Person: AKŞİMŞEK, HÜSEYİN SİNAN
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Dr. Öğr. Üyesi
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AKŞİMŞEK
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HÜSEYİN SİNAN
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Publication Metadata only A Novel Compact, Broadband, High Gain Millimeter-Wave Antenna for 5G Beam Steering Applications(IEEE Institute of Electrical and Electronics Engineers, Inc., 2020) ÖZPINAR, HÜRREM; AKŞİMŞEK, HÜSEYİN SİNAN; Tokan, Nurhan TürkerThe millimeter-wave (mmWave) antennas for smartphones are one of the key components to complete the transition to 5G mobile networks. Although research and development of mmWave 5G antennas for cellular handsets are currently at the center of a significant research effort in both academia and telecommunication industry, a systematic antenna design approved by wireless community has not been proposed yet. With this communication, we propose a novel, high gain, wide band and compact mmWave 5G antenna, namely clover antenna for cellular handsets. The presented antenna has clover like conductor profile whose parameters can be adjusted to obtain high gain or wide band. The designed antennas are simulated with a widely used full-wave analysis tool. Numerical results of the mmWave antenna are confirmed successfully by the experimental results in ${{\text{24}}}$-${\text{28}}$ GHz band. The antenna achieves measured peak gain of ${\text{ 7.8}}$-${\text{9}}$ dBi in the band. Besides, with a ${\text{16}}$-element clover antenna array, the beam steering capability of the antenna is demonstrated. Beam steering between ${{ \pm \text{45}<^>\circ }}$ is achieved with low side lobe levels. Practical design considerations for the integration of the arrays in handset to obtain full-coverage in horizontal plane are investigated. The calculated spatial peak power density values of the proposed array on the outer surface of a head phantom are demonstrated for different scan angles.Publication Metadata only Graphene-MoS2-Metal Hybrid Structures for Plasmonic Biosensors(Elsevier, 2018-12-01) Jussila, Henri; Sun, Zhipei; AKŞİMŞEK, HÜSEYİN SİNAN; 107154Surface Plasmon Resonance (SPR) biosensors are widely used for real-time label-free detection in medical diagnostics, pharmaceutical researches and food safety. Although there is a growing interest in miniaturization of biosensors for self-detection and diagnostics at out of laboratory, the performance of conventional metal SPR sensors is still limited. In this paper, we propose graphene–MoS 2 – metal hybrid structures based plasmon sensors under the best minimum light intensity approach, which represents the performance analysis in case of the lowest reflected light strength. It is demonstrated that the metal thickness can be reduced from 55 nm to 32 nm and 37 nm meanwhile the performance of the background sensor can be improved by 87% and 13% with the 4 additional MoS2 and graphene layers, respectively. We show that MoS2 based SPR devices provide much better sensitivity performance than graphene based devices. Our results reveal the another promising property of MoS2: The sensitivity of SPR sensors can be greatly increased with a few number of MoS2 within the angular SPR system while reducing the size of the device, especially for particular applications such as detecting a single molecule and biosensing at low biomolecule concentration. Furthermore, we show that the equivalent optical properties of multilayered nanostructures also depend on the layer thickness which is a novel knowledge for the next studies on 2D material based SPR plasmonic devices.Publication Metadata only TEM Wave Scattering by a Step Discontinuity on the Outer Wall of a Coaxial Waveguide(2013-08) Çınar, Gökhan; Nilsson, Börje; Nordebo, Sven; AKŞİMŞEK, HÜSEYİN SİNAN; 107154; 35397In this paper, the propagation of TEM waves along a coaxial waveguide with a step discontinuity on its outer wall is investigated rigorously by applying the direct Fourier transform and reducing the problem into the solution of a modified Wiener-Hopf equation. The solution for the field terms are determined in terms of an infinite number of unknown coefficients, which satisfy an infinite set of linear algebraic equations. These equations are solved numerically and the effect of area ratio is presented graphically at the end of the analysis. The same problem is also analyzed by applying the mode-matching technique and the results of the two approaches are compared. It is observed numerically that the Wiener-Hopf technique provides a better convergence than the mode-matching technique.Publication Metadata only Wide-Band Gain Enhancement of a Pyramidal Horn Antenna with a 3D-Printed Epsilon-Positive and Epsilon-Near-Zero Metamaterial Lens(Cambridge University Press, 2021) Keskin, Nesem; AKŞİMŞEK, HÜSEYİN SİNAN; Turker Tokan, NurhanIn this article, we present a simple, low-cost solution for the gain enhancement of a conventional pyramidal horn antenna using additive manufacturing. A flat, metamaterial lens consisting of three-layer metallic grid wire is implemented at the aperture of the horn. The lens is separated into two regions; namely epsilon-positive and epsilon-near-zero (ENZ) regions. The structure of the ENZ region is constructed accounting the variation of relative permittivity in the metamaterial. By the phase compensation property imparted by the metamaterial lens, more focused beams are obtained. The simulated and measured results clearly demonstrate that the metamaterial lens enhances the gain over an ultra-wide frequency band (10-18 GHz) compared to the conventional horn with the same physical size. A simple fabrication process using a 3D printer is introduced, and has been successfully applied. This result represents a remarkable achievement in this field, and may enable a comprehensive solution for satellite and radar systems as a high gain, compact, light-weighted, broadband radiator.Publication Metadata only Graphene actively Q-switched lasers(2017-05-05) Li, Diao; Xue, Hui; Qi, Mei; Wang, Yadong; Chekurov, Nikolai; Kim, Wonjae; Li, Changfeng; Riikonen, Juha; Ye, Fangwei; Dai, Qing; Ren, Zhaoyu; Bai, Jintao; Hasan, Tawfique; Lipsanen, Harri; Sun, Zhipei; AKŞİMŞEK, HÜSEYİN SİNAN; 107154Graphene electro-optic modulators (GEOMs) are emerging as a viable alternative to conventional material-based modulators mainly due to their broadband and ultrafast performance. These GEOMs with combined advantages of small footprint and low energy consumption can potentially enable various high-performance applications that are not possible using conventional approaches. Here, we report the first actively Q-switched lasers with a GEOM. In contrast to the previously reported lasers that are passively modulated by two-dimensional layered material-based saturable absorbers, our actively modulated laser concept represents significant advantages, such as electrically tunable output parameters (e.g. output repetition rate, pulse duration and pulse energy) and electro-optical synchronization. Using a single GEOM, we generate broadband Q-switched pulses at ~1.55 and 2 μm with output energies of up to 123 nJ. This indicates the broadband pulse generation capability of the graphene-based active devices, superior to widely used bulk material-based active modulation approaches. Our results demonstrate a simple and viable design towards broadband, high-repetition-rate, electrically modulated ultrafast lasers for various applications, such as telecommunications and spectroscopy.