1,721,160 research outputs found
Probing the frequency-dependent elastic moduli of lattice materials
No full textAn insightful mechanics-based concept is developed for probing the frequency-dependence in in-plane elastic moduli of microstructured lattice materials. Closed-form expressions for the complex elastic moduli are derived as a function of frequency by employing the dynamic stiffness matrix of beam elements, which can exactly capture the sub-wavelength scale dynamics. It is observed that the two Poisson's ratios are not dependent on the frequency of vibration, while the amplitude of two Young's moduli and shear modulus increase significantly with the increase of frequency. The variation of frequency-dependent phase of the complex elastic moduli is studied in terms of damping factors of the intrinsic material. The tunable frequency-dependent behaviour of elastic moduli in lattice materials could be exploited in the pseudo-static design of advanced engineering structures which are often operated in a vibrating environment. The generic concepts presented in this paper introduce new exploitable dimensions in the research of engineered materials for potential applications in various vibrating devices and structures across different length-scales
Analysis of conformal antennas in the generalized curvilinear reference systems with bianisotropic inhomogeneous substrates
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Generalized Transmission Line and Helmholtz Equations for the Analysis of Integrated Conformal Antennas and Circuits
No full textTheoretical limits for negative elastic moduli in subacoustic lattice materials
No full textAn insightful mechanics-based bottom-up framework is developed for probing the frequency dependence of lattice material microstructures. Under a vibrating condition, effective elastic moduli of such microstructured materials can become negative for certain frequency values, leading to an unusual mechanical behavior with a multitude of potential applications. We have derived the fundamental theoretical limits for the minimum frequency, beyond which the negative effective moduli of the materials could be obtained. An efficient dynamic stiffness matrix based approach is developed to obtain the closed-form limits, which can exactly capture the subwavelength scale dynamics. The limits turn out to be a fundamental property of the lattice materials and depend on certain material and geometric parameters of the lattice in a unique manner. An explicit characterization of the theoretical limits of negative elastic moduli along with adequate physical insights would accelerate the process of its potential exploitation in various engineered materials and structural systems under dynamic regime across the length scales
Dynamic Beam Steering with Reconfigurable Metagratings
No full textMetagratings have recently shown promising features for wavefront manipulation, overcoming the efficiency limitations of gradient metasurfaces and their demanding fabrication requirements. Extreme functionalities, such as perfect anomalous reflection and refraction, focusing, and holography, have been proposed and tested. However, most of the developed analytical models concern the manipulation of the reflected field. In this article, we present a theoretical formulation that allows a complete manipulation of both reflected and transmitted fields through a metagrating consisting of arrays of capacitively loaded strips. In addition, the proposed solution enables the design of electronically reconfigurable metagratings for the dynamic control of the diffraction pattern at microwave frequencies. The theoretical formulation is numerically validated and a possible practical implementation of the metagrating is also discussed, as well as the effects of losses and parasitic reactances
U-patch antenna loaded by complex substrates for multifrequency operation
No full textIn this paper, the analysis of patch antennas with U-shaped
metalization loaded by bianisotropic media is deeloped. A theoretical
study is performed to obtain transmission-line equations for bianisotropic
materials, and then a method-of-lines (MoL) procedure is applied to
obtain the radiatie characteristics. Presented results assure, for particular
patch dimensions and feed application geometry, a multifrequency
operation in the microwae range, een for isotropic substrates. The
application of bianisotropic materials gies better performances for bandwidth
and input impedance at the central frequency, but degrades other
frequency operation performances
Advanced functionalities enabled by dipolar and multipolar all-dielectric metasurfaces
No full textIn this contribution, we summarize some of our recent results about the design of dipolar and multipolar all-dielectric metasurfaces featuring advanced wave-manipulation effects. We focus our attention on both dipolar and multipolar metasurfaces and we show how it is possible to engineering their complex scattering response for designing several electromagnetic devices, such as angular filters, optical forward scatterers, high-Q passband filters and polarizers working for extreme angles of incidence
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