Circular Reflector Research Articles

Electrically reflectance-tunable circular polarization reflector based on thin polymer-stabilized cholesteric liquid crystals

This paper presents a reflectance-tunable circular polarization reflector that utilizes thin polymer-stabilized cholesteric nematic liquid crystals (PSCLCs) with negative anisotropy. The switching mechanism involves direct-current (DC) field-induced movement in the polymer network, which generates the mechanical force that causes a pitch-gradient helical structure and thus a distorted Bragg reflection. The pitch-gradient helical structure of the 5 μm-thick cells only allows for a limited number of pitch lengths, resulting in a decrease in reflectance at the designed Bragg reflectance and a reflectance tunable range determined by applying DC voltages. The PSCLCs reflecting red, green, and blue colors were measured for their reflectance tuning ability and circular polarization selectivity. A tunable polarization volume grating was fabricated using a PSCLC cell, and the ability of the grating to diffract light intensity was demonstrated.

High Gain Defected Slots 3D Antenna Structure for Millimeter Applications

The antenna is designed as a 3D structure and is made from a conductible cylindrical antenna cone. The cone structure is realized using etching of elliptical slot array on the antenna. We use a conductible circular reflector under the proposed cone and increase the gain of the antenna. The proposed antenna provides effective bandwidth from 1GHz to 30GHz, but the gain of the proposed antenna is varying between 3dBi and 15dBi in the frequency band we are interested in. Geometrical details of the antenna are optimized numerically using parametric study using CST MWS Software Package. Once the optimal design is arrived at, the results are validated with another software package using HFSS Simulation Technology. The obtained results from both software packages agree very well.

ORBITAL ANGULAR MOMENTUM-BASED SLOT ARRAY ANTENNA FOR MODERN APPLICATIONS

Millimeter waves are the most promising waves for different modern wireless communication networks. This is due to their ability to carry big data with enhanced channel capacity. However, mm-waves suffer from low propagation due to the effects of high attenuation factors with high frequencies. Therefore, in this work, a three-dimensional structural antenna design with a slot array is proposed to achieve high gain through a two-port feeding operation for orbital angular momentum applications of modern communication systems. Also, the improved bandwidth of the proposed antenna makes it an excellent candidate for fifth-generation (5G) communications systems. The antenna depends on two concentric structures with conductive circular cross-sectional area. The first structure is shaped as a three-dimensional cone with a cylindrical waveguide. The second structure is shaped as a circular disc with a circular aperture. The two parts of the proposed antenna are concentered to be fed with two discrete ports from the side with a 900phase difference. It is determined that the proposed antenna offers an exceptional gain to vary from 10dBi to 20dBi within the frequency band from 3GHz to 30GHz. It is realized that such enhancement after introducing a conductive circular reflector underneath the conductive cone. The antenna shows a matching impedance below -10dB over the entire frequency band of interest. The antenna radiation proprietors at 25GHz and 26GHz at the E-plane and H-plane are characterized. Finally, the antenna performance is validated using two software packages based on CST studio and HFSS algorithms.

Experience in deploying radar corner reflectors for InSAR monitoring

This work aims to analyze the effectiveness of corner reflectors deployment designed in various for InSAR monitoring by the Sentinel-1 satellite. Method. The accuracy of determining the spatial movements of the surface by the InSAR method in the places where the corner reflectors are deployed depends on their size, as well as the signal-to-clutter ratio on the radar images. Therefore, it is necessary to assess the backscattering intensity on radar images for the selected territory before installing the corner reflector. In places where corner reflectors are to be deployed, an increase in backscatter should be at least 10 dB. The orientation of the corner reflectors was performed based on Sentinel-1 satellite orbit parameters, which were obtained from the Heavens Above web resource. The analysis of the backscatter intensity time series on radar images was carried out using the online platform EO Browser. Results. The effectiveness of deployment and monitoring of trihedral triangular corner reflectors measuring 0.5 m and 1 m was studied. The research results made it possible to generalize the experience of deploying temporary corner reflectors and use them to design reflector structures for permanent monitoring using radar sensing. The maximum autonomy and constant value of the effective scattering area of the triangular corner reflector is ensured thanks to the equipped protective screen that prevents atmospheric precipitation from entering the reflector. Unlike three-sided corner reflectors, which are oriented to the ascending or descending orbit of the satellite, the circular four-sided corner reflector provides an increase in the intensity of backscatter on radar images taken from different orbits and different satellites. The circular quadrilateral reflector, which was deployed for continuous monitoring, is characterized as a universal reflector for all possible sensors that will conduct radar imaging. Scientific novelty and practical significance are in the confirmation of the effectiveness of the use of ground corner reflectors to increase the intensity of backscattering on radar images. Tested and improved designs of reflectors can be used when creating a network for constant monitoring, which will ensure millimeter accuracy in determining the spatial movements of the earth's surface and engineering structures by the InSAR method.

Evaluation test of circular acoustic reflector based on number theory prototyped made utilizing additive manufacturing

As an application of number theory to the field of acoustics, acoustic reflectors with phase diffraction grating based on Galois fields or primitive roots have been studied. These reflectors have a structure with equally spaced depressions of irregular depth that diffuse acoustic wave in various directions. To generate the sequence of irregular numbers needed to determine the depth of the concavity, methods such as using a primitive element of a Galois field the remainder of the power of a primitive root of a prime number have been proposed. In either method, the depth of the depressions is taken from 0 to half of the wavelength of the sound wave to be diffused, and the spacing between the protrusion or depression is designed to be quarter of the wavelength, resulting in a rectangular shaped reflector. The proposed method not only allows the design to change from rectangular to circular, but also makes it possible to construct a structure corresponding to multiple wavelengths on a single reflector. In this report, the effectiveness of the proposed reflector will be demonstrated through a model experiment of a prototyped reflector by using additive manufacturing.

On‐Demand Indistinguishable and Entangled Photons Using Tailored Cavity Designs

AbstractThe biexciton‐exciton emission cascade commonly used in quantum‐dot systems to generate polarization entanglement yields photons with intrinsically limited indistinguishability. In the present work, it focuses on the generation of pairs of photons with high degrees of polarization entanglement and simultaneously high indistinguishability. It achieves this goal by selectively reducing the biexciton lifetime with an optical resonator. It demonstrates that a suitably tailored circular Bragg reflector fulfills the requirements of sufficient selective Purcell enhancement of biexciton emission paired with spectrally broad photon extraction and twofold degenerate optical modes. The in‐depth theoretical study combines (i) the optimization of realistic photonic structures solving Maxwell's equations from which model parameters are extracted as input for (ii) microscopic simulations of quantum‐dot cavity excitation dynamics with full access to photon properties. It reports non‐trivial dependencies on system parameters and use the predictive power of the combined theoretical approach to determine the optimal range of Purcell enhancement that maximizes indistinguishability and entanglement to near unity values, here specifically for the telecom C‐band at 1550 nm.

Low-profile closed cavity backed spiral antennas with circular AMC reflector for V/UHF bands

In this study, two low-profile wideband spiral antennas that are backed by Circular Artificial Magnetic Conductors (C-AMC) are proposed for V/UHF bands. Rather than using a C-AMC design that has single resonance frequency, different C-AMC structures that have different resonance frequencies are used beneath corresponding active regions of spiral antenna, such that frequency independent radiation characteristics are achieved. The C-AMC surface is designed to aim of covering the entire frequency band of antenna so that frequency regions where reflection phase of C-AMC rings are between +90° and −90° will follow each other. It is observed that using frequency-independent C-AMC and a thin absorber between C-AMC and outer region of spiral antenna element provides wideband antenna characteristics and improves axial ratio of antennas. Proposed Antenna 1 in this paper has low-profile (0.47λ0×0.47λ0×0.055λ0) at 300 MHz and high gain at frequencies between 300 MHz and 950 MHz. An absorbing material is used at the inner wall of the closed cavity to improve performance of Proposed Antenna 2 at lower frequencies. In this manner, 0 dBi realized gain transition point is achieved at 235 MHz. Proposed Antenna 2 has also low-profile (0.37λ0×0.37λ0×0.043λ0) at 235 MHz.

Triple-Mode Resonant Backfire Feed Antenna With Nearly Equal E-/H-Plane and Inverse Taper Patterns

A design approach to triple-mode resonant feed antenna is advanced for parabolic reflector antenna system. The antenna is composed of a slit-loaded 1.5-wavelength sectorial dipole, a primary corner reflector, and an auxiliary circular reflector. The corner angle of the primary reflector can be employed to properly narrow down the H-plane half-power beam width (HPBW), while with the E-plane one rarely affected, such that equal E-/H-plane characteristic can be yielded accordingly. Unlike traditional backfire antennas, high-order resonant modes are employed to generate inverse taper radiation pattern at the high frequency band. As is numerically demonstrated and experimentally validated, the corner angle of the primary reflector can be eventually determined as 45∘. The antenna exhibits an impedance bandwidth of up to about 79.7%, and a nearly equal E-/H-plane bandwidth of up to about 29.4%. Average HPBW of about 65∘, gain up to about 8.9 dBi with fluctuation of less than 1 dB can be achieved within the equal E-/H-plane bandwidth. The inverse taper radiation pattern at the high frequency band can provide effective edge illumination and uniform aperture field distribution in parabolic reflector antenna systems.

Single quantum dot selection and tailor-made photonic device integration using nanoscale focus pinspot.

Among the diverse platforms of quantum light sources, epitaxially grown semiconductor quantum dots (QDs) are one of the most attractive workhorses for realizing quantum photonic technologies owing to their outstanding brightness and scalability. However, the spatial and spectral randomness of most QDs severely hinders the construction of large-scale photonic platforms. In this work, we present a methodology to deterministically integrate single QDs with tailor-made photonic structures. We apply a nondestructive luminescence picking method termed as nanoscale focus pinspot (NFP) using helium ion microscopy to reduce the luminous QD density while retaining the surrounding medium. We extract only a single QD emission out of the high-density ensemble QDs. Then the tailor-made photonic structure of a circular Bragg reflectors (CBR) are designed and deterministically integrated with the selected QD. Given that the microscopy can image with nanoscale resolution and apply NFP in situ, photonic devices can be deterministically fabricated on target QDs. The extraction efficiency of the NFP-selected QD emission is improved by 25 times after the CBR integration. Since the NFP method only controls the luminescence without destroying the medium, it is applicable to various photonic structures such as photonic waveguides or photonic crystal cavities regardless of materials. This article is protected by copyright. All rights reserved.

Hemispherical solar distiller with truncated circular cone-shaped reflector mirrors (TCC-RM): optimum inclination of reflector mirrors.

The present study aims to achieve the highest cumulative yield of the hemispherical distillers, by designing and constructing new reflector mirrors, which are truncated circular cone-shaped reflector mirrors (TCC-RM). To obtain the optimum inclination of TCC-RM that achieves the highest hemispherical distiller's performance, eight inclination angles (10°, 15°, 20°, 25°, 30°, 35°, 40°, and 45° with vertical) were experimentally studied. To achieve this, a series of experimental tests were carried out on the three hemispherical solar distillers: the first represents the reference distiller (traditional hemispherical solar distiller (THSD)) and the other two devices are the hemispherical solar distiller with truncated circular cone-shaped reflector mirrors (HSD-TCCRM) with different inclination angles. The experimental results indicate that utilizing TCC-RM with a 25° inclination angle achieves the maximum cumulative yield of 8.35 L/m2 with an improvement of 42.74% compared to THSD. While the utilization of TCC-RM with the inclination angles of 30°, 35°, 20°, 40°, and 15° achieves the cumulative yield of 7.9, 7.3, 7.05, 6.67, and 6.6 L/m2 compared with 5.85 L/m2 for THSD. On the contrary, adjusting the inclination angle of TCC-RM at 10° and 45° affects negatively the cumulative yield of the HSD with TCC-RM in comparison with THSD. Based on the data of cumulative yield, daily efficiency, and the economic analysis it is recommended to utilize TCC-RM with a 25° inclination angle to achieve the highest performance and minimum distillate cost of hemispherical solar distillers.

Performance investigation of active double slope solar stills incorporating internal sidewall reflector, hollow circular fins, and nanoparticle-mixed phase change material

Productivity and efficiency augmentation of solar stills have been receiving significant importance owing to their cost and energy-effectiveness in addition to cleaner operation in producing potable water. The present work aims on improving the performance of active modified double slope solar distiller units by the integrated impact of internal sidewall reflector, hollow circular fins, and nanoparticle-mixed phase change material (nano-PCM). The experimentation includes a total of five individual stills, one conventional, and four others modified with the mentioned attachments. The results indicate the achievement of a maximum productivity output of 1853 mL/day by the solar still modified with reflector, fins, and nano-PCM. The use of paraffin wax-Al2O3 nanoparticle (nano-PCM) mixture in the system is found to be the most effective modification providing almost twice as much accumulated productivity compared to the pure PCM (only paraffin) case. The distillate accumulation is found to surpass the conventional case by 61.36 % and 92 %, respectively in the pure PCM and nano-PCM cases. Moreover, the maximum energy efficiency of 21.56 % is achieved with the combined influence of circular fin, reflector, and nano-PCM. The economic analyses of the solar still cases have estimated the cost of water remaining within the ranges of 0.0199–0.022 $/L. Also, it is found that the projected payback period of 284 days for the conventional case can be reduced to as less as 258 days through the proposed modifications, with the best outcome attained by the nano-PCM case.

Improved generalized moveout approximation with a novel parameterization

Reflection moveout approximations written as explicit functions of offset are convenient tools commonly applied in seismic data modeling, processing, and inversion. The generalized moveout approximation (GMA) has a flexible functional form that accommodates various causes of moveout nonhyperbolicity. We have developed a novel parameterization for the existing six-parameter version of GMA by changing the definition of one of its parameters. Three parameters of the proposed GMA approximation are obtained by fitting the traveltime, the normal moveout velocity, and the fourth-order Taylor series coefficient of traveltime squared at zero offset. The remaining three parameters are obtained by fitting kinematic properties at another two nonzero reference offsets. Through numerical tests on linear sloth models, circular reflector models, and acoustic transversely isotropic media with a vertical symmetry axis (acoustic VTI media), the proposed new GMA method is compared with other published GMA methods in terms of their accuracy. Numerical tests on the three models demonstrate that, when the far reference offset is fixed, the location of the middle reference offset has a considerable impact on the proposed GMA accuracy. We propose a moveout inversion method in a layer-stripping fashion for layered acoustic VTI media based on the proposed and other published GMA methods.

Wideband slot antenna gain enhancement using metasurface reflector

Wideband slot antenna gain enhancement using concentric square and circular loop metasurface reflector (SCLMR) is presented in this paper. In two steps, the design is realized. The analysis design of a FSS-based SCLMR unit cell is included in the first step. The SCLMR structure is made up of resonant metallic square-loop and inner circular loop structures. In terms of bandwidth, the unit cell structure can be considered as a stop-band filter (2.5 GHz-6.5 GHz). The design of a wideband slot antenna (29 mm × 24 mm × 1.57 mm) is included in the second step. EM simulation tool is used to analyze, design, optimize, and validate the proposed unit cell and slot antenna combination. CST microwave studio is utilized to design and analyze a slot antenna and a unit cell in this study. The computed result of an antenna with SCLMR indicates a 101.21 % operational impedance bandwidth (2.76 GHz to 8.41 GHz). With SCLMR, the antenna has a high gain of 8.75 dBi. The designed antenna structure provides a gain enhancement of 5.50 dBi while in comparison to the same antenna without SCLMR.

Sidelobe Modification for Reflector Antennas by Electronically Reconfigurable Rim Scattering

Dynamic modification of the pattern of a reflector antenna system traditionally requires an array of feeds. This paper presents an alternative approach in which the scattering from a fraction of the reflector around the rim is passively modified using, for example, an electronically-reconfigurable reflectarray. This facilitates flexible sidelobe modification, including sidelobe canceling, for systems employing a single feed. Applications for such a system include radio astronomy, where deleterious levels of interference from satellites enter through sidelobes. We show that an efficient reconfigurable surface occupying about 11% of the area of an axisymmetric circular paraboloidal reflector antenna fed from the prime focus is sufficient to null interference arriving from any direction outside the main lobe with little change in the main lobe characteristics. We further show that the required surface area is independent of frequency and that the same performance can be obtained using 1-bit phase control of the constituent unit cells for a reconfigurable surface occupying an additional 6% of the reflector surface.

An open-aperture partially-evacuated receiver for more uniform reflected solar flux in circular-trough reflectors: Comparative performance in air heating applications

Trough reflectors can produce a reflected solar flux density that is highly concentrated in specific regions of the receiver surface causing higher thermal losses as well as increasing the likelihood of mechanical damage to the receiver. Time-dependent three-dimensional computational fluid dynamics models were developed and used to compare optical and thermal performances of unglazed tubular, evacuated tubular, and open-aperture evacuated receivers for air heating applications. An evacuated partial-annulus receiver with a non-evacuated open-aperture in the high-density solar flux area produced a more uniform concentrated solar flux distribution. With an open aperture to high-density solar flux, an open-aperture evacuated receiver (i) avoids a dense distribution of reflected solar flux in a specific area of an absorber surface thereby contributing to realizing long-term mechanical integrity, (ii) gives a greater optical performance in all types of trough reflector than an evacuated tubular receiver, (iii) tolerates optical mispositioning and (iv) is particularly suited for use with circular trough reflectors.

Triple‐resonant wideband 1.5‐wavelength sectorial dipole antenna

A novel wideband, triple-resonant sectorial dipole antenna with simple configuration is advanced. The antenna is evolved from a 1.5-wavelength prototype electric dipole, which is backed by a circular metallic planar reflector. The flared angle of the sectorial radiator and the corresponding usable resonant modes for wideband radiation is determined by mode synthesis chart. As numerically and experimentally validated, the flared angles of the principal dipole should be 300°, with its radius approximately equal to 0.23-wavelength centered at 2.4 GHz. By introducing a pair of tuning stubs and a pair of slits along circumference, three resonant modes simultaneously excited in a single sectorial dipole to generate a wideband, triple-resonant radiation characteristic. Prototype antennas are then fabricated to experimentally validate the design approach. It is shown that the proposed antenna exhibits a unidirectional pattern with its impedance bandwidth over 73.3%. Meanwhile, stable radiation patterns with gain fluctuation less than 2.4 dB, low cross polarization level of −27 dB, and maximum gain of 6.9 dBi are realized within the same frequency range.

High-Gain Conical-Beam Planar Antenna for Millimeter-Wave Drone Applications

In this communication, a high-gain planar antenna with a conical beam (CB) is presented for millimeter-wave drone applications. The proposed antenna comprises a vertical monopole and a circular side reflectors. The high-gain CB is achieved by in-phase reflections from the planar annular-distributed side reflectors which is realized by a series of via walls using the printed-circuit-board (PCB) fabrication. The proposed structure was numerically and experimentally demonstrated. Full-wave analysis shows a 10 dB impedance bandwidth (BW) of 26.50–29.96 GHz, corresponding to 12.26% of the fractional BW, whereas the measured data account for 11.6% in the frequency range of 26.63–29.91 GHz. Meanwhile, a maximum peak gain of 8.51 dBi is observed at a beam-pointing angle of 22°, with a high radiation efficiency of 88.3%. Owing to these valuable features of high gain, good CB radiation performance, and simple planar structure, the proposed antenna is a promising candidate for millimeter-wave drone applications.

Signatures of folded branches in the scanning gate microscopy of ballistic electronic cavities

We demonstrate the emergence of classical features in electronic quantum transport for the scanning gate microscopy response in a cavity defined by a quantum point contact and a micron-sized circular reflector. The branches in electronic flow characteristic of a quantum point contact opening on a two-dimensional electron gas with weak disorder are folded by the reflector, yielding a complex spatial pattern. Considering the deflection of classical trajectories by the scanning gate tip allows to establish simple relationships of the scanning pattern, which are in agreement with recent experimental findings.

A novel ISM band reflector type applicator design for microwave ablation systems

ABSTRACT In this paper, a radiation performance improved novel applicator is proposed which is called as reflector type microwave applicator as a part of microwave ablation (MWA) system operating at 2.45 GHz with experimentally measured bandwidth of 300 MHz in Industrial Scientific Medical (ISM) band for the local extermination of tumor with highly localized microwave power. The design principle of MW applicator is based on the structural formation of coaxial transmission line fed dielectric loaded with the metallic circular reflector for the near field energy concentration inside the tumorous tissue. To generate localized electromagnetic waves, a novel reflector type microwave applicator is designed by placing an aluminum disk near the 10 mm dielectric radiator section. The proposed applicator design has been numerically studied with finite integration technique (FIT) in CST Microwave Studio to develop the near field radiation pattern affecting the ablation level of tumorous tissue. In the light of performed numerical calculations, maximum SAR (Specific Absorption Rate) value on 1.76 g tumorous sample can be achieved to 208 W/kg under 15 W microwave power accepted by proposed probe. The experimental results confirm that proposed applicator can be utilized highly localized MWA applicator for cancer treatment hence the surface temperature of cylindrical shaped tumor sample which has the dimensions of 14.4 mm diameter and 8 mm height reaches from 25 to 68.3°C in 10 min.

Dual-Resonant High-Gain Wideband Yagi-Uda Antenna Using Full-Wavelength Sectorial Dipoles

A novel design approach to high-gain, wideband, dual-resonant, closely-spaced, three-element Yagi-Uda antenna is advanced. The antenna is comprised by a full-wavelength, principal sectorial dipole, a circular metallic flat reflector, and a sectorial director. At first, a multi-source model is developed to predict the initial values of the key antenna parameters, e.g., the flared angle/radius of the director, and the separation between them. Then, as theoretically predicted, numerically simulated and experimentally validated, the flared angles of the principal radiator and the director are eventually determined as 270° and 180°, respectively. They are further tightly coupled at a close separation of 0.024-wavelength to yield relatively compact size and high gain simultaneously. Prototype antenna with a circular metallic reflector successfully exhibits an impedance bandwidth up to about 40%, with in-band maximum gain up to 10.4 dBi and gain fluctuation less than 3 dB. Finally, the antenna is comparatively studied with other Yagi-Uda antennas to highlight its unique wideband and high gain characteristics.