Waveguide Theory Research Articles

The Effect of Attenuation from Fish Shoals on Long-Range, Wide-Area Acoustic Sensing in the Ocean

Acoustics is the primary means of long-range and wide-area sensing in the ocean due to the severe attenuation of electromagnetic waves in seawater. While it is known that densely packed fish groups can attenuate acoustic signals during long-range propagation in an ocean waveguide, previous experimental demonstrations have been restricted to single line transect measurements of either transmission or backscatter and have not directly investigated wide-area sensing and communication issues. Here we experimentally show with wide-area sensing over 360° in the horizontal and ranges spanning many tens of kilometers that a single large fish shoal can significantly occlude acoustic sensing over entire sectors spanning more than 30° with corresponding decreases in detection ranges by roughly an order of magnitude. Such blockages can comprise significant impediments to underwater acoustic remote sensing and surveillance of underwater vehicles, marine life and geophysical phenomena as well as underwater communication. This makes it important to understand the relevant mechanisms and accurately predict attenuation from fish in long-range underwater acoustic sensing and communication. To do so, we apply an analytical theory derived from first principles for acoustic propagation and scattering through inhomogeneities in an ocean waveguide to model propagation through fish shoals. In previous experiments, either the attenuation from fish in the shoal or the scattering cross sections of fish in the shoal were measured but not both, making it impossible to directly confirm a theoretical prediction on attenuation through the shoal. Here, both measurements have been made and they experimentally confirm the waveguide theory presented. We find experimentally and theoretically that attenuation can be significant when the sensing frequency is near the resonance frequency of the shoaling fish. Negligible attenuation was observed in previous low-frequency ocean acoustic waveguide remote sensing (OAWRS) experiments because the sensing frequency was sufficiently far from the swimbladder resonance peak of the shoaling fish or the packing densities of the fish shoals were not sufficiently high. We show that common heuristic approaches that employ free space scattering assumptions for attenuation from fish groups can lead to significant errors for applications involving long-range waveguide propagation and scattering.

Local acoustic field enhancement of single cell photoacoustic signal detection based on metamaterial structure

The photoacoustic signal from single cell plays an important role in medical diagnosis. Currently, the single-cell photoacoustic detection has limitations. To overcome the limits, an acoustic metamaterial model based on the acoustic waveguide theory for local enhancement of the ultrahigh frequency (UHF) acoustic signals was implemented in this study and it was applied to study the acoustic signal characteristics of individual cells. The local field enhancement effect at different frequencies and the specific mechanism of the model was evaluated in the simulation experiment. This proposing acoustic metamaterial structure of good practical value can be used in various applications for acoustic signal processing.

Heat transfer in the boundary layer in an incompressible fluid in terms of waveguide turbulence model

The possibility of the description of the heat transfer processes in the developed turbulent boundary layer on the flat plate at zero angle attack with zero longitudinal pressure gradient in incompressible fluid is considered as a consequence of the waveguide theory of turbulent boundary layer. It is shown that the logarithmic distribution of temperature along normal coordinates arises in a natural way. It is pointed out the possibility of the intensification of the heat transfer due to generation of own modes of the temperature pulsations. The problem of heat transfer in a boundary layer on a plate flow round an incompressible fluid using the collocation method with Chebyshev polynomial is considered. The dependence of the eigen frequency of the least damped mode on the wave number is obtained. The amplitude of the exicted mode obeys the direct resonance equation if external excitation is applied to the system.

A systematic wave-based method for analysis of large planar frame structures based on Timoshenko waveguide theory

This paper presents a new hybrid analytical/numerical systematic approach for continuous modeling of wave propagation in planar structural systems. To do so, a structure is considered as a number of waveguide elements that are connected to each other through different types of discontinuities. The wave propagation in waveguides is modeled using advanced Timoshenko beam theory to account for the rotary inertia, which provides accurate results for high-frequency excitations. The refraction matrices for different types of discontinuities such as change of material and cross section, various types of boundary conditions, and two- and three-member joints are presented using the existing literature, and the refraction matrices for a right-angled four-member joint is derived analytically for the first time. To provide a robust methodology for the analysis of large structural systems, a general new assembly procedure is introduced that is capable of assembling all of the propagation and refraction matrices in a single global system matrix. To insure the validity of the proposed methodology, detailed numerical examples are provided and their results are verified with finite element numerical method.

A novel approach to solve eigenvalue and forced response problems in waveguide theory by means of bi-orthogonality relations

In this paper recent advances on solving challenging problems in dynamics of multimodal symmetric waveguides (having identical properties of positive/negative going waves) using bi-orthogonality are summarised. It has already been shown by the authors that bi-orthogonality, valid for arbitrarily complicated unbounded symmetric waveguides, greatly facilitates analysis of their forced response in any excitation conditions. Recent findings have shown that bi-orthogonality is a powerful tool also for bounded waveguides and by direct use it resolves the classical Boundary Integral Equations (BIE) into a set of individual relations between modal amplitudes at the boundaries. Moreover, bi-orthogonality permits to uniquely identify special sets of boundary conditions for which the eigenfrequency spectra may be found directly from the dispersion diagrams. These solutions are available simply by drawing horizontal lines specifying an inverse of the wave length of interest in the (Ω, k)-dispersion diagram and so the eigenfrequency spectrum may be read directly as intersections of these lines with dispersion curves. This paper therefore serves to promote this method, discuss applications, new possibilities, physical interpretation and its generalisation to a broader class of waveguide problems.

Angle-insensitive dual-functional resonators combining cavity mode resonance and magnetic resonance.

An angle-insensitive dual-functional resonator composed of a compound metallic grating is proposed and characterized numerically. The resonator exhibits different response characteristics for TE and TM polarization, thus enabling two functions, corresponding to a high-sensitivity sensor and a low Q-factor absorber. For TE polarization, the Q-factor, refractive index sensitivity, and figure of merit of the resonator can reach 283.4, 2577.6nm/RIU, and 181.5 RIU-1, respectively, due to the excitation of cavity mode resonance. For TM polarization, the resonator can be regarded as an absorber with high absorptivity (>97%) based on magnetic resonance. Accordingly, these two mechanisms can be explained well by the waveguide theory and inductor-capacitor circuit model. The electromagnetic fields in the system can be selectively concentrated in the cavity or slit by simply adjusting the polarization angle, exhibiting unique energy localization characteristics. The resonator can also exhibit polarization-sensitive behavior due to the different bandwidths for the same wavelength. This simple structure provides a good paradigm for designing high-performance multi-functional devices.

Ultra-narrowband absorption enhancement in monolayer transition-metal dichalcogenides with simple guided-mode resonance filters

A simple guided-mode resonance filter composed of a single layer of molybdenum disulfide (MoS2), a dielectric grating, and a dielectric substrate is designed to enhance light absorption in the visible range. The absorption characteristics of the system are investigated and analyzed by using the rigorous coupled-wave analysis method and the slab waveguide theory. The results reveal that the high absorption over 65% can be obtained for TE polarization and over 53% for TM polarization. Intriguingly, the structure exhibits an ultranarrow absorption bandwidth under TM polarization, the full width at half maximum is only 0.51 nm, and the quality factor can be more than 1200. In addition, multichannel absorption can be realized by increasing the thickness of the grating layer. The resonant wavelength can be dynamically selected by merely tuning the incident angle. The proposed device with its simple design can be applied to enhance the absorption of other two-dimensional materials.

A planar waveguide in terbium gallium garnet crystal produced by carbon ion implantation

Terbium-gallium-garnet (TGG) crystals have attracted considerable attention as one of the most suitable magneto-optical materials to produce optical isolators. In this work, we report an improved TGG planar waveguide fabricated by the carbon-ion implantation. Considering that the previously reported carbon-implanted TGG waveguide with a dose of 5.0 × 1014 ions cm−2 cannot propagate light waves, we increase the fluence to 1.0 × 1015 ions cm−2 and collect the near-field light intensity profile by the end-face coupling measurement. By simulating the energy loss distribution and analyzing the reconstructed refractive index profile, we figure out the formation theory of the planar waveguides. Moreover, we observe the guided modes in the dark-mode spectrum and further verify the confinement of light in the TGG waveguide. The investigation on planar waveguides in TGG crystals will be beneficial to the progress of micro-isolators in the integrated optical systems.

Random matrix theory for an adiabatically-varying oceanic acoustic waveguide

The problem of sound propagation in the ocean is considered. A novel approach of K. Hegewisch and S. Tomsovic for statistical modelling of acoustic wavefields in the random ocean is examined. The approach is based on construction of a wavefield propagator by means of random matrix theory. It is shown that this approach can be generalized onto acoustic waveguides with adiabatic longitudinal variations. The generalization is obtained by means of the stepwise approximation for the propagator. Accuracy of the generalized approach is confirmed numerically for a model of an underwater sound channel crossing a cold synoptic eddy. It is found that a cold eddy with the core located near the waveguide axis suppresses the effect of the sound scattering on internal waves.

To the Question of the Independence of the Surface Electromagnetic Wave Frequency

Earth's the surface is often strongly inductive, consisting of a dielectric layer thickness endpoint, lying on an unlimited conductor basis. Electromagnetic wave, spreading along the surface, it appears captured dielectric layer, spreading it as in the waveguide channel. Waveguide theory it is known that the spread in the waveguide can only electromagnetic waves with a discrete set of frequencies. And experience shows that the captured waveguide channel electromagnetic waves can be any frequency. The article found that this behavior is due to the fact that electromagnetic waves in free space border - dielectric layer damped height in several wavelengths. Thus the thickness of the dielectric layer becomes more effectively, and this leads to a reduction of the minimum frequency of the waveguide. A discrete set of frequencies is blurred so that cover each other. Thus, a discrete set of frequencies becomes solid, and captured waveguide channel electromagnetic waves are independent of frequency.

The dynamic stress analysis of a piezoelectric bi-material strip with an inclusion

With the aid of guided wave theory, the scattering of SH guided wave by a circular inclusion in an infinite piezoelectric bi-material strip is considered. Firstly, a harmonic out-of-plane line source force is applied on the vertical boundary of a strip. By the means of the repeated image superposition method, Green’s function is constructed, which satisfies the stress-free and electric insulation conditions on the upper and lower horizontal boundaries. Secondly, the bi-material media is divided into two parts along the vertical boundary, and a pair of anti-plane forces and a pair of in-plane electric fields are applied on the vertical boundary. According to boundary conditions, the first kind of Fredholm integral equations are established by ‘the conjunction method’, then the integral equations are reduced to the algebraic equations by effective truncation. Finally, the dynamic stress concentration factor (DSCF) and electric field intensity concentration factor (EFICF) around the circular inclusion are calculated, besides, the influences of the order of guided wave, the position of the inclusion, the combination of parameters, etc. on the DSCF and EFICF are discussed.

Sound absorption performance of underwater anechoic coating in plane wave normal incidence condition

On account of the theory of non-uniform waveguide and the wave propagation theory in layered media, a complete theoretical model is established for predicting the sound absorption performance of multi-layer underwater composite anechoic coating. Furthermore, the correctness of the theoretical calculation is verified by the finite-element simulation results. Then, the velocity nephograms corresponding the three absorption peak frequencies of the overburden are analyzed to reveal the sound-absorbing mechanism.

An Equivalent Circuit Model for Rectangular Waveguide Performance Analysis Considering Rough Flanges’ Contact

In order to investigate the rough flanges’ impact on the electrical performance of rectangular waveguides in the high-power-microwave and high-frequency-microwave communications, a new equivalent circuit model for the contact problem in waveguide flanges is established. Different from the present method that expresses the contact resistance with the contact radius, this method expresses the contact resistance with the incremental stiffness. The equivalent circuit of the waveguide connection is deduced by combining the mechanical contact model with the contact resistance model. Both metal–insulator–metal contacts and metal–metal contacts are considered. The relationship between electrical characteristics and mechanical characteristics is finally established with the transmission line theory of waveguides. The experimental results are given to demonstrate the proposed methodology.

Analysis of Graphene-Based Multilayer Comb-Like Absorption System Based on Multiple Waveguide Theory

We propose the monolayer graphene with a periodic stack of the dielectric materials to achieve comb-like absorption enhancement. The number of absorption peaks corresponds to the stacked period number of two dielectric materials. The simulation and theoretical results illustrate that the appearance of multiple absorption peaks is attributed to the excitation of multiple waveguide modes confirmed by using the multiple waveguide theory. The perfect absorption peaks at any desired wavelength in the visible range can be tuned by carefully optimizing the structural parameters and the stacked period number of two dielectric materials.

A hybrid method for shielding effectiveness estimation of a perforated enclosure against planewave excitation

ABSTRACTThis paper develops a hybrid model based on the combination of full-wave simulation method and circuit model analytic algorithm, which can predict the shielding effectiveness of a perforated rectangular enclosure irradiated by a planewave with arbitrary incident and polarization direction. In order to take the effect of the electromagnetic losses of the aperture into account, the full-wave simulation method is adopted to calculate the coupling voltage of the aperture. The circular aperture or rectangular aperture with arbitrary length–width ratio can be positioned anywhere in the front panel of the enclosure. Taking the effect of the thickness into account, we establish the equivalent circuit model of the perforated enclosure with aperture coupling voltage as an equivalent voltage source. Then, the TEmn and TMmn modes of the coupling electric field at arbitrary observation point within the enclosure are calculated based on waveguide theory. Simulation results of the hybrid model are in good agreement with those of transmission line matrix method within the frequency range of 0–3 GHz. Solution times using the hybrid model are far less than those required by pure numerical methods.

Model for confined Tamm plasmon devices

It is shown that cavities formed between a multilayer quarter-wave Bragg reflector and a metal mirror which support Tamm plasmons can be modelled by using a hard-mirror approximation including appropriate penetration depths into the mirrors. Results from this model are in excellent agreement with those found by numerical methods. In addition Tamm modes that are laterally confined by the presence of a metallic disc deposited on the Bragg reflector can be described by the effective index model that is commonly used for vertical-cavity surface-emitting lasers (VCSELs). This enables the lateral modes confined by a circular disc to be found from conventional weakly-guiding waveguide theory similar to that used for optical fibres. The resonant wavelengths of these linearly-polarised (LP) guided modes are calculated as functions of disc diameter and other parameters.

A Novel Package Lid Using Mushroom-Type EBG Structures for Unintentional Radiation Mitigation

Conventional package lid induces additional unintentional radiation due to the resonances between the conventional metal lid and ground plane on package board. In this paper, a novel package lid is proposed based on the gap waveguide theory, which adopts mushroom-type electromagnetic bandgap structures to mitigate the increased unintentional emission. In addition, a scalable equivalent circuit model is presented as an assistance for designing the proposed package lid. Both the simulation and measurement results confirm that the proposed lid can significantly reduce the unintentional radiation within the specific frequency range as designed.

Numerical analysis of high-Q multiple Fano resonances

We design and numerically analyze high-quality (Q) multiple Fano resonances based on a hybrid metamaterial waveguide structure, which consists of T-shaped gold cut wires placed on a dielectric board waveguide. There are three sharp Fano peaks arising from the interference between plasmon dipole mode and different guided modes. The physical origin of obvious Fano behaviors is explained by the three-level plasmonic system and slab waveguide theory. The largest Q-factor reaches 547, and modulation depth of the peak C can get to nearly 100%, making it possible to perfectly realize the Fano switch function. Combining the cramped spectral lines with large near-field confinement, we demonstrate an optical refractive index sensor with a sensitivity of 4920 nm/RIU and a figure of merit of 188. This work provides a way to obtain multiple high Q-factor Fano resonances, which can widen channels for fabricating devices in biochemical sensing and optical switching.

A 0.1 THz low-loss 3D printed hollow waveguide

Bottlenecks in the application of terahertz (THz) technology are high transmission loss and expensive functional devices. Therefore, the paper proposes a novel low-loss THz hollow waveguide and demonstrates its design, fabrication, and characterization. Firstly, the waveguide’s material is characterized by a THz time domain spectrometer. Secondly, the influences of five different design parameters on the transmission loss coefficient are simulated and analyzed. Combined with anti-resonant waveguide theory, an optimal low-loss hollow waveguide (theoretical loss is 0.009 cm−1 at 0.1 THz) is proposed. Thirdly, the waveguide is fabricated by 3D printing technology. Its transmission loss (=0.015 cm−1) and beam divergence angle (=6.8°) are measured respectively. These results prove the effectiveness of the waveguide and will bring potential applications in THz remote transmission and imaging.

Metalenses Based on Symmetric Slab Waveguide and c-TiO₂: Efficient Polarization-Insensitive Focusing at Visible Wavelengths.

A key goal of metalens research is to achieve wavefront shaping of light using optical elements with thicknesses on the order of the wavelength. Here we demonstrate ultrathin highly efficient crystalline titanium dioxide metalenses at blue, green, and red wavelengths (λ0 = 453 nm, 532 nm, and 633 nm, respectively) based on symmetric slab waveguide theory. These metalenses are less than 488 nm-thick and capable of focusing incident light into very symmetric diffraction-limited spots with strehl ratio and efficiency as high as 0.96 and 83%, respectively. Further quantitative characterizations about metalenses’ peak focusing intensities and focal spot sizes show good agreement with theoretical calculation. Besides, the metalenses suffer only about 10% chromatic deviation from the ideal spots in visible spectrum. In contrast with Pancharatnam–Berry phase mechanism, which limit their incident light at circular polarization, the proposed method enables metalenses polarization-insensitive to incident light.