Showing papers on "Plane wave published in 2019"

Emission and propagation of 1D and 2D spin waves with nanoscale wavelengths in anisotropic spin textures

Abstract: Spin waves offer intriguing perspectives for computing and signal processing, because their damping can be lower than the ohmic losses in conventional complementary metal–oxide–semiconductor (CMOS) circuits. Magnetic domain walls show considerable potential as magnonic waveguides for on-chip control of the spatial extent and propagation of spin waves. However, low-loss guidance of spin waves with nanoscale wavelengths and around angled tracks remains to be shown. Here, we demonstrate spin wave control using natural anisotropic features of magnetic order in an interlayer exchange-coupled ferromagnetic bilayer. We employ scanning transmission X-ray microscopy to image the generation of spin waves and their propagation across distances exceeding multiples of the wavelength. Spin waves propagate in extended planar geometries as well as along straight or curved one-dimensional domain walls. We observe wavelengths between 1 μm and 150 nm, with excitation frequencies ranging from 250 MHz to 3 GHz. Our results show routes towards the practical implementation of magnonic waveguides in the form of domain walls in future spin wave logic and computational circuits. Sub-micrometre spin waves are excited in anisotropic spin textures and they can propagate as 2D plane waves over several micrometres and as 1D waves along curved domain walls.

A novel model of plane waves of two-temperature fiber-reinforced thermoelastic medium under the effect of gravity with three-phase-lag model

Abstract: In the present paper, the three-phase-lag (3PHL) model, Green-Naghdi theory without energy dissipation (G-N II) and Green-Naghdi theory with energy dissipation (G-N III) are used to study the influence of the gravity field on a two-temperature fiber-reinforced thermoelastic medium.,The analytical expressions for the displacement components, the force stresses, the thermodynamic temperature and the conductive temperature are obtained in the physical domain by using normal mode analysis.,The variations of the considered variables with the horizontal distance are illustrated graphically. Some comparisons of the thermo-physical quantities are shown in the figures to study the effect of the gravity, the two-temperature parameter and the reinforcement. Also, the effect of time on the physical fields is observed.,To the best of the author’s knowledge, this model is a novel model of plane waves of two-temperature fiber-reinforced thermoelastic medium, and gravity plays an important role in the wave propagation of the field quantities. It explains that there are significant differences in the field quantities under the G-N II theory, the G-N III theory and the 3PHL model because of the phase-lag of temperature gradient and the phase-lag of heat flux.

High-energy behavior of strong-field QED in an intense plane wave

Abstract: Analytical calculations of radiative corrections in strong-field QED have hinted that in the presence of an intense plane wave the effective coupling of the theory in the high-energy sector may increase as the ($2/3$)-power of the energy scale. These findings have raised the question of their compatibility with the corresponding logarithmic increase of radiative corrections in QED in vacuum. However, all these analytical results in strong-field QED have been obtained within the limiting case of a background constant crossed field. Starting from the polarization operator and the mass operator in a general plane wave, we show that the constant-crossed-field limit and the high-energy limit do not commute with each other and identify the physical parameter discriminating between the two alternative limits orders. As a result, we find that the power-law scaling at asymptotically large energy scales pertains strictly speaking only to the case of a constant crossed background field, whereas high-energy radiative corrections in a general plane wave depend logarithmically on the energy scale as in vacuum. However, we also confirm the possibility of testing the ``power-law'' regime experimentally by means of realistic setups involving, e.g., high-power lasers or high-density electron-positron bunches.

Plane waves in nonlocal thermoelastic solid with voids

Abstract: This work is concerned with the propagation of time harmonic plane waves in an infinite nonlocal thermoelastic solid having void pores. Three sets of coupled dilatational waves and an independent transverse wave may travel with distinct speeds in the medium. All these waves are found to be dispersive in nature, but the coupled dilatational waves are attenuating, while transverse wave is nonattenuating. Coupled dilatational waves are found to be influenced by the presence of voids, thermal field and elastic nonlocal parameter. While the transverse wave is found to be influenced by the nonlocal parameter, but independent of void and thermal parameters. For a particular model, the effects of frequency, void parameters, thermal parameter and nonlocality have been studied numerically on the phase speeds, attenuation coefficients and specific losses of all the propagating waves. All the computed results obtained have been depicted graphically and explained.

Experimental observation of non-reciprocal band-gaps in a space-time modulated beam using a shunted piezoelectric array

Abstract: In this work we experimentally achieve 1 kHz-wide directional band-gaps for elastic waves spanning a frequency range from approximately 8 to 11 kHz. One-way propagation is induced by way of a periodic waveguide consisting in an aluminum beam partially covered by a tightly packed array of piezoelectric patches. The latter are connected to shunt circuits and switches which allow for a periodic modulation in time of the cell properties. A traveling stiffness profile is obtained by opportunely phasing the temporal modulation of each active element, mimicking the propagation of a plane wave along the material, therefore establishing unidirectional wave propagation at bandgap frequencies.

Effect of electromagnetic radiation on the dynamics of spatiotemporal patterns in memristor-based neuronal network

Abstract: Modulational instability, as a mechanism of wave trains and soliton formation in biological system, is explored in the frame work of the new FitzHugh–Nagumo model. This model considered chain networks with memristive synaptic connection between adjacent neurons. This connection replaces the synaptic coupling and neurons bridged for signal exchange. From the physical law of electromagnetic induction, we interpret the traditional current term as magnetic flux variable. Magnetic flux is used to describe time-varying electromagnetic field setup in cells as a result of internal bioelectricity of the nervous system as well as when cells are exposed to external electromagnetic field. We reduced the whole network dynamical equations through multi-scale expansion to obtain a single differential–difference nonlinear equation of Schrodinger type. Linear stability is then performed with emphasis on memristive synaptic coupling. The conditions under which uniform plane waves propagating in the network become stable or unstable under small perturbation are calculated and plotted. Numerical experiments confirm our analytical predictions as the network supports localized mode excitations, spike-like, identified as quasi-periodic patterns, with some features of synchronization. It is confirmed that under strong electromagnetic radiation, the propagating waves encountered turbulent electrical activities, with patterns breakdown into a homogeneous state. This disordered state, collapse and instability of traveling pulse are monitored and analyzed using the sampled time series for membrane potential. It decreases to quiescent state under strong electromagnetic field. This could provide some guidance to understanding some neurodegenerative manifestations linked with high radiation exposure.

Fast Acoustic Wave Sparsely Activated Localization Microscopy: Ultrasound Super-Resolution Using Plane-Wave Activation of Nanodroplets

Abstract: Localization-based ultrasound super-resolution imaging using microbubble contrast agents and phase-change nanodroplets has been developed to visualize microvascular structures beyond the diffraction limit. However, the long data acquisition time makes the clinical translation more challenging. In this study, fast acoustic wave sparsely activated localization microscopy (fast-AWSALM) was developed to achieve super-resolved frames with subsecond temporal resolution, by using low-boiling-point octafluoropropane nanodroplets and high frame rate plane waves for activation, destruction, as well as imaging. Fast-AWSALM was demonstrated on an in vitro microvascular phantom to super-resolve structures that could not be resolved by conventional B-mode imaging. The effects of the temperature and mechanical index on fast-AWSALM were investigated. The experimental results show that subwavelength microstructures as small as $190~\mu \text{m}$ were resolvable in 200 ms with plane-wave transmission at a center frequency of 3.5 MHz and a pulse repetition frequency of 5000 Hz. This is about a 3.5-fold reduction in point spread function full-width-half-maximum compared to that measured in the conventional B-mode, and two orders of magnitude faster than the recently reported AWSALM under a nonflow/very slow flow situations and other localization-based methods. Just as in AWSALM, fast-AWSALM does not require flow, as is required by current microbubble-based ultrasound super-resolution techniques. In conclusion, this study shows the promise of fast-AWSALM, a super-resolution ultrasound technique using nanodroplets, which can generate super-resolution images in milliseconds and does not require flow.

Second-harmonic generation in Mie-resonant dielectric nanoparticles made of noncentrosymmetric materials

Abstract: We develop a multipolar theory of second-harmonic generation (SHG) by dielectric nanoparticles made of noncentrosymmetric materials with bulk quadratic nonlinearity. We specifically analyze two regimes of optical excitation: illumination by a plane wave and single-mode excitation, when the laser pump drives the magnetic dipole mode only. Considering two classes of nonlinear crystalline solids (dielectric perovskite material and III-V semiconductor), we apply a symmetry approach to derive selection rules for the multipolar composition of the nonlinear radiation. The developed description can be used for design of efficient nonlinear optical nanoantennas with reconfigurable radiation characteristics.

Quantum Simulation of Chemistry with Sublinear Scaling in Basis Size

Abstract: We present a quantum algorithm for simulating quantum chemistry with gate complexity $$\tilde {\cal{O}}(N^{1/3}\eta ^{8/3})$$ where η is the number of electrons and N is the number of plane wave orbitals. In comparison, the most efficient prior algorithms for simulating electronic structure using plane waves (which are at least as efficient as algorithms using any other basis) have complexity $$\tilde {\cal{O}}(N^{8/3}{\mathrm{/}}\eta ^{2/3})$$ . We achieve our scaling in first quantization by performing simulation in the rotating frame of the kinetic operator using interaction picture techniques. Our algorithm is far more efficient than all prior approaches when N ≫ η, as is needed to suppress discretization error when representing molecules in the plane wave basis, or when simulating without the Born-Oppenheimer approximation.

Plane wave backgrounds and colour-kinematics duality

Abstract: We consider perturbative gauge theory on a fixed Yang-Mills plane wave background, describing its Feynman rules in detail. Using these rules, the tree-level 4-point gluon amplitude is computed. As an application, we investigate whether some notion of colour-kinematics duality — a relation between the colour and kinematic constituents of the amplitude — holds on the plane wave background. Although the duality is obstructed, the obstruction has an interesting and highly-constrained structure. This plane wave version of colour-kinematics duality reduces on a flat background to the well-known identities underpinning the BCJ relations for colour-ordered partial amplitudes, and constrains representations of tree-level amplitudes beyond 4-points.

Broadband and High-Transmission Metasurface for Converting Underwater Cylindrical Waves to Plane Waves

Abstract: Plane waves are required for underwater acoustic locating, navigation, and survey, but generating them efficiently with traditional approaches is impractical, particularly at low frequencies. This study proposes an easy means to transform cylindrical waves into plane waves, through phase rectification with graded aluminum honeycomb structures. The honeycomb metasurface allows mimicking of the acoustic behavior of fluids, and its effective acoustic index and impedance can be independently tailored as desired. Experiment verifies efficient wave-front modulation of the metasurface with high transmission over a broad frequency range.

Wideband Phase-Gradient Metasurface Antenna With Focused Beams

Abstract: A transmitting lens antenna with focused beams by employing four-layer phase-gradient metasurface (PGMS) is proposed. A wideband slot-coupled antenna is mounted close to the focal position of the PGMS acting as a feed. The electromagnetic wave radiated through the feed source is transformed to plane wave within a wide frequency covering from 9.4 to 10.6 GHz. The in-band measured gain is from 16.7 to 19.4 dBi and a 3-dB gain bandwidth of around 10% is achieved, which demonstrates that the proposed four-layer PGMS still has the ability to focus electromagnetic wave within a wide frequency band efficiently though its transmission phase range at some specific frequency bands does not meet 360°.

Realization of Split Beam Antenna Using Transmission-Type Coding Metasurface and Planar Lens

Abstract: In this paper, a novel compact split beam configuration of the transmission-type coding metasurface (MS) in combination with the planar lens and the patch antenna is presented. In the first stage, the spherical electromagnetic waves originating from the patch antenna are converted to plane waves by placing the planar MS lens at a height of $0.55\lambda _{0}$ above the antenna aperture. This lens enhances the radiation along the broadside direction resulting in high-gain operation. Furthermore, a concept of the digital metamaterial is adopted by realizing 1 bit transmission-type coding MSs, capable of splitting the aforementioned high-gain beam pattern. These digital MSs (DMSs) have two different types of metaatoms with phase responses of 0 and $\pi $ , corresponding to two basic digital elements 0 and 1, respectively. The assembly of these metamaterial bits (either 0 or 1) leads to a lattice of size $D \times D$ . The proper spatial mixture of these lattices with different sequences facilitates different elemental metamaterial-pattern resulting in multiple-lobe radiation patterns, which are angularly oriented and symmetrical to the antenna axis. The designed planar lens and the DMS with the individual thickness of $0.057\lambda _{0}$ are placed in the near field of antenna leading to an overall compact configuration with a total height of $1.08\lambda _{0}$ . The aforementioned beam splitting using the proposed configuration is also validated both quantitatively (mathematically) and qualitatively (through the simulation and the measurement) for different types of DMSs.

Multi-twist polarization ribbon topologies in highly-confined optical fields

Abstract: Electromagnetic plane waves, solutions to Maxwell's equations, are said to be 'transverse' in vacuum. Namely, the waves' oscillatory electric and magnetic fields are confined within a plane transverse to the waves' propagation direction. Under tight-focusing conditions however, the field can exhibit longitudinal electric or magnetic components, transverse spin angular momentum, or non-trivial topologies such as Mobius strips. Here, we show that when a suitably spatially structured beam is tightly focused, a three-dimensional polarization topology in the form of a ribbon with two full twists appears in the focal volume. We study experimentally the stability and dynamics of the observed polarization ribbon by exploring its topological structure for various radii upon focusing and for different propagation planes.

Wide-Angle Beam Steering Based on an Active Conformal Metasurface Lens

Abstract: This work experimentally demonstrates a wide-angle beam steering based on an active conformal metasurface lens. Integrated with microwave varactors, the transmission phase of this cylindrical metasurface lens can be tuned in a range up to 195° by direct-current (DC) bias voltages. By compensating the phase difference between different incidences, the proposed cylindrical lens can collimate the incident spherical wave front into a plane wave front with predefined deflection angle. By increasing the number of feeding sources, the beam steering range of conformal lens can be expanded to ±60°. Having advantages of low cost and simple structure, the proposed conformal lens can be extended to millimeter-wave band and enable a wide range of applications.

Comparison of first-principles methods to extract magnetic parameters in ultrathin films: Co/Pt(111)

Abstract: We compare three distinct computational approaches based on first-principles calculations within density functional theory to explore the magnetic exchange and the Dzyaloshinskii-Moriya interactions (DMI) of a Co monolayer on Pt(111), namely, (i) the method of infinitesimal rotations of magnetic moments based on the Korringa-Kohn-Rostoker (KKR) Green function method, (ii) the generalized Bloch theorem applied to spiraling magnetic structures and (iii) supercell calculations with noncollinear magnetic moments, the latter two being based on the full-potential linearized augmented plane wave (FLAPW) method. In particular, we show that the magnetic interaction parameters entering micromagnetic models describing the long-wavelength deviations from the ferromagnetic state might be different from those calculated for fast rotating magnetic structures, as they are obtained by using (necessarily rather small) supercell or large spin-spiral wave vectors. In the micromagnetic limit, which we motivate to use by an analysis of the Fourier components of the domain-wall profile, we obtain consistent results for the spin stiffness and DMI spiralization using methods (i) and (ii). The calculated spin stiffness and Curie temperature determined by subsequent Monte Carlo simulations are considerably higher than estimated from the bulk properties of Co, a consequence of a significantly increased nearest-neighbor exchange interaction in the Co monolayer $(+50%)$. The calculated results are carefully compared with the literature.

High- Q resonant modes in a finite array of dielectric particles

Abstract: We trace the $Q$ factor of the resonant modes which are limited to bound states in the continuum (BICs) for $N=\ensuremath{\infty}$ in the finite array of $N$ dielectric spheres and disks. For the symmetry-protected BICs we observe the quadratic dependence of the $Q$ factor on $N$ for high-refractive-index particles, while for low-refractive-index particles there is an interplay between the quadratic and cubic dependencies. The $Q$ factor of accidental BICs grows cubically with $N$. We show that a plane wave can excite these quasi-BICs for tuning of the angle of incidence.

Nondipole strong-field approximation for spatially structured laser fields

Abstract: The strong-field approximation (SFA) is widely used to theoretically describe the ionization of atoms and molecules in intense laser fields. We here propose an extension of the SFA to incorporate nondipole contributions in the interaction between the photoelectron and the driving laser field. To this end, we derive Volkov-type continuum wave functions of an electron propagating in a laser field of arbitrary spatial dependence. Based on previous work by L. Rosenberg and F. Zhou [Phys. Rev. A 47, 2146 (1993)], we show how to construct such Volkov-type solutions to the Schr\"odinger equation for an electron in a vector potential that can be written as an integral superposition of plane waves. These solutions are therefore not restricted to plane waves but are also appropriate to deal with more complex laser fields like twisted Bessel or Laguerre-Gaussian beams, where the magnetic field plays an important role. As an example, we compute photoelectron spectra in the above-threshold ionization of atoms with a single-mode plane-wave laser field of midinfrared wavelength. Especially, we demonstrate how peak offsets in the ${p}_{z}$ direction can be extracted that result from the nondipole nature of the interaction. Here, we find good agreement with previous theoretical and experimental studies for circular polarization and discuss differences for linear polarization.

Single-pixel phase imaging by Fourier spectrum sampling

Abstract: We present a single-pixel imaging technique that enables phase extraction from objects by complex Fourier spectrum sampling. The technique exploits a digital micromirror device to scan a wavevector-varying plane wave, which interferes with a stationary reference beam to produce time-varying spatial frequencies on the object. Synchronized intensity measurements are made using a single-pixel detector, and four-step phase-shifting is adopted in spectrum acquisition. Applying inverse Fourier transform to the obtained spectrum yields the desired image. The proposed technique is demonstrated by imaging two digital phase objects. Furthermore, we show that the image can be reconstructed from sub-Nyquist measurements via compressive sensing, considerably accelerating the acquisition process. As a particular application, we use the technique to characterize the orbital angular momentum of vortex beams, which could benefit multiplexing techniques in classical and quantum communications. This technique is readily integrated into commercial microscopes for quantitative phase microscopy.

Fundamental solution of steady oscillations for porous materials with dual-phase-lag model in micropolar thermoelasticity

Abstract: This article deals with the study of propagation of plane waves in an isotropic thermoelastic medium for porous materials with the linear theory of micropolar thermoelasticity. The problem is treat...

Target reconstruction with a reference point scatterer using phaseless far field patterns

Abstract: An important property of the phaseless far field patterns with incident plane waves is the translation invariance. Thus it is impossible to reconstruct the location of the underlying scatterers. By...

Analysis and Experiments on Reflection and Refraction of Orbital Angular Momentum Waves

Abstract: In this paper, a theoretical analysis of orbital angular momentum (OAM) wave propagation properties in terms of reflection and refraction is introduced by decomposing OAM waves into infinite plane waves in the spectral domain with different elevation and azimuth angles. Transformations of phases and amplitudes at the interface of two media for different incident angles and elevation angles are numerically analyzed. Similarly, based on the idea of decomposing OAM waves, reflection and refraction properties of OAMwave propagating through slabs are also analyzed and simulated. Finally, experiments on OAM waves with both mode numbers 1 and 2 are conducted to demonstrate the reflection and refraction properties of OAM waves.

Effect of hall current on propagation of plane wave in transversely isotropic thermoelastic medium with two temperature and fractional order heat transfer

Abstract: This research is devoted to the study of plane wave propagation in homogeneous transversely isotropic magneto-thermoelastic rotating medium with combined effect of hall current and two temperature. The research is applied to fractional order theory with three-phase lag heat transfer. It is analysed that, for 2-D assumed model, three types of coupled longitudinal waves (quasi-longitudinal, quasi-transverse and quasi-thermal) are present. The wave characteristics like phase velocity, specific loss, attenuation coefficients, energy ratios, penetration depths and amplitude ratios of transmitted and reflected waves are computed numerically and illustrated graphically. The impact of hall current parameter by taking different values is represented graphically. Some particular cases are also derived from this research.

Photonic nanojets with mesoscale high-index dielectric particles

Abstract: In this work, we demonstrate the ability of high-index dielectric particles immersed in air to generate photonic nanojets with extreme resolution (∼0.06λ0). Both 2D (cylindrical) and 3D (spherical) particles are analyzed, and their profile is truncated using the Weierstrass formulation for solid immersion lenses to produce a photonic nanojet at the output surface under plane wave illumination. Their focusing capability is evaluated in terms of the spatial resolution achieving subwavelength values of ∼0.14λ0 and ∼0.06λ0 for a truncated cylinder and sphere, respectively. The capability of the truncated sphere to enhance the backscattering produced by two small metallic spherical scatterers placed near the photonic nanojet is evaluated by using a scanning-probe microscopy configuration. The imaging capabilities of this technique are also analyzed by moving the metallic spheres in the transversal plane where the photonic nanojet is produced. The results presented here improve greatly the typical resolution of photonic nanojets generated with dielectric particles with a small index contrast. In addition, the high-index material allows using mesoscale particles, leading to a more compact setup. These results may find applications in areas such as microscopy, imaging, and sensing devices where a subwavelength resolution below the diffraction limit is needed.In this work, we demonstrate the ability of high-index dielectric particles immersed in air to generate photonic nanojets with extreme resolution (∼0.06λ0). Both 2D (cylindrical) and 3D (spherical) particles are analyzed, and their profile is truncated using the Weierstrass formulation for solid immersion lenses to produce a photonic nanojet at the output surface under plane wave illumination. Their focusing capability is evaluated in terms of the spatial resolution achieving subwavelength values of ∼0.14λ0 and ∼0.06λ0 for a truncated cylinder and sphere, respectively. The capability of the truncated sphere to enhance the backscattering produced by two small metallic spherical scatterers placed near the photonic nanojet is evaluated by using a scanning-probe microscopy configuration. The imaging capabilities of this technique are also analyzed by moving the metallic spheres in the transversal plane where the photonic nanojet is produced. The results presented here improve greatly the typical resolution of...

Dual-band transmission-type circular polariser based on frequency selective surfaces

Abstract: A design of dual-band transmission-type linear-to-circular polarisation converter based on frequency selective surfaces (FSSs) has been presented in this study. The proposed converter is implemented by cascading a two-dimensional periodic array of split-ring resonators bisected by metal strips and an array of rectangular patches surrounded by rectangular microstrip rings. The structure composed of metal layers and dielectric layers is designed to behave differently for field components of the two orthogonal polarisations and transmit a circularly polarised wave once illuminated by a linearly polarised plane wave within two frequency bands. Using the equivalent circuit models of the FSSs, the operating principle of the converter is presented and discussed in detail. Also, as an illustrating example, a prototype of the proposed polarisation converter operating in two frequency bands of 6.4-8.8 GHz and 12.1-13.9 GHz is simulated, fabricated and experimentally characterised. The measurement results demonstrate that the dual-band polarisation converter operates <;3 dB axial ratio in a field view of ±25° with fractional bandwidths of 31.6 and 13.8%.