1,721,052 research outputs found
Hyperparameter Optimization of Long Short-Term Memory Based Forecasting DNN for Antenna Modeling through Stochastic Methods
Full text linkThis letter presents an impressive optimization method for determining the optimal model hyperparameters of a deep neural network (DNN) targeted to model the characteristics of antennas. In this paper we propose an innovative approach of efficient yield analysis for modeling and sizing antennas. It is based on the long short-term memory (LSTM) DNN aiming to forecast the extended frequency responses, where various stochastic methods are applied for determining the optimal hyperparameters while training a DNN. Among the various methods, the one which models the antenna accurately in terms of input scattering parameter, gain, and radiation patterns is the winner. The proposed method is compact and addresses the problem of heavy reliance to the designer experience in determining the hyperparameters. Additionally, forecasting the future frequency responses of the antenna reduces the designers effort substantially in measuring large frequency band; hence, measuring whole frequency band would not be needed. For validating the effectiveness of the proposed method, the fabricated two element antenna array is used for modeling where the results demonstrate that the Thompson sampling (TS) algorithm can determine optimal hyperparameters with minimum error in comparison with other reported stochastic methods leads to predict the future frequency band accurately. IEE
Numerical investigation on graphene based mantle cloaking of a PEC cylinder
Full text linkA specific coating for the achievement of the mantle cloaking of a metallic cylinder in the Terahertz frequencies is investigated. The coat is realized starting from a dielectric layer covering the cylinder, over which a certain number of modulated strips of graphene are laid. Properly set the values of the available parameters (chemical potential of graphene μc, dielectric constant, dielectric thickness h, number of modulated strips n and variation of width of each strip w(z)), a combination of the values that allows to reach the cloaking of the object is obtained. In order to quantify the cloaking at the desired frequency f0, the Maximum Radar Cross Section is computed and compared to the various structures
Multidisciplinary investigations on the use of TiNb alloy orthopedic device equipped with low profile antenna as smart sensor
Full text linkIn this paper, a new complex medical device is proposed using TiNb based metallic alloy, acting also as a ground plane for a low profile printed antenna sited on a Polydimethylsiloxane (PDMS) substrate. The first step of the research is oriented on the experimental study of the properties of TiNb based alloy and on the development of the orthopedic device. The second step is focalized on the electromagnetic characterization of the implanted printed antennas. The resulting smart orthopedic device incorporating the antenna and when embedded in a body environment is numerically analyzed from communication point of view. In particular, the radiation characteristics, necessary for the calculation of the link budget when the device is used for communication with the external to the body receiver is considered. Such scenario finds its applications in monitoring some vital human functions for example in post chirurgical rehabilitation or other long-term surveys
Multi-objective Optimization Methods for Passive and Active Devices in mm-Wave 5G Networks
Full text linkDue to the exponential growth of data communications, millimeter-wave (mm-Wave) new radio specification becomes key enablers for fifth generation (5G) communication systems. However in the mm-Wave band frequency, the propagation loss is intensively large and cannot cover all the determined specifications. To tackle this drawback, the transceiver parts must sense the high radiated output power from power amplifiers. Hence by using high performance wideband antennas, the amplifiers can facilitate massive multiple-input multiple-output (MIMO) 5G systems. The figure of merit (FoM) of an amplifier is determined by the output power that must be challenged by other design specifications as: power gain, drain efficiency, and linearity. Therefore, powerful multi-objective optimization methods are required for welcoming appointed passive (antennas) and active (power amplifiers) characteristics in the determined frequency band. On the other side, high performance antennas in the 5G networks are also needed that can be designed using potent optimization methods. In this chapter, we provide collection of various optimization methods which have been recently applied for designing and optimizing high performance high power amplifiers and antennas. Hence, any designer can access to the nominated algorithms and can select the ones that are suitable for their problems
Harmonic analysis and reduction of the scattered field from electrically large cloaked metallic cylinders
Full text linkIn this paper, an analysis of the spectral composition of the scattered field from coated metallic cylinders is performed, focusing particularly on the cloaking of electrically large structures. An expression of the scattering coefficients is derived, considering both a dielectric and a metasurface coating. Modeling the metasurface as a surface impedance boundary condition, the surface impedance, which annuls one harmonic of the scattered field, is formulated in a closed and compact form. Moreover, in the case of cylinders with radius comparable with the wavelength of interest, it is demonstrated that a reduction of the scattering is possible by using a homogeneous metasurface coating, which presents a positive surface reactance. In particular, a reduction of the scattering width of 4 dB is achieved for a cylinder radius of a = 0.917λ0
Controlling frequency distance between individual modes of dielectric resonator nanoantenna using uniaxial anisotropic materials
Full text linkA technique to significantly shift down the resonant frequency of the higher order modes of a uniaxial anisotropic rectangular dielectric resonator nanoantenna (DRNA) without any considerable change in the resonant frequency of the fundamental mode is presented. The method aims to adjust the ratio of the resonant frequency of the higher order modes without changing the physical dimensions of DRA. This method can be used to adjust the frequency distance between the high-order and fundamental modes of the antenna. The performances of the method are numerically validated for different contrast values between the dielectric tensor entries
Dual-Polarized Tunable Mantle Cloaking with a Metasurface Based on graphene Strips
Full text linkA metasurface based on graphene strips is proposed to cloak a dielectric cylinder under illumination of TEz and TMz polarized incident waves in terahertz range. According to the in plane effective surface impedance tensor for the considered metasurface and the required surface impedance for achieving invisibility under TE and TM polarized impinging waves, the geometrical parameters of the covering structure and characteristics of graphene are obtained. Numerical simulations show radar cross section reduction for both TE and TM polarizations. Furthermore, the introduced metasurface is able to cloak the cylinder for incoming waves with circular polarization. In addition, it is shown that by properly adjusting the chemical potential of graphene, the required surface impedance to have cloaking for the two polarizations in other frequencies can also be achieved, which results in a tunable dual polarized cloaking
Tunable Frequency Selective Surface Design Using Automated Random Optimization
Full text linkWe present an automated approach to design a high performance, tunable frequency selective surface (FSS). The main goal of this study is to provide the simultaneous optimization of the FSS structure in two states of the 4 incorporated varactors, aiming to get an acceptable polarization filtering and polarization control. Generally, microwave designs are dealing with a large amount of data and they depend on the engineer's experiences. In order to get rid of this dependency and providing a ready-to-fabricate layout, we propose an optimization-oriented method based on the random optimization (RO). The RO method is applied in an automated environment where HFSS and Matlab are collaborating together forming a co-simulation platform where the design parameters are optimized up to achieve suitable output performances
Symmetry-breaking manipulation in the design of multifunctional tunable frequency selective surface
Full text linkThe design and characteristics of a PIN diode based tunable Frequency Selective Surface (FSS) is provided. Spatial filtering, polarization filtering and polarization control are all features the FSS exhibits in the considered 2-14 GHz frequency band. The proper symmetries required for the different features are explained and controlled by a holistic approach that includes the effects of the biasing network in the design. Symmetry breaking due to the presence of the biasing network used to bias the active elements are compensated by predistorsion of the initial geometry of the main structure that presents rotational symmetry. The proof of concept presented here allows extending the method to achieve proper design goals
Optimal Huygens' Metasurface for Wireless Power Transfer Efficiency Improvement
Full text linkIn this paper, we investigate the electromagnetic response of a Huygens' metasurface (HMS) embedded between the transmitter and receiver coils of a near field wireless power transfer (WPT) system and their interactions for the feasibility of increasing efficiency. To analyze the proposed configuration, we use the point-dipole approximation to describe the electromagnetic fields and boundary conditions governing HMS to calculate the mutual inductance between the coils and to obtain closed-form analytical expressions. The proposed theory shows that by optimally designing the HMS inclusions, the amplitude of the mutual inductance between the transmitter and receiver coils in the near-field WPT can be increased, resulting in improved efficiency. Finally, by drawing on the proposed theory, we design a thin layer and finite-size HMS consisting of 64 elements. The bianisotropic Omega-type particle is used to design the HMS to improve the efficiency of the sample WPT system at the frequency of 100 MHz. The results of the full-wave simulation show that the power transfer efficiency in the free space increases from 25% to 42% in the presence of the proposed HMS
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