Ideal Waveguide Research Articles

A unidirectional air waveguide basing on coupling of two self-guiding edge modes

Nonreciprocal waveguide plays the key role in optical communication devices because of the robustness of one-way transport along the edge. We present a 2D honeycomb magnetic-optical photonic crystal frame and realize a unidirectional air waveguide based on the coupling effect of two self-guiding one-way edge modes in proper the waveguide width. A great ideal nonreciprocal air waveguide with condensed-energy, strong stability, great nonreciprocity is achieved, and its transmission features of superiority over others configuration are demonstrated.

Modeling underwater noise propagation from marine hydrokinetic power devices through a time-domain, velocity-pressure solution.

Marine hydrokinetic (MHK) devices generate electricity from the motion of tidal and ocean currents, as well as ocean waves, to provide an additional source of renewable energy available to the United States. These devices are a source of anthropogenic noise in the marine ecosystem and must meet regulatory guidelines that mandate a maximum amount of noise that may be generated. In the absence of measured levels from in situ deployments, a model for predicting the propagation of sound from an array of MHK sources in a real environment is essential. A set of coupled, linearized velocity-pressure equations in the time-domain are derived and presented in this paper, which are an alternative solution to the Helmholtz and wave equation methods traditionally employed. Discretizing these equations on a three-dimensional (3D), finite-difference grid ultimately permits a finite number of complex sources and spatially varying sound speeds, bathymetry, and bed composition. The solution to this system of equations has been parallelized in an acoustic-wave propagation package developed at Sandia National Labs, called Paracousti. This work presents the broadband sound pressure levels from a single source in two-dimensional (2D) ideal and Pekeris wave-guides and in a 3D domain with a sloping boundary. The paper concludes with demonstration of Paracousti for an array of MHK sources in a simple wave-guide.

Array invariant-based calibration of array tilt using a source of opportunity.

The array invariant, a robust approach to source-range estimation in shallow water, is based on the dispersion characteristics of broadband signals in ideal waveguides. It involves time-domain plane-wave beamforming using a vertical line array (VLA) to separate multiple coherent arrivals in beam angle and travel time. Typically, a probe signal (i.e., a cooperating source) is required to estimate the Green's function, but the array invariant has been recently extended to a ship of opportunity radiating random signals using a ray-based blind deconvolution [Byun, Kim, Cho, Song, and Byun, J. Acoust. Soc. Am. 142, EL286-EL291 (2017)]. Still, one major drawback is its sensitivity to the array tilt, shifting the beam angles and adversely affecting the array invariant parameter that determines the source range. In this paper, a simple optimization algorithm for simultaneous estimation of the array tilt and the source range is presented. The method is applied to a ship of opportunity (200-900 Hz) circling around a 56-m long VLA at a speed of 3 knots (1.5 m/s) at ranges of 1.8-3.6 km in approximately 100-m deep shallow water. It is found that the standard deviation of the relative range error significantly reduces to about 4%, from 14% with no compensation of the array tilt. The estimated tilt angle displayed as a function of the ship's azimuth angle reveals that the VLA is tilted about 3° towards the northwest, suggesting that the array invariant can serve as a remote sensing technique for calibration of the array tilt using a source of opportunity.

Sound radiation of cylinder in shallow water investigated by combined wave superposition method

It can be a difficult problem to precisely predict the sound field radiated from a finite elastic structure in shallow water channel because of its strong coupling with up-down boundaries and the fluid medium, whose sound field cannot be calculated directly by current methods, such as Ray theory, normal mode theory and other different methods, which are adaptable to sound fields from idealized point sources in waveguide. So far, there is no reliable prediction method to solve this kind of problem. A combined wave superposition method is proposed for such a problem, which combines the traditional wave superposition method with the transfer function in shallow water channel and the multi-physics field coupling numerical model. This method mainly consists of three sections:1) obtaining the normal velocity on the elastic structure surface in shallow water channel by the finite element method (FEM), whose FEM model includes the up-down boundaries and the completely absorbent sound boundaries in the horizontal direction; 2) getting the equivalent point source strength by traditional wave superposition method; 3) calculating the total sound field by adding up each point source field which is obtained by normal mode method. This method is verified by numerical simulation and theoretical analysis by using an imaginary and elastic spherical sound source respectively, and the results demonstrate that the method is valid and has high precision and calculating efficiency. The acoustic radiation characteristics from elastic cylindrical shells is investigated for different acoustic radiation sources, ocean environments and measurements. The cylindrical shell material is steel, whose radius and length are 3 m and 30 m respectively. The shallow water channel is an ideal waveguide with 50 m in depth, at the upper boundary, i.e., the free surface, the lower boundary is the Neumann boundary, i.e., the normal derivative of the acoustic pressure should be zero. The analysis frequency range is from 30 Hz to 200 Hz. The results show that due to a significant coupling effect of up-down direction boundaries on the sound field, the elastic structure can be equivalent to the point source only in low frequency and far field. The spatial field directivity distribution is more obvious at high frequency. The acoustic power measured by vertical line arrayis greatly influenced by ocean boundary and the depth of target.

Design of Planar Leaky Wave Antenna Fed by Substrate Integrated Waveguide Horn

AbstractA metal strip grating leaky wave antenna (MSG-LWA) fed by substrate integrated waveguide (SIW) horn is proposed. The planar horn shares the same substrate with the MSG-LWA, which leads to a compact structure of the proposed antenna. Furthermore, through introducing phase-corrected structure by embedding metallized vias into the SIW horn, a nearly uniform phase distribution at the horn aperture is obtained, which effectively enhances the radiating performance of the MSG-LWA. Results indicate that the proposed antenna scans from –50° to –25° in the frequency band ranging from 15.3 GHz to 17.3 GHz. Besides, effectiveness of the proposed design is validated by comparing with a same MSG-LWA fed by an ideal rectangular waveguide.

Finite impulse response of an ocean acoustic waveguide by compressed sensing

The usual approach to calculating the time domain acoustic response of an ocean waveguide is to Fourier synthesize it from a regularly sampled collection of frequency domain solutions. Depending on the details of the waveguide and the excitation signal, the resulting time series may be very sparse with significant time intervals of relative quiet between energetic multipath arrivals. This observed sparsity in the time domain suggests a computational advantage to synthesizing the time series by solving a convex optimization problem involving a much smaller set of solutions computed at random frequencies. The efficiency of the compressed sensing approach will depend on the sparsity of the time domain solution; the greater the sparsity in the time domain signal the greater the expected advantage of the compressed sensing approach. In this talk we examine the compressed sensing method of time series synthesis for a sequence of waveguides that range from extremely simple and ideal waveguides where the sparsity is expected to be great to the more realistic and complicated where the sparsity is expected to be reduced. [This work was supported by the U.S. Office of Naval Research.]

Array invariant-based localization using ships of opportunity

The array invariant (AI) proposed for robust source-range estimation with minimal knowledge of the environment in shallow water is based on the dispersion characteristics in ideal waveguides. This approach involves plane wave beamforming, utilizing coherent multiple arrivals separated in beam angle and travel time, referred to as “beam-time migration.” To resolve multipath arrivals in beam-time domain, AI requires either an impulsive source or Green’s function typically estimated from a known probe signal. For unknown source waveforms, it is possible to estimate the Green’s function using a ray-based blind deconvolution (RBD) which also utilizes simple conventional beamforming. Recently, the cascade of RBD and AI has been demonstrated for a towed source at 50-m depth broadcasting communication waveforms [J. Acoust. Soc. Am. 141, 3270–3273 (2017)]. Rather than the towed source, this study focuses on the feasibility of tracking a ship radiating random and anisotropic noise. The combination of RBD and AI is ...

Cascade of blind deconvolution and array invariant for robust source-range estimation

The array invariant proposed for robust source localization in shallow water is based on the dispersion characteristics in ideal waveguides. It involves conventional plane-wave beamforming using a vertical array, exploiting multiple arrivals separated in beam angle and travel time, i.e., beam-time migration. The approach typically requires either a short pulse emitted by a source or the Green's function that can be estimated from a probe signal to resolve distinct multipath arrivals. In this letter, the array invariant method is extended to unknown source waveforms by extracting the Green's function via blind deconvolution. The cascade of blind deconvolution and array invariant for robust source-range estimation is demonstrated using a 16-element, 56-m long vertical array at various ranges (1.5–3.5 km) from a towed source broadcasting broadband communication waveforms (0.5–2 kHz) in approximately 100-m deep shallow water.

Coupled thermal and optical analysis of a planar waveguide concentrator-receiver

Harvesting solar energy using optical concentrators such as parabolic troughs or heliostats involve active tracking that requires costly drives and sizable support structures. This study explores the use of optical waveguides based on total internal reflection for concentrating sunlight onto thermal receivers, with the goal of minimizing or eliminating moving parts, tracking structures and cost. To this end, the paper presents an analytical closed-form solution for the coupled optical and thermal transport of solar irradiation through an ideal planar waveguide concentrator integrated with linear receiver at both ends. The effects of various design and operating parameters are systematically investigated on the system performance, which is quantified in terms of net thermal power delivered, aperture area required and collection efficiency. Design envelopes that identify feasible waveguide configurations based on thermal stress, maximum continuous operation temperature and structural constraints are illustrated. The study provides an upper bound for the maximum performance achievable with planar waveguide concentrator-receiver configuration that can be used asa benchmark to compare different practical designs. Further, a cost analysis is presented to determine the preferred design configurations that minimize the cost per unit area of the planar waveguide concentrator coupled to the receiver. Considering applications to thermal desalination and concentrated solar thermal power generation, optimal design configuration of waveguide concentrator-receiver system is identified that results in the least levelized cost of power (LCOP). Sensitivity analysis of the total cost per unit area and LCOP to waveguide material parameters and cost is used to derive improvements needed to meet the U.S. Department of Energy (DOE) SunShot’s solar field cost target of $75/m2.

Design and Fabrication of a 300 GHz Modified Sine Waveguide Traveling-Wave Tube Using a Nanocomputer Numerical Control Machine

The sine waveguide slow-wave structure is a promising interaction circuit for traveling-wave tubes in the terahertz region because it possesses advantageous properties such as high transmission, easy fabrication, and elimination of the electron beam tunnel. These waveguides could be fabricated by nanocomputer numerical control (CNC) machining, a fabrication method capable of fabricating microscale components. In our study, we evaluate the practical feasibility of manufacturing 300-GHz sine waveguides with the ideal design, using nano-CNC machining. It is found that the ideal sine waveguide circuit must be modified, because of the limitations imposed by the actual tool size of the nano-CNC machine. Simulations of cold- and hot-tests of the circuit—including the electron beam effect—were conducted for both the ideal and the modified sine waveguide circuits. A modified sine waveguide was successfully machined using a nano-CNC machine with a 0.12-mm diameter tool tip. The S-parameters of the fabricated circuit were measured and compared to simulation data. A detailed analysis of the measured transmission loss was performed, and this loss was found to be attributable to a gap left by the assembly process between the two copper plates.

Cascade of blind deconvolution and array invariant for robust source-range estimation.

The array invariant proposed for robust source localization in shallow water is based on the dispersion characteristics in ideal waveguides. It involves conventional plane-wave beamforming using a vertical array, exploiting multiple arrivals separated in beam angle and travel time, i.e., beam-time migration. The approach typically requires either a short pulse emitted by a source or the Green's function that can be estimated from a probe signal to resolve distinct multipath arrivals. In this letter, the array invariant method is extended to unknown source waveforms by extracting the Green's function via blind deconvolution. The cascade of blind deconvolution and array invariant for robust source-range estimation is demonstrated using a 16-element, 56-m long vertical array at various ranges (1.5-3.5 km) from a towed source broadcasting broadband communication waveforms (0.5-2 kHz) in approximately 100-m deep shallow water.

Impact of array tilt on source-range estimation in shallow water using the array invariant.

The array invariant proposed for robust source-range estimation in shallow water is based on the dispersion characteristics in ideal waveguides for broadband signals. With minimal knowledge of the environment, the approach involves plane-wave beamforming using a vertical array, utilizing multiple arrivals (i.e., eigenrays) separated in beam angle and travel time. In the presence of array tilt, however, the beam angle estimates are shifted, which potentially affects the range estimation based on the array invariant. Conversely, the array tilt could be estimated for a known source range. In this paper, the sensitivity to array tilt is analyzed theoretically and examined using simulations and data. It is found that even a small tilt angle (e.g., <2°) of a 1.2 -m long vertical array near the surface, if not compensated for, can result in a relative range error of 20% or more, for a high-frequency source (7-19 kHz) at 3-km range in approximately 100 -m deep shallow water. Moreover, the power spectrum of the time-evolving array tilt estimated for 9 min shows a dominant period of 5.6 s, which is consistent with the surface wave period concurrently measured from a waverider buoy.

Array invariant-based source localization in shallow water using a sparse vertical array

The array invariant proposed for robust source localization in shallow water exploits the beam-time migration of broadband signals. The approach requires minimal knowledge of the environment, but involves plane wave beamforming using a short-aperture vertical array in stratified acoustic waveguides. In this paper, the array invariant approach is extended to a large-aperture vertical array that is sparse with significant variation of the sound speed across the aperture for conventional beamforming. The extension is feasible because the array invariant in shallow water utilizes surface/bottom-reflected arrivals that behave like those in ideal waveguides. Robust source-range estimation is demonstrated using data from a 16-element, 56-m long vertical array at various ranges (1.5-3.5 km) from a broadband source (0.5-2 kHz) in approximately 100-m deep shallow water.

Quantum modes of atomic waveguides by series techniques

Atom waveguides are used to manipulate cold atoms in atom interferometers. The creation of atom interferometers using cold atoms in miniature magnetic waveguides is one of many goals of current atom chip research. To achieve a complete understanding of atom propagation in a complicated device such as a guided atom interferometer, a detailed understanding of the ground state and other nearby states is needed. The Frobenius series solutions for the bounded transverse modes of an atomic waveguide are presented here and arbitrary precision arithmetic is used to evaluate the series solutions without roundoff errors. The waveguide potential considered is an infinitely long quadrupole magnetic potential as used in various atom chip waveguides. The simplest case of a guided spin-12 particle is presented here. However, the basic series techniques can be extended to both higher order multipole potentials and higher spin particles, including atoms with hyperfine splitting. The low-field and the high-field seeking states together form the spectrum of the waveguide Hamiltonian. In the limit where the transverse dimension of the guide tends to infinity, the spectrum of the guide changes from a discrete set of low- and high-field seeking states to a continuum of high-field seeking states embedded with a discrete set of low-field seeking states. Although the low-field seeking states are not truly bound, the system is an approximate example of bound states in a continuum first discussed by von Neumann and Wigner. Depending on boundary conditions, the solutions form either a discrete set or a continuum of orthogonal waveguide modes. These are useful for further analysis of ideal waveguide behavior as well as the detailed perturbation studies necessary for analysis of atomic waveguide interferometers.

Target localization in a reverberant shallow ocean waveguide with environmental uncertainty using a nonlinear frequency-difference signal processing technique

Model-based signal processing for active sonar localization is typically infeasible due to insufficient knowledge of the acoustic environment. Additionally, in a shallow ocean environment, surface or bottom roughness create diffuse reverberation that can often obscure a desired target echo. Recently, a nonlinear signal processing technique was developed for passive acoustic source localization (Worthmann, et al., 2015) that is applicable to high frequency sources in uncertain shallow ocean environments. This technique exploits a nonlinear field product (the autoproduct) and uses in-band hydrophone array measurements to determine field information in a lower, out-of-band, frequency regime where environmental uncertainties are less detrimental. When extended to monostatic active sonar with a vertical array, this technique allows a model-based signal processing algorithm to combat the detrimental effects of reverberation. The nonlinear signal processing algorithm is presented, along with simulations in a 5-km range, 200-m deep ideal waveguide with environmental uncertainties and significant reverberation at frequencies between 2- and 5-kHz. Successful detection and localization of a mid-water-column target is found to be possible at simulated signal-to-reverberation levels as low as −5 dB. Comparisons to existing signal processing detection and localization algorithms are provided. [Sponsored by the Office of Naval Research and the National Science Foundation.]

Transforming Unidirectional Edge Waveguide Into Unidirectional Air Waveguide

A unidirectional waveguide plays the key role in optical communication system. The unidirectional edge modes in two-dimensional magneto-optical photonic crystals have a unique feature because they are robust against imperfections or disruptions along the edge, but they can hardly form an optical beam. In order to obtain a unidirectional air waveguide, we have studied the coupling effect of two unidirectional edge modes basing on band calculations and numerical simulations. With a waveguide width of 1.5a, an ideal unidirectional air waveguide is achieved. The unidirectional air waveguide has great performance because of its broad working bandwidth, high extinction ratio, single-mode feature, and air waveguide configuration. It has an advantage over the unidirectional edge waveguide because it can focus the wave energy and form a one-way beam. An analytical analysis is also given for the results.

Passive impulsive source range estimation based on warping operator in shallow water

An approach to passive impulsive source range estimation in shallow water is proposed. The approach is based on warping transformation of the energy density function of the received signal. Because of the influence of the sea bottom, it is difficult to find a warping operator adapted to the dispersion characteristics of modes in shallow water. Even though the modes can be separated from each other by using the warping operator adapted to the ideal waveguide, it is impossible to obtain the analytic solutions of the characteristic frequencies, while the energy density function of the received signal is not affected by the sea bottom. Like the received signal and the autocorrelation function of the signal, the frequency spectrum of the warped energy density function of the received signal also owns invariable frequency features. These characteristic frequencies equal the difference in the cut-off frequency between two modes in ideal waveguide, which are easy to calculate with the knowledge of the depth and the average sound speed of the water. What is more, the warping operator transforms mode pairs in energy density function with the same mode number difference into one monotone, which means one characteristic frequency is not unique for one mode pair. In shallow water, the acoustic field is typically composed of a group of modes with close mode numbers. Therefore, the smaller the mode number difference, the more the mode pairs, and the higher the spectral peak of the corresponding monotone is. When the source range is unknown, the approximate relation formula between the extracted characteristic frequency in a supposed source range and the real characteristic frequency is derived, based on which a fast passive source range estimation method is proposed. The proposed method successfully avoids using the guide source and the calculation of replica field, which is necessary in existing passive range estimation algorithms. And applying warping operator to the energy density function of the received signal makes it easy to obtain the analytic solutions of the characteristic frequencies, which is impossible in previous researches. The method is successfully applied to the Yellow Sea impulsive signal data collected by a single hydrophone in November 2011. The mean relative error of range estimation is less than 8%.

Multiple modes of surface plasmonic polaritons in transversely-truncated metal/dielectric superlattices

The surface plasmonic polariton (SPP) of a transversely-truncated metal/dielectric superlattice (SL) structure has been solved with an approximate method. The effect of inter-layer interfaces in the SL is taken into consideration efficiently in comparison with the effective-medium method. The silver/air and silver/SiO2 SLs with a shorter period are regarded as two specific examples in numerical calculation. A series of separated SPP modes are found and highly localized at the surface, and the highest-frequency mode is the only one also predicated by the effective-medium method. These results obviously show the effect of inter-layer interfaces in the case of short period, whilst the reliability and limitation of the effective-medium method is presented as well. Because the skin depths of the modes are extremely small, the SLs can be used as ideal surface-wave waveguides.

Source estimation with incoherent waves in random waveguides

We study an inverse source problem for the acoustic wave equation in a random waveguide. The goal is to estimate the source of waves from measurements of the acoustic pressure at a remote array of sensors. The waveguide effect is due to boundaries that trap the waves and guide them in a preferred (range) direction, the waveguide axis, along which the medium is unbounded. The random waveguide is a model of perturbed ideal waveguides which have flat boundaries and are filled with known media that do not change with range. The perturbation consists of fluctuations of the boundary and of the wave speed due to numerous small inhomogeneities in the medium. The fluctuations are uncertain in applications, which is why we model them with random processes, and they cause significant cumulative scattering at long ranges from the source. The scattering effect manifests mathematically as an exponential decay of the expectation of the acoustic pressure, the coherent part of the wave. The incoherent wave is modeled by the random fluctuations of the acoustic pressure, which dominate the expectation at long ranges from the source. We use the existing theory of wave propagation in random waveguides to analyze the inverse problem of estimating the source from incoherent wave recordings at remote arrays. We show how to obtain from the incoherent measurements high fidelity estimates of the time resolved energy carried by the waveguide modes, and study the invertibility of the system of transport equations that model energy propagation in order to estimate the source.

A Benchmark Model for Three-Dimensional Sound Propagation in an Ideal Wedge-Shaped Waveguide

A benchmark model is developed to compute the three-dimensional acoustic field excited by a harmonic point source in a homogeneous wedge-shaped waveguide with impenetrable boundaries. A derivation of the exact solution is presented based on Fourier synthesis, which reduces the three-dimensional ideal wedge problem to a sequence of two-dimensional line-source ideal wedge problems, to which the analytical solution is well established. The details of the numerical implementation of this solution are also provided. Our numerical results indicate that this model is efficient and capable of providing accurate three-dimensional acoustic fields for arbitrary receiver locations, and hence can serve as a benchmark model for sound propagation in a continental shelf environment.