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In this paper, the nonlocal strain gradient theory and a new quasi 3D plate theory are employed to investigate the wave propagation in functionally graded (FG) porous graphene platelets (GPLs)-reinforced nanoplates on elastic foundations subjected to in-plane mechanical load and magnetic field. The present theory takes into account the shear deformation as well as the thickness stretching effect. The internal porosities and the GPLs are uniformly or non-uniformly distributed into the matrix according to four different types. The properties of the nanocomposites plates are calculated by utilizing the modified Halpin-Tsai pattern. Lorentz magnetic force is derived from Maxwell's equations for the conducting material. The motion equations are derived employing Hamilton's principle according to a new shear and normal deformations plate theory. Detailed parametric investigations on the wave frequency and phase velocity of the porous GPLs-reinforced nanoplates are implemented considering the influences of porosity coefficient, GPLs weight fraction, magnetic parameter and foundation stiffnesses on the results. It can be found that an increment occurs in the wave frequency with increasing the GPLs weight fraction and magnetic field parameter. While, it decreases as the pore coefficient increases. [ABSTRACT FROM AUTHOR]

A compact multiband planar inverted-F antenna (PIFA) suitable for distributed radio-over-fiber repeater networks is modified into a planar structure. It is shown that the planar antenna performance is not degraded with respect to the original PIFA and further, a two layer design is demonstrated to offer improved feed matching. The European bands for GSM, DCS-1800, DECT, UMTS, Bluetooth and HiperLAN2 are all covered. A model of the antenna is introduced as a first stage to developing an equivalent circuit. Index Terms--Multiband antennas, planar antennas, planar inverted-F antenna (PIFA), printed antennas, radio-over-fiber.

A quasi-3D refined plate theory is presented with the nonlocal strain gradient theory to investigate the wave propagation in bi-layer porous FG nanoplates surrounded by an elastic medium. Both layers are exposed to in-plane 2D-magnetic field. Maxwell's relations for perfectly conducting nanoplates are employed to derive the Lorentz magnetic force. The two porous FG nanoplates are coupled together using Winkler elastic medium. The mechanical properties of the nanoplates are continuously varied according to an exponential rule considering the porosity volume fraction. The governing equations of both layers are derived containing the plate interaction, elastic medium interaction, Lorentz magnetic force and the material length scale parameters. The frequency and phase velocity under the effects of magnetic parameter, porosity factor, elastic medium parameters, nonlocal parameter, strain gradient coefficient and nanoplate geometry are presented and discussed in detail. [ABSTRACT FROM AUTHOR]

Based on the differential quadrature method (DQM), the bending of sandwich-curved beams with graphene platelets/aluminum (GPLs/Al) nanocomposite face sheets and aluminum honeycomb core is investigated using a new shear and normal deformations curved beam theory. The present new model is resting on elastic foundation and subjected to a circumferential magnetic field, thermal load, and humid conditions. The face sheets are made of several bonded composite layers with randomly oriented and uniformly distributed graphene platelets in each layer. The mechanical and hygrothermal properties of the faces are assumed to be functionally graded (FG) using a piece-wise law by varying the weight fraction of the GPLs in the face thickness direction. Four governing differential equations are derived based on a novel four-variable curved beam theory taking into account the thickness stretching effect. The governing equations are solved for various boundary conditions on the basis of the DQM. The displacements presented by the DQM are compared with those obtained by Navier solution. Impacts of various parameters such as geometric shape parameters, magnetic parameter, temperature, moisture, elastic foundation parameters, core thickness, boundary conditions, and graphene weight fraction on the displacements and stresses of the functionally graded graphene/aluminum sandwich-curved beams are illustrated. [ABSTRACT FROM AUTHOR]

In this paper, the effects of hygrothermal conditions on various behaviors, such as bending, free vibration, mechanical and thermal buckling, of exponentially graded microplates lying on two-parameter elastic foundations are investigated. The trigonometric four-variable plate theory incorporated to the modified couple stress theory (MCST) is employed to derive the equations of motion. The present MCST contains an internal material length scale parameter, thus it can capture the size effect. The microplate is assumed to be subjected to a temperature rise and moisture concentration which are varied linearly through the thickness of the plate. Based on an exponential law, the material properties of the microplate are graded only in z direction. The equations of motion are solved analytically to obtain the displacements, stresses, eigenfrequencies and critical buckling load and temperature of the microplates. The present results are validated by comparing them with those previously published. The numerical examples reveal that considering the size effect and/or the elastic foundations leads to an increment in plate stiffness and thereby leads to a decrement in the deflection and an increment in eigenfrequency and buckling loads. It is also shown that the size effect is negligible for the thicker plate. [ABSTRACT FROM AUTHOR]

The modified couple stress theory (MCST) is utilized to investigate the bending of viscoelastic nanobeams laying on visco-Pasternak elastic foundations based on a new shear and normal deformations beam theory. This model consists of the material length scale coefficient that captures the size impact on small-scale beams. The simply supported beam is made of viscoelastic material, subjected to time harmonic transverse load. The nanobeam is presumed to be laying on double layers of foundations. The first layer is modeled as Kelvin–Voigt viscoelastic model and the second is taken as a shear layer. Based on the proposed beam theory and MCST, the differential motion equations are deduced using Hamilton's principle. To check the validity of the obtained formulations, the predicted results are compared with those available in the open literature. In addition, the influences of various parameters such as the material length scale parameter, length-to-depth ratio, viscoelastic damping structure, the stiffness and damping coefficients of the viscoelastic substrate, and shear and normal strains on the deflection and stresses are illustrated. [ABSTRACT FROM AUTHOR]

AbstractThe purpose of this study is to analyze the influence of geometric parameters and material properties on the free and forced vibration of bi-directional functionally graded sandwich (2D-FGSW) plates lying on an elastic foundation (EF) using an effective finite element method (FEM) based on the trigonometric shear deformation theory (TrSDT). The mechanical properties of 2D-FGSW are variable in both the x- and z-directions. The EF includes the springer stiffness k1 and the shear layer stiffness k2. Moreover, the impacts of structural damping and periodic loading on the behavior of 2D-FGSW plates are considered. Element matrices are created using a four-node quadrilateral plate element (Q4) with eight degrees of freedom per node. The effectiveness and accuracy of the current formulation are confirmed by contrasting the acquired results with those of earlier works. Then, many studies are carried out to illustrate how input parameters might affect the vibration characteristics of 2D-FGSW plates lying on EF. In addition, the eigenfrequencies of different types of 2D-FGSW plates with a center hole are investigated. [ABSTRACT FROM AUTHOR]

This paper presents a novel hybrid design technique to minimize the number of layers of the transmitarray (TA) panel while maintaining 360° phase shift range. Two types of unit cells, the receive–transmit unit cell and the frequency selective surface (FSS), are placed in the same aperture. The resulting TA panel is very thin but does not sacrifice the radiation efficiency of the array. The receive–transmit unit cell is an aperture-coupled square patch, and the FSS unit cell is a novel wide bandpass FSS. Both types of unit cells have three conductive layers and are printed on two substrates with a total thickness of 0.07λ0. The developed hybrid TA shows better gain than a homogeneous TA using the same elements. Meanwhile, it has comparable radiation performance but with a much lower profile compared to the conventional FSS-based TA designs that use several substrates separated by air layers. To verify the design concept, two hybrid TAs of different sizes with central frequency at 13.3 GHz were designed and fabricated. The measurements show that the TAs have at least 6.7% 1 dB gain bandwidth and higher than 30% aperture efficiency. Compared to the existing ultrathin designs of similar panel thickness, the presented TAs do not suffer from the phase quantization loss and achieve better or similar bandwidths. [ABSTRACT FROM AUTHOR]