Field In Waveguide Research Articles

ON THE WAVE GENERATION IN A MAGNETOACTIVE WAVEGUIDE

The conditions for generation in the superradiance regime and the formation of a waveguide field taking into account reflection from the ends are discussed. In different generation modes, as shown in this work, both the waveguide field, determined by reflection effects and the geometry of the system, and the field of the total radiation of core particles, that is, the superradiance field, can dominate.

Novel energy exchange behaviors and mechanisms in nonlinear acoustic metamaterials with multiple nonlinear resonators

Wave-wave interactions in a nonlinear metamaterial or structure with two propagating waves can induce energy exchange within the nonlinear systems. The effects of nonlinear resonators on these interactions and energy exchanges in a nonlinear acoustic metamaterial have not been extensively studied in the literature. In this paper, a nonlinear monatomic acoustic metamaterial with multiple nonlinear resonators (NMAM-MNR) is constructed to investigate the new behaviors and mechanisms introduced by these nonlinear resonators. Stability analyses reveal that stability can be tuned by adjusting the number of nonlinear resonators and by selecting different intensities or masses of the resonators and the chain. Additionally, direct numerical simulations are performed to study the novel energy exchange behaviors and mechanisms in NMAM-MNR systems. The results demonstrate that the degree and frequency of energy exchange can be tuned by altering the mass ratios, stiffness ratios, intensities, and natural frequencies of the nonlinear resonators and the chain. The influence of mass and stiffness ratios on the time taken for the B-wave magnitude to first reach its maximum value in NMAM-MNR systems is also studied, showing that the rate of energy exchange induced by wave-wave interactions can be tuned by changing the stiffness and mass ratios of multiple nonlinear resonators. These properties have potential applications in the fields of energy harvesters, waveguides, and resonant energy transfer mechanisms.

Visualization of electromagnetic fields in a circular waveguide using Mathematica

This paper employs Mathematica for visualizing electromagnetic fields (EMF) in circular waveguides, effectively addressing pedagogical challenges related to theoretical abstraction and computational complexity. We first derive the exact solutions for guided modes, then summarize the steps for visualizing EMF using Mathematica, propose educational strategies, and showcase simulation results. The Mathematica code is provided, allowing for dynamic parameter adjustment and real-time field change observation. This approach significantly enhances undergraduate students’ understanding of electromagnetism through engaging visual and interactive learning experiences.

Enhancement of terahertz fields in LiTaO3 waveguides using a conical pulse front.

The development of methods for the generation of strong ultrafast electromagnetic pulses in the terahertz (THz) spectral range has led to a surge of progress in nonlinear THz spectroscopy and THz control of molecular and collective responses. For spectroscopy in the 1-THz range, the submillimeter wavelengths and associated large spot sizes, large optical elements, and short distances between final focusing elements and samples can lead to cumbersome experimental setups that are incompatible with some sample environments. Here, we introduce a novel terahertz ring excitation (TREx) optical pumping geometry to generate superposing, focusing fields in planar THz waveguides made out of the electro-optic material lithium tantalate. High THz fields, >175 kV/cm, are generated and measured optically with no free-space THz propagation. The field level achieved by pumping with a sequence of concentric rings of excitation light exceeds by about 20× the result of a single cylindrically focused line of pump light that has been used routinely in previous work. The technique opens new prospects for compact waveguide-based linear and nonlinear THz spectroscopy and signal processing.

Micron-sized fiber diamond probe for quantum precision measurement of microwave magnetic field

Abstract We present a quantitative measurement of the horizontal component of the microwave magnetic field of a coplanar waveguide using a quantum diamond probe in fiber format. The measurement results are compared in detail with simulation, showing a good consistence. Further simulation shows fiber diamond probe brings negligible disturbance to the field under measurement compared to bulk diamond. This method will find important applications ranging from electromagnetic compatibility test and failure analysis of high frequency and high complexity integrated circuits.

Trans-dimensional joint inversion of modal amplitude and arrival- time data for geoacoustic properties in layered muddy sediments

Long-range sound fields in a shallow-water waveguide can be expressed as a summation of several dispersive propagating modes. Modal arrival times as a function of frequency, extracted via warping time-frequency analysis, have been used by many researchers to estimate sound speeds and densities for layered models of the seabed sediments. This paper explores joint inversion of modal amplitude spectra together with arrival times to also estimate sediment-layer attenuations. To consider the common case in underwater-acoustic applications where the source amplitude spectrum is unknown, we include this spectrum as unknown parameters in the inversion, formulated implicitly within the likelihood function. Trans-dimensional Bayesian inversion is applied to estimate marginal probability profiles of the geoacoustic properties, providing quantitative uncertainties. The data considered here were collected on the New England Mud Patch during the 2017 Seabed Characterization Experiment. [Work supported by the Office of Naval Research.]

Structure of interferogram and hologram of non-moving source in presence of shallow water internal waves

The results of holographic signal processing of the oceanographic experiment SWARM-95 on the coast of New Jersey are presented in the paper. The used acoustic signals were obtained on stationary acoustic track (non-moving airgun source) in the presence of shallow water intensive internal waves (IIW). The IIW led to significant 3D acoustic effects [Badiey et al., JASA 117(2), 613–625]. Within framework of holographic signal processing [Pereselkov and Kuz’kin, JASA 151(2), 666–676] the source interferogram (sound intensity distributions in frequency-time coordinates) is analyzed by two-dimensional Fourier transform (2D-FT). The result of the 2D-FT is called the Fourier hologram (source hologram). In result of holographic signal processing, the two separated sets of spectral spots are obtained in hologram domain. The first set of spectral spots corresponds to sound field in nonperturbed waveguide (without of IIW). The second set of spectral spots in hologram corresponds to hydrodynamic field perturbation by IIW. This structure of the hologram allows the reconstruction of interferogram of nonperturbed field for waveguide in the absence of IIW. The error in the reconstruction of the nonperturbed interferogram is estimated. [Work supported by grant from the Russian Science Foundation 23-61-10024.]

Semi-analytical solution for sound propagation from a moving directional source in a shallow-water waveguide

Understanding the waveguide fields produced by moving directional sources is of crucial importance in underwater acoustic detection. In practice, moving underwater targets often exhibit directionality, especially at high frequencies. Herein, we present a semi-analytical method to calculate the Doppler-shifted field (DSF) from a directional source moving horizontally in a range-independent, shallow-water waveguide. We develop a novel normal-mode model using a modal-projection approach with a perfectly matched layer. This comprehensively accounts for changes in modal shape, eigenvalue shifts, and the branch-integral contribution. We derive an analytical expression for the DSF based on Huygens’ principle, and the solution is presented as a sum over propagating eigenmodes, with the modal excitation determined by the source directivity depending upon the grazing angle of each pair of modal plane waves. This expression is valid for any type of radiator moving in a range-independent environment with a smoothly varying sound-speed profile. We then present a theoretical analysis of the Doppler beam shift produced by a piston-like radiator. This reveals that the observed angular offset of modal plane waves can be attributed to the Doppler beam shift and confirms that this is a new mechanism causing considerable differences between the fields generated by a directional moving source and by the same source at rest. This has potential value in various applications, particularly for underwater acoustic detection of moving targets.

Toward a10 dB net-gain waveguide amplifier in an Er3+-Yb3+ co-doped phosphate glass.

High-gain materials and high-quality structures are the two main conditions that determine the amplification performance of optical waveguides. However, it has been hard to balance each other, to date. In this work, we demonstrate breakthroughs in both glass optical gain and optical waveguide structures. We propose a secondary melting dehydration technique that prepares high-quality Er3+-Yb3+ co-doped phosphate glass with low absorption loss. Additionally, we propose a femtosecond laser direct-writing technique that allows controlling the cross section, size, and mode field of waveguides written in glass with high accuracy, leveraging submicron-resolution multi-scan direct-writing optical waveguide technology, which is beneficial for reducing insertion loss. As a proof of concept demonstration, we designed and fabricated two kinds of waveguides, namely, LP01- and LP11-mode waveguides in the Er3+-Yb3+ co-doped phosphate glass, enabling insertion loss as low as 0.9 dB for a waveguide length of 2 mm. Remarkably, we successfully achieved an optical amplification for both the waveguides with a net gain of >7 dB and a net-gain coefficient of >3.5 dB/mm, which is approximately one order of magnitude larger than that in the Er3+-Yb3+ co-doped phosphate glass fabricated by the traditional melt-quenching method. This will open new avenues toward the development of integrated photonic chips.

Guided wave propagation in a double-layer plate with a nonlinear spring-interface

This article derives the solution to the guided wave fields in a double-layer plate consisting of two sublayers. It is assumed that the two sublayers are linearly elastic. They are bonded together at their interface by a nonlinear adhesive layer of infinitesimal thickness. This allows us to propose a nonlinear spring-interface model. Based on such an idealized model for the double-layer plate, guided wave fields in the plate are solved using the modified normal mode expansion method. It is found that the nonlinearity of the spring-interface can generate resonant guided waves in the double-layer plate. Specifically, when certain conditions are met, mixing of two primary guided waves will generate resonant guided waves whose frequencies are either the sum or difference of those of the two primary waves. Amplitudes of such resonant mixed waves are proportional to the compliance of the nonlinear spring-interface. As a special case, if the two primary waves have the same frequency, a resonant second harmonic guided wave may be generated. In addition, the conditions that generate resonant mixed waves are identified. We believe that the results of this work provide the theoretical foundation on which nondestructive evaluation techniques using nonlinear guided waves can be developed to nondestructively evaluate, for example, the bond strength of thin coating on a substrate.

Eigenvalues bifurcating from the continuum in two-dimensional potentials generating non-Hermitian gauge fields

It has been recently shown that complex two-dimensional (2D) potentials Vɛ(x,y)=V(y+iɛη(x)) can be used to emulate non-Hermitian matrix gauge fields in optical waveguides. Here x and y are the transverse coordinates, V(y) and η(x) are real functions, ɛ>0 is a small parameter, and i is the imaginary unit. The real potential V(y) is required to have at least two discrete eigenvalues in the corresponding 1D Schrödinger operator. When both transverse directions are taken into account, these eigenvalues become thresholds embedded in the continuous spectrum of the 2D operator. Small nonzero ɛ corresponds to a non-Hermitian perturbation which can result in a bifurcation of each threshold into an eigenvalue. Accurate analysis of these eigenvalues is important for understanding the behavior and stability of optical waves propagating in the artificial non-Hermitian gauge potential. Bifurcations of complex eigenvalues out of the continuum is the main object of the present study. Using recent mathematical results from the rigorous analysis of elliptic operators, we obtain simple asymptotic expansions in ɛ that describe the behavior of bifurcating eigenvalues. The lowest threshold can bifurcate into a single eigenvalue, while every other threshold can bifurcate into a pair of complex eigenvalues. These bifurcations can be controlled by the Fourier transform of function η(x) evaluated at certain isolated points of the reciprocal space. When the bifurcation does not occur, the continuous spectrum of 2D operator contains a quasi-bound-state which is characterized by a strongly localized central peak coupled to small-amplitude but nondecaying tails. The analysis is applied to the case examples of parabolic and double-well potentials V(y). In the latter case, the bifurcation of complex eigenvalues can be dampened if the two wells are widely separated.

A Method for Estimating Source Depth Based on the Adjacent Mode Group Acoustic Pressure Field

In order to effectively estimate the depth of the source in the acoustic pressure field, this study investigated the relationship between the distribution of acoustic pressure fields in different adjacent mode groups and the depth of the source in shallow waveguides and proposed a method to estimate the depth of the source on the basis of the adjacent mode group acoustic pressure field. We first derived and calculated the adjacent mode group acoustic pressure field of a typical shallow waveguide, then verified the accuracy of this derivation process through simulations. In addition, combined with singular value decomposition mode extraction, the adjacent mode group acoustic pressure field of the SACLANT experimental data was obtained and used as a comparative parameter for the method presented in this paper. By using the depth of the source as the estimation variable, a simulated annealing algorithm and related parameters were designed, and the feasibility of this method was verified through simulation and experiments. The proposed method achieved a higher localization accuracy without the need for accurate modeling of underwater acoustic channels. Under the conditions of the simulation environment, the average estimation error rate of the method was 0.24%, and with increases in the temperature coefficient and Markov chain length, the average estimation error rate of the method decreased. In the experimental environment, the average estimation error rate of the method was 0.45%. This study provides a method to obtain the depth of source in a shallow waveguide via the adjacent mode group acoustic pressure field.

Physics-informed neural network for predicting unmeasured ocean acoustic pressure field

This study employs a physics-informed neural network in an ocean waveguide to predict the unmeasured acoustic pressure field, leveraging partially measured data. The method addresses a scenario where an acoustic source transmits signals across different ranges and is measured by multiple receivers. The acoustic pressure field in ocean waveguides exhibits rapid spatial variations over kilometer-range scales. The fully connected neural networks encounter challenges when approximating high-frequency functions, known as spectral bias. To mitigate this problem, the measured pressure field is transformed into a low-frequency function for training the neural network. We propose two methods sharing the same neural network architecture but utilizing different information. The first method uses a complex value of the pressure field (i.e., both magnitude and phase), while the second method uses only magnitude. We validate the proposed methods using simulations and experimental data from the SWellEx-96 environment. Results demonstrate that the first method exhibits superior performance with sparse data, while the second method works better in real-world scenarios.

Broadband Acoustic Field in a Shallow-Water Waveguide with an Inhomogeneous Bottom

Broadband Acoustic Field in a Shallow-Water Waveguide with an Inhomogeneous Bottom

Optical readout and actuation of plasmonic nano-optomechanical drum resonators

We demonstrate optical readout and actuation of nanomechanical motion using plasmonic fields in a nanoscale gap waveguide. The top gold layer of the waveguide is free to vibrate like a drumhead, and patterned with an optical grating to facilitate efficient coupling to free-space radiation. The change of the plasmonic gap mode with the top layer position couples the plasmonic resonance to the mechanical displacement of the drum. We characterize optical and mechanical resonances of the system, and demonstrate sensing of nanomechanical vibrations with ∼10−14 m/Hz sensitivity. The mechanical resonators are actuated through plasmonic forces. Quantifying their magnitude shows that plasmonic forces can significantly exceed pure radiation pressure, indicating that their nature is dominated by a photothermoelastic effect. This work opens avenues to the use of plasmonic readout and control in nanomechanical sensing applications.

Broadband Acoustic Field in a Shallow-Water Waveguide with an Inhomogeneous Bottom

A broadband (35–1000 Hz) sound field formed by a point source in a shelf zone with inhomogeneous bottom sediment structure is studied using numerical modeling. The shelf depth is about 30 m and the maximum distance is 10 km. The transitional zone from the bottom with a sound speed of 1400 m/s to the bottom with a speed of 1600 m/s is chosen as the model inhomogeneity. The normal mode theory and wide-angle parabolic equations are used for sound field calculations. Numerical experiments show that the manifestation of horizontal refraction is noticeable at low frequencies (below 100 Hz). It leads to an increase in the amplitude of the low-frequency sound pulse propagating along the transitional zone by more than 10 dB in comparison with a similar waveguide with a homogeneous bottom. At frequencies above 100 Hz, the dominant effect is the mode coupling, causing the appearance of quasi-periodic oscillations of modal amplitude in the frequency domain. The conclusions from the simplified model are confirmed by calculations for the real structure of bottom sediments in the Kara Sea.

Singular Points Location Pattern Analysis based on Modes Interference

<p>Given the lack of research on the regularity of distribution of singular points, the singular points under different influence factors are analyzed. The location of singular points for adjacent modes group (AMG) generated by the interference modes is derived using normal modes theory in the far field of the ideal shallow waveguide. The singular points are verified by simulation, which compares the distribution of the acoustic field and singular points. Moreover, it is concluded that the number and distribution of singular points in the period of the interference structure of the field (PISF) has a relationship with order (lower order of AMG) and adjacent order (difference between two orders of AMG). The arrangement of upper-lower-two-points increases by 2 with each increase of order and is distributed at both ends of PISF. The arrangement of rhombic-four-points increases by 1 with each increase of adjacent order and increases alternately at both ends of PISF. Meanwhile, there is a periodic relationship between the depth of the source and the location of singular points.</p> <p> </p>

Power Pattern Synthesis With Peripherally Excited Phased Arrays

Peripherally excited phased arrays have been demonstrated as an effective way to realize some aspects of phased array performance with a simple design and reduced cost. This work develops a method to realize shaped beams with peripherally excited arrays by controlling the relative magnitude and phase of the antenna’s peripheral sources. Through a simple model of fields in a parallel-plate waveguide, a linear system of equations can be defined and solved to find the peripheral source excitations that best approximate a desired field pattern. This model is used to solve for a uniform broadside beam, and yields a higher aperture illumination efficiency than a broadside beam obtained from an equal-amplitude excitation. A cosecant beam is also synthesized, showing good agreement with the goal beam pattern. The linear system of equations can be easily integrated into other beam synthesis techniques for increased design flexibility. A particle swarm optimization is used to solve for controlled side lobe-levels, flat-top and multi-beam patterns. Beams realized with full-wave simulation show good agreement with the ideal and predicted beams.

Reciprocity-based closed-form solutions to guided waves in multilayered structures subjected to time-harmonic excitations

Ultrasonic guided waves provide an efficient tool for nondestructive evaluation and characterization of multilayered structures, e.g., of adhesively bonded joint in aerospace industry. In this article we investigate the propagation of guided waves in fully bonded multilayered plates excited by time-harmonic sources. By using the transfer matrix method, we propose explicit expressions of the free guided waves that depend on only one unknown constant representing amplitude. From these expressions, theoretical predictions of guided wave fields arising from a time-harmonic source are derived by using the reciprocity relations in elastodynamics. These very first closed-form solutions offer several distinct advantages, including efficient solution of inverse problems for materials characterization, direct calculation of guided waves at every point with a low computational cost and a benchmark to verify and improve numerical analysis of guided waves in multilayered structures. The obtained results are illustrated by computing guided wave motions in the bond region of an adhesively bonded lap joint, commonly used in automotive and aeronautical industries. The dispersion curves produced here are significant improvement upon those available in literature, as they are superimposed with the amplitude spectra values, enabling optimal selection of modes and frequencies for ultrasonic inspection. The analytical predictions of guided wave amplitudes in a three-layer adhesive joint model are numerically verified through finite element simulations, showing excellent agreement with the lowest guided wave modes.

A wideband and compact Quasi-Yagi antenna based on spoof surface plasmon polaritons

In this paper, a novel wideband end-fire antenna, based on a spoof surface plasmon polaritons (SSPP) transmission line, is proposed. Periodically modulated corrugated metal strips are used as a transmission line for quasi-TEM conversion in the microstrip line to the state of SSPP and the best impedance matching. Due to the strong confinement of the field in the SSPP waveguide and its high transmission performance, it has been used as a transmission line. The antenna consists of SSPP waveguides for the transmission line, a metal plate on the ground as the reflector of the antenna, a metal strip director, and two half-rings to realize the radiation, reaching a wide bandwidth in the range of 4.1 to 8.1 GHz. The simulation results show that this antenna achieves a gain of 6.5 dBi, a bandwidth of 65%, and an efficiency of 97% across a wide operating frequency band, from 4.1 to 8.1 GHz. The proposed end-fire antenna has been fabricated, and the measured results agree well with the simulated results. The end-fire antenna implemented on a dielectric layer also has the advantages of high efficiency, good directivity, high gain, a wide bandwidth, easy fabrication, and a compact size.