Seismic surface waves with low frequencies results in higher effects. The aim of the utilization of seismic metamaterials is to prevent or minimize the effects of this waves particularly wide ...frequency ranges. This study presents the investigation of the reducing effects of seismic metamaterials composed of circular array concrete piles on surface waves. The investigation of circular array concrete piles has been carried out numerically between 5-15 Hz. The effectiveness of the periodic structure has been observed numerically for fields including metamaterials by comparing empty field. The observations have been depicted according to transmission losses for two cases by using finite element method (FEM) simulations. The wave propagation also presented at the related frequencies where the transmission losses seen. Effective dimensions of radius and length of the structures have been obtained by using parametric approach. It has been proved numerically that the suggested concrete piles reduces the hazardous effects of surface waves.
In this manuscript, a resonator layer is presented for the purpose of reducing the mutual coupling effect between each antenna element of a cross dipole antenna. In design processes, an artificial ...neural network approach was used for various resonator designs. In the operating frequency band of 2.2–2.7 GHz, 48 different 6 × 6 resonator layers were created and integrated into the cross dipole antenna to reduce transmission and improve isolation between each antenna elements. Moreover, when training an artificial neural network in the Matlab program, 48 different resonator layers were used with the return losses and transmission values of cross dipole antenna elements. After training process, eight unknown resonator designs were tested and accurate results were obtained. Finally, one of the resonator planes, which was obtained from the artificial neural network, was fabricated and experimentally tested, then an accurate result was obtained. This study provides a good solution, especially for improving isolation in multiport antenna systems, using an artificial neural network approach.
In this paper, a new design of high gain and wide bandwidth microstrip patch antenna array containing double meander dipole structure is proposed. Two in-phase resonant frequencies in the Ku-band ...(12–18 GHz) could be achieved in the double meander dipole array structure, which lead to enhance impedance bandwidth without costing extra design section. Besides, further enhanced gain of 2 dBi of the array over the entire operating frequency range has been achieved by introducing a double-layer substrate technique. The proposed antenna has been fabricated using the E33 model LPKF prototyping PCB machine. The measurement results have been performed, and they are in very good agreement with the simulation results. The measured –10 dB impedance bandwidth indicates that the array provides a very wide bandwidth which is around 30% at the center frequency of 15.5 GHz. A stable gain with a peak value of 10 dBi is achieved over the operating frequency range. The E- and H-plane radiation patterns are simulated, and a very low sidelobe level is predicted. The proposed antenna is simple and has relatively low-profile, and it could be a good candidate for millimeter wave communications.
In this study, cement additives were replaced with cement in mortar mixtures by mass. Mortar specimens were prepared with different additives and dosages which were mechanically and ...electromagnetically tested. According to the compressive strength test results, mortars containing ground granulated blast furnace slag had weak early age strength and strong later age compressive strengths values, mortars containing fly ash had lower compressive strength value with increasing amount of additives in the mortar mixture for both 7 and 28-day samples, mortars containing silica fume had the maximum strength values at 20% replacement level and lastly the mortars including more than 10% rice husk ash showed weaker strength behaviors with increasing amount of rice husk ash. Besides, electromagnetic responses of the mortar samples were investigated in the frequency range of 3–18 GHz. The reflection and transmission values were measured and the absorption characteristics were calculated. According to the electromagnetic test results, it is revealed that the mortars including ground granulated blast furnace slag can be utilized in the applications of high stealth technology and electromagnetic shields in a wide frequency range of communication field. An increase in the ratio of fly ash in the mortars reduces the transmission of the electromagnetic wave. Mortars including silica fume had very low values of reflection and transmission. Hence, it is expected that the absorption values must be high due to dependency of absorption to reflection and transmission, and it can be said that mortar with rice husk ash exhibits a strong absorber behavior.
It is known that the low frequencies of seismic surface waves have a destructive effect. The main purpose of seismic metamaterials is to protect structures from seismic waves at low frequencies, ...especially in a wide band. In this study, the effects of seismic metamaterials formed using circular array concrete piles on surface waves were investigated. Each concrete pile has been selected due to symmetric properties to investigate the band diagram. Therefore, the direction independence can also be determined with respect to frequency. This study was conducted both numerically and experimentally in the low-frequency range of 5–15 Hz. Two fields, with and without metamaterials, have been designed and compared. In numerical analysis, transmission loss graphs were drawn using the finite element method (FEM), and wave propagation at frequencies where the loss happened was simulated. In numerical analysis, optimum dimensions such as radius and depth were determined, and these dimensions were applied exactly in the experimental field. The results obtained from the experiment using a harmonic vibration device are mapped. In this numerical and experimental study, it has been revealed that the proposed structure prevents the propagation of seismic surface waves.
In this study, a novel octagonal shaped metamaterial based broadband absorber is proposed for energy harvesting at WIMAX wireless communication band. The proposal has an absorption of 99.97 % at ...5.5 GHz with a bandwidth of 1 GHz between 5 GHz and 6 GHz in Transverse Electric (TE) mode. Transverse Electric (TE), Transverse Magnetic (TM) and Transverse Electromagnetic (TEM) modes are studied numerically in this paper. In TM and TEM modes, proposed structure has absorption of nearly 96 % and 98 % respectively at 6 GHz. The proposed structure is polarization angle independent which is important for energy harvesting applications. Energy harvesting application is realized by using resistive loads on the design, simulations are parametrically studied on resistive loads and experimental study is realized for reflection coefficient measurement and compared with simulated results. Both experimental and simulated results are complying with each other. The proposed structure has different usage areas in stealth areas, detection and imaging. DOI: http://dx.doi.org/10.5755/j01.ms.24.3.18625
High performance electromagnetic wave (EMW) absorbing material systems are required for stealth applications and sensitive electronic devices. Absorbing of an incident EMW in a wide band range still ...has limitations in terms of materials system and engineering. It is required to extend the bandwidth and minimize the reflection from the material system for the next level stealth technologies. In this work, hybrid nanocomposite structures are developed by semiconductor flower-like MoS2 nanosheets, Fe3O4 magnetic nanoparticles and conductive polyaniline. A systematic study is presented by investigation the structural, magnetic, morphological, thermal, electronic and electromagnetic characteristic of hybrid nanocomposites (Fe3O4:MoS2, PANI@Fe3O4, PANI@MoS2 and PANI@Fe3O4:MoS2). EMW absorption characteristics results showed that Fe3O4:MoS2 and PANI@Fe3O4:MoS2 hybrid nanocomposites exhibit excellent EMW absorption characteristics. While the minimum reflection loss (RL) value was found as − 54.97 dB at 15.99 GHz for the Fe3O4:MoS2 nanocomposite, the broad bandwidth (7.65 GHz) was observed in PANI@Fe3O4:MoS2 hybrid nanocomposite having − 39.96 dB RL. According to the experimental results, a lightweight and high temperature resistance PANI@Fe3O4:MoS2 like-hybrid nanocomposite can absorb almost 90% of incident EMW in a wide bandwidth.
•The minimum reflection loss has been achieved as − 54.97 dB at 7.86 GHz in the Fe3O4 decorated MoS2 nanosheets.•A broadband EM wave absorbing in X and Ku bands has been observed in PANI Coated Fe3O4 decorated MoS2 hybrid nanocomposite.•The effective absorption bandwidth enhances up to 7.65 GHz via PANI coated Fe3O4 decorated MoS2 hybrid nanocomposite.
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