Yazar "Karaaslan, Muharrem" seçeneğine göre listele

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    Prevention of Wave Propagation via Circular Arrangement of Seismic Metamaterials Formed with Concrete Piles
    (Mdpi, 2023) Kacin, Selcuk; Ozturk, Murat; Sevim, Umur Korkut; Karaaslan, Muharrem; Akgol, Oguzhan; Ozer, Zafer; Demirci, Mustafa
    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.
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    Radiation pattern reconfigurable cubical antenna array for 2.45 GHz wireless communication applications
    (Springer, 2023) Alkurt, Fatih Ozkan; Unal, Emin; Palandoken, Merih; Abdulkarim, Yadgar, I; Hasar, Ugur Cem; Karaaslan, Muharrem
    In this paper a single-fed four-faced multidirectional compact antenna is introduced for 2.45 GHz indoor wireless applications. Firstly, a slotted patch antenna is designed to operate at 2.45 GHz and its equivalent circuit model is synthesized, and then 2 x 1 patch antenna arrays are modelled and placed over the four faces of a cube structure and the final cube antenna is called as 4 x 2 x 1 antenna array. Meanwhile, a 50 omega fed line is positioned at the bottom of this cube with a power dividing network for the feeding line. For this purpose, a T-junction power divider network is designed at the bottom layer of the cube structure. Besides, the RF switches are located at each arm of four faces to transfer microwave energy selectively to each individual antenna element. Therefore, the reflection and radiation characteristics of proposed compact antenna are analysed to improve the performance under various switching conditions by the numerical analysis. The possibility of controlling selective radiation in a given direction is confirmed. The main advantage of the proposed design is to have capability of radiation control while preserving the reflection coefficient stability by RF switches. Finally, the proposed compact antenna is fabricated using a conventional printed circuit technology and the radiation performance is tested by the experimental measurements conducted. It is observed that measurement results are in a good agreement with the numerical computation results.
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    Sinusoidally located concrete metastructures for attenuation of seismic surface vibrations
    (Springer, 2023) Kacin, Selcuk; Ozturk, Murat; Sevim, Umur Korkut; Karaaslan, Muharrem; Akgol, Oguzhan; Ozer, Zafer; Demirci, Mustafa
    In this numerical and experimental study, we designed sinusoidal located concrete-based boreholes which are candidate for seismic shielding applications. To attenuate seismic wave transmission in an area, proposed design is created in most dangerous part of seismic frequencies which corresponds 1-15 Hz band. Firstly, transmission loss characteristics of proposed design is obtained numerically, and it is clearly shown that proposed design has multiband blocking capability. Afterwards, total surface displacements were plotted, analysed and explained. Thus, proposed design attenuates seismic wave transmission according to numerical results. Moreover, to support proposed design, various experimental measurements were carried out by using a harmonic vibration source and 14 accelerometers as sensors. Experiments conducted in time domain and obtained results were converted to the frequency domain by fast Fourier transform, and mapping processes were done by interpolation technique. The obtained measured map of the seismic radiation between 5 and 15 Hz bands is given, and a good matching between simulations and experiments has been seen. As obtained numerical and experimental results, the proposed metamaterial structure could be used in seismic shielding applications because of its highly blocking capability of seismic wave transmission.
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    A study on electronically controllable beamforming monopole antenna for telecommunication applications
    (Taylor & Francis Ltd, 2023) Alkurt, Fatih Ozkan; Unal, Emin; Palandoken, Merih; Altintarla, Gizem; Abdulkarim, Yadgar I.; Hasar, Ugur Cem; Karaaslan, Muharrem
    The design, analysis, and prototyping of an electronically controllable beamforming monopole antenna (ECBMA), which could be a good candidate for ceil-mounted wireless telecommunication systems, are reported. The proposed ECBMA targeting the 2.45 GHz center frequency is based on the 'on-off' ground reflectors, which are connected to the main ground layer by twelve RF switches to implement digital logic states. There are twelve ground reflectors symmetrically positioned over azimuthal angle direction in the ECBMA structure controlled by RF switches and a microcontroller unit, thus resulting in a pattern change when the states of the switches change logically. The designed ECBMA has the following three main features. First, it has a good and stable reflection coefficient (S11) characteristic at the 2.45 GHz centre frequency. Second, it has a wideband characteristic between 2.15 and 2.85 GHz (700 MHz operational bandwidth). Third, it has the capability to create single, double, or multi-beam characteristics (multi-purpose) which is a highly desired feature in many modern wireless communication systems mainly suitable for indoor applications. The prototype of our ECBMA is fabricated, and the performance analysis is investigated experimentally and S11 and radiation characteristics have good performance and are in good agreement with the simulation results. The proposed ECBMA has a good candidate for wireless telecommunication purposes such as WLAN, ISM, Wi-Fi, Bluetooth and other RF peripherals like indoor applications.