Electromagnetic Lens Research Articles

Reflection modulation generated by scale-free network resonator periodic structure

The pattern of resonator in a periodical array is decisive for its response under impinging electromagnetic wave. A scale-free network resonator is proposed by connecting sub-units in the form of scale free network. Scale-free network resonator array’s reflectivity near resonant frequency could be modulated at arbitrary value between zero and unity, which is different from known resonator array or frequency selective surface. Reflection amplitude modulation could generate rich behaviors, as effective medium property in wide band could be maintained near zero constant, which means zero phase shift and is favorable in radar radome structure. S-parameter analysis indicates amplitude modulation is owing to polarization conversion generated by network links. Scale-free network resonator array has application potentials in future radar radomes, electromagnetic wave lens and microwave antenna panels.

Electromagnetic lensing using the Aharonov–Bohm effect

We demonstrate theoretically and experimentally an electromagnetic lensing concept using the magnetic vector potential—in a region free of classical electromagnetic fields—via the Aharonov–Bohm (AB) effect. This toroid-shaped lens with poloidal current flow allows for electromagnetic lensing which can be tuned to be convex or concave with a spherical aberration coefficient of opposite polarity to its focal length. This field-free lens combines the advantages of traditional electromagnetic and electrostatic field-based lenses and opens up additional possibilities for the optical design of charged-particle systems. More generally, these results demonstrate that the AB effect can shape charged particle wavefronts beyond simple step shifts if topologies beyond simple flux lines are considered and further supports the physical significance of the magnetic vector potential.

Multi-beam high gain steerable transmitarray lens for satellite communication and 5G mm-Wave systems

This paper presents the design of a high gain multi-beam transmitarray antenna. Designed antenna is capable of independently steering multiple beams in the azimuth and elevation plane by the two dimensional displacement of feed radiators placed in front of the passive meta-surface. The meta-surface acts as an electromagnetic lens. Unit cell of the meta-surface consists of three layers of Rogers 5880 substrate and four layers of etched copper. Unit cell is designed such that the phase of unit cell transmission coefficient is varied from 0° to 360° by changing length of the etched copper pattern. As a proof of concept, meta-surface is designed by using uni-focal phase distribution. Multi-beam steering of 0° to 360° in azimuth plane and 0° to 40° in elevation plane has been achieved. Measured antenna peak gain is 34.2 dBi at 30 GHz. Later on, scan loss was optimized by synthesizing a meta-surface with bi-focal phase distribution. This is a mission enabling technology as the antenna supports seamless hand-off between satellites by forming multiple high gain independently steerable beams. Comparable antennas to the date are low gain, bulky, support limited number of beams, and have limited field of view. To the best of the author’s knowledge, it is first time that high gain multi-beam antenna has been demonstrated by using a passive bi-focal meta-surface for continuous beam steering. Due to absence of active components the designed antenna is low cost and robust. Moreover, the substrate is selected such that the antenna can withstand harsh deep space environment and it can be folded for easy deployment. Due to potentially low fabrication cost and ability to support multiple beams, the proposed antenna is a good candidate for next generation satellite communication and mm-Wave 5G systems.

Focusing and Linear-to-Circular Polarization Conversion of a Hemispherical Metasurface

With the aim of enhancing the radiation of the antenna system conventionally containing a protective dome, a transmission-type linear-to-circular polarization conversion electromagnetic metasurface lens which approximates a hemispherical shell profile is presented in this study. The presented design bearing structural compatibility with the existing dome geometry can facilitate the link enhancement of compact system through its potential for a circularly-polarized high gain antenna. To fulfill both the focusing and polarization conversion requirements, transmission phase distribution on the hemispherical surface is analyzed first. Then, polarization-dependent unit cell geometry is designed to achieve the objective transmission phase distribution. The hemispherical metasurface is thus obtained through building all unit cells with determined dimensions and orientations onto the corresponding hemispherical surface positions. Finally, using an aperture-coupled linearly-polarized patch antenna as the primary radiating source of the metasurface, enhanced main lobe gain and circularly-polarized secondary radiation is observed within a wide band. The agreement between simulation and measurement validates the design.

Transformation design of in-plane elastic cylindrical cloaks, concentrators and lenses

We analyse the elastic properties of a class of cylindrical cloaks deduced from linear geometric transforms x→x′ in the framework of the Milton–Briane–Willis cloaking theory [New Journal of Physics 8, 248, 2006]. More precisely, we assume that the mapping between displacement fields u(x)→u′(x′) is such that u′(x′)=A−tu(x), where A is either the transformation gradient Fij=∂xi′/∂xj or the second order identity tensor I. The nature of the cloaks under review can be three-fold: some of them are neutral for a source located a couple of wavelengths away; others lead to either a mirage effect or a field confinement when the source is located inside the concealment region or within their coated region (some act as elastic concentrators squeezing the wavelength of a pressure or shear polarized incident plane wave in their core); the last category of cloaks is classified as an elastic counterpart of electromagnetic perfect cylindrical lenses. The former two categories require either rank-4 elastic tensor and rank-2 density tensor and additional rank-3 and 2 positive definite tensors (A=F) or a rank-4 elasticity tensor and a scalar density (A=I) with spatially varying positive values. However, the latter example further requires that all rank-4, 3 and 2 tensors be negative definite (A=F) or that the elasticity tensor be negative definite (and non fully symmetric) as well as a negative scalar density (A=I). We provide some illustrative numerical examples with the Finite Element package Comsol Multiphysics when A is the identity.

Near-real-time diagnosis of electron optical phase aberrations in scanning transmission electron microscopy using an artificial neural network

The key to optimizing spatial resolution in a state-of-the-art scanning transmission electron microscope is the ability to measure and correct for electron optical aberrations of the probe-forming lenses precisely. Several diagnostic methods for aberration measurement and correction have been proposed, albeit often at the cost of relatively long acquisition times. Here, we illustrate how artificial intelligence can be used to provide near-real-time diagnosis of aberrations from individual Ronchigrams. The demonstrated speed of aberration measurement is important because microscope conditions can change rapidly. It is also important for the operation of MEMS-based hardware correction elements, which have less intrinsic stability than conventional electromagnetic lenses.

Towards a new level of quantitative treatment of 3D electron diffraction data - in-pattern optical distortions.

Electron diffraction patterns unavoidably contain in-plane distortions introduced by electromagnetic lens systems. Geometric correction of different distortion types allows the accuracy of lattice parameter determination to be improved in 3D electron diffraction data.

Evolution of an accelerated charged vortex particle in an inhomogeneous magnetic lens

We present a detailed analysis of the capture and acceleration of a nonrelativistic charged vortex particle (electron, positron, proton, etc.) with an orbital angular momentum in the field of an axisymmetric electromagnetic lens, typical for a linear accelerator. We account for the acceleration and the inhomogeneity of both electric and magnetic fields that may arise from real-life imperfections. We establish the conditions for this wave packet to be captured and successfully transported through the lens. We describe the transition process and explain how a free Laguerre-Gaussian packet can be captured into the Landau state of the lens and how its structure is preserved for all moments in time. We illustrate the developed formalism with several representative examples.

Compact electromagnetic lens antennas using cascaded metasurfaces for gain enhancement and beam steering applications

Compact electromagnetic lens antennas using cascaded metasurfaces for gain enhancement and beam steering applications

Deep Learning-Aided Signal Enumeration for Lens Antenna Array

This work investigates a data-driven approach to detect the number of incoming signals for a lens antenna array (LAA). First, the energy-focusing property of an electromagnetic (EM) lens is utilized to generate an input spectrum, which can be used to enumerate both the multipath and independent signals. Next, we present the deep learning (DL)-assisted sharp peak recognition method referred to as the power spectrum-based convolutional neural network (PSCNet). Unlike classical techniques, such as constant false alarm rate (CFAR) detection, this data-driven detector can count received signals adaptively based on the LAA power spectrum without requiring any initial configurations. In addition, the PSCNet outperforms other state-of-the-art subspace-based detectors, even under challenging conditions, such as a low signal-to-noise ratio (SNR), a small observation size, and angular ambiguity. For the training phase, we propose a pretrained-model reusing strategy and an input pre-processing approach referred to as the power spectrum shortening (PSS) to alleviate the training burden and achieve lower complexity compared to fully retraining all isolated networks. The simulation results demonstrate that our proposed sharp peak-recognition algorithm not only accomplishes the improved signal enumeration performance but also requires lower computational resources than other subspace-based approaches.

IMPROVEMENT OF HELIUM IONS BEAM FORMATION AND TRANSPORT SYSTEM

Works on improvement of a beam formation and transport system from an accelerating section output to the target complex on NSC KIPT helium ions linear accelerator with output energy of 4 MeV, used for carrying out of radiating researches are continued. Results of researches spent with electromagnetic quadrupole lenses, forming a triplet are presented. Experiments with injected (120 keV) and accelerated (4 MeV) helium ions beams by means of advanced beam formation and transport system to a target are continued. The proposal on decrease in thermal loading of a triplet is formulated.

Limits for scattering resonances in azimuthally inhomogeneous nanotubes

Resonant electromagnetic scattering has been optimized for angularly inhomogeneous nanotubes characterized by different surface admittances along the two complementary arcs. The optimal designs are substantially more efficient compared to their best homogeneous counterparts and the spatial distribution of the scattering power reveals the nature of the sustained resonances. In this sense, the reported scattering scores constitute limits for the response of that simple class of structures and can be employed as optimized components in a wide spectrum of photonic devices from wave transformers and field sensors to electromagnetic filters and optical lenses.

ENGINEERING OF THE LOW-ENERGY BEAM TRANSPORT LINE IN THE Не⁺ IONS LINAC

The design of a low-energy beam transport line in the helium ions linear accelerator is proposed. For experiments with the low-energy helium ions the vacuum chamber in a transport line is in addition included for an irradiation of investigated materials. The mathematical modeling method investigates coordination variants of an injector beam output emittance with an accelerating structure acceptance with use of electromagnetic quadrupole lenses, electrostatic lenses and the focusing solenoid. It is shown that the optimal variant, ad hoc, is the focusing solenoid application. The calculated value of a current of the helium accelerated ions makes 4.5 mА.

Computer-aided design of free rotation and distortion doublet electromagnetic lenses

In this research, a free rotation and distortion projector doublet electromagnetic lens was designed by computer-aided using electron optical design (EOD) program. This lens consists of two identical lenses. This lens's focal and projector characteristics were calculated in the two max magnification regions by changing the axial magnetic flux density in one of the two single lenses by changing its axial bore diameter. The results showed the possibility of obtaining a free rotation and distortion projector doublet electromagnetic lens in the first max magnification regions, and it has the min magnitude for the projector focal length.

A novel method to realize a non-uniform heat flux distribution through the variable-speed scanning of an electron beam

Quartz lamp heaters and hypersonic wind tunnel are currently applied in thermal assessment of heat resistant materials and surface of aircraft. However, it is difficult to achieve precise heat flux distribution by quartz lamp heaters, while enormous energy is required by a large scale hypersonic wind tunnel. Electron beam can be focused into a beam spot of millimeter scale by an electromagnetic lens and electron-magnetically deflected to achieve a rapid scanning over a workpiece. Moreover, it is of high energy utilization efficiency when applying an electron beam to heat a metal workpiece. Therefore, we propose to apply an electron beam with a variable speed to establish a novel method to realize various non-uniform heat flux boundary conditions. Besides, an electron beam thermal assessment equipment is devised. To analyze the feasibility of this method, an approach to calculate the heat flux distribution formed by an electron beam with variable-speed scanning is constructed with beam power, diameter of the beam spot and dwell duration of the electron beam at various locations as the key parameters. To realize a desired non-uniform heat flux distribution of the maximum gradient of 1.1 MW/m3, a variable-speed scanning strategy is constructed on basis of the conservation of energy. Compared with the desired heat flux, the maximum deviation of the scanned heat flux is 4.5% and the deviation in the main thermal assessment area is less than 3%. To verify the method, taking the time-average scanned heat flux as the boundary condition, a heat transfer model is constructed and temperature results are calculated. The experiment of variable-speed scanning of an electron beam according to the scanning strategy has been carried out. The measured temperatures are in good agreement with the predicted results at various locations. Temperature fluctuation during the scanning process is analyzed, and it is found to be proportional to the scanned heat flux divided by volumetric heat capacity, which is applicable for different materials up to 3.35 MW/m2. This study provides a novel and effective method for precise realization of various non-uniform heat flux boundary conditions.

Magnetically tuning microwave propagation parameters in ferrofluids.

The paper reports on the frequency (f) and static magnetic field (H) dependencies of the microwave propagation parameters, in the ranges 0.1-6 GHz and 0-90.7 kA/m, of a kerosene-based ferrofluid with magnetite particles, filtered in magnetic field gradient. In the investigated range, the sample exhibits ferromagnetic resonance phenomenon and Maxwell-Wagner dielectric relaxation. Unlike the usual way of studying the propagation of microwaves through different media, in this paper we have defined an overall reflection coefficient, Rw(f, H), of a material with thickness, w, deposited on a total reflective support, which takes into account both the attenuation of wave within the material and the reflection at the air-material interface. Based on the measured relative magnetic permeability, [Formula: see text], and relative dielectric permittivity, [Formula: see text], a comprehensive and meaningful set of microwave propagation parameters are determined. Apart from Rw(f, H), this set of parameters of ferrofluid includes the attenuation constant of the electromagnetic wave, [Formula: see text](f, H), the phase constant [Formula: see text](f, H), the real, n'(f, H), and imaginary, n"(f, H), components of the refractive index, the reflection coefficient at the interface air-material, R(f, H), and the quarter wavelength in material, [Formula: see text](f, H). Based on the theoretical considerations and characteristics of ferrofluid, simplified and practical formulas of the propagation parameters are given and also possible applications of the results are suggested (such as electromagnetic absorber, phase shifter, microwave lenses and vibration sensor). This connection between theory and experimental results offers an example for the preliminary design of microwave applications of ferrofluids and, by extension, for any material consisting of magnetic nanoparticles dispersed in a dielectric matrix.

Theoretical Analysis of Plasma Parameters on Film Deposition in planer and Cylindrical Magnetron Sputtering

Thin film deposition using plasma sputter is done by experimental methods, though Numerical simulation and theory are capable of generating realistic and useful results. In present exploration a theoretical model for sputtering with consequence of different plasma parameters with the help of electromagnetic lenses for planar ( T p ) and cylindrical ( T c ) magnetron sputteringhas been conversed. The plasma of helium gas on nickel metal objectwhich contains the velocity shear instability is considered, and T p , T c , under the influence of shear scale length(A i ), homogeneous DC electric field(E 0 ), magnetic field (B 0 ), density gradient ( e n r i ) have been evaluated. T p , and T c are found to be maximum in the range of 0.815–0.91, and 0.57–0.90, respectively. Also growth rate showed direct relation to E 0 and A i but inversely varies with B 0 and e n r i .

Metasurface-Based Cylindrical Lenses and Their Antenna Gain Enhancement

Electromagnetic metasurface lenses with the characteristic of being conformal to a cylindrical geometry are presented in this study. Based on the formulated principle of the cylindrical metasurface lens operating with transmission or reflection mode, the transmission or reflection phase gradient varying along the circumferential direction of a cylinder is implemented. A focused beam is observed at the objective focal point for each lens illuminated by a plane electromagnetic wave with transverse magnetic or transverse electric polarization. A coaxial-fed microstrip patch antenna element is used as a feeding of cylindrical metasurface lenses and positioned at their focal points, so as to evaluate their application in the enhancement of antenna gain along the boresight direction. By virtue of the focusing ability of presented lenses, effectively enhanced boresight gain from the cylindrical metasurface lens antennas are obtained, in comparison with the freestanding feeding antenna. The agreement between simulation and measurement validates the designs. Conformal integration or embedment of the electromagnetic lens into a certain platform skin with cylindrical characteristics is therefore potentially demonstrated, which implies an enhancement of boresight gain without obviously disturbing the local shape of the skin by apparent weight or drag.

Fabrication of Single Crystals through a µ-Helix Grain Selection Process during Electron Beam Metal Additive Manufacturing

Selective Electron Beam Melting (SEBM) is a powder bed-based additive manufacturing process for metals. As the electron beam can be moved inertia-free by electromagnetic lenses, the solidification conditions can be deliberately adjusted within the process. This enables control over the local solidification conditions. SEBM typically leads to columnar grain structures. Based on numerical simulation, we demonstrated how technical single crystals develop in IN718 by forcing the temperature gradient along a µ-Helix. The slope of the µ-Helix, i.e., the deviation of the thermal gradient from the build direction, determined the effectiveness of grain selection right up to single crystals.

Gain enhancement of microstrip antenna with a novel DNG material

AbstractIn this study, a novel double‐negative compact metamaterial (MM) that can operate in Ku‐band (12 GHz) is designed and fabricated. It is shown that the proposed structure can be used as a MM for a wide bandwidth of 6 GHz. A double electromagnetic lens layer is then formed using this MM unit cell in an array. Afterwards, obtained lens layers are used together with a conventional microstrip patch antenna (CMPA) operating at 12 GHz. The effect of the MM on the antenna gain and directivity is examined. The CMPA and MMs are fabricated, and measurements are performed in Akdeniz University Microwave Laboratory and simulated with Microwave Studio by Computer Simulation Technology. 71% and 50% improvement in antenna gain and directivity are obtained by using it as a double MM lens layer.