Field Magnitude Distribution Research Articles

Microwave plasma interaction in a printed transmission line for a power limiting application: from surface-wave-sustained to leaky-wave-sustained discharge

The coupling between a microwave signal and a plasma discharge in a suspended microstrip transmission line is analytically studied. Maxwell’s equations are solved in a 2D approximation to get the expressions of the electromagnetic field. The wave propagation in the guiding structure is first explored without plasma, and for several modes and frequencies. A unified characterization of the three different modes that can propagate at the interface between two dielectric media, namely the leaky waves, the pseudo-surface wave and the pure surface wave, is given in terms of of both wave vectors and electromagnetic field magnitude distribution. This analyze allow to conclude that the fundamental mode in this case is a pseudo-surface wave. Thereafter, we focus on the microwave propagation with a uniform plasma inside the guiding structure. In the non collisional limit, it appears that the plasma discharge is sustained by the so-called pure surface wave, whereas in the collisional limit, a leaky wave propagates along the plasma column. Finally, a non-uniform density profile is taken into account in the calculation. The numerical results obtained from the self-consistent simulation of the microwave-plasma coupling, in a previous work, are thus analyzed with the aid of the analytical formulas to identify the microwave coupling involved in our plasma-based microwave power limiter. The computed propagation constant from numerical data confirmed the type of coupling exhibited for a uniform electron density. Furthermore, we highlight the role of the dielectric slab, from which electromagnetic power transfer occurs into the plasma discharge.

Strong multi-band nonreciprocal radiation with Fibonacci multilayer involving Weyl semimetal

The strong multi-band nonreciprocal radiation with Fibonacci multilayer is studied. It consists of a Weyl semimetal planar and a dielectric layer on a Fibonacci multilayer and a metal reflector. Here, without loss of generality, a quad-band nonreciprocal radiation effect is investigated as an illustration. The results show that four pairs of near-perfect absorption and emission are achieved that do not overlapped with each other, leading to perfect quad-channel nonreciprocal radiation. The underlying physical origin is revealed by investing the magnetic field magnitude distributions and is further verified by impedance matching theory. In addition, the influence of incident angle and geometric parameters on spectral nonreciprocity is investigated, and it is found that the performance can remain excellent in a wide range of geometric parameters, which reduces manufacturing costs. What’s more, the scheme can be easily expanded to achieve multi-band nonreciprocal radiation with the channel number larger than four by simply increasing the Fibonacci order. We believe that the designed structure should pave the way for the development of nonreciprocal thermal emitters with more advanced functions.

Gain Enhancement of Horn Antenna Using a Metal Lens

A compact wideband open-horn antenna is proposed for point-to-point wireless communications. The antenna consists of a spatial power divider and an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> -plane lens. Both the power divider and lens are metallic, fabricated by using 3-D-printing technology. Our proposed lens has wrinkled subchannels of different lengths to convert the original quasi-cylindrical wavefront into a nearly planar wavefront across a wide frequency range, giving a wideband high-gain antenna. The operating principle and the design guideline are given. Using the guideline, two design examples with different <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -field magnitude distributions are studied and fabricated for Ku-band applications. The first design has a uniform <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -field magnitude distribution, with its maximum measured gain and normalized sidelobe level (SLL) being 18.1 dBi and −9.4 dB, respectively. The second design has a tapered <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -field magnitude distribution. In this case, the maximum measured gain and normalized SLL are 19.6 dBi and −15.0 dB, respectively. The overall measured 3-dB gain bandwidths of the two designs are more than 46.7%. It is found that the sizes (axial lengths) of the proposed designs are smaller than those of optimum horn antennas by more than 60%.

Bayesian Cross-matching of High Proper-motion Stars in Gaia DR2 and Photometric Metallicities for ∼1.7 million K and M Dwarfs

Abstract We present a Bayesian method to cross-match 5,827,988 high proper-motion Gaia sources (μ &gt; 40 mas yr−1) to various photometric surveys: Two Micron All Sky Survey, AllWISE data release from the Wide-field Infrared Explorer (WISE) mission, Galaxy Evolution Explorer, Radial Velocity Experiment, Sloan Digital Sky Survey, and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). To efficiently associate these objects across catalogs, we develop a technique that compares the multidimensional distribution of all sources in the vicinity of each Gaia star to a reference distribution of random field stars obtained by extracting all sources in a region on the sky displaced 2′. This offset preserves the local field stellar density and magnitude distribution, allowing us to characterize the frequency of chance alignments. The resulting catalog with Bayesian probabilities &gt;95% has a marginally higher match rate than current internal Gaia data release 2 (DR2) matches for most catalogs. However, a significant improvement is found with Pan-STARRS, where ∼99.8% of the sample within the Pan-STARRS footprint is recovered, as compared to a low ∼20.8% in Gaia DR2. Using these results, we train a Gaussian process regressor to calibrate two photometric metallicity relationships. For dwarfs of 3500 &lt; T eff &lt; 5280 K, we use metallicity values of 4378 stars from the Apache Point Observatory Galactic Evolution Experiment and Hejazi et al. to calibrate the relationship, producing results with a 1σ precision of 0.12 dex and few systematic errors. We then indirectly infer the metallicity of 4018 stars with 2850 &lt; T eff &lt; 3500 K, which are wide companions of primaries whose metallicities are estimated with our first regressor, to produce a relationship with a 1σ precision of 0.21 dex and significant systematic errors. Additional work is needed to better remove unresolved binaries from this second sample to reduce these systematic errors.

T-shaped reflective polarizer under second Bragg incidence

A T-shaped reflective grating device under the second Bragg angle is proposed for polarizer. This grating device is mainly made of fused silica with T-shaped ridges, which can diffract the energy of the TE-polarized light and the TM-polarized light to the −2nd order and the 0th order with the reflective efficiency of each order more than 95%. Normalized field magnitude distribution and overlap integral are analyzed to explain the physical mechanism and energy exchange. Based on the optimized results, the beam splitter exhibits high efficiency, good extinction ratio and optical properties of the incident bandwidth. Moreover, grating can have longer period for easy fabrication under second Bragg incidence compared to reported Bragg incidence. Therefore, the T-shaped reflective grating device should be useful for the future optical communication industry.

A Low Impact Ionization Rate Poly-Si TFT with a Current and Electric Field Split Design

In this study, a novel low impact ionization rate (low-IIR) poly-Si thin film transistor featuring a current and electric field split (CES) structure with bottom field plate (BFP) and partial thicker channel raised source/drain (RSD) designs is proposed and demonstrated. The bottom field plate design can allure the electron and alter the electron current path to evade the high electric field area and therefore reduce the device IIR and suppress the kink effect. A two-dimensional device simulator was applied to describe and compare the current path, electric field magnitude distributions, and IIR of the proposed structure and conventional devices. In addition, the advantages of a partial thicker channel RSD design are present, and the leakage current of CES-thin-film transistor (TFT) can be reduced and the ON/OFF current ratio be improved, owing to a smaller drain electric field.

Rubbing-Induced Site-Selective Growth of MoS2 Device Patterns.

The superior electronic and mechanical properties of two-dimensional layered transition-metal dichalcogenides could be exploited to make a broad range of devices with attractive functionalities. However, the nanofabrication of such layered material-based devices still needs resist-based lithography and plasma etching processes for patterning layered materials into functional device features. Such patterning processes lead to unavoidable contaminations, to which the transport characteristics of atomically thin-layered materials are very sensitive. More seriously, such lithography-introduced contaminants cannot be safely eliminated by conventional semiconductor cleaning approaches. This challenge seriously retards the manufacturing of large arrays of layered material-based devices with consistent characteristics. Toward addressing this challenge, we introduce a rubbing-induced site-selective growth method capable of directly generating few-layer MoS2 device patterns without the need of any additional patterning processes. This method consists of two critical steps: (i) a damage-free mechanical rubbing process for generating microscale triboelectric charge patterns on a dielectric surface and (ii) site-selective deposition of MoS2 within rubbing-induced charge patterns. Our microscopy characterizations in combination with finite element analysis indicate that the field magnitude distribution within triboelectric charge patterns determines the morphologies of grown MoS2 patterns. In addition, the MoS2 line patterns produced by the presented method have been implemented for making arrays of working transistors and memristors. These devices exhibit a high yield and good uniformity in their electronic properties over large areas. The presented method could be further developed into a cost-efficient nanomanufacturing approach for producing functional device patterns based on various layered materials.

Rainbow trapping and releasing in InSb graded subwavelength grooves by thermal tuning at the terahertz range

Research in terahertz (THz) science and technology has been booming in view of its potential application in a variety of light-matter interaction areas. Intrinsic indium antimonide (InSb) is an excellent tunable candidate material that supports surface plasmon polaritons (SPPs) in the THz range. In this paper, we present calculations to demonstrate the feasibility of exciting SPPs using an InSb graded grating structure. The InSb structure exhibits an extraordinary property of trapping and releasing electromagnetic waves in terahertz regimes (0.084–0.326 THz). With a fixed frequency, the electric field magnitude distributions of the gradient InSb grating waveguide at different temperatures are compared; these show that the InSb grating structure is an excellent candidate for trapping and releasing SPPs in the THz range. The thermo-optic property of InSb permits the meaningful application for compact low-frequency surface-plasmon optical devices in the future.

Effect Of Incident Field Magnitude And Phase Distribution On Rfinduced Heating Due To Hip Implants.

We investigated how the distribution of magnitude and phase of incident electric field affects RFinduced heating near a hip implant. The results showed that varying the incident electric field, for example due to different phantom shape or different landmark position, for two-or three-dimensional implants can result in up to 50% variation of estimated RF-induced temperature rise. To avoid systematic errors in predicting the RF-induced heating, varied distributions of the incident electric field should be applied.

Rainbow Trapping in Highly Doped Silicon Graded Grating Strip at the Terahertz Range

In this paper, we propose surface plasma polaritons (SPPs) propagating along the structure of grating grooves based on highly doped silicon, which exhibits better performance of exciting SPPs than metal at low frequency (e.g., microwaves, mid infrared, and terahertz). The dispersive properties of the gradient-corrugated grating waveguides are characterized using the computer simulation technology microwave studio. Moreover, the propagation characteristics of the highly doped silicon grating structure are analyzed in detail by the dispersion curves, two-dimensional electric field magnitude distributions, the propagation loss, and the SPP lifetime. It is demonstrated that the gradient-corrugated grating waveguides based on heavily doped silicon could excite SPPs and realize rainbow trapping. The lifetime of the plasmonic mode can reach a value of 1200 ps, which may be long enough for some meaningful nanophotonic applications. The highly doped silicon is an ideal candidate for making practical use of the slow-light system in optical communication and various nanophotonic circuits, which permits further application for compact plasmonic devices.

Antenna array in 3D to improve tracking of small HF RFID tag

This paper presents an improvement of small RFID tags detection in HF near field, whatever their lateral and angular misalignments, using a complementary sub-coils reader antenna, enhanced by coplanar weakly-coupled resonators, and conformed on a 3D tube. The key ideas of detection improvement are: (i) modification of B -field vector distribution with the complementary coils above the common edge of consecutive loops; (ii) increase of B -field vector diversity and magnitude distribution by a 3D structure conformed on the tube, by realising 2 pairs of Identical Coaxial Loops (ICLs) with face-to-face sub-coils in forward current, and (iii) enhancement of B -field magnitude distribution by resonators included in the complementary sub-coils. Numerical simulations are carried out using High Frequency Structure Simulator (HFSS). The studied figure-of-merit is the mutual inductance between the tag and the reader coil. Results are reported for the 4 planar complementary sub-coils, the previous structure conformed on the tube and for the structure in which RCL resonators are added in the 3 planar complementary sub-coils. Experimental detection range measurements of each fabricated structure drives to the enhancement of the 3D complementary 4 × 3 sub-coils structure with weakly-coupled RLC resonators in each-sub-coil in terms of read-out distance and detection surface area.

Effect of aperture field distribution on the maximum radiated power at atmospheric pressure**Project supported by the National Natural Science Foundation of China (Grant Nos. 61501358, 11622542, 61431010, and 61627901) and the Fundamental Research Funds for the Central Universities, China.

The air breakdown in the high-power antenna near-field region limits the enhancement of the radiated power. A model coupling the field equivalent principle and the electron number density equation is presented to study the breakdown process in the near-field region of the circular aperture antenna at atmospheric pressure. Simulation results show that, although the electric field in the near-field region is nonuniform, the electron diffusion has small influence on the breakdown process when the initial electron number density is uniform in space. The field magnitude distribution on the aperture plays an important role in the maximum radiated power above which the air breakdown occurs. The maximum radiated power also depends on the phase difference of the fields at the center and edge of the aperture, especially for the uniform field magnitude distribution.

Engineering rainbow trapping and releasing in ultrathin THz plasmonic graded metallic grating strip with thermo-optic material.

In this paper, we propose an ultrathin THz plasmonic metallic strip based on graded grating structure with thermo-optic material, which exhibits a strong engineering of trapping and releasing electromagnetic waves in terahertz regimes. The dispersion properties of the ultrathin spoof slow-wave plasmonic graded grating waveguide are characterized using the finite element method, and the propagation characteristics of the grating structures are thoroughly analyzed by the dispersion curves, electric field magnitude distribution, and electric field vertical distribution. The gradient grating waveguide is demonstrated to be an ideal slow-wave system for trapping and releasing surface plasmon polaritons (SPPs) waves through tuning the refractive index of the thermo-optic material. The reflected location for the SPPs waves on the graded corrugated metal strip at 1.1 THz at different temperatures are compared. It is proved that such ultrathin gradient grating waveguide provides an excellent performance for trapping and releasing surface waves at THz, which permits applications for future optical communications.

Synchronization in the random-field Kuramoto model on complex networks.

We study the impact of random pinning fields on the emergence of synchrony in the Kuramoto model on complete graphs and uncorrelated random complex networks. We consider random fields with uniformly distributed directions and homogeneous and heterogeneous (Gaussian) field magnitude distribution. In our analysis, we apply the Ott-Antonsen method and the annealed-network approximation to find the critical behavior of the order parameter. In the case of homogeneous fields, we find a tricritical point above which a second-order phase transition gives place to a first-order phase transition when the network is either fully connected or scale-free with the degree exponent γ>5. Interestingly, for scale-free networks with 2<γ≤5, the phase transition is of second-order at any field magnitude, except for degree distributions with γ=3 when the transition is of infinite order at K_{c}=0 independent of the random fields. Contrary to the Ising model, even strong Gaussian random fields do not suppress the second-order phase transition in both complete graphs and scale-free networks, although the fields increase the critical coupling for γ>3. Our simulations support these analytical results.

The Measured Electric Field Spatial Distribution Within A Metamaterial Subwavelength Cavity Resonator

Through experimental investigation, a thin subwavelength cavity resonator was physically realized using a bilayer structure composed of air and a negative permeability metamaterial structure one unit cell in thickness. We designed and built the metamaterial slab with periodic metallic ring structures and measured the spatial electric field magnitude in a cavity formed from this slab and a region of air, showing that a subwavelength cavity can be realized. The measured electric field magnitude distribution in the cavity matched very well with effective medium theory, showing that even a slab one unit cell in thickness may be effectively equivalent to a thin homogeneous medium as far as the construction of a sub-wavelength cavity is concerned, provided that the unit cell size is significantly smaller than the free space wavelength.

Theoretical analysis of finite-size surface plasmon polariton band-gap structures

Surface plasmon polariton (SPP) band-gap (BG) structures with finite-size gold scatterers arranged periodically on a gold-air interface are analyzed theoretically by making use of the Lippmann-Schwinger integral equation method. Transmission and reflection of SPP waves being incident on 450-nm-period triangular lattice structures are investigated with respect to the size of cylindrical scatterers in the wavelength range 700--900 nm. It is found that 50-nm-high and 125-nm-radius scatterers ensure low transmission and high reflection for both main orientations of the lattice at wavelengths close to 800 nm, indicating that the structure possesses a complete (in-plane) BG for SPP waves. Electric field magnitude distributions calculated above the scattering structure illustrate SPP transmission and reflection for different wavelengths as well as the effect of out-of-plane scattering resulting in non-SPP waves propagating away from the surface. Transmission spectra and field distributions are also presented for wave guides obtained by removing a number of rows of scatterers in the SPPBG structures. The results obtained are discussed and compared with the available experimental and theoretical results. Finally, the possibilities for SPP guiding around sharp bends with relatively low insertion loss are considered.

Electron magnetohydrodynamic turbulence in a high-beta plasma. III. Conditionally averaged multipoint fluctuation measurements

A large discharge plasma is generated whose electron pressure exceeds that of an external magnetic field. A magnetic cavity exists in the plasma interior. The ions are unmagnetized while the electron magnetization varies from complete to none. In the region of pressure and field gradients a strong instability is observed. It is a cross-field instability driven by the electron diamagnetic drift through the unmagnetized ions, creating large density and magnetic field fluctuations near the lower hybrid frequency that propagate at the sound speed in the diamagnetic drift direction. The basic plasma parameters leading to the instability have been presented in Part I of three companion papers. Spectra, correlations, amplitude distributions, and magnetic hodograms derived from single-point fluctuation measurements have been presented in Part II. These led to the discovery of density cavities and current sheet formation by nonlinear wave steepening. The present Part III deals with multipoint fluctuation measurements using on-line conditional averaging, which resolves the structure of typical fluctuations in space and time. Propagation velocity and coherence of the flutelike density perturbations is measured. The topology of the magnetic fluctuations and associated current density is investigated and shown to consist of flux ropes of negative self-helicities. Superposition of the nonuniform mean field and fluctuating fields yields the net field and current density. Instantaneous field lines and magnitude distributions in three-dimensional space are presented for a turbulent high-beta plasma. The results suggest that the demagnetization of electrons in large positive density fluctuations provides a new saturation mechanism for the instability.

Magnetic field strength distribution in interplanetary turbulence

The distribution of magnetic field magnitudes is derived for the special case of a constant mean field and uncorrelated components having Gaussian distributions. Of the three cases considered (isotropic, transverse, and axisymmetric) the latter most closely resembles a lognormal distribution when the parallel variance is less than the perpendicular variance. Thus a normally distributed, nonintermittent vector field can produce a magnitude distribution that closely resembles a functional form often associated with models of intermittency. This result is illustrated by comparison with a magnetic field magnitude distribution computed from the 1 AU Omni dataset. The parameters of the Gaussian component magnitude distribution can be chosen to compare with the data which is also well fit as a lognormal type. We conclude that the magnitude distribution may not be a sensitive indicator of intermittency and that further examination of the sensitivity of such indicators is warranted.

SAR and B1 field distributions in a heterogeneous human head model within a birdcage coil. Specific energy absorption rate.

Calculations of radiofrequency magnetic (B1) field and specific energy absorption rate (SAR) distributions in a sphere of tissue and a multi-tissue human head model in a 12-element birdcage coil are presented. The coil model is driven in linear and quadrature modes at 63, 175, 200, and 300 MHz. Plots of B1 field magnitude and SAR distributions, average SAR, maximum local SAR, and measures of B1 field homogeneity and signal-to-noise ratio are given. SAR levels for arbitrary pulse sequences can be estimated from the calculated data. Maximum local SAR levels are lower at lower frequencies, in quadrature rather than in linear coils, and in linear fields oriented posterior-to-anterior rather than left-to-right in the head. It should be possible to perform many experiments in the head at frequencies up to 300 MHz without exceeding standard limits for local or average SAR levels.

General expressions for dielectrophoretic force and electrorotational torque derived using the Maxwell stress tensor method

We explore the application of the Maxwell stress tensor (MST) method to dielectrophoresis (DEP) and electrorotation (ROT) studies. By integrating the Maxwell stress tensor over the surface of a dielectric particle, we derive the general expressions for DEP force and ROT torque generated by electrical fields of arbitrary configuration. This is the first time that such complete expressions are derived from first principles using the MST formalism. The results are compared and shown to be in agreement with those obtained from the effective moment approach. The origin of DEP forces in a harmonic field is discussed in terms of field magnitude and phase distributions.