Beams In Different Directions Research Articles

Generating terahertz multiple vortex beams using graphene metasurfaces

This paper investigates the generation of orbital angular momentum vortex beams using a graphene metasurface in the terahertz frequency band. The proposed design consists of 20 × 20 unit-cell elements to operate in 1.2 THz applications. Each element is a graphene ring patch printed on a silicon dioxide substrate backed with a polysilicon ground plane of size 75 × 75 × 25 µm3. The graphene reconfigurable surface conductivity is used to control the beam shape, direction, and directivity radiated from the metasurface, through the application of DC biasing voltages. A parametric study on the effect of graphene chemical potential, relaxation time and temperature on the unit-cell reflection properties is introduced. The reflection magnitude varies from − 2.1 dB to -0.8 dB with a 350-degree phase variation for µc ranging from 0.25 eV to 1.6 eV at \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au$$\\end{document} =5 ps, and T = 300 K. The effect of graphene relaxation time from 0.3 ps to 10 ps on the reflection coefficient at µc = 0.7 eV, and T = 300 K is investigated. The metasurface radiation characteristics are investigated under the illumination of two types of incidence sources, plane-wave, and focused-waves. A depiction of a single vortex beam in various orientations θ = 0, 30o, 50o, and 70o, φ = 90o for l = 1 is presented. The purity of the OAM single beam shows that 94% of the power is concentrated in the designed mode. A graphene metasurface can to convert linearly polarized input into multiple beams exhibiting orthogonal modes. Two/four vortex beams in different directions are demonstrated. The capacity for wireless communication in the terahertz band can be enhanced by utilizing a graphene metasurface.

Beam Steering using Space-Time Modulated Coding Metasurface Based on Reconfigurable Plasma Ionization

This paper explores the use of space-time coding in beam steering, using 1-bit, 2-bit, and 3-bit reconfigurable coded meta-surfaces. By periodically changing the code arrangement in the time domain, a metasurface with code order in space and time is achieved. Selected codes are used to steer the beam in different directions for radar sensing systems applications. The phase of the harmonic signal is changed by controlling the position of different bits in each code sequence. The construction of 8×8 unit-cell elements (120×120×3.2 mm3) involves the use of a grounded dielectric container filled with inert-argon gas. The metasurface logic-state is controlled via the ionization degree of inert-gas with time-switching controlling the harmonic frequencies. Different time-switching sequences are investigated for beam steering. The proposed coding metasurface is analysed using CST Microwave Studio and the results are compared with the analytical solution using MATLAB.

Frequency-multiplexed multifunctional coding metasurface based on transmission and reflection modes

In this work, a frequency-multiplexed multifunctional coding metasurface is proposed, which can realize focusing lens at the lower frequency and multiple scattering beams at the higher frequency. The two functions can be manipulated independently. The proposed metasurface is composed of the top metal patch with a circular ring, two fan rings and two rectangle patches (CFRP), the bottom metal patch with C-shaped and rectangular metal slots (CRS) and a dielectric substrate. By changing the opening direction and size of CRS and the tilt direction and fan ring size of CFRP, the amplitude and phase of transmission and reflection can be modulated, respectively. The transmission mode works at 7 GHz, which can form focal points in different focal planes. The reflection mode works at 17.5 GHz, which can form multiple scattered beams in different directions in the far field. To further verify its practical feasibility, the proposed metasurface is fabricated and measured, the experimental results are in good agreement with the numerical simulation results. The proposed metasurface provides new possibilities to develop multifunctional devices.

Machine learning-based design and optimization of double curved beams for multi-stable honeycomb structures

Curved beams with bistable and negative stiffness properties can be used to design multi-stable metamaterials or honeycomb structures. Consequently, the deformation patterns and mechanical properties of curved beams under load have attracted many attentions. However, due to the nonlinear characteristics of variable thickness double curved beams, it is impossible to exhaust all possible structural forms through experimental and theoretical approaches. This paper presents a machine learning (ML) method for designing and optimizing double curved beam structures. The ML model is used to establish the underlying mapping relationship between thickness parameters and mechanical properties. After optimizing the double curved beam in different directions, the optimal thickness distributions of the backward snapping force and energy absorption are obtained. Double curved beams with optimal thickness distributions are used to construct multi-stable honeycomb structures, demonstrating the optimization process from single cell structure to periodic structure. Under the same mass, compared to the constant thickness honeycomb structure, the optimized variable thickness honeycomb structures exhibit a 140% increase in backward snapping force and a 57% increase in energy absorption. The objective of this study is to utilize machine learning technique to obtain a general approach for optimizing model of ‘multi-parameter input’ to ‘single-parameter output’, which is valuable for guiding the optimization and design of metamaterial structures in the future. This paper is a good case study of the mechanical structure performance optimization, whose implementation path is given detailly in appendix. Other disciplines with similar optimization goals can also use this method to carry out researches.

Circular polarization-agile and beam switching enabled reconfigurable cavity-backed antenna

In this paper, a circular polarization-agile and beam switching enabled reconfigurable cavity-backed antenna having the ability to steer its radiation beam in different directions is presented. The antenna consists of two E-shaped driven patches, a tunable phase shifter integrated with PIN diodes for pattern switching and four switchable feeding probes for implementing polarization agility. The proposed antenna can simultaneously change its polarization and pattern. Beam switching and polarization agility are independently controlled by altering the OFF-ON states of diodes loaded on the feed network and switchable feeding probes. For validity of the proposed concept, the antenna prototype is fabricated and tested. The proposed antenna has measured impedance bandwidth (S11 < -10 dB) and 3 dB axial ratio bandwidths of 23% and 17.4% respectively for all states over the frequency range 4.7–5.6 GHz. The measured and simulation results show that the antenna can scan up to ± 30° with five reconfigurable beams and two polarizations states for each reconfigurable beam.

Actively Controllable Beam Steering Optical Wireless Communication (OWC) Using Integrated Optical Phased Array (OPA)

We put forward and present a demonstration of an actively controlled optical beam steering optical wireless communication (OWC) system based on an integrated actively steerable optical phased array (OPA). We theoretically and experimentally analyze the emitted optical beam full-width-half-maximum (FWHM) divergence angle and field-of-view (FOV) of the proposed integrated actively steerable OPA. Experimental results show that the beam steering can be achieved over a range of 17° with a minimum optical beam FWHM divergence angle of 1.49°. Besides, the integrated OPA chip design, beam forming optimization, packaging, as well as temperature stabilization are also discussed. Genetic Algorithm (GA) is utilized to optimize the applied voltages for the 30 phase shifters to produce low-divergence optical beams in different directions. A proof-of-concept bit-error-rate (BER) measurement using 10 Gbit/s on-off-keying (OOK) signal is also carried out, and the beam steered optical signal satisfying the pre-forward error correction BER limit (pre-FEC BER = 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> ) is achieved.

Design and Fabrication of the Split Ring Resonator Shaped Two-Element MIMO Antenna with Multiple-Band Operation for WiMAX/5G/Zigbee/Wi-Fi Applications.

In this manuscript, we proposed the split ring resonator loaded multiple-input multiple-output (MIMO) antenna design for the frequency range of 1 and 25 GHz. The proposed antenna is numerically investigated and fabricated to analyze the different antenna parameters. We provided statistics on a wide range of antenna parameters for five different designs, including a simple circular patch antenna, a single-split-ring antenna, and a double-split-ring antenna. Reflectance, gain, directivity, efficiency, peak gain, and electric field distribution are all analyzed for all proposed antennas. The maximum achievable bandwidth is 5.28 GHz, and the double-split-ring resonator structure achieves this with a return loss of -20.84 dB. The radiation patterns of all the antenna with different port excitation conditions are presented to identify the behavior of the antenna radiation. We found the effect of the split-ring resonators to form radiation beams in different directions. We found the maximum and minimum half-power beam widths of 75° and 2°, respectively, among the different antenna designs. It was found that the split-ring resonator geometries in patch antenna convert wide-beam antenna radiation patterns to several narrow-beam radiation patterns. We found that each antenna's bandwidth, gain, and return loss performance significantly differs from the others. Overall, the proposed results of the antenna may apply to a wide range of communication applications, including those for Wi-Fi, WiMAX, and 5G.

Generation of multi-OAM beams using a compact dual-mode source and a 3D-printed Luneburg lens.

In this paper, a Luneburg lens-based multi-beam orbital angular momentum (OAM) antenna is proposed to achieve the 2D beam scanning capability of dual-mode OAM beams. The proposed design is composed of nine compact dual-mode antennas as sources, and a 3D-printed Luneburg lens. The sources, i.e., octagonal patch antennas, can radiate both right-handed circularly polarized (RHCP) and left-handed circularly polarized (LHCP) OAM beams with mode number l = ±1 by switching the input ports. Then, the sources are put at multiple focal points of the Luneburg lens to generate the OAM beams in different directions, and the directivities of the OAM beams are also enhanced by the Luneburg lens. The proposed design can realize nine dual-mode OAM beams with ±30° beam scanning range in two orthogonal planes. It should be noted that the proposed design can be expanded to achieve a larger number of beams with a periodic extension of the source antennas, also a wider beam scanning range with a Luneburg lens of a larger radius.

Dual-Polarized Shaped-Beam Transmitarray to Obtain a Multizone Coverage for 5G Indoor Communications

A dual-polarized transmitarray antenna is proposed to generate a multizone coverage at 28 GHz for fifth-generation (5G) indoor communications. The transmitarray radiates a constant power density within its near-field region over a specific area generating different spots in dual polarization. The different spots are produced by feeding the transmitarray with a cluster of horn antennas, which are spatially distributed to obtain beams in different directions. The performance of the coverage is improved with a phase-only synthesis of the transmission coefficients. The transmitarray is designed with dielectric-only elements, which provides a low-cost solution. The prototype is measured in a planar acquisition range, showing a high agreement with simulations. The proposed transmitarray together with the spatial feed distribution provides a potential alternative to generate multizone coverages in millimeter frequencies.

A Scanning Angle Adjustment Method for Array-Fed Lens Antenna Systems

With the ability to increase the gain of the millimeter-wave antenna system effectively, lenses have attracted wide attention. Researchers proposed a large number of lens-based array systems. When each array element works alone, the system can transmit beams in different directions. However, it is difficult to adjust the scanning angle flexibly. In this letter, we propose a method to synthesize the radiation pattern of the lens-array system, which can flexibly adjust the scanning angle by weighted array elements. First, we derive an approximate mathematical model of the lens-array system. Then, the influence of the weighting coefficients on the far-field radiation pattern of the system is analyzed. By setting coefficients as the optimization parameters and combining it with the desired beampattern, we establish an optimization model. Then we optimize the coefficients. Full-wave simulation results performed by CST studio and measured results demonstrate that the proposed method can approach the desired radiation pattern by the optimized coefficients. What's more, measured results show that the proposed method is suitable for wideband signals. Hence, the presented method can flexibly adjust the scanning angle.

Intelligent Autonomous User Discovery and Link Maintenance for mmWave and TeraHertz Devices With Directional Antennas

Use of smart directional antennas in handheld devices to generate a narrow beam in different directions for mmWave/TeraHertz communications present significant challenges. Devices using such antennas may have to scan several different directions in three-dimensional (3D) space to discover another user or an access point, a process that can result in problematic delays. Moreover, small movements of a user/device in the form of rotation and/or displacement may cause the discovered link to be lost. This paper proposes adaptive link discovery algorithms for devices in both infrastructure/ad hoc networks and evaluates their performance in terms of time-to-discovery. We show that one of the two proposed methods provides guaranteed discovery. We use an inertial measurement unit sensor to help intelligently rediscover a lost/degraded link. We propose sensor assisted link prediction methods for low-latency rediscovery in 3D space. We evaluate the effectiveness of our prediction-based rediscovery methods by testing them with real datasets representing various user/device 3D rotation patterns. We show that the smoothing based rediscovery can reach the prediction accuracy to 100% when two antenna sectors are searched, and it reduces the time-to-rediscovery by up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}\text{x}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}$ </tex-math></inline-formula> times) as compared to the time-to-discovery, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}$ </tex-math></inline-formula> is the number of antenna sectors.

Analytical scannable‐shaped beam pattern synthesis via superposition principle

A shaped beam pattern (SBP) synthesis algorithm, which obtains the desired SBP in an analytical way, is proposed. The new algorithm describes the SBP with the weighted superposition of a set of pencil beam patterns (PBPs). First, the array weight of the PBP is obtained via analytical algorithms, such as; Chebychev and Taylor, etc. Then, by computing the weights of the PBPs with the least-square method, the synthesized SBP is expressed explicitly. Different from the state-of-the-art algorithms, the proposed algorithm can obtain the desired SBP analytically, avoiding the time-consuming iteration processes. Moreover, the proposed algorithm enables the array antenna to scan the beam in different directions. Simulations with linear and planar array antennas are provided to assess the superiority and effectiveness of the proposed algorithm.

Design of Dual-Band Beam Switching Array for Adaptive Antenna Applications Using Hybrid Directional Coupler and E-Shape Slot Radiator

The proposed research work presents a design of a dual-band 4-element planar beam-steering antenna array with a feed network. Beam steering array is implemented with two different schemes for S-Band adaptive antenna applications. A design procedure is derived in detail, and a prototype, including the array and a planar feeding network, is built and tested for the first scheme. The array is capable to generate 4 beams in different directions based on the input applied to the port of the Hybrid Directional Coupler. Scanning range covered by this array is, in E-plane from − 45° to + 10° and in H-plane from − 25° to + 25°. Inter-element spacing is optimized with D1 = 86 mm and D2 = 40 mm to achieve maximum directive gain, which is 12.6 dBi at 3.6 GHz and 9.29 dBi at 2.4 GHz. Return Loss obtained is − 40.76 dB at 3.6 GHz and − 24.58 dB at 2.4 GHz. The planar feed network is designed with Wilkinson Power Dividers and Hybrid Directional Coupler. When the array is operated with 3.6 GHz, beam steering will be in positive directions and when it is operated with 2.4 GHz, beam steering will be in negative directions for E-Plane. Beam switching, based on the input applied to the port of directional coupler will be in the H-Plane for both frequency bands.

Broadband transmission-type 1-bit coding metasurface for electromagnetic beam forming and scanning

Coding metasurfaces make it possible to manipulate electromagnetic (EM) waves digitally by means of several discrete particles. Hence, there have been rapid advances in this field recently. Here we propose a novel design of a broadband transmission-type coding metasurface, which is valid to both x - and y -polarized EM incidences from 8.1-12.5 GHz while satisfies the requirements of 1-bit coding without changing the polarization. Two types of multi-layer coding particles with different geometrical parameters are adopted to represent the digital states “0” and “1”, which are easily promoted to terahertz and optics through modifying the size scale. To verify the ability to manipulate the EM waves, we first adopt the coding metasurface to achieve broadband beam forming by converting spherical waves to plane waves and realize high-directivity pencil beam in far field with low side lobes. We further arrange the particles according to the coding sequence 010101… to steer two symmetrical beams in different directions controlled by frequencies with the maximum range of the scanning angle of 30°-50.5°. The good agreements between the simulated and measured results validate the proposed broadband coding metasurface, indicating its huge potential in communication and radar imaging systems.

Reconfigurable Transparent All-Dielectric Water-Based Metamaterial for Microstrip Patch Antenna Gain Enhancement

This paper present transparent, all dielectric water-based metamaterial (MM) superstrates with reconfigurable characteristics is employed for gain and bandwidth enhancement of a water-based microstrip patch antenna. The water-based microstrip patch antenna is fed by an L-shape probe. All dielectric water-based MM unit-cell element consists of dielectric cubic boxes filled with water is designed and analyzed. The reconfigurable electric properties are achieved via changing the water height in the MM unit-cell element. Different arrangements of the MM array with water height tapering are optimized and designed for microstrip patch antenna gain enhancement. The MM array is used as a single layer superstrate placed normal to the microstrip patch. A water-based MM lens consists of three layers is designed to collimate the radiation from the microstrip patch antenna. The phase compensation in the MM lens is achieved via changing the water height in the MM unit-cell elements of the lens. A reconfigurable beam in different directions from −30° to +30° is steered by changing the water level distribution over the MM lens unit-cell elements. A full-wave analysis using the finite integration technique is used for the design and analysis of the water-based MM lens arrangements.

Privacy Protection for Audio Sensing Against Multi-Microphone Adversaries

Abstract Audio-based sensing enables fine-grained human activity detection, such as sensing hand gestures and contact-free estimation of the breathing rate. A passive adversary, equipped with microphones, can leverage the ongoing sensing to infer private information about individuals. Further, with multiple microphones, a beamforming-capable adversary can defeat the previously-proposed privacy protection obfuscation techniques. Such an adversary can isolate the obfuscation signal and cancel it, even when situated behind a wall. AudioSentry is the first to address the privacy problem in audio sensing by protecting the users against a multi-microphone adversary. It utilizes the commodity and audio-capable devices, already available in the user’s environment, to form a distributed obfuscator array. AudioSentry packs a novel technique to carefully generate obfuscation beams in different directions, preventing the multi-microphone adversary from canceling the obfuscation signal. AudioSentry follows by a dynamic channel estimation scheme to preserve authorized sensing under obfuscation. AudioSentry offers the advantages of being practical to deploy and effective against an adversary with a large number of microphones. Our extensive evaluations with commodity devices show that protects the user’s privacy against a 16-microphone adversary with only four commodity obfuscators, regardless of the adversary’s position. AudioSentry provides its privacy-preserving features with little overhead on the authorized sensor.

Electronic Beam Switching of Circularly Polarized Plasma Magneto-Electric Dipole Array with Multiple Beams

In this paper, different array arrangements based on magneto-electric (ME) dipole antenna with wideband circular polarization (CP) characteristics are designed and investigated. Planar, triangular prism, square prism, and hexagonal prism array arrangements are considered. Each prism face has a sub-array comprises 2 × 2 ME-dipole elements. Each sub-array has wide impedance matching of 73.7%, a maximum gain of 16.6 dBi, and CP bandwidth of 78.2%. It employs the plasma frequency of the ME-dipole antenna to control its radiation characteristics. Frequency-independent lumped element equivalent circuit is constructed for a single antenna element. It is used to represent the antenna input impedance at different plasma electron densities with fixed physical structure. The proposed equivalent circuit comprises a single series section used for matching enhancement with feeder circuit, and three parallel tuned circuits corresponding to the three resonance frequencies in the input impedance. The best values of the equivalent circuit elements are computed using the particle swarm optimization (PSO) technique. Different array arrangements, planar, triangular, square, and hexagonal prism are designed to create single or multiple beams in different directions. An electronic beam switching is achieved by tuning in the plasma inside the ME-dipole in the desired direction. The radiation characteristics are analyzed and investigated using the finite integration technique (FIT).

Multidirectional smoothing by spectral dispersion scheme based on hybrid dispersion grating

A hybrid dispersion grating consisting of several segments of different groove types and groove densities is designed to disperse the laser beam and eventually to redistribute the speckles of the laser beam in different directions (linear, radial, and azimuthal). The elaborately designed redistribution of the speckles significantly improves the irradiation uniformity of the focal spot. As the focal spot is smoothed in at least two of the three directions, the scheme using the hybrid dispersion grating is called multidirectional smoothing by spectral dispersion. Results indicate that the performance and feasibility of the multidirectional smoothing scheme are better than the smoothing scheme based on a linear grating or a star grating.

Channel Optical Waveguides with Spatial Longitudinal Modulation of Their Parameters Induced in Photorefractive Lithium Niobate Samples

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Calculation of gyrotropy coefficients in media with low-pitch helical structures.

Chiral smectic liquid crystals are known for their huge optical activity due to the precession of the anisotropic dielectric tensor around the helicoidal axis. For an oblique direction of the propagating wave, the helix acts as a grating which splits an incident beam in different directions as long as the pitch is not too small with respect to the light wavelength. When the pitch of the helix is smaller than the wavelength, the effect of the helix is a renormalization of the gyrotropic coefficients (g_{⊥} and g_{∥}) of the resulting uniaxial medium. We report here on a method to compute these coefficients in that limit. Resolution of the Maxwell equations, using a perturbative approach, gives expressions for g_{⊥} and g_{∥} as a power development of the ratio (p/λ). The various terms of these developments coincide with the approximate expressions of these coefficients known in the literature.