Synthesis Of Beams Research Articles

Synthesis, characterization, and modeling of gelatin-based magnetic hydrogel beams

Hydrogels are soft materials that can be designed to be responsive to external stimuli such as temperature, pH change, and electric and magnetic fields. Magnetically responsive hydrogels consisting of polymer, water, and magnetic nanoparticles (MNPs) are emerging candidates in biomedical fields due to their remote application. In this work, cobalt ferrite-based MNPs prepared by the auto-combustion method are embedded in gelatin hydrogels. Cobalt ferrite-based magnetic hydrogels (HCFO) having high water content are prepared using the solvent casting method. The effective magnetic properties, such as coercivity and remnant magnetization of the hydrogels, are determined from the magnetization response (m-h curve) obtained through a vibrating sample Magnetometer (VSM). Subsequently, the HCFOs are subjected to uniaxial tensile loading to obtain mechanical properties. The size and shape of MNPs are obtained using X-ray Diffraction (XRD) and scanning electron microscopy (SEM) analysis. Furthermore, the magnetic hydrogel beams (cantilever) have been prepared and subjected to the external magnetic field. A unique phenomenological model has been proposed which can predict the finite deflection of the beam under magnetic loading exploiting the hard magnetic behavior of the HCFO. The proposed model takes into account particle concentration, finite elasticity, and magneto-mechanical coupling. The softness of the hydrogels matrix and hard magnetic properties of the MNPs results in large deflection. Further, the experimental observations and modeling predictions are in good agreement.

Multitarget Wireless Power Transfer System Strategy Based on Metasurface-Holography Multifocal Beams

Aiming at the critical problem of wireless power transfer (WPT) for the current growing number of wireless devices, the multitarget WPT system based on metasurface-holography multifocal beams and the design methods is investigated and analyzed in this article. As the propagator in near-field synthesis, a new field calculation formula is derived based on the Friis formula between the metasurface unit (MU) and the field point, which breaks the limitation of paraxial approximation and makes metasurface holography applicable in a wide-angle, long-distance, and nonplane space. Besides the phase response of MUs, the amplitude response is also introduced, which achieves the simultaneous amplitude–phase optimization of the metasurface to improve transmission efficiency. A metasurface with holography multifocal beams is first designed and engaged in forming a planar multitarget WPT system, which has been proven to radiate the designed multifocal beam and transfer power to each focal spot uniformly and efficiently after simulated, fabricated, and measured. To verify that the proposed method can achieve a near-field synthesis of multifocal beams in nonplane space over a wide angular range, a metasurface with 23-focus beam distribution on a spherical surface with an elevation angle from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> to 60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> , omnidirectional azimuth, and 66.67 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\uplambda $</tex-math> </inline-formula> radius is designed and simulated, which shows that the simulated radiation field distribution is in good agreement with the initial preset target field. This work demonstrates a feasible high-efficiency and long-distance WPT strategy for multiple targets in wide-angle and spatial scenarios.

Synthesis of Reconfigurable Multiple Shaped Beams of a Concentric Circular Ring Array Antenna Using Evolutionary Algorithms

The approach described in this paper uses evolutionary algorithms to create multiple-beam patterns for a concentric circular ring array (CCRA) of isotropic antennas using a common set of array excitation amplitudes. The flat top, cosec2, and pencil beam patterns are examples of multiple-beam patterns. All of these designs have an upward angle of θ = 0◦. All the patterns are further created in three azimuth planes (φ = 0◦, 5◦, and 10◦). To create the necessary patterns, non-uniform excitations are used in combination with evenly spaced isotropic components. For the flat top and cosecant-squared patterns, the best combination of common components, amplitude and various phases is applied, whereas the pencil beam pattern is produced using the common amplitude only. Differential evolutionary algorithm (DE), genetic algorithm (GA), and firefly algorithm (FA) are used to generate the best 4-bit discrete magnitudes and 5-bit discrete phases. These discrete excitations aid in lowering the feed network design complexity and the dynamic range ratio (DRR). A variety of randomly selected azimuth planes are used to verify the excitations as well. With small modifications in the desired parameters, the patterns are formed using the same excitation. The results proved both the efficacy of the suggested strategy and the dominance of DE over GA as well as FA.

A Time-Modulated Antenna Array With Continuous Sideband Spectrum Distribution

Traditional time-modulated antenna arrays (TMAs) usually introduce sideband radiations at a multiple of discrete harmonic frequencies. To improve radiation efficiency of TMAs, various evolutionary algorithms become very popular in sideband suppressions. Apparently, the sideband radiation levels highly depend on the performance of these evolutionary algorithms. To achieve robust sideband suppression through physical designs, a novel pseudorandom hybrid phase–amplitude modulation technique is proposed to distribute the sideband radiation power over a continuous spectrum, rather than only at discrete harmonic frequencies. Following the law of energy conservation, sideband levels (SBLs) in this case naturally become extremely low, which eliminates the difficulty arising in TMAs’ sideband suppressions. Moreover, the novel modulation technique allows the synthesis of scanning beams with ultralow sidelobe levels, and the corresponding time modulation sequences could be directly calculated from analytical formulations. Therefore, evolutionary optimization algorithms are not necessary in the proposed TMA design procedure, which facilitates the real-time on-board calculation with an field-programmable gate array (FPGA) board. As compared with traditional TMAs, the proposed TMA achieves ultralow SBLs ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; -35.0$ </tex-math></inline-formula> dB) with much fewer time modulation statuses. Numerical and experimental results are presented to demonstrate the effectiveness of the proposed TMA.

Optimum Synthesis of Pencil Beams with Constrained Dynamic Range Ratio

In antenna array design, low dynamic range ratio (DRR) of excitation coefficients is important because it simplifies array’s feeding network and enables better control of mutual coupling. Optimization-based synthesis of pencil beams allows explicit control of DRR. However, incorporating DRR into an optimization problem leads to nonconvex constraints, making its solving challenging. In this paper, a framework for global optimization of linear pencil beams with constrained DRR is presented. By using this framework, the methods for synthesis of pencil beams with minimum sidelobe level and minimum sidelobe power are developed. Both methods utilize convex problems suitable for the synthesis of pencil beams whose coefficients’ signs are known in advance. By incorporating these problems into a branch and bound algorithm, the procedures for global optimizations are formed which systematically search the space of all coefficient signs. The method for minimization of sidelobe power is further analyzed in the context of beam efficiency. It is shown that this method can be utilized in an approximate and at the same time global design of pencil beam arrays with maximum beam efficiency and constrained DRR. Based on this approach, a method for the design of pencil beam arrays with minimum DRR and specified beam efficiency is proposed.

Shared meta-aperture system for the frequency-induced reconfigurable multiple beams

We demonstrate the perfect synthesis of multiple beams with different radiating states at dual frequencies through a shared meta-aperture system, consisting of a checkerboard meta-lens with two kinds of gradient meta-atoms distributed in a diagonally staggered manner and a polarization converting meta-mirror possessing periodic skew double-headed arrow array. The co-linearly polarized (co-LP) waves reflected by the inner surface of the checkerboard meta-lens would be twisted into the cross-LP counterparts by the meta-mirror and then penetrate the checkerboard meta-lens to form the high-purity cross-LP directive multi-beams at one frequency. Meanwhile, the other polarization orthogonal meta-array over the outer surface of the checkerboard meta-lens would also be capable of transforming the released cross-LP fields back and create the co-LP multi-beams at another frequency. Especially, the frequency sensitivity of such shared meta-aperture system is discussed through comparing different sets of the synthesized multiple beams, and the multi-functional meta-surface coating over the checkerboard meta-lens will fundamentally determine the overall radiating patterns and the operating bandwidth. In addition, the proposed design through integrating composite functional meta-surfaces also possesses the merits of generating high-polarization purity multiple beams at different frequencies, thus should pave the way for building up more advanced shared-aperture meta-radiators with highly efficient connections in the contemporary wireless communications.

Compact cascaded meta-surface system for controlling the spin and orbital angular momentum of electromagnetic fields simultaneously.

We propose a compact cascaded meta-surface system (CCMS) to produce well converged orbital angular momentum (OAM) vortex waves with tailored spin angular momentum (SAM) by integrating a meta-surface lens (ML) with an assistant meta-mirror (AM). Specifically, the co-linearly polarized (LP) waves from the feed would be reflected by the ML firstly and then twisted into the cross-LP counterparts by the AM to penetrate the ML for the perfect synthesis of the OAM vortex beams while performing the linear-to-circular polarization conversion. Especially, the CCMS can pack the ML and the AM closely together with a quarter of the ML focal length when we apply proper phase distributions on the AM. In addition, the proposed CCMS can readily be extended to the generation of multiple circularly polarized OAM vortex waves with different modes. Our design should thus pave the way for building up more efficient wireless communication systems with expanded channel capacity.

Twisted Spatiotemporal Optical Vortex Random Fields

We present twisted spatiotemporal optical vortex (STOV) beams, which are partially coherent light sources that possess a coherent optical vortex and a random twist coupling their space and time dimensions. These beams have controllable partial coherence and transverse orbital angular momentum (OAM), which distinguishes them from the more common spatial vortex and twisted beams (known to carry longitudinal OAM) in the literature and should ultimately make them useful in applications such as optical communications and optical tweezing. We present the mathematical analysis of twisted STOV beams, deriving the mutual coherence function and linear and angular momentum densities. We simulate the synthesis of twisted STOV beams and investigate their free-space propagation characteristics. We discuss how to physically generate twisted STOV fields and lastly conclude with a summary and brief discussion of future research.

Field Synthesis of High Directivity Beams for Conformal Sources

The role of the source geometry in the radiation of focusing beams by conformal antennas is examined by the comparison of their directivity functions at different maximum directions. An inverse source problem approach is adopted, where solutions stable with respect to data uncertainties are to be found by relying on the analysis of the pertinent operator by the Singular Values Decomposition. This general framework allows to connect the mean value of the maximum directivity function to the Number of Degrees of Freedom of the conformal source, which depends only on its electrical length. For each source geometry the focusing far field ensuring the maximum directivity for every pointing direction and the corresponding source current are obtained. The comparison with the ones achieved by the usual phase compensation technique of the source current reveals their optimal behavior. The usefulness of the approach as a tool in antenna synthesis is shown by comparing different geometries for those applications where identical beams are required to be radiated for the coverage of a large angular domain.

Synthesis of Angle Arrays by the NDF of the Radiation Integral

Linear arrays have been well studied for their widespread applications, but they suffer from severe limitations in the scanning capabilities due to the inherent main beam spreading. The combination of two linear arrays, radiating simultaneously, may provide the coverage of a wide angular domain by identical beams. More in general, first, we consider the radiation properties of a collection of continuous linear sources by following an inverse source approach which aims at investigating the spectral decomposition of the relevant radiation operator by discussing its singular value decomposition and the number of degrees of freedom of the source according to its geometry. Then, a connection with the known closed-form results of the single line case is established. Next, for an angle geometry, the discussion of the point spread function reveals the condition to be achieved for an angle source to radiate identical beams with a coverage larger than the one of a single linear source with the same total length. Finally, we consider the power synthesis of identical focusing beams by linear arrays, arranged in an angle geometry, also including the effect of the element factor, without excitation constraints, so to show how possibly to drive the design of electrically large arrays by such an analytical approach.

Singular Atmospheric Optics: From Wavefront Dislocations to Synthesis of Vortex Laser Beams

Studies on the singular optics of scalar wave fields carried out in the world and at V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences (IAO SB RAS) are reviewed. The study results of the processes of origination and annihilation of phase singularities are generalized. The methods for singular phase reconstruction and their applicability to the problems of adaptive focusing of radiation in randomly inhomogeneous media are examined. The energy, statistical, and topological properties of vortex optical beams propagating through a turbulent atmosphere are analyzed. The results of the synthesis of vortex beams with quickly controllable orbital angular momentum by the matrix approach developed at IAO SB RAS are described.

High-resolution and extended-depth-of-field photoacoustic endomicroscopy by scanning-domain synthesis of optical beams.

Photoacoustic endomicroscopy (PAEM) is capable of imaging fine structures in digestive tract. However, conventional PAEM employs a tightly focused laser beam to irradiate the object, which results in a limited depth-of-field (DOF). Here, we propose a scanning-domain synthesis of optical beams (SDSOB) to optimize both transverse resolution and the DOF by synthetic effective focused beams in scanning domain for the PAEM. By utilizing the SDSOB technique, multiple defocused and scattered beams are refocused to synthesize virtual focuses covering a large range of depth. A transverse point spread function that is 5.7-time sharper, and a transverse spatial bandwidth that is 8.5-time broader than those of the conventional PAEM were simulatively obtained through SDSOB-PAEM at the defocus distance of 2.4 mm. We validated the transverse resolution improvement at both in- and out-focus positions via phantom experiments of carbon fibers. In addition, in vivo rabbit experiments were conducted to acquire vascular images over radial depth range of 900 µm. And further morphological analysis revealed that the SDSOB images were acquired with abundant vascular branches and nodes, large total-length and small average-length of blood vessels, which indicated that the SDSOB-PAEM achieved high-resolution imaging in distinct rectal layers. All these results suggest that the SDSOB-PAEM possesses high transverse resolution and extended DOF, which demonstrates the SDSOB-PAEM can provide more accurate information for clinical assessment.

Pattern synthesis of the multimode orbital angular momentum beams based on the fruit fly optimization algorithm

The multimode orbital angular momentum (OAM) radio waves can be used to multiplex multiple transmission channels to increase the capacity of communication system without adding additional bandwidth. However, the divergence of the OAM beams and beam inconsistency escalate by increasing OAM mode number. Moreover, the worse sidelobe level (SLL) always appears along with a better convergent beam. In this article, the fruit fly optimization algorithm (FOA) is proposed to suppress the SLL in multimode OAM scenario. Based on the concentric circular array antenna (CCAA), the feeding amplitudes and the radii of the array are synthesized simultaneously to realize less than −30 dB SLL of the multimode OAM patterns. When the main lobes with different OAM modes steered to a uniform azimuth of θ = 0°, the SLLs of these OAM modes are also suppressed to less than −21 dB. The advantages of FOA used in the OAM pattern synthesis are verified by comparing it with the genetic algorithm (GA). The FOA-based synthesis has a simpler implementation flow diagram which reduces the time of synthesis to 39.5% of GA.

An effective hybrid approach for the synthesis of pencil beams and shaped beams through 4D linear antenna arrays with constrained DRR

ABSTRACTIn this work, a novel hybrid approach combining differential evolution (DE) algorithm and convex programming (CP) is proposed for the synthesis of four-dimensional (4D) antenna arrays. To achieve ultra-low sidelobe level while suppressing sideband radiations simultaneously, the hybrid approach is applied to optimize static excitation coefficients and switch-on duration time separately. In particular, the hybrid approach fully makes use of the partial convexity of the problem with respect to the static excitation coefficients. CP is used to optimize static excitation coefficients for each set of switch-on duration time generated by the DE algorithm, while the DE algorithm is used to optimize the switch-on duration time only. Consequently, fewer optimization variables are needed and less iterations are required. The approach converges faster as compared to stochastic algorithms including all the optimization variables, especially for large arrays. Several numerical examples of the 4D antenna arrays are presented to demonstrate the effectiveness of the proposed hybrid approach.

Atmospheric singular optics: from wave front dislocations to synthesis of vortex laser beams

Atmospheric singular optics: from wave front dislocations to synthesis of vortex laser beams

Hybrid Method for the Synthesis of Isophoric Phase-Shaped Beams

A novel hybrid approach to the power synthesis of mask-constrained shaped beams by means of concentric-ring isophoric arrays is presented. The basis of this procedure is to use the complex aperture distribution obtained by Elliott–Stern method as a starting point of an innovative algorithm that combines a classical density tapering method with a simulated annealing one. The proposed technique allows to outperform the previous procedures.

Gaussian approach versus Dolph‐Chebyshev synthesis of pencil beams for linear antenna arrays

A very simple and fast method for the synthesis of pencil beams with linear antenna arrays of equally spaced elements is presented. The proposed procedure starts selecting the desired pencil beam as a Gaussian function. This is very convenient for two reasons: first, the continuous line-source distribution that exactly produces the desired pencil beam (i.e. the Fourier transform of it) is in turn a Gaussian function and is immediately calculated. Second, a suitable weighted sampling of this distribution gives the excitations of the array elements in closed form. Two numerical examples reveal the good performances of the proposed approach, also in comparison with the classical method by Dolph-Chebyshev. It is shown that the synthesised array factors well approximate the desired pencil beams in real time, in particular ensuring a very good behaviour in the side lobe regions. Furthermore, the ‘dynamic range ratio’ of the excitations, defined as the ratio between the maximum and the minimum amplitude of the excitations, is very low and close to unity when the array length is sufficiently small.

Arbitrary Beam Synthesis of Hybrid Beamforming Systems for Beam Training

For future millimeter wave mobile communication systems, the use of analog/hybrid beamforming is envisioned to be an important aspect. The synthesis of beams is a key technology to enable the best possible operation during beam search and data transmission. The method for synthesizing beams developed in this letter is based on previous work in radar technology considering only phased array antennas. With this technique, it is possible to generate a desired beam of any shape with the constraints of the desired target transceiver antenna frontend. It can cope with 1-D, 2-D, and even 3-D antenna array geometries, e.g., cylindrical arrays. The numerical examples show that the method can synthesize beams by considering a user defined tradeoff between gain, transition width, and passband ripples. Since this beam synthesis method is computationally complex, it is only suitable for offline calculation during the design or calibration of a device.

Arrays of Concentric Rings of Elements: Synthesis of Pencil Beams With and Without Allowance for Nonexcitation Blockage

Pencil beams may be synthesized for arrays of concentric rings of radiating elements by fitting the field pattern to that of a Taylor pattern for a circular aperture of the same radius. Nonexcitation blockage suppresses inner rings. Here we examine whether this needs to be taken into account in the synthesis procedure.

Phase-space measurement and coherence synthesis of optical beams

Researchers use spatial light modulators to create beams with locally varying spatial coherence, and show that the space and spatial frequency information of the beams can be measured simultaneously.