Circular Cylindrical Waveguide Research Articles

On the Existence of Nonlinear Coupled Surface TE and Leaky TM Electromagnetic Waves in a Circular Cylindrical Waveguide

On the Existence of Nonlinear Coupled Surface TE and Leaky TM Electromagnetic Waves in a Circular Cylindrical Waveguide

Nonreciprocal guided waves in the presence of swift electron beams

Breaking the reciprocity of electromagnetic interactions is of paramount importance in photonic and microwave technologies, as it enables unidirectional power flows and other unique electromagnetic phenomena. Here we explore a method to break the reciprocity of electromagnetic guided waves utilizing an electron beam with a constant velocity. By introducing an effective dynamic conductivity for the beam, we theoretically demonstrate how nonreciprocal guided waves and a one-way propagating regime can be achieved through the interaction of swift electrons with electromagnetic waves in two-dimensional (2D) parallel-plate and three-dimensional (3D) circular-cylindrical waveguides. Unlike the conventional electron beam structures such as traveling wave tubes and electron accelerators, here the goal is neither to generate and/or amplify the wave nor to accelerate electrons. Instead, we study the salient features of nonreciprocity and unidirectionality of guided waves in such structures. The relevant electromagnetic properties such as the modal dispersion, the field distributions, the operating frequency range, and the nonreciprocity strength and its dependence on the electron velocity and number density are presented and discussed. Moreover, we compare the dispersion characteristics of waves in such structures with some electric-current-based scenarios in materials reported earlier. This broadband tunable magnet-free method offers a unique opportunity to have a switchable strong nonreciprocal response in optoelectronics, nanophotonics, and THz systems.

On the acoustic trapped modes and their symmetry properties in a circular cylindrical waveguide with a cavity

On the acoustic trapped modes and their symmetry properties in a circular cylindrical waveguide with a cavity

Nonreciprocal propagation in optical fibers

Nonreciprocal propagation in the structures compatible with optical fiber waveguides presents practical interest. The present work treats the problem of nonreciprocal propagation in nonabsorbing cylindrically layered structures at axial magnetization characterized by magneto-optic electrical permittivity, , and magnetic permeability, , tensors, using transverse circularly polarized representation. The solutions to the vector Helmholtz Eqs. restricted to the terms linear in the off-diagonal elements of and are expressed analytically. The results are applied to a magneto-optic circular cylindrical waveguide and illustrated on fiber waveguides with an yttrium iron garnet (YIG) core and a cladding formed by gallium substituted yttrium iron garnet (GaYIG) at the optical communication wavelength of 1.55 μm. The propagation distance in the waveguide for a azimuth rotation of a transverse linearly polarized incident wave on the waveguide axis required in isolators is about 100 μm.

Numerical Method for Electromagnetic Wave Propagation Problem in a Cylindrical Anisotropic Waveguide with Longitudinal Magnetization

The propagation of monochromatic electromagnetic waves in metal circular cylindrical dielectric waveguide with longitudinal magnetization filled with anisotropic inhomogeneous waveguide is considered. The physical problem is reduced to solving a transmission eigenvalue problem for a system of ordinary differential equations. Spectral parameters of the problem are propagation constants of the waveguide. Numerical results are obtained using a modification of the projecting methods. The comparison with known exact solutions (for particular values of parameters) are made.

Resonance and beating phenomenon in a nonlinear rigid cylindrical acoustic waveguide: The axisymmetric mode

A rigid-walled semi-infinite circular cylindrical waveguide enclosing a weakly nonlinear fluid is considered. A quadratic nonlinear interaction is assumed as a model. A flat rigid piston generates an axisymmetric harmonic pressure that is prescribed as the input at the finite end of the waveguide. The objective is to study the modal interactions of waves. A regular perturbation method is used to separate the linear (primary) and the quasilinear (second harmonic) equations. First, linear solutions are established. Their quasilinear interactions then lead to modal interactions. Typically, the linear wavenumbers at the quasilinear order generate homogenous wavenumbers. Intersections of both these wavenumbers in the wavenumber-frequency plane are considered as resonances since the resulting pressure grows in amplitude in the axial propagating direction. The conditions under which the solutions become resonant or non-resonant are presented. In this last case, a beating phenomenon occurs with distance. It is found that the resonances are rare, except for the plane wave. Generally, the forced linear wavenumbers and the quasilinear generated wavenumbers acquire numerical values close to each other and create the beating phenomenon.

Magnetooptics in Cylindrical Structures

Understanding magnetooptics in cylindrical structures presents interest in the development of magnetic sensor and nonreciprocal devices compatible with optical fibers. The present work studies wave propagation in dielectric circular cylindrical structures characterized by magnetic permeability and electric permittivity tensors at axial magnetization. The Helmholtz equations deduced from the Maxwell equations in transverse circularly polarized representation provide electric and magnetic fields. With the restriction to terms linear in off-diagonal tensor elements, these can be expressed analytically. The results are applied to magnetooptic (MO) circular cylindrical waveguides with a step refractive index profile. The nonreciprocal propagation is illustrated on waveguides with an yttrium iron garnet (YIG) core and a lower refractive index cladding formed by gallium substituted yttrium iron garnet (GaYIG) at the optical communication wavelength. The propagation distance required for the isolator operation is about one hundred micrometers. The approach may be applied to other structures of cylindrical symmetry in the range from microwave to optical frequencies.

Modeling and simulation of an acoustic well stimulation method

This paper presents a mathematical model and a numerical procedure to simulate an acoustic well stimulation (AWS) method for enhancing the permeability of the rock formation surrounding oil and gas wells. The AWS method considered herein aims to exploit the well-known permeability-enhancing effect of mechanical vibrations in acoustically porous materials, by transmitting time-harmonic sound waves from a sound source device—placed inside the well—to the well perforations made into the formation. The efficiency of the AWS is assessed by quantifying the amount of acoustic energy transmitted from the source device to the rock formation in terms of the emission frequency and the well configuration. A simple methodology to find optimal emission frequencies for a given well configuration is presented. The proposed model is based on the Helmholtz equation, a sound-hard boundary condition at the casing, and an impedance boundary condition that effectively accounts for the porous solid–fluid interaction at the interface between the rock formation and the well perforations. Exact non-reflecting boundary conditions derived from Dirichlet-to-Neumann maps are utilized to truncate the circular cylindrical waveguides considered in the model. The resulting boundary value problem is then numerically solved by means of the finite element method. A variety of numerical examples are presented in order to demonstrate the effectiveness of the proposed procedure for finding optimal emission frequencies.

Selective modal excitation for optimization of waveguide based bulk ultrasonic transducers

The use of waveguides for ultrasonic transduction is advantageous in numerous applications such as measurement of flow, temperature and material properties under harsh environments. However, typically waveguide transducers do not use any mode control. This paper describes aspects of mode selection for waveguide based transduction of bulk longitudinal ultrasonic waves in a target metallic specimen. It is proposed that specific waveguide modes with suitable modal structure and matched acoustical impedance can significantly enhance the transduction of bulk ultrasonic waves in the specimen sample. Using circular cylindrical waveguides excited by magnetostriction, experimental results guided by finite element simulations and analysis are presented, demonstrating the feasibility of the approach. An example application in the form of a bulk longitudinal wave ultrasonic transducer is also provided illustrating the improvement in the signal quality using the proposed concept.

Nonlinear propagation of coupled electromagnetic waves in a circular cylindrical waveguide

The problem of the propagation of coupled surface electromagnetic waves in a two-layer cylindrical circular waveguide filled with an inhomogeneous nonlinear medium is considered. A nonlinear coupled TE-TM wave is characterized by two (independent) frequencies ωe and ωm and two propagation constants $${\widehat \gamma _e}$$ and $${\widehat \gamma _m}$$ . The physical problem reduces to a nonlinear two-parameter eigenvalue problem for a system of nonlinear ordinary differential equations. The existence of eigenvalues ( $${\widehat \gamma _e}$$ , $${\widehat \gamma _m}$$ ) in proven and intervals of their localization are determined.

NUMERICAL METHOD FOR ELECTROMAGNETIC WAVE PROPAGATION PROBLEM IN A CYLINDRICAL INHOMOGENEOUS METAL DIELECTRIC WAVEGUIDING STRUCTURES

The propagation of monochromatic electromagnetic waves in metal circular cylindrical dielectric waveguides filled with inhomogeneous medium is considered. The physical problem is reduced to solving a transmission eigenvalue problem for a system of ordinary differential equations. Spectral parameters of the problem are propagation constants of the waveguide. Numerical results are found with a projection method. The comparison with known exact solutions (for particular values of parameters) is made.

Reconstruction of annular bi-layered media in cylindrical waveguide section

We consider a radial transverse resonance model for a circular cylindrical waveguide composed into two layers with different frequency dependent complex dielectric constants. An inverse problem with four unknowns - three physical material parameters and one dimensional dielectric layer thickness parameter - is solved by employing TE110 and TE210 modes with different radial field distribution. First the resonance frequencies and quality factors are found fitting a Lorentzian function to the ‘measured’ data, using the method of least squares. Then found resonance frequencies and quality factors are used in a second inverse Newton-Raphson algorithm which solves four transverse resonance equations in order to get four unknown parameters. The use of TE110 and TE210 models offers one-dimensional radial tomographic capability. An open ended coaxial waveguide quarter-wave resonator is added to the sensor topology, and the effect on the convergence of numerical method is investigated.

A Faraday isolator based on graphene

A Faraday isolator based on magnetically biased graphene is proposed and analyzed. The isolator consists of two rectangular waveguides, two circular-rectangular transitions and a circular cylindrical waveguide loaded multiple graphene sheets, with a static magnetic field which parallel to the signal transmission direction biased. The principles of the isolator have been investigated using the mode-matching technique. The isolation is calculated by the signal flow diagram combined with the transmission matrix method. The theoretical results show that its isolation is more than 30dB in the working frequency (1.8GHz–2.2GHz). The isolation can be tuned by varying the chemical potential or varying the magnetic field. The novel isolator has a simple structure and a wider bandwidth compared to the conventional Faraday isolator. Simultaneously the transmission direction of the isolator can be changed easily by changing the direction of the magnetic field.

Active manipulation of EM fields in open waveguides

The central question addressed in this paper is whether we can introduce an antenna array into a circular cylindrical waveguide to accurately control or determine the local field around the array with vanishingly small reflection from the boundary of the waveguide. We ask this question since we perceive the answer to be important to the applied community through its relevance for applications to electromagnetic shielding or slot antennas. We make use of the results presented in Onofrei (2014) for the scalar Helmholtz equation and show, by using the Debye representation in waveguides, how they apply to the current EM waveguide model. We prove the existence of a class of solutions and include a feasibility discussion for the antenna synthesis problem together with relevant simulations.

Coupled electromagnetic wave propagation in a cylindrical dielectric waveguide filled with Kerr medium: nonlinear effects

Propagation of the coupled electromagnetic wave, which is a superposition of TE and TM waves, in a dielectric circular cylindrical waveguide filled with non-linear inhomogeneous medium is studied (if the permittivity is linear, the coupled wave does not exist). Non-linear coupled TE–TM wave is characterized by two (independent) frequencies and two (coupled) propagation constants (PCs). The physical problem is reduced to a non-linear two-parameter transmission eigenvalue problem for Maxwell’s equations. The system of dispersion equations with respect to PCs is derived and solved numerically. Two types of coupled PCs and coupled guided modes are found: non-linear solutions of the first type become solutions of the corresponding linear problems as the nonlinearity coefficient tends to zero; solutions of the second type seem to be ’purely’ non-linear as they stay away from any linear solutions as coefficient of the nonlinearity tends to zero. Coupled PCs and coupled eigenmodes are calculated and plotted.

Weakly nonlinear acoustic wave propagation in a nonlinear orthotropic circular cylindrical waveguide.

Nonlinear acoustic wave propagation is considered in an infinite orthotropic thin circular cylindrical waveguide. The modes are non-planar having small but finite amplitude. The fluid is assumed to be ideal and inviscid with no mean flow. The cylindrical waveguide is modeled using the Donnell's nonlinear theory for thin cylindrical shells. The approximate solutions for the acoustic velocity potential are found using the method of multiple scales (MMS) in space and time. The calculations are presented up to the third order of the small parameter. It is found that at some frequencies the amplitude modulation is governed by the Nonlinear Schrödinger Equation (NLSE). The first objective is to study the nonlinear term in the NLSE, as the sign of the nonlinear term determines the stability of the amplitude modulation. On the other hand, at other specific frequencies, interactions occur between the primary wave and its higher harmonics. Here, the objective is to identify the frequencies of the higher harmonic interactions. Lastly, the linear terms in the NLSE obtained using the MMS calculations are validated. All three objectives are met using an asymptotic analysis of the dispersion equation.

Dispersion analysis and measurement of circular cylindrical wedge-like acoustic waveguides

This study investigated the propagation of flexural waves along the outer edge of a circular cylindrical wedge, the phase velocities, and the corresponding mode displacements. Thus far, only approximate solutions have been derived because the corresponding boundary-value problems are complex. In this study, dispersion curves were determined using the bi-dimensional finite element method and derived through the separation of variables and the Hamilton principle. Modal displacement calculations clarified that the maximal deformations appeared at the outer edge of the wedge tip. Numerical examples indicated how distinct thin-film materials deposited on the outer surface of the circular cylindrical wedge influenced the dispersion curves. Additionally, dispersion curves were measured using a laser-induced guided wave, a knife-edge measurement scheme, and a two-dimensional fast Fourier transform method. Both the numerical and experimental results correlated closely, thus validating the numerical solution.

Guided Electromagnetic Waves Propagating in a Two-Layer Cylindrical Dielectric Waveguide with Inhomogeneous Nonlinear Permittivity

The paper focuses on the problem of monochromatic electromagnetic TM wave propagation in a two-layer circular cylindrical dielectric waveguide. The space outside the waveguide is filled with isotropic medium having constant permittivity. The inner core of the waveguide is filled with isotropic medium having constant permittivity; the cladding of the core is filled with isotropic inhomogeneous nonlinear permittivity (the nonlinear term is expressed by Kerr law). Existence of guided modes which depend harmonically onz(the waveguide axis coincides withz-axis) is proved and their localization is found. Numerical results including different type of nonlinearities are presented. A comparison with the linear case is given. The existence of a new propagation regime is predicted.

A Generalized Approach for Computation of Near Field Radiation Pattern of an Antenna

A generalized procedure in the form of an analytical formulation for the determination of radiation pattern of an antenna at any arbitrary distance which covers the near field as well as far field is presented in this paper. With the prior knowledge of either the current or field distribution on the radiating aperture, the proposed near field analysis is generic and can be applied for wide variety of antenna elements. The underlying principle of the generalized procedure is tantamount to considering the radiating aperture as an array of point electric and magnetic dipoles. The validity and novelty of the proposed new approach have been substantiated considering an open ended circular cylindrical waveguide and a conical horn as case studies and treating the far field as a special case of near field with pertinent distance criterion. The effect of change in the distance of observation ranging from reactive near field to far field on the radiation patterns of these antennas has also been discussed. The simulation studies reveal that the depicted normalized phase patterns of both the circular waveguide and conical horn follow the changes in the profile of the corresponding amplitude patterns.

Analysis of a coaxial probe‐fed circular waveguide

ABSTRACTThis article presents the investigation on the applicability of variational technique for the estimation of input impedance of a coaxial line fed probe in a circular cylindrical waveguide based on thin current approximation. In this work, the lower limit of diameter of the probe for which thin current approximation is valid has been established. The variation of input impedance has been studied as a function of probe height, short length from the probe as well as diameter of the probe. The convergence of the solution based on variational technique is checked in terms of the number of higher order modes of circular cylindrical waveguide excited at the asymmetrical junction of probe. The limitation of the existing technique has been ascertained using the finite element method based simulator high frequency structure synthesizer (HFSS) and experimental validation. The simulated result based on HFSS is in excellent agreement with the experimental results. Bandwidth performance with variation in diameter has also been studied using HFSS simulator with varying probe diameter. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2652–2656, 2013