Parallel Plane Waveguide Research Articles

Application of partial areas method in the problem of sound radiation by a sphere in a waveguide with soft acoustically boundaries

The paper considers the features of the formation of an acoustic field by a spherical source with complicated properties in a regular plane-parallel waveguide, which is of practical importance in marine instrumentation and oceanographic research. The calculation algorithm is based on the use of the Helmholtz equation and the Fourier method for each partial region and the conjugation conditions on their boundaries. The presented calculation allows one to get rid of the idealized boundary conditions on the source surface, with the subsequent determination of the excitation coefficients of the waveguide modes within the framework of the Sturm-Liouville problem. In this case, the attraction of the boundary conditions on the surface and the bottom of the sea, as well as the Sommerfeld conditions, makes it possible to obtain the real distribution of the field in the vertical sections of the waveguide. The obtained frequency dependences of the pressure and vibrational velocity components show their amplitude-phase differences, which reach 90 degrees, which partially explains the appearance of singular points in the intensity field in a regular waveguide. It has been determined that multiple reflections of sound waves from the boundaries of the working space and the space of the waveguide cause oscillations of the pressure components with a change in the amplitude level up to 6 dB. It was found that with an increase in the size of the source, a kind of resonance is formed in the working space, the frequency of which depends on the depth of the sea and corresponds to the region kr=x=5.8. It was found that when the acoustic field is formed in the working space, the frequency response of the impedance components is represented as a multiresonant dependence formed on the basis of the frequency characteristics of the lower modes and their combinations. Experimental studies have shown that the results of calculations of the mode composition of the acoustic field of the emitter, obtained in the conditions of the pool, correspond to the spatial characteristics of the mode components of the acoustic field with an error of up to 3 dB

Sound Pressure Interference and Phase Velocities in Shallow Water: Calculation and Experiment

A study was carried out on the interference structure of sound pressure amplitudes, longitudinal projections of phase gradients, and calculated phase velocities in a plane-parallel waveguide. It has been established that the phase velocity values of the sound pressure field and the effective phase velocities in the zones of interference maxima calculated by various methods are quite stable and agree well both with each other and the experimental data. It is shown that at the frequencies for which an array is located in zones of interference maxima, using an equivalent plane wave model and effective phase velocities instead of the sound speed in water reduces the bearing estimation error.

Investigation of waveguide antenna arrays with layered dielectrics

A general methodology for calculating antenna arrays with layered dielectric is considered. To demonstrate the proposed methodology, we consider the solution of the problem of radiation of linear waveguide array. Plane-parallel waveguides have a finite wall thickness. Antenna array scans in E and H planes. This problem is solved using Fredholm integral equations of the second kind. To solve the problem, the entire domain of the electromagnetic field is divided into partial intersecting regions An example of constructing Green’s functions of selected partial regions with allowance for their dielectric filling is considered. The formulation of the boundary-value problem for the antenna array in the form of Fredholm integral equations of the second kind using the technique of dividing the determination domain into partial regions with Green’s functions allows us to solve the following problem: calculations of the antenna array with dielectric plugs in the waveguides and with a dielectric coating over the antenna array. This technique allows optimization of dielectric parameters with the aim of aperture matching of the antenna array. The calculation results of the dependence of the reflection coefficient on the phase shift between waveguides in the H-plane are presented. The calculations are performed for different values of the dielectric constant of the plugs in the waveguides and the dielectric constant of the dielectric layer above the antenna array. The influence of the geometric dimensions of the plugs in the waveguides and the dielectric coating above the array is studied.

Impedance Characteristics of a Plane-Parallel Acoustic Waveguide with Acoustically Mellow Borders аt Two-Frequency Acoustical Exitation

The impedance characteristics of a waveguide with combined boundaries are considered in the propagation of a wave packet by a two-frequency signal. A plane-parallel waveguide with acoustically mellow boundaries was modeled by a shallow sea with a bottom surface represented by an acoustically rigid boundary. The boundary between media water-air is an acoustically soft boundary also. As a result of solving the problem of determining the acoustic impedance along the horizontal and along the vertical section of the waveguide, the main analytical expressions, which described propagation process in such boundary condition. For the determination of task solution was used the superposition of average values of the oscillations velocity components and acoustic pressures. The problems of the formation in the waveguide average for the observation interval meanings of power flux densities and acoustic energy densities are considered. The aim of this work is to determine the specific acoustic impedances to normal waves propagating in a plane-parallel waveguide with mellow boundaries and their effect on the main energy characteristics of an acoustic field, which excited by a two-frequency source. Under conditions of dispersion, for the low-frequency region and the first mode of the waveguide, the dependences are calculated. In paper shown the features of the impedance characteristics and their influence on the distribution along the waveguide channel average for the observation interval meanings power flux densities and acoustic energy density. In the paper also shown the dependence the impedance of a waveguide along the horizontal axis on the coordinate and on frequency values of the original packet. Bibl.12, Fig. 4

Tunable Mid-Infrared Nanoscale Graphene-Based Refractive Index Sensor

A nanoscale refractive index sensor comprising of input–output graphene parallel plane waveguides coupled through a resonator is proposed. Operating as a wavelength selective structure in mid-infrared region, the sensor performance is based on the variation of the resonance wavelength of the structure. The simulation results obtained by numerical method of the finite difference time domain reveal linear dependency between the resonance wavelengths and the refractive indices of the material injected into the coupling resonator of the sensor, predictable by the resonance criterion of the resonator. The wavelength resolution of the detection system determines the overall sensor resolution. To utilize voltage dependency of graphene chemical potential, the wavelength range of the performance of the sensor can be tuned appropriately. The proposed sensor can be used as a platform for design of the sensors utilizing in various chemical and biomedical systems.

MODELING OF THE COMPRESSION OF WAVE PACKETS INDUCED BY A CURRENT FILAMENT IN A PLANE-PARALLEL WAVEGUIDE

The possibility of rigorous simulation of the compression of electromagnetic pulses excited by a filament with a current in a plane-parallel waveguide cavity is investigated. The technique of determining the modulation law of the pulses to be compressed, that has been developed in our previous papers, here is generalized to the case where the pulse source is an extraneous current. The process of compression is modeled with this technique for two symmetrical wave packets propagating towards each other in a ring-shaped waveguide. The interference of these packets is demonstrated in the performed numerical experiment. The result of the interference is doubling of the electric field intensity (regarding to the intensity in each separate wave packet) at the point of the waveguide which is diametrically opposed to that one where the external current is located. The obtained results could be used for the design of passive microwave power compressors and in the accelerator engineering.

THE BLOCKAGE EFFECT IN WAVEGUIDE BENDS IN THE VICINITY OF THE CUTOFF FREQUENCY OF THE SECOND-ORDER MODE

In the paper, a rigorous mathematical model of electromagnetic wave diffraction in the bend of a plane-parallel waveguide is developed. Numerical simulation of such a waveguide bend has revealed the effect of its complete blockage at a frequency close to the cutoff frequency of the second-order mode. The resonant nature of this effect has been established to be consisting in excitation of a blocking oscillation in such a waveguide irregularity. It is concluded that a waveguide bend can be considered as an open waveguide resonator. Importance of the solved problem is determined by wide application of waveguide bends in the microwave technology.

Hybrid Ray-Mode Analysis of E-Polarized Plane Wave Diffraction by a Thick Slit

A high-frequency asymptotic method has been applied to formulate E-polarized plane wave diffraction by a thick slit. The slit structure is regarded as an open-ended parallel plane waveguide cavity, and the excitation of the waveguide modes and their reradiation are derived from a ray-mode conversion technique. Comparison with another method reveals the validity and effectiveness of our formulation.

A Parabolic Equation Approach to Modeling Acousto-Gravity Waves for Local Helioseismology

A wide-angle parabolic-wave-equation algorithm is developed and validated for local-helioseismic wave propagation. The parabolic equation is derived from a factorization of the linearized acousto-gravity wave equation. We apply the parabolic-wave equation to modeling acoustic propagation in a plane-parallel waveguide with physical properties derived from helioseismic data. The wavenumber power spectrum and wave-packet arrival-time structure for receivers in the photosphere with separation up to \(30^{\circ}\) is computed, and good agreement is demonstrated with measured values and a reference spectral model.

An Efficient Coupled-Mode Formulation for Acoustic Propagation in Inhomogeneous Waveguides

The direct-global-matrix coupled-mode model (DGMCM) for sound propagation in range-dependent waveguides was recently developed by Luo et al. [A numerically stable coupled-mode formulation for acoustic propagation in range-dependent waveguides, Sci. China G: Phys. Mech. Astron. 55 (2012) 572–588]. A brief review of the formulation and characteristics of this model is given. This paper extends this model to deal with realistic problems involving an inhomogeneous water column and a penetrable sloping bottom. To this end, the normal mode model KRAKEN is adopted to provide local modal solutions and their associated coupling matrices. As a result, the extended DGMCM model is capable of providing full two-way solutions to two-dimensional (2D) realistic problems with a depth- and range-dependent sound speed profile as well as a penetrable sloping bottom. To validate this model, it is first applied to a benchmark problem of sound propagation in a plane-parallel waveguide with a depth- and range-dependent sound speed profile, and then it is applied to a problem involving both an inhomogeneous water column and a sloping bottom. Comparisons with the analytical solution proposed by DeSanto and with the numerical model COUPLE are also provided, which show that the extended DGMCM model is accurate and efficient and hence can serve as a benchmark for realistic problems of sound propagation in an inhomogeneous waveguide.

Grazing diffraction of X-ray radiation in a planar single-crystal waveguide

The propagation of an X-ray beam through a plane-parallel waveguide is studied with allowance for Bragg grazing diffraction on the crystalline structure of the plates. Expressions for the waveguide modes are obtained and nondecaying waveguide modes are shown to exist at angles that are larger than the critical one (the angle of total external reflection), which permits one to increase the capture angle of radiation incident on the waveguide. The calculated intensity at the waveguide output is compared with the intensity of waveguide modes in the absence of grazing diffraction in the waveguide material.

Dispersion characteristics of plasma-filled cylindrical waveguide

An analytical and numerical study is made on the dispersion properties of a cylindrical waveguide filled with plasma. An electron beam and static external mag- netic field are considered as the mechanisms for controlling the field attenuation and possible stability of the wave- guide. The effects of plasma warmness and inhomogeneity are also considered. Dispersion relations in x describing different physical situations that govern the mode propa- gation in the waveguide are obtained. The plasma dielectric tensors and the dispersion relations which describe E and H waves and, hence, the damping rate of these waves are calculated and studied. The necessary conditions for the field stability in the waveguide and amplification coeffi- cients for these waves are also obtained. H-wave modes are always attenuated by collisional effect. The growth of the excited E wave is calculated in the resonance case, and the stability condition for the E wave is obtained. E waves are found to be more stable in warm plasma compared to cold plasma. The results obtained here are of great interest and may be used to analyze how the plasma affects the electromagnetic properties of the cavity of the 1-2 MW 140-170 GHz continuous-wave gyrotron (for W7-X stell- arator and ITER), for MW gyrotron development for fusion plasma applications, and for second harmonic generation in a plasma-filled parallel plane waveguide.

Waves of a plane-parallel waveguide in the form of a channel with multilayer walls

We study numerically rigorous dispersion relations for a plane-parallel waveguide in which the impedance of the walls is determined as either the impedance of a multilayer magneto-dielectric wall having a finite thickness, or as the impedance of a corresponding finite or infinite layer. Solutions for complex waves are obtained on the basis of the numerical iterative method. The corresponding analytical relationships are found in some limiting cases.

Efficiency of excitation of a quasioptical open resonator by a waveguide

We study theoretically and experimentally the efficiency of excitation of an open resonator by a waveguide. A two-dimensional model of a quasioptical two-mirror open resonator, which is excited through a coupling element in the form of an open end of a plane-parallel waveguide, is proposed. The field of the open resonator is represented as the superposition of Gaussian wave beams and its scattering on the coupling element is described by solving the problem of diffraction of waveguide waves and Gaussian wave beams on an open end of a flanged waveguide. Properties of the mirrors and the resonator loss are specified from physical considerations. The calculation results are compared with the experimental data, and a physical interpretation of the obtained results is offered. The factors which influence the efficiency of excitation of an open resonator are identified.

Description and simulation of physical effects in chiral guiding structures

Methods of mathematical simulation of chiral guiding structures are considered. A rectangular chiral waveguide is calculated with the use of the mixed-finite-element method. For a plane-parallel waveguide with a chiral filling, the fields are obtained on the basis of an analytic solution via the finite-difference method.

WIENER-HOPF ANALYSIS OF PLANAR CANONICAL STRUCTURES LOADED WITH LONGITUDINALLY MAGNETIZED PLASMA BIASED NORMALLY TO THE EXTRA-ORDINARY WAVE PROPAGATION

The canonical problem of an extra-ordinary Transverse Electromagnetic wave propagating in a parallel plane waveguide with a semi-infinite upper conductor and loaded with magnetized plasma is considered. The homogeneous biasing constant magnetic field is assumed parallel to the substrate and normal to the wave propagation,which incidents normally on the truncated edge. The Wiener-Hopf technique is employed and the corresponding equations are formulated for the open-radiating structure as well as for a closed one resulting from the placement of a metallic shield parallel to the waveguide planes. Closed form field expressions are obtained for the shielded geometry,while the open geometry Kernel factorization is left for future extensions. Important non-reciprocal wave propagation phenomena are involved,which lend non-even function properties to the involved Kernels. Hence,their factorization becomes non-trivial requiring new mathematical approaches. Finally,a review of the involved non-reciprocal and/or unidirectional surface waves is given, which is related to the involved mathematical complexities.

Sideband Instability in the Compact THz Free-Electron Laser at KAERI

A frequency offset of the Sideband instability has been observed in a compact waveguide-mode terahertz (THz) free-electron laser (FEL). The spectra of the FEL pulses were measured by using a Fabry-Perot spectrometer having a resolution of 10−4 of the central wavelength at 2 − 3 THz range. The shift of the sideband was measured to be 0.5 − 1.2 μm, depending on the FEL wavelengths from 110 to 165 μm. An increase in the sideband shift for a longer wavelength could be explained by a change in the wave’s group velocity in a plane-parallel waveguide. Mode competition between the sidebands and the primary wave was observed by changing the cavity length of the FEL. We could decrease the number of modes and reduce the linewidth of the spectra by controlling the cavity detuning. We discuss the dependence of the complexity of the sideband instability on the FEL wavelengths and its gain characteristics.

T-wave diffraction from a metal sphere located in a plane-parallel waveguide

We study the diffraction of a T-wave from a metal sphere located between perfectly conducting planes. The problem is solved using the method of separation of variables in combination with the method of mirror images. Significant intensification of the Mie phenomenon is found.

Scattering of Nonsinusoidal Waves by an Array of Rectangular Beams in a Parallel-Plane Waveguide

Scattering of Nonsinusoidal Waves by an Array of Rectangular Beams in a Parallel-Plane Waveguide

Excitation of a Dielectric Layer by the Beveled End of a Plane-Parallel Waveguide (Large Protrusions)

Excitation of a Dielectric Layer by the Beveled End of a Plane-Parallel Waveguide (Large Protrusions)