Waveguide Approach Research Articles

HF radio path modeling by waveguide approach

We present a scheme for modeling HF radio signal characteristics along paths of different lengths, which is based on the waveguide approach — the normal mode method. We use a representation of the recorded signal field in the form of Green function products of the angular operator, excitation coefficients, and reception coefficients of individual normal modes. Algorithms have been developed for calculating distance-frequency, frequency-angular, and amplitude characteristics of signals in large spatial regions through analysis and numerical summation of normal mode series. We have implemented a complex algorithm for simulating propagation conditions of HF radio signals, which includes a medium model, algorithms for calculating signal characteristics, and operational diagnostics of radio channel. We have compared the results of the HF signal propagation characteristic modeling and the experimental oblique sounding data obtained along paths of different lengths and orientation. To analyze experimental ionograms, determine the maximum usable frequencies for propagation modes along radio paths, we employ the method of automatic processing and interpretation of oblique sounding ionograms.

Моделирование КВ-радиотрасс на основе волноводного подхода

We present a scheme for modeling HF radio signal characteristics along paths of different lengths, which is based on the waveguide approach — the normal mode method. We use a representation of the recorded signal field in the form of Green function products of the angular operator, excitation coefficients, and reception coefficients of individual normal modes. Algorithms have been developed for calculating distance-frequency, frequency-angular, and amplitude characteristics of signals in large spatial regions through analysis and numerical summation of normal mode series. We have implemented a complex algorithm for simulating propagation conditions of HF radio signals, which includes a medium model, algorithms for calculating signal characteristics, and operational diagnostics of radio channel. We have compared the results of the HF signal propagation characteristic modeling and the experimental oblique sounding data obtained along paths of different lengths and orientation. To analyze experimental ionograms, determine the maximum usable frequencies for propagation modes along radio paths, we employ the method of automatic processing and interpretation of oblique sounding ionograms.

HF radio channel modeling by a waveguide approach

We present a modified method of HF radio channel modeling based on a waveguide approach. The waveguide approach represents the electromagnetic field of radiation inside the Earth—ionosphere waveguide as an eigenfunction series of a radial boundary problem with impedance conditions on the Earth surface and radiation conditions at infinity. The transfer function of the radio channel is represented as a series of products of angular-operator Green functions, excitation coefficients, and coefficients for receiving individual normal modes. We have obtained a solution of the boundary value problem of determining the eigenfunctions and eigenvalues of the radial operator. The solution can be applied to the frequency range below the ionospheric F-layer critical frequency. We examine algorithms for calculating distance-frequency, frequency-angular, and amplitude characteristics of signals by analyzing and numerically summarizing the series in terms of strongly damped normal modes.

Моделирование КВ-радиоканала на основе волноводного подхода

We present a modified method of HF radio channel modeling based on a waveguide approach. The waveguide approach represents the electromagnetic field of radiation inside the Earth—ionosphere waveguide as an eigenfunction series of a radial boundary problem with impedance conditions on the Earth surface and radiation conditions at infinity. The transfer function of the radio channel is represented as a series of products of angular-operator Green functions, excitation coefficients, and coefficients for receiving individual normal modes. We have obtained a solution of the boundary value problem of determining the eigenfunctions and eigenvalues of the radial operator. The solution can be applied to the frequency range below the ionospheric F-layer critical frequency. We examine algorithms for calculating distance-frequency, frequency-angular, and amplitude characteristics of signals by analyzing and numerically summarizing the series in terms of strongly damped normal modes.

Structural characterization of thin-walled microbubble cavities

Whispering gallery mode (WGM) microbubble cavities are a versatile optofluidic sensing platform owing to their hollow core geometry. To increase the light–matter interaction and, thereby, achieve higher sensitivity, thin-walled microbubbles are desirable. However, a lack of knowledge about the precise geometry of hollow microbubbles prevents us from having an accurate theoretical model to describe the WGMs and their response to external stimuli. In this work, we provide a complete characterization of the wall structure of a microbubble and propose a theoretical model for the WGMs in this thin-walled microcavity based on the optical waveguide approach. Structural characterization of the wavelength-scale wall is enabled by focused ion beam milling and scanning electron microscopy imaging. The proposed theoretical model is verified by finite element method simulations. Our approach can readily be extended to other low-dimensional micro-/nanophotonic structures.

Electromagnetic wave absorption mechanism for nanocomposites of holmium orthoferrite decorated poly(3,4-ethylenedioxythiophene -5-cyanoindole)

New microwave absorbents with low thickness, minimum reflection loss and effective absorption bandwidth microwave absorption capabilities are urgently needed, but their realization remains still challenging. For this study, we used an innovative nanocomposite architecture comprised of polygonal HoFeO3 powder encapsulated with Poly(EDOT-co-CNIn) to create an electromagnetic wave absorption material optimized for the X-band frequency. Structural, morphological, magnetic, and microwave absorption characteristics of synthesized nanocomposite materials were evaluated utilizing XRD, FTIR, FESEM, VSM, and VNA techniques. With 35 wt.% filler loading, HoFeO3@Poly(EDOT-co-CNIn) composite absorber achieves a minimum reflection loss (RLmini) of -40 dB having 1.6 mm thickness, as measured by the waveguide method. Compared to other absorber samples optimal sample featured improved impedance matching abilities, better attenuation coefficient and a high absorption capacity. The optimal sample is also tested using the free-space measurement technique having dimensions of 200 mm × 200 mm and thus the findings show that they accord well with those of the waveguide approach. This work presents a design strategy for an effective microwave absorbent with practical measuring strategies for both waveguide and free-space setups.

Terahertz optical solitons from dispersion-compensated antenna-coupled planarized ring quantum cascade lasers.

Quantum cascade lasers (QCLs) constitute an intriguing opportunity for the generation of on-chip optical dissipative Kerr solitons (DKSs). Originally demonstrated in passive microresonators, DKSs were recently observed in mid-infrared ring QCL paving the way for their achievement even at longer wavelengths. To this end, we realized defect-free terahertz ring QCLs featuring anomalous dispersion leveraging on a technological platform based on waveguide planarization. A concentric coupled waveguide approach is implemented for dispersion compensation, while a passive broadband bullseye antenna improves the device power extraction and far field. Comb spectra featuring sech2 envelopes are presented for free-running operation. The presence of solitons is further supported by observing the highly hysteretic behavior, measuring the phase difference between the modes, and reconstructing the intensity time profile highlighting the presence of self-starting 12-picosecond-long pulses. These observations are in very good agreement with our numeric simulations based on a Complex Ginzburg-Landau Equation (CGLE).

Photonic integrated beam delivery for a rubidium 3D magneto-optical trap

Cold atoms are important for precision atomic applications including timekeeping and sensing. The 3D magneto-optical trap (3D-MOT), used to produce cold atoms, will benefit from photonic integration to improve reliability and reduce size, weight, and cost. These traps require the delivery of multiple, large area, collimated laser beams to an atomic vacuum cell. Yet, to date, beam delivery using an integrated waveguide approach has remained elusive. Here we report the demonstration of a 87Rb 3D-MOT using a fiber-coupled photonic integrated circuit to deliver all beams to cool and trap > 1 ×106 atoms to near 200 μK. The silicon nitride photonic circuit transforms fiber-coupled 780 nm cooling and repump light via waveguides to three mm-width non-diverging free-space cooling and repump beams directly to the rubidium cell. This planar, CMOS foundry-compatible integrated beam delivery is compatible with other components, such as lasers and modulators, promising system-on-chip solutions for cold atom applications.

A Waveguide Model of the Developed Turbulent Boundary Layer

A study of the developed turbulent boundary layer that emerges when incompressible viscous fluid flows around a plate at a zero angle of attack and with zero longitudinal pressure gradient is presented. The waveguide approach is used for describing the turbulent boundary layer; in this approach, turbulent fluctuations are related with Tollmien–Schlichting waves that are in three-wave resonance. To study the original nonlinear system of equations, an estimate of hydrodynamic quantities is proposed that does not violate the generally accepted approach in the boundary layer but leads to the appearance of a new small parameter—the ratio of the thickness of the boundary layer momentum loss to the damping length of the least damped mode of the Tollmien–Schlichting waves. Equations for the coherent and stochastic parts of fluctuations are obtained on the basis of the method of multiple scales. The dispersion characteristics of waves of the least damped mode on the profile of the average longitudinal velocity of the developed turbulent boundary layer are determined, and the conditions for the multiple three-wave resonance of this mode of the Tollmien–Schlichting waves are analyzed. For the coherent part of the fluctuations, the fluctuation characteristics are compared with the known numerical results.

Photonic Crystal Circuitry and its Impact on Wireless Networks

Wireless networks are considered a hot topic in dealing with data without need to routers or other infrastructures. Each node has a part of routing responsibility. This result to a huge of data in forwarding to other nodes and will need high speed to process. Photonic crystal applications come to solve the necessity for such speed with small circuitry area. One of the main factors that affect their operation is the structure topology. Ring resonator, cavity based structures, self-collimation, and waveguide approaches are some of these topologies. OR gate is proposed in this paper to be simulated and evaluated as one of the basic element block. This design is built on a square lattice- photonic crystal construction on a ring resonator basis. Rotation of 90, 180, and 270 degrees are applied in clockwise direction. Sensitivity analysis, and carefully rod locations are considered to obtain remarkable performance. Minimum size and highly data rate are two characteristics that discriminates this design. The minimum size of 51.48 μm2 is obtained. The bit rates of 1.35, 6.35, 3.2, and 2.53 Tbs are calculated with the 0, 90, 180, and 270 degrees, respectively. Comparison table is well organized for the recently published photonic crystal OR-gate that based on ring resonator. Finite difference time domain and Plan wave expansion method are used to analyze the proposed structure at 1.55μm wavelength to verify OR- gate operation.

3D Printed Hemispherically Radiating Antenna for Broadband Millimeter Wave Applications

Nowadays, additive manufacturing provides far-reaching possibilities for use in radio frequency components. In addition to almost unlimited freedom of design as compared to conventional manufacturing, the absence of further assembly steps is a key aspect of 3D printing. In this paper, a 3D printed monolithic antenna for millimeter wave-sensing applications is presented with a full hemispherical coverage. The antenna is designed as an ensemble of a waveguide horn antenna and a differentially fed dipole antenna. The slotted waveguide approach was utilized to improve the manufacturing quality on the waveguide inside. The influence of two optimized antenna elements, a metal plane, and a cut-out window, on the beam pattern is comprehensively investigated. A huge half power beam width of 142° in both directions, elevation and azimuth, is presented at 79 GHz and a boresight gain of 4.7 dBi was measured. The beam pattern in the frequency range from 76 to 81 GHz is studied in greater detail, where a half power beam width of at least 112° is achieved. Due to the −10 dB matching capability bandwidth of over 28 GHz, the antenna is also suitable for extremely broadband applications with a −5 dB angular width of better than 100°. Furthermore, the system design describes how to integrate the antenna into hybrid circuit designs and the manufacturing tolerances are examined. The antenna offers attractive possibilities for millimeter wave-sensing applications in the area of assisted living and industrial monitoring, especially whenever blind spots have to be avoided.

Epoxy-Nanoceramic Composites for 5G Antennas

Epoxy–nanoceramic composites of BiVO4 (BVO), LaNbO4 (LNO), and Li6Mg7Ti3O16 (LMT) were prepared using the solvent mixing method. The ceramic nano-fillers volume fractions were (5, 8, 10, and 12%). X-ray diffraction (XRD) and Atomic Force Microscopy (AFM) were used to investigate the crystal structure and size distribution of nanoceramics, respectively. The dielectric constant and loss tangent were measured in the frequency range of (4-8) GHz. The measurement technique was the waveguide approach via a Vector Network analyzer (VNA). The effect of the volume fraction of ceramic fillers on the dielectric constant and loss tangent of the composites at 5.28 GHz (5G) was investigated. This work aims to design composite materials for 5G antennas of lower cost while maintaining the properties of 5G antennas. The results show that an optimum volume fraction of the ceramic filler brings the dielectric properties to their best value. However, epoxy composite with a 5% volume fraction of LMT shows good microwave dielectric properties (dielectric constant = 2.17 and loss tangent = 0.011) at 5.28 GHz. In addition, epoxy- LMT composite with an exceptionally low volume fraction of 5% provides a low-cost material for a 5G antenna. Another aspect of the cost reduction is the elimination of the costly and troublesome compaction and high-temperature sintering process. Furthermore, the epoxy composite overcomes the disadvantages of the high brittleness of the sintered all-ceramic products. As a result, epoxy composite with the 5% volume fraction of LMT is a potential candidate for 5G antenna materials.

Measuring the Electromagnetic Field of the Human Brain at a Distance Using a Shielded Electromagnetic Field Channel.

IntroductionThe electromagnetic field (EMF) of the human brain generated by the movement of ions in the brain can be measured in a novel manner. The measurement can be completed through the skull, in a non-contact, non-invasive, continuous manner using a lightweight helmet. This investigation was conducted to determine if brain activity from movement and thoughts of movement can be measured at a distance and if that measurement can be readily evaluated at a distance using shielding with a shielded helmet and a shielded EMF channel surrounding a sensor.MethodsNon-clinical human subject volunteers donned a lightweight sensor helmet and performed a variety of specific tasks synchronized with an audible tone generated by a metronome. Constructs were created to determine if the human subjects’ brain EMF can be recorded at a distance using sensors surrounded by shielding acting similar to a waveguide in an EMF channel connected to a shielded helmet.ResultsThe EMF sensors appeared to record brain electromagnetic activity as it is funneled into a shielded channel acting as a waveguide at a considerable distance including distances as far as 63 cm away.ConclusionSpecific brain EMFs from movement, thoughts of movement, and emotional thought can be continuously measured in a non-contact fashion at a distance using an EMF waveguide approach with an EMF channel and shielded helmet.

Intermixed Time-Dependent Self-Focusing and Defocusing Nonlinearities in Polymer Solutions.

Low-power visible light can lead to spectacular nonlinear effects in soft-matter systems. The propagation of visible light through transparent solutions of certain polymers can experience either self-focusing or defocusing nonlinearity, depending on the solvent. We show how the self-focusing and defocusing responses can be captured by a nonlinear propagation model using local spatial and time-integrating responses. We realize a remarkable pattern formation in ternary solutions and model it assuming a linear combination of the self-focusing and defocusing nonlinearities in the constituent solvents. This versatile response of solutions to light irradiation may introduce a new approach for self-written waveguides and patterns.

THz frequency combs form dispersion-compensated antenna-coupled ring quantum cascade lasers

We report comb operation of RF injected ring Quantum Cascade Lasers. A coupled waveguide approach is implemented for dispersion compensation while passive bullseye antenna improves the device power extraction and far field. Phase sensitive measurements are presented which hints at the presence of soliton state.

Additive Manufactured Waveguide for E-Band Using Ceramic Materials

Ceramic materials are chemical- and temperature-resistant and, therefore, enable novel application fields ranging from automotive to aerospace. With this in mind, this contribution focuses on developing an additive manufacturing approach for 3D-printed waveguides made of ceramic materials. In particular, a special design approach for ceramic waveguides, which introduces non-radiating slots into the waveguides sidewalls, and a customized metallization process, are presented. The developed process allows for using conventional stereolithographic desktop-grade 3D-printers. The proposed approach has, therefore, benefits such as low-cost fabrication, moderate handling effort and independence of the concrete waveguide geometry. The performance of a manufactured ceramic WR12 waveguide is compared to a commercial waveguide and a conventionally printed counterpart. For that reason, relevant properties, such as surface roughness and waveguide geometry, are characterized. Parsing the electrical measurements, the ceramic waveguide specimen features an attenuation coefficient of 30–60 dB/m within the E-Band. The measured attenuation coefficient is 200% and 300% higher compared to the epoxy resin and the commercial waveguide and is attributed to the increased surface roughness of the ceramic substrate.

Ultra-Low-Loss Mid-Infrared Plasmonic Waveguides Based on Multilayer Graphene Metamaterials.

Manipulating optical signals in the mid-infrared (mid-IR) range is a highly desired task for applications in chemical sensing, thermal imaging, and subwavelength optical waveguiding. To guide highly confined mid-IR light in photonic chips, graphene-based plasmonics capable of breaking the optical diffraction limit offer a promising solution. However, the propagation lengths of these materials are, to date, limited to approximately 10 µm at the working frequency f = 20 THz. In this study, we proposed a waveguide structure consisting of multilayer graphene metamaterials (MLGMTs). The MLGMTs support the fundamental volume plasmon polariton mode by coupling plasmon polaritons at individual graphene sheets over a silicon nano-rib structure. Benefiting from the high conductivity of the MLGMTs, the guided mode shows ultralow loss compared with that of conventional graphene-based plasmonic waveguides at comparable mode sizes. The proposed design demonstrated propagation lengths of approximately 20 µm (four times the current limitations) at an extremely tight mode area of 10−6 A0, where A0 is the diffraction-limited mode area. The dependence of modal characteristics on geometry and material parameters are investigated in detail to identify optimal device performance. Moreover, fabrication imperfections are also addressed to evaluate the robustness of the proposed structure. Moreover, the crosstalk between two adjacent present waveguides is also investigated to demonstrate the high mode confinement to realize high-density on-chip devices. The present design offers a potential waveguiding approach for building tunable and large-area photonic integrated circuits.

Alterations in the magnetic and electrodynamic properties of hard-soft Sr0.5Ba0.5Eu0.01Fe12O19/NixCuyZnwFe2O4 nanocomposites

Hard/soft (H/S) Sr0.5Ba0.5Eu0.01Fe12O19/NixCuyZnwFe2O4 nanocomposites (NCs) were produced via a one-pot sol–gel auto-combustion procedure. Phase and surface analyses were performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM). Magnetization measurements for H/S NCs with different x, y, and w ratios were investigated at two different temperatures (300 and 10 K). The M−H curves were not smooth for the different H/S NCs, revealing that the exchange interaction was incomplete. The derivative of the magnetization (dM/dH versus H) exhibited two separate peaks, confirming the non-coupled H/S mixtures. Maximum saturation magnetization (Ms) values of 93.9 and 63.1 emu/g were obtained at 10 and 300 K, respectively, for the H/S Sr0.5Ba0.5Eu0.01Fe11.99O19/Ni0.3Cu0.3Zn0.4Fe2O4 NC, which contained the highest content of Zn and the same contents of Ni and Cu within the soft magnetic phase. The calculated squareness ratios (SQR = Mr/Ms) were less than 0.5, indicating incomplete exchange coupling. The coercive field (Hc) of the produced NCs reached a maximum value of approximately 2485 Oe at 300 K and 2331 Oe at 10 K with a decrease in the Ms values to 56.9 emu/g at 300 K and 78.5 emu/g at 10 K for the H/S Sr0.5Ba0.5Eu0.01Fe11.99O19/Ni0.8Cu0.1Zn0.1Fe2O4 NC, which contained lower fractions of Zn and Cu and the highest fraction of Ni. The reflection/transmission-based waveguide approach was employed to investigate the electrodynamic properties of the H/S NC samples within a frequency band of 7–18 GHz. The reflection and transmission coefficients (S11/S21) were measured using a vector network analyzer (VNA) for the sample placed inside a waveguide. The frequency dispersions of the magnetic permeability and electric permittivity were calculated.

Permittivity Estimates of Dielectric Spheres Using Radar Scattering Measurements

Broadband coherent radar scattering measurements were used to estimate the complex permittivity of homogeneous isotropic spheres. A Nelder-Mead optimization minimized differences between measured coherent scattering data and a corresponding forward solution provided by the dielectric Mie series. The method was applied across a range of dielectric materials to include Teflon, polystyrene foam, alumina oxide, neoprene rubber, and shungite. Dielectric constant estimates were achieved to within 0.1-6.85% of published values using traditional waveguide or cavity approaches. The method could not satisfactorily estimate dielectric loss tangent for low loss materials (e.g., foam and Teflon) but increased in accuracy with increasing dielectric loss.

Using Waveguides to Model the Dynamic Stiffness of Pre-Compressed Natural Rubber Vibration Isolators.

A waveguide model for a pre-compressed cylindrical natural rubber vibration isolator is developed within a wide frequency range—20 to 2000 Hz—and for a wide pre-compression domain—from vanishing to the maximum in service, that is 20%. The problems of simultaneously modeling the pre-compression and frequency dependence are solved by applying a transformation of the pre-compressed isolator into a globally equivalent linearized, homogeneous, and isotropic form, thereby reducing the original, mathematically arduous, and complex problem into a vastly simpler assignment while using a straightforward waveguide approach to satisfy the boundary conditions by mode-matching. A fractional standard linear solid is applied as the visco-elastic natural rubber model while using a Mittag–Leffler function as the stress relaxation function. The dynamic stiffness is found to depend strongly on the frequency and pre-compression. The former is resulting in resonance phenomena such as peaks and troughs, while the latter exhibits a low-frequency magnitude stiffness increase in addition to peak and trough shifts with increased pre-compressions. Good agreement with nonlinear finite element results is obtained for the considered frequency and pre-compression range in contrast to the results of standard waveguide approaches.