmonic nanostructures that can be directly compared to the corresponding far-field response.
Abstract: The near-field and far-field spectral response of plasmonic systems are often assumed to be identical, due to the lack of methods that can directly compare and correlate both responses under similar environmental conditions. We develop a widely-tuneable optical technique to probe the near-field resonances within individual plasmonic nanostructures that can be directly compared to the corresponding far-field response. In tightly-coupled nanoparticle-on-mirror constructs with nanometer-sized gaps we find >40meV blueshifts of the near-field compared to the dark-field scattering peak, which agrees with full electromagnetic simulations. Using a transformation optics approach, we show such shifts arise from the different spectral interference between different gap modes in the near- and far-field. The control and tuning of near-field and far-field responses demonstrated here is of paramount importance in the design of optical nanostructures for field-enhanced spectroscopy, as well as to control near-field activity monitored through the far-field of nano-optical devices.

Journal ArticleDOI
TL;DR: In this article, a 2D periodic pair-array of cavity resonance based (CRB) plasmonic nanoantennas (PNAs) is numerically investigated by using the finite element method.
Abstract: A 2D periodic pair-array of cavity resonance based (CRB) plasmonic nanoantennas (PNAs) on the tailoring near field enhancement and optical spectrum of surface plasmon resonance (SPR) modes is numerically investigated by using the finite element method. The CRBPNAs consist of a single cavity or double cavities in each antenna arm. Detailed physical explanations of the simulation results and consistent dependencies of the SPR features on the structural and material parameters of CRBPNAs are presented. Compared to the solid case of counterpart, the proposed CRBPNAs display outstanding SPR characteristics and tune the peak resonance wavelength by varying the outline thickness and the cavity material. In addition, the field enhancement and optical spectrum can be precisely controlled by cavity material and outline thickness in the broad band of ultraviolet, visible and near-infrared, resulting in increased sensitivity and supporting resonances with gaps and cavity surface plasmom as well as the high value of Q factors. We interpret the optical properties of the proposed CRBPNAs and show tuning and optimizing through choice of geometric and material parameters.

Journal ArticleDOI
TL;DR: This paper proposes a periodically repeated ring-disk complementary structure to break the near-field diffraction limit via plasmonic Fano resonance, originating from the interference between the complex hybrid plAsmon resonance and the continuum of propagating waves through the silver film.
Abstract: The past decade has witnessed a great deal of optical systems designed for exceeding the Abbe's diffraction limit. Unfortunately, a deep subwavelength spot is obtained at the price of extremely short focal length, which is indeed a near-field diffraction limit that could rarely go beyond in the nanofocusing device. One method to mitigate such a problem is to set up a rapid oscillatory electromagnetic field that converges at the prescribed focus. However, abrupt modulation of phase and amplitude within a small fraction of a wavelength seems to be the main obstacle in the visible regime, aggravated by loss and plasmonic features that come into function. In this paper, we propose a periodically repeated ring-disk complementary structure to break the near-field diffraction limit via plasmonic Fano resonance, originating from the interference between the complex hybrid plasmon resonance and the continuum of propagating waves through the silver film. This plasmonic Fano resonance introduces a pi phase jump in the adjacent channels and amplitude modulation to achieve radiationless electromagnetic interference. As a result, deep subwavelength spots as small as 0.0045 lambda(2) at 36 nm above the silver film have been numerically demonstrated. This plate holds promise for nanolithography, subdiffraction imaging and microscopy.

Journal ArticleDOI
TL;DR: A novel microwave high-resolution near-field imaging technique is proposed and experimentally evaluated in reflectometry imaging scenarios involving planar metal-dielectric structures and it is shown that printed elements features with subwavelength size ~λ/15 or smaller can be characterized with at least 10-dB resolution contrast.
Abstract: A novel microwave high-resolution near-field imaging technique is proposed and experimentally evaluated in reflectometry imaging scenarios involving planar metal-dielectric structures. Two types of resonance near field probes—a small helix antenna and a loaded subwavelength slot aperture are studied in this paper. These probes enable very tight spatial field localization with the full width at half maximum around one tenth of a wavelength, $\lambda $ , at $\lambda $ /100– $\lambda $ /10 standoff distance. Importantly, the proposed probes permit resonance electromagnetic coupling to dielectric or printed conductive patterns, which leads to the possibility of very high raw image resolution with imaged feature-to-background contrast greater than 10-dB amplitude and 50° phase. In addition, high-resolution characterization of target geometries based on the cross correlation image processing technique is proposed and assessed using experimental data. It is shown that printed elements features with subwavelength size $\sim \lambda $ /15 or smaller can be characterized with at least 10-dB resolution contrast.

Journal ArticleDOI
TL;DR: In this article, a planar Bessel-beam launcher supporting multiple modes was analyzed and the energy-transfer characteristics of the coupled system were analyzed and discussed, and it was shown that the system can both transmit and receive Bessel beams.
Abstract: The generation of propagating Bessel beams is typically limited to optical frequencies with bulky experimental setups. Recent works have demonstrated Bessel-beam generation at microwave and millimeter-wave frequencies utilizing low-profile, planar, leaky-wave antennas. These studies have assumed a single leaky mode in the antenna. In this work, the rigorous analysis of a planar Bessel-beam launcher supporting multiple modes is presented. By employing the mode-matching technique, a complete electromagnetic solution of the structure, its supported modes, and radiated fields is obtained. Additionally, a coupled system of two planar Bessel launchers is analyzed, and it is shown that the system can both transmit and receive Bessel beams. The energy-transfer characteristics of the coupled system are analyzed and discussed. An analysis of the coupled system's even and odd modes of operation show that efficient power transfer is possible, and that an odd mode is preferred since it yields higher field confinement and power-transfer efficiency.

01 Jan 2016
TL;DR: The electromagnetic surface modes is universally compatible with any devices to read and is available in the digital library an online access to it is set as public so you can get it instantly.
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Journal ArticleDOI
TL;DR: In this paper, the scalar metasurfaces can be used to generate linear and circular polarizations for a fixed pointing direction in the far field by properly changing locally scalar impedance boundary condition.
Abstract: This paper deals with the design of scalar metasurface antennas capable of radiating a well-polarized beam in the far-field or near-field zones. The equivalent electric current over the metasurface is used to derive design equations to generate the desired field pattern based on the scalar impedance condition. In particular, it is shown that scalar metasurfaces can be used to generate linear and circular polarizations for a fixed pointing direction in the far field by properly changing locally the scalar impedance boundary condition. In addition, they can also be used to generate normal polarized Bessel beams in the near-field region. Several solutions are presented at 20 GHz, with different polarizations and feeders developed in the framework of a two-year research project financed by the French space agency (Centre National d’Etudes Spatiales). Measurements and full-wave results validate the proposed approach.

Journal ArticleDOI
TL;DR: It is shown that M-SONAH produces accurate field reconstructions for both inward and outward propagation in the region spanned by the physical hologram measurement, which suggests that directivity depends mainly on estimated source location.
Abstract: The identification of acoustic sources is critical to targeted noise reduction efforts for jets on high-performance tactical aircraft. This paper describes the imaging of acoustic sources from a tactical jet using near-field acoustical holography techniques. The measurement consists of a series of scans over the hologram with a dense microphone array. Partial field decomposition methods are performed to generate coherent holograms. Numerical extrapolation of data beyond the measurement aperture mitigates artifacts near the aperture edges. A multisource equivalent wave model is used that includes the effects of the ground reflection on the measurement. Multisource statistically optimized near-field acoustical holography (M-SONAH) is used to reconstruct apparent source distributions between 20 and 1250 Hz at four engine powers. It is shown that M-SONAH produces accurate field reconstructions for both inward and outward propagation in the region spanned by the physical hologram measurement. Reconstructions across the set of engine powers and frequencies suggests that directivity depends mainly on estimated source location; sources farther downstream radiate at a higher angle relative to the inlet axis. At some frequencies and engine powers, reconstructed fields exhibit multiple radiation lobes originating from overlapped source regions, which is a phenomenon relatively recently reported for full-scale jets.

Journal ArticleDOI
TL;DR: In this paper, a zero-permeability near-field metamaterial (NF-MM) shield is proposed to cancel the incident magnetic flux without significant additional loss to the system.
Abstract: Wireless power transfer and other near-field applications can generate large magnetoquasistatic fields that can potentially be harmful to humans or interact negatively with the environment. Several shields have been proposed for the magnetic near field, such as ferrite sheets or metallic shields. While each can be effective, there are tradeoffs to each, namely loss, weight, and cost. In addition, metallic and ferrite shields are broadband and block large portions of the electromagnetic spectrum. In this letter, we introduce a new type of magnetic near-field shield, a zero-permeability near-field metamaterial (NF-MM) shield. This shield operates by canceling the incident magnetic flux without significant additional loss to the system. Moreover, the zero-permeability shield is frequency-selective, blocking only a single or small bandwidth of frequencies, enabling shielding only at the desired frequency while allowing the remainder of the electromagnetic spectrum through. We show that a zero-permeability NF-MM shield can reduce magnetic field strength by 22.84 dB in simulation and demonstrate 77% reduction in an experimental prototype.