Two-layer Waveguide Research Articles

Theoretical investigation of sound propagation from a moving directional source in a shallow-water waveguide

Doppler phenomena resulting from a moving directional source can be complicated in shallow water environments. This study presents a semi-analytical method to calculate the Doppler-shifted field (DSF) caused by a directional source moving horizontally in a shallow-water waveguide. First, an improved normal-mode (NM) model is developed to comprehensively account for the Doppler-induced changing modal shapes, eigenvalue shifts, and the contribution of the branch cut integral. Next, an analytical, modal expression for the DSF is derived based on the principles of Huygens and Taylor series expansion. The solution is expressed 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 modal expression is applicable to any type of radiators moving in a shallow-water environment with an arbitrary sound speed profile. By employing the proposed theoretical model, we analyze the beam Doppler shift produced by a piston-like radiator moving in a two-layer waveguide. The simulation indicates that an apparent asymmetry arises in the DSF when the beam grazing angle sweeps over the critical angle of the seafloor. This finding confirms that the beam Doppler shift acts as the third mechanism causing significant differences between the field generated by a directional moving source and that by the same source at rest, which may have practical applications in underwater acoustic detection for moving sources.

Распространение невзаимных спиновых волн в многослойном магнонном кристалле

The possibility of frequency-selective propagation of spin waves in a magnonic microwave guide with a magnonic crystal consisting of two layers with different values of the saturation magnetization in the layers is demonstrated. It is shown that multimode propagation of spin waves can occur inside a two-layer structure in two frequency ranges, while the presence of a magnonic crystal on the surface of the structure leads to the manifestation of a band gap in one of the frequency ranges. At the same time, the process of propagation of a spin-wave signal is accompanied by a strong nonreciprocity, which manifests itself in a change in the amplitude-frequency characteristics when the direction of the external magnetic field is reversed, while the frequency range of the band gap differs depending on the direction of the field. The proposed concept of a two-layer spin-wave waveguide can underlie the manufacture of multichannel filters or magnonic logic devices.

Propagation of nonreciprocal spin waves in a multilayer magnonic crystal

The possibility of frequency-selective propagation of spin waves in a magnonic microwave guide with a magnonic crystal consisting of two layers with different values of the saturation magnetization in the layers is demonstrated. It is shown that multimode propagation of spin waves can occur inside a two-layer structure in two frequency ranges, while the presence of a magnonic crystal on the surface of the structure leads to the manifestation of a band gap in one of the frequency ranges. At the same time, the process of propagation of a spin-wave signal is accompanied by a strong nonreciprocity, which manifests itself in a change in the amplitude-frequency characteristics when the direction of the external magnetic field is reversed, while the frequency range of the band gap differs depending on the direction of the field. The proposed concept of a two-layer spin-wave waveguide can underlie the manufacture of multichannel filters or magnonic logic devices. Keywords: magnonics, nonlinearity, nonlinear systems, multilayer systems, spin waves.

Dispersive waves in magneto-electro-elastic periodic waveguides

Magneto-electro-elastic (MEE) materials are attracting an increasing amount of scientific interest in physics, for their valuable potential in the functional management of mechanical-to-magnetoelectric energy conversions. The present paper focuses on heterogeneous MEE media – artfully realized by virtue of the periodic repetition of a multi-phase elementary cell – which represent promising solutions to passively control the propagation of multifield Bloch waves. Specifically, the linear continuum model governing the coupled free dynamics of a cellular non-dissipative MEE material is formulated for the unbounded three-dimensional domain. Then, the governing equations are specialized for a periodic layered waveguide with perfect inter-layer interfaces. The Floquet–Bloch decomposition is employed to analytically determine the uni-modular transfer matrix of the heterogeneous multi-layered cell. The related eigenproblem, governed by a palindromic characteristic polynomial in the Floquet multipliers, is solved in closed form to analyze the dispersion properties in the real-valued frequency domain and complex-valued wavenumber domain. Alternatively, a perturbation scheme is outlined to asymptotically approximate the exact eigensolutions. The dispersion spectra, composed of propagation and attenuation branches, are parametrically investigated for a two-layered periodic waveguide. The corresponding band structures are assessable a priori by leveraging the formal analogy with the stability analysis for non-autonomous dynamical systems. As main findings, slow-propagating quasi-shear-elastic waves and fast-propagating quasi-magneto-electric waves are found to dominate the low-frequency and high-frequency ranges, respectively, although some crossing points between the respective spectral branches can be detected. Quantitatively different but qualitatively similar behaviors of propagation and/or attenuation are observed for the quasi-shear-elastic waves and quasi-magneto-electric waves. Consequently, pass–pass, pass–stop and stop–stop bands of frequencies can be recognized and tuned by varying the key physical parameters. This rich spectral scenario opens the way for the functional customization of MEE-based metafilters or metapropagators, purposely designed to govern the transfer, localization, conversion, harvesting of energy across large frequency ranges.

Nonreciprocal propagation of spin waves in a bilayer magnonic waveguide based on yttrium-iron garnet films

Objectives. Nonreciprocal spin wave effects can manifest themselves in metalized films of ferrite garnets. By studying the dynamics of spin waves in micro- and nano-scale magnetic films, the possibility of using multilayer dielectric films of yttrium iron garnet (YIG) to ensure the manifestation of the nonreciprocity effect is demonstrated. This approach offers advantages compared to the use of a layered YIG/metal structure due to significantly lower spin-wave losses in the two-layer YIG film consisting of layers with different values of magnetization. Such films can be used in logical elements to create controllable Mach-Zehnder interferometers based on magnonic principles. The purpose of this work is to reconcile the concept of nonreciprocal spin-wave propagation of a signal with the simultaneous manifestation of the effects arising from the propagation of spin waves in microwave guides formed by finite-width YIG films.Methods. We used an experimental microwave spectroscopy method based on a vector network analyzer along with a finite difference method to perform a numerical simulation of the dispersion characteristics of spin waves in two-layer magnonic microwave guides. An analytical model was also used to obtain a dispersion equation based on the magnetostatic approximation.Results. Based on measurements of the amplitude and phase responses, the possible coexistence of two frequency ranges for the propagation of a spin-wave signal in a two-layer magnon microwave guide based on a YIG film formed by two layers with different values of saturation magnetization was demonstrated. Regimes of nonreciprocal propagation of a spin-wave signal were revealed. A numerical model was using to study the formation mechanisms of spin wave modes in the spectrum of a two-layer structure formed due to the finite dimensions of the microwave guide. An analytical model was used to evaluate the transformation of the mode spectrum. The experimental data are in good agreement with the results of the proposed numerical and analytical models.Conclusions. The possibility of frequency-selective propagation of spin waves in a magnon microwaveguide consisting of two layers with different saturation magnetization values is demonstrated. Multimode propagation of spin waves can occur inside a two-layer structure in two frequency ranges. At the same time, this process is accompanied by a strong nonreciprocity of spin-wave signal propagation, which manifests itself in a change in the amplitude and phase responses when the direction of the external magnetic field is reversed. The proposed two-layer spin-wave waveguide concept can be used in the manufacture of magnon interconnects and magnon interferometers with the support of multiband regimes of operation.

Эффекты нелинейности при распространении спиновых волн в двуслойном магнонном волноводе

The possibility of frequency-selective propagation of spin waves in a linear and nonlinear mode in a magnon microwave medium consisting of two layers with different values of the magnetization saturation of each layer is demonstrated. It is shown that multimode propagation of spin waves can be carried out inside the two-layer structure in two frequency ranges, with an increase in the power of the input microwave signal leading to a change in the boundaries of both frequency ranges. At the same time, this process is accompanied by a strong nonreciprocity of the spin-wave signal propagation, which manifests itself in a change in the amplitude-frequency characteristics when the direction of the external magnetic field is reversed, with a nonlinear mode change in the frequency bandwidth borders can change with increasing pumping power. The proposed concept of a two-layer spin-wave waveguide can form the basis for the fabrication of nonlinear magnon elements demonstrating interconnection functions with support for multiband modes of operation

Nonlinear effects of spin wave propagation in a bilayer magnon waveguide

The possibility of frequency-selective propagation of spin waves in a linear and nonlinear mode in a magnon microwave medium consisting of two layers with different values of the magnetization saturation of each layer is demonstrated. It is shown that multimode propagation of spin waves can be carried out inside the two-layer structure in two frequency ranges, with an increase in the power of the input microwave signal leading to a change in the boundaries of both frequency ranges. At the same time, this process is accompanied by a strong nonreciprocity of the spin-wave signal propagation, which manifests itself in a change in the amplitude-frequency characteristics when the direction of the external magnetic field is reversed, with a nonlinear mode change in the frequency bandwidth borders can change with increasing pumping power. The proposed concept of a two-layer spin-wave waveguide can form the basis for the fabrication of nonlinear magnon elements demonstrating interconnection functions with support for multiband modes of operation. Keywords: magnonics, nonlinearity, nonlinear systems, multilayer systems, spin waves.

Design and Implementation of a Wideband Antenna Subarray for Phased-Array Applications

A wideband antenna subarray with a hybrid feeding network is proposed for phased-array applications. The subarray is a multilayer structure, where the top four-layer printed circuit board (PCB) is for antennas, middle two-layer metallic waveguides are for interconnections, and bottom eight-layer PCB is for the transition between the feeding network and active circuits. The middle metallic waveguides can not only improve the isolation between the antenna and active circuits but also serve as the heat dispersion structure of the active circuits and a low-loss power distribution network. Two kinds of novel transitions with bandpass filtering function and a technique for broadening the impedance bandwidth of the antenna element are proposed. Besides, a subarray with the SIW feeding network is proposed focusing on the wideband characteristic. The experimental results of the subarray prototypes show that the impedance bandwidths of 26.7%, 19%, and 51% are achieved. An array with 16 subarrays is fabricated and the beam-scanning characteristic is measured for validating the phased-array applications of the subarray. A phased-array system can be designed with such subarrays followed with transceivers and phase shifters. Combined with a low-accuracy mechanical tracking system, it can be efficiently used for the dynamic intersatellite communications.

On the resonant properties of the THz metal-dielectric waveguide impedance

Various asymptotic representations for the longitudinal monopole impedance of a two-layer metal-dielectric cylindrical waveguide with finite-conducting external walls and a lossy internal dielectric layer are derived. Areas of their applicability are determined and their properties are investigated. New features for the resonance properties of the structure under consideration are revealed and described.

Wakefields in conducting waveguides with a lossy dielectric channel

The resonant properties of the impedance of a two-layer circular metal-dielectric waveguide are investigated by taking into account the finite conductivity of the metallic pipe and the dissipation of the radiated energy in the dielectric layer. The dispersion relations for azimuthally symmetric monopole TM modes are analyzed. It is shown that, for an outer metallic layer with finite conductivity and a thin internal dielectric cover, the waveguide has only a single slowly propagating ${\mathrm{TM}}_{01}$ mode. The point charge longitudinal wake potentials are evaluated for thin and thick internal layers.

Non-PT-symmetric two-layer cylindrical waveguide for exceptional-point-enhanced optical devices.

We investigate the exceptional points in a two-layer cylindrical waveguide structure consisting of absorbing and non-absorbing dielectrics. We show that, by tuning the core to total radius ratio and the refractive index of the core layer in such a structure, the complex effective indices of two waveguide modes can coalesce so that an exceptional point is formed. We show that the sensitivity of the effective index of the waveguide mode to variations of the refractive index of the material filling the shell layer is enhanced at the exceptional point. In addition, we show that larger sensitivity enhancement is obtained for smaller perturbations. Our results could potentially contribute to the development of a new generation of chip-scale exceptional-point-enhanced optical waveguide devices for modulation, switching, and sensing.

On geoacoustic inversions, sediment acoustics, and deep ocean ambient noise

During the period of 2005–2011, three topics in acoustical oceanography were actively investigated in the Buckingham Lab which combined field, lab, and theoretical work. Geoacoustic inversions in the low frequency (<500 Hz) band were carried out using the noise generated by a light aircraft off the coast of La Jolla, California, and during the MAKAI experiment in Kauai, Hawaii. The inversion relied on a comparison of data to an analytical model of a moving airborne source over a two-layer shallow water waveguide. In an effort to investigate the link between grain roughness and porosity to support the development of a theory of acoustic propagation in sediments, a statistical model for the two-dimensional shape of sand grains was developed from the digitized outlines of grains from a dozen locations, including deserts, beaches, and seabeds. Lastly, a family of autonomous free-falling ambient noise profilers known as Deep Sound, were designed, manufactured, and deployed, returning measurements of ambient noise from below the critical (or reciprocal) depth in the deep ocean. Field experiments were carried out in the San Diego trough, the Philippine Sea, the Tonga Trench, and the Sirena Deep and Challenger Deep in the Mariana Trench.

Directly inscribed multimode polymer waveguide and 3D device for high-speed and high-density optical interconnects.

A 75-cm-long circular-core polymer waveguide compatible with standard 50-μm-core multimode fibers (MMFs) is designed and fabricated by using a direct inscribing method for high-speed and high-density optical interconnects. The fabricated waveguide has low loss (<0.044 dB/cm at 850 nm) and low crosstalk (<-34 dB with a core pitch of 62.5 μm) with a negligible coupling loss with the MMFs. It also exhibits a low bending loss (<0.08 dB/mm with a bending radius of 4 mm), which agrees well with calculated results. Error-free NRZ data transmission over the 75-cm-long waveguide at 25 Gb/s is demonstrated, and 4 × 25 Gb/s short wavelength division multiplexing (SWDM) is realized on a straight waveguide. Moreover, a two-layer waveguide and a 3-dimensional (3D) Y-splitter/combiner are also fabricated for 3D integration.

Simulation of an electro-optic modulator based on the quantum-confined Stark effect in a two-layer InAlGaAs rib waveguide on an InP substrate

An electro-optic Mach – Zehnder modulator based on the quantum-confinement Stark effect in layered multiple-quantum-well InAlGaAs structures on InP substrate is numerically simulated. The novelty of the modulator design is the use of a two-layer rib optical waveguides, which provide technologically efficient (loss of 1.5 dB per element) coupling of the modulator with optical fibre. It is shown that, changing the electrode width and the distance between two waveguides in two Mach – Zehnder interferometer arms, one can match the impedance of the modulator with an external 50-Ω load and the velocities of microwave and optical waves in the modulator. The results of the study can be used in integrated optics, optical communication, and radiophotonics devices.

High performance refractive index sensor with stacked two-layer resonant waveguide gratings

Abstract A refractive index (RI) sensor which contains a dielectric cavity composed of two parallel planar waveguide gratings (WGGs) is proposed. Reflection and transmittance through stacked gratings are studied after converting the diffraction problem into the two coupled resonances. The method of analysis is applied to estimate the performance when used as a biosensor. The sensor achieves its high-sensitive detection by tracking a narrow resonant reflection peak via a tunable wavelength light source, and the desired RI can be determined from the resonant wavelength shift. It will be shown that, in comparison with conventional single grating guided mode resonance (GMR) sensor with equal available area, extremely narrow resonance linewidth can be obtained by using stacked gratings. The sensitivity of the sensor can reach to 497.83 nm/RIU, and the value of the figure of merit (FOM) can reach up to 551. Because of its advantages such as high-sensitivity, label-free, small size and non-destructive, the sensor has an extremely broad application prospect in the field of biomedicine detection.

Analysis and Design of a Compact Leaky-Wave Antenna for Wide-Band Broadside Radiation

A low-cost compact planar leaky-wave antenna (LWA) is proposed offering directive broadside radiation over a significantly wide bandwidth. The design is based on an annular metallic strip grating (MSG) configuration, placed on top of a dual-layer grounded dielectric substrate. This defines a new two-layer parallel-plate open waveguide, whose operational principles are accurately investigated. To assist in our antenna design, a method-of-moments dispersion analysis has been developed to characterize the relevant TM and TE modes of the perturbed guiding structure. By proper selection of the MSG for a fabricated prototype and its supporting dielectric layers as well as the practical TM antenna feed embedded in the bottom ground plane, far-field pencil-beam patterns are observed at broadside and over a wide frequency range, i.e., from 21.9 GHz to 23.9 GHz, defining a radiating percentage bandwidth of more than 8.5%. This can be explained by a dominantly excited TM mode, with low dispersion, employed to generate a two-sided far-field beam pattern which combines to produce a single beam at broadside over frequency. Some applications of this planar antenna include radar and satellite communications at microwave and millimeter-wave frequencies as well as future 5G communication devices and wireless power transmission systems.

Efficient Analysis of Multiple Microstrip Transmission Lines With Anisotropic Substrates

Our aim with this letter is to exhibit the extension of discrete mode-matching method to analyze multilayered microstrip transmission lines with anisotropic dielectric layers. The mathematical formulation is presented to deal with multilayered structures with metallizations in the interfaces. The application is demonstrated by computing propagation constant and characteristic impedance for multilayered microstrip and two-layer coplanar waveguide with uniaxial anisotropic dielectric. The validation of the results has been done by comparing with simulations with ANSYS HFSS and some of them also with open literature. A very good agreement has been observed.

Influence of high loss liquid on the bandwidth of a circular two-layer waveguide at microwaves

ABSTRACTThe electromagnetic waves propagation in a circular two-layer metal waveguide with a central low-loss dielectric rod surrounded by high loss liquid is studied in the microwave range. The dependence of the complex wave propagation coefficient on frequency and liquid layer thickness is obtained. The presence of high loss liquid surrounding the dielectric rod allows expanding the range of operating wavelengths of the standard waveguide from the millimeter to centimeter range, because the wave attenuation coefficient remains relatively small. We find that owing to a high loss liquid, such a waveguide does not have fixed values of cut-off frequencies. An extra low value of the wave attenuation coefficient is found in the centimeter wavelength range at certain liquid layer thicknesses. The proposed structure can be applied as a measuring cell for the determination of the complex permittivity of high loss liquids in small volumes and in a wide range of wavelengths.

Full‐wave equivalent circuit for the analysis of multilayered microwave structures with anisotropic layers

A simple formalism is presented as a basis to analyse planar microwave structures with uniaxial anisotropic materials having either electric or magnetic anisotropy or both. It involves a generalised relation of the field components of the multilayered structure, which can be represented by a full-wave hybrid matrix for each layer. Thus, for stratified structures, the system equation can be obtained by using a full-wave equivalent circuit. The application is demonstrated by analysing the well-known example of a two-layer waveguide filled with different uniaxial anisotropic dielectric material.

Polarization-independent and colorless switching operation of three-dimensional 4 × 4 polymer optical switch with two-layered waveguide structure

We fabricated a three-dimensional (3D) 4 × 4 polymer optical interconnection switch with a two-layered waveguide structure equipped with four Mach–Zehnder interferometer optical switches (MZ-OSs), two vertical directional couplers (VDCs), and a multimode interferometer (MMI) coupler. The experimental result for the device shows polarization-independent and colorless switching operation by the thermo-optic (TO) effect in the 1550-nm-wavelength range with a switching power of about 18 mW.