Array Of Metallic Strips Research Articles

Bidirectional Gain Enhancement of Folded Dipole Antenna Using Midstrips Array

A novel low-profile method to improve the bidirectional gain of a dual-element folded dipole antenna (DFDA) is presented. The proposed technique employs surface current distribution conditioning using integrated parasitic elements while preserving the radiators. We introduce a middle layer consisting of a 1-D array of metal strips embedded between the upper and lower surfaces of the dipole, called midstrips. The midstrips are designed as parallel resonators and play the key role of current polarizing of the dipole currents. At the presence of the midstrips, the cross currents on the dipole surface are polarized out of phase and cancel each other, improving radiation-polarization purity consequently. The co- components are changed from a distributed form to a triple current form, which leads to the excitation of a new resonance. The geometric-progression-based array factor is extracted to model the gain enhancement mathematically. Two DFDA prototypes with and without midstrips are fabricated with identical thickness ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.014\lambda _{0}$ </tex-math></inline-formula> at 2.7 GHz) and 10 dB-S11 bandwidth of over 18.5%, which shows a bidirectional-gain enhancement of more than 2.9 dB and an efficiency of over 84% at the presence of the midstrips.

Ultra-Wideband Planar End-Fire Antenna Based on High-Order Modes of Spoof Surface Plasmon Polaritons

In this article, an ultrawideband planar end-fire antenna based on high-order modes of spoof surface plasmon polaritons (SSPPs) is proposed. First, a quad-band end-fire antenna is designed by using the first four high-order SSPP modes. An SSPP transmission line with gradually decreasing groove depth is used to radiate the high-order modes. Moreover, to improve the gain and sidelobe level at high frequencies, the SSPP units in the quad-band antenna are tilted. Then, an SSPP structure consisting of a periodic array of metal strips is proposed. By adding two arrays of tilted I-shaped strip resonators to the quad-band antenna, the first two bandgaps are eliminated. The proposed antenna achieves a fractional bandwidth of 140.8% from 6.9 to 39.7 GHz. Minimum and maximum measured gains of 6.4 and 15.2 dBi are achieved at 6.9 and 38 GHz, respectively. The proposed antenna has a great potential for applications in imaging and wireless communication.

Eigenmode analysis of the waveguide-plasmon structure based on a-Si1-xCx:H layer with 1D gold grating

Resonant structure consisting of waveguide layer with metallic strips array is a promising design for various optical effects control and enhancement at the nanoscale due to its strong resonant properties and light localization phenomena. However, different applications require understanding the nature of eigenmodes of the structure, that possess peculiar properties. In this research, the optical properties of the planar waveguide with one-dimensional periodic gold grating on it was examined. Emitting layer of a-Si1-xCx:H was deposited by plasma chemical vapour deposition technique and the gold array was created by the e-beam lithography. Angle-resolved reflection and photoluminescence spectra in s- and p-polarizations were measured by the Fourier-imaging spectroscopy method. The theoretical analysis was performed to reveal the physical nature of the observed spectral features and their effect on the waveguide layer emitting properties was studied.

Energy properties and spatial plume profile of ionic liquid ion sources based on an array of porous metal strips

An ionic liquid ion source (ILIS) is a kind of high brightness ion source capable of providing high-speed positive or negative ion beams. This paper presents a miniaturized ILIS based on an array of porous metal strips. The porous emitter array, integrated with seven 10 mm long strips, is fabricated using wire electrical discharge machining (WEDM) combined with electrochemical etching. The assembled ILIS is 30 mm × 30 mm × 17.5 mm in size and weighs less than 25 g. A series of experiments, including an I–V characteristic test, a retarding potential analyzer (RPA) test, and a spatial plume distribution test, have been conducted in vacuo to characterize the performance of the ILIS. Results show that the emitted current is up to about 800 μA and ion transparency is as high as 94%. Besides, RPA curves reveal that the total fragmentation rate of the emitted particles accounts for 48.8% in positive mode and 59.8% in negative mode. Further, with the increase in applied acceleration voltage, the voltage loss rises while the energy efficiency decreases. It is also found that the plume perpendicular to the strips has a higher divergence than the one parallel to the strips. A numerical simulation by COMSOL reveals that the electric field distribution between the two electrodes results in such a spatial plume profile.

Wideband RCS reduction of thin metallic edges mediated by spoof surface plasmon polaritons

The back-scattering from front edge diffraction contributes significantly to mono-static radar cross section under TE-polarization when the specular reflection of an object is eliminated by elaborate shaping. With the aim to suppress the back-scattering of thin metallic edge, we propose to achieve wideband radar cross section (RCS) reduction by integrating an absorbing structure (AS) in front of the edge. The unit cell of AS is composed of a longitudinal array of metallic strips with linearly decreasing lengths. Under TE-polarized illumination, spoof surface plasmon polariton (SSPP) can be excited with high efficiency. Due to the deep-subwavelength property of SSPP, electromagnetic waves are highly confined around the AS, leading to strong local field enhancement and hence to wideband absorption. In this way, back-scattering of the edge is suppressed and the mono-static RCS can be reduced significantly over wide band. To verify this method, we designed, fabricated and measured a prototype. The results of both simulation and measurement indicate that our proposal can significantly suppress edge scattering, whose RCS reduction more than 10 dB achieves at range of 8.8–17.8 GHz under TE polarization. This work provides a new alternative of suppressing edge diffraction and may find applications in electromagnetic compatibility, radar stealth, etc.

3D micro/nanoshaping of metal strip arrays by direct imprinting for chiral metasurfaces

An original hybrid method for three-dimensional (3D) shaping of micro- and nanostructures by direct imprinting of lithographically patterned metal 2D-elements on a polymer substrate is proposed. The technological features of the method are demonstrated by transforming Au micro/nanostrip arrays into 3D half-turn helices. The metasurface formed by an array of 3D half-turn Au microhelices in the surface layer of a polymer substrate rotates the polarization plane of transmitted 3 THz radiation through an angle in excess of 50°. Both experimentally and numerically, it is established that the metasurface permits to control the state of polarization and the intensity of transmitted linearly polarized THz radiation using half-wavelength and guided-mode resonances as well as diffraction effects. The proposed approach enables the fabrication of double-layer arrays of half-helices, designed for infrared metasurfaces, from 80 nm wide Au nanostrips. These studies not only pave the way towards the fabrication of large-area chiral metamaterials but, also, open a new avenue in the development of 3D micro/nanostructures for other applications.

Wideband Absorbing Plasmonic Structures via Profile Optimization Based on Genetic Algorithm

Plasmonic structures that support the spoof surface plasmon polariton (SSPP) mode can be tailored to achieve strong absorption of electromagnetic (EM) waves. In particular, the profile of an absorbing plasmonic structure (APS) plays an important role in realizing its wideband absorption performance. In this paper, we propose a method of optimizing the longitudinal profile of APS based on Genetic Algorithm (GA), with the aim of obtaining high-efficiency wideband absorption of EM waves. The APS unit cell is composed of a longitudinal array of metallic strips, the length profile of which can be optimized to improve k-matching between free-space waves and SSPPs and meanwhile to customize absorption at each frequency within a wide band. Our investigation shows that nonlinear variation of the strip lengths will make better k-matching and wideband absorption. As an example, a wideband APS is demonstrated using this method. The simulated and measured results show that the absorbance is higher than 90% in 10-30GHz, which convincingly verifies the effectiveness of this method. This method provides an efficient approach to the design of radar absorbing structures and can also be extended to optimized design of other metamaterials.

Electrical tree reconstruction method for oil-impregnated pressboards based on the inverse problem for the electrostatic field

There is still a lack of effective means of observation for electrical trees in opaque materials, which hampers experimental and theoretical research on the growth of such trees in the oil-impregnated pressboards of power transformers. This presents a great obstacle to the accurate diagnosis and prediction of partial discharge (PD) defects. This paper describes a method to monitor the growth process of electrical trees in pressboards based on solution of the inverse problem for the electrostatic field. The three-dimensional structure of the carbonized branches is reconstructed from the positions of PDs. Each PD is located by the charge remaining in the material. This charge is calculated from the electric field intensity or potential at some points in the field using the mirror image method and solution of the inverse problem for the electrostatic field. The electric field intensity is measured using an array of metal strips near the zero-potential border while PDs are occurring. High-voltage PD experiments are performed on oil-impregnated pressboard strips to verify the feasibility of the method. From the results of these experiments, the accuracy of PD site location is found to be as good as 0.35 mm in the χ direction (the horizontal coordinate), which is sufficient to describe the general structure of electrical trees in oil-impregnated pressboard. The movement of the PD positions indicates the growth process of tree branches. The calculated positions and lengths of the branches are consistent with observations of carbonized tracks after the pressboard has been torn open. The results obtained here will be of benefit to establishing a real-time monitoring method for three-dimensional reconstruction of electrical trees to reveal their internal growth mechanism in opaque materials such as oil-impregnated pressboards.

On ion transport regulation with field‐effect nonlinear electroosmosis control in microfluidics embedding an ion‐selective medium

We study herein numerically the use of induced-charge electrokinetic phenomena to enable a flexible control of ion transport of dilute electrolyte in a straight ion concentration polarization system. The effect of three convection modes of induced-charge electrokinetic phenomena, including induced-charge electroosmosis, flow-field effect transistor, and alternating-current electroosmosis (ACEO), on convective arrestment of diffusive wave-front propagation is investigated by developing a cross-scale and fully coupled transient numerical simulation model, wherein multiple frequency electrochemical polarization and nonlinear diffuse charge dynamics in spatiotemporally varying solution conductivity are taken into account. We demonstrate by detailed comparative simulation studies that ACEO vortex flow field above a metal strip array arranged along the anodic chamber's bottom surface serves as the most efficient way for adjusting the salt density distribution at micrometer and even millimeter dimension, due to its high flexibility in controlling the stirring flow state with the introduction of two extra electrical parameters. The specific operating status is determined by whether the electrode array is floating in potential (induced-charge electroosmosis) or biased to ground (flow-field effect transistor) or forced to oscillate at another Fourier mode (ACEO). These results prove useful for on-chip electric current control with electroconvective stirring.

Metasurface bilayer for slow microwave surface waves

We present a simple two-layer discontinuous crossed metal-strip array that guides microwaves having very high phase and group indices. The strips are arranged on a square lattice with a two-layer unit cell. The difference in this structure resides in the length of the metal strips, which extend to several unit cells. This work focuses on the isotropic wave dispersion at the lower frequencies. In addition, two of the higher-frequency bands give rise to a very strong negative dispersion, and strong beaming occurs, which can be tailored easily by modifying the relative orientation of the layers.

High gain millimeter wave leaky wave antennas with low side lobe level of the radiation pattern

Two linearly polarized millimeter wave planar leaky wave antennas designed for broadside radiation at 61 GHz with high gain and low sidelobes of radiation patterns are presented. Both antennas have a center-fed single-layer structure composed of two one-dimensional periodic symmetric arrays of metal strips of variable width on a grounded dielectric waveguide, but with different excitation devices for the dielectric waveguide, represented by a microstrip combline and a waveguide-fed linear substrate integrated slotted waveguide array. The antennas exhibit low return loss, antenna gain 26-27 dBi and radiation pattern sidelobe level in both E- and H-planes, not exceeding −20 dB. The antennas may be used, for example, in security sensors.

Quantum Regime of a Two-Dimensional Phonon Cavity.

We realize the quantum regime of a surface acoustic wave (SAW) resonator by demonstrating vacuum Rabi mode splitting due to interaction with a superconducting artificial atom. Reaching the quantum regime is physically difficult and technologically challenging since SAW devices consist of large arrays of narrow metal strips. This work paves the way for realizing analogues of quantum optical phenomena with phonons and can be useful in on-chip quantum electronics.

Electrically tunable mid-infrared antennas based on VO2

A large change in optical constants of phase-change vanadium dioxide enables active control over the transmission and reflection properties of structures incorporating VO2. In this paper, we demonstrate electrically tunable mid-infrared strip array antennas based on metal–insulator transition of vanadium dioxide. The antennas consist of an interdigitated metal strip array separated from a metallic ground plane by a film of vanadium dioxide. The interdigitated metal strips serve as both antennas and electrodes. As the insulator-to-metal phase transition of vanadium dioxide is induced with applied voltages, resonance of the strip antenna array redshifts with reduced absorbance before it is eventually switched off. A tuning magnitude of 30% in reflectivity is measured at 25.5 THz. Our measurements of sample temperature reveal that tuning mechanism of the antennas is primarily thermal in nature. The demonstrated electrical tuning of mid-infrared antennas could be used for reconfigurable bolometric sensing, camouflaging and modulation of infrared radiations.

Ku-Band Low-Profile Asymmetric Bull's-Eye Antenna With Reduced Sidelobes and Monopole Feeding

In this letter, a linearly polarized low-profile and asymmetric bull's-eye leaky-wave antenna fed by a monopole operating at 13 GHz is presented. Broadside radiation from the monopole is achieved by surrounding it with an asymmetric array of semicircular metallic strips on a grounded dielectric slab. With this implementation, we demonstrate high gain with a weight of less than 80 g and lower sidelobe levels compared to previous designs fed by a resonant slot. The measured antenna shows an experimental gain of 19.4 dBi with only 5 periods and a sidelobe level of −16 dB (−20.3 dB for the numerical ideal case at f = 12.6 GHz), along with a narrow 6° beamwidth.

Development of a Low Radar Cross Section Antenna With Band-Notched Absorber

A low radar cross section (RCS) antenna designed with band-notched absorber is described. First, a dual-polarization absorber with relative bandwidth more than 80% is designed using loaded resistors. Pairs of circular slot resonators and metal strip array resonators are introduced in the absorber to realize a notch band with full reflectance in the vertical polarization, while a wide absorption band in the horizontal polarization is maintained. The proposed band-notched absorber is thus realized. Within the notch band, the absorber can be served as a metal ground for antenna; while a great RCS reduction is obtained out of the notch band and in the horizontal polarization band. Then, a dipole antenna rigorously designed is mounted above the band-notched absorber, whose operating frequency is exactly in accordance with that of the notch band. The proposed low RCS antenna is established based on assembling the dipole antenna and the band-notched absorber together. The measured results demonstrate that the proposed antenna has fairly good radiation patterns. Added to that, more than 10 dB RCS reduction in two polarizations is realized simultaneously compared with that one of a conventional dipole antenna.

Single-layer Linear-to-Circular Polarization Transformer Based on Periodic Strips Array

In this paper, single-layer linear-to-circular polarization transformer is proposed, which is composed of 3×3 metallic strips array. Firstly, the novel approach of “fission transmission of EM waves” based on the sequence of incident and transmission waves product cause additional transmission of orthogonal components. The axial ratio is less than 1.0 dB and accumulative axial ratio bandwidth of 17.05% is achieved at four frequency bands ranging from 12-18GHz for circular polarization. Theoretical analysis and microwave experiments are presented to validate the performance of the structure. While the measured results are in good agreement with simulation.

Voltage-controlled nanoscale reconfigurable magnonic crystal

A nanoscale reconfigurable magnonic crystal is designed using voltage-controlled perpendicular magnetic anisotropy (PMA) in ferromagnetic-dielectric heterostructures. A periodic array of gate metallic strips is placed on top of a MgO/Co structure in order to apply a periodic electric field and to modify the PMA in Co. It is numerically demonstrated that the introduction of PMA, which can be realized experimentally via applying a voltage, modifies the spin-wave propagation and leads to the formation of band gaps in the spin-wave spectrum. The band gaps can be controlled, i.e., it is possible to switch band gaps on and off within a few tens of nanoseconds. The width and the center frequency of the band gaps are defined by the applied voltage. Finally, it is shown that the introduction of PMA to selected, rather than to all gate strips allows for a predefined modification of the band-gap spectra. The proposed voltage-controlled reconfigurable magnonic crystal opens a way to low power consumption magnonic applications.

Multi-band circular polariser based on periodic metallic strip array

The multi-band circular polariser is proposed to convert linear-to-circular polarisation using 3 × 3 metallic strips array. The metallic periodic strips are printed on both sides of the dielectric substrate which enhances the axial ratio bandwidth at resonance frequencies. In this paper, the novel approach of 'fission transmission of electromagnetic waves' is utilised to obtain strong optical activity within the structure. It means that the incident linearly polarised wave is converted into two orthogonal components through the lower printed metallic strips layer of the structure. Similarly, when two transmitted orthogonal components impinge on the upper printed strips, they are converted into four orthogonal vector components at the end of structure. This projection and transmission sequence of incident and transmitted wave sustain the chain transmission of electromagnetic wave and can achieve strong circular dichroism. Moreover, the axial ratio of Txx to Txy is greater than 1 dB and the cumulative multi-band axial ratio bandwidth of 20.47% was obtained at frequency bands for the circular polarisation. This new concept and performance are theoretically investigated and verified by experimental results. Theoretical analysis and microwave experiments are presented to validate the performance of the structure which has successfully proven to operate in tandem.

Resonant response in mechanically tunable metasurface based on crossed metallic gratings with controllable crossing angle

We report on a modern class of mechanically tunable planar metamaterials comprising resonating units formed by crossed metallic strip gratings. We observe a resonant response in transmission spectra of a linearly polarized wave passing through a system of crossed gratings in the microwave regime. Each grating consists of an array of parallel metallic strips located on the top of a dielectric substrate. It is revealed that the resonant position appears to be dependent on the angle of crossed gratings. It is found theoretically and experimentally that the resonant shift on the frequency scale appears as a result of increasing in the length of the resonating portion of the parallelogram periodic cell formed by the crossed metallic strips with decreasing crossing angle. The proposed design can be used in innovative types of planar metamaterials and filters.

A design of ultra-broadband metamaterial absorber

In this paper, an ultra-broadband, wide-angle polarization-insensitive metamaterial absorber is designed at microwave frequencies. The absorber consists of a periodic array of metallic strips with the lumped resistances fabricated on a dielectric substrate with a ground plane. The proposed absorber is single-layered and symmetric, thus leading to very thin and polarization-insensitive characteristics. According to the surface current distributions, the proposed absorber can operate three resonant modes including two dipole resonances and an LC resonance. By adjusting the geometry and lumped resistances of the structure, three resonant modes can be effectively connected together, and thus an ultra-broadband response can be realized. The simulated and experimental results demonstrate that the proposed absorber produces a good absorption above 80% at normal incidence and above 60% at oblique incidence with the incident angle smaller than 45° between 6 and 16.2 GHz.