Browsing by Subject "Wave transmission"

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    Optimization and tunability of deep subwavelength resonators for metamaterial applications: complete enhanced transmission through a subwavelength aperture
    (Optical Society of American (OSA), 2009) Alici, K.B.; Bilotti F.; Vegni L.; Özbay, Ekmel
    In the present work, we studied particle candidates for metamaterial applications, especially in terms of their electrical size and resonance strength. The analyzed particles can be easily produced via planar fabrication techniques. The electrical size of multi-split ring resonators, spiral resonators, and multi-spiral resonators are reported as a function of the particle side length and substrate permittivity. The study is continued by demonstrating the scalability of the particles to higher frequencies and the proposition of the optimized particle for antenna, absorber, and superlens applications: a multi-spiral resonator with ë/30 electrical size operating at 0.810 GHz. We explain a method for tuning the resonance frequency of the multi-split structures. Finally, we demonstrate that by inserting deep subwavelength resonators into periodically arranged subwavelength apertures, complete transmission enhancement can be obtained at the magnetic resonance frequency. © 2009 Optical Society of America.
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    Sabit karasal mikrodalga LOS/NLOS radyo linklerin enterferans analizi
    (IEEE, 2015-05) Göktaş, Polat; Topcu, Satılmış; Karaşan, Ezhan; Altıntaş, Ayhan
    Bu çalışmada, NATO Band 3+ (1350-2690 MHz) ve NATO Band 4 (4400-5000 MHz) frekans bantlarında çalışan sabit karasal mikrodalga LOS (karasal görüş çizgisi)/ NLOS (ufuk ötesi) radyo linkleri için enterferans modellenmesi ele alınmıştır. Sabit karasal noktadan-noktaya haberleşme sistemlerinde enterferansa maruz kalan istasyonlardaki hem açık havadaki hem de yağmurdaki saçılmadan kaynaklanan enterferansın hesaplanması yapılmıştır. Ayrıca, ITU-R P.452 Tavsiyesinde bahsedilen açık havadaki enterferans kaybının hesabındaki enterferans yayılım mekanizmaları incelenmiştir. Enterferansa neden olan verici ve enterferansa maruz kalan alıcı istasyonların koordinat bilgileri, enterferansa neden olan verici ve enterferansa maruz kalan alıcı istasyonların antenlerinin yerden yükseklikleri, anten ayrımcılıgı, ˘ polarizasyon tipi, radyo kırılma indeksi, deniz seviyesinden ortalama kırıcılık, zaman yüzdesi, yığın kategorisi, sayısal arazi yükseklik haritası ve iklimsel veriler gibi enterferans yayılım parametreleri kullanılarak çeşitli mikrodalga radyo linkler için enterferans analizleri yapılmıştır.
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    Terahertz Bandpass Frequency Selective Surfaces on Glass Substrates Using a Wet Micromachining Process
    (Springer New York LLC, 2017) Ramzan, Mehrab; Khan, Talha Masood; Bolat, Sami; Nebioglu, Mehmet Ali; Altan, Hakan; Okyay, Ali Kemal; Topallı, Kağan
    This paper presents terahertz (THz) frequency selective surfaces (FSS) implemented on glass substrate using standard microfabrication techniques. These FSS structures are designed for frequencies around 0.8 THz. A fabrication process is proposed where a 100-μm-thick glass substrate is formed through the HF etching of a standard 500-μm-thick low cost glass wafer. Using this fabrication process, three separate robust designs consisting of single-layer FSS are investigated using high-frequency structural simulator (HFSS). Based on the simulation results, the first design consists of a circular ring slot in a square metallic structure on top of a 100-μm-thick Pyrex glass substrate with 70% transmission bandwidth of approximately 0.07 THz, which remains nearly constant till 30° angle of incidence. The second design consists of a tripole structure on top of a 100-μm-thick Pyrex glass substrate with 65% transmission bandwidth of 0.035 THz, which remains nearly constant till 30° angle of incidence. The third structure consists of a triangular ring slot in a square metal on top of a 100-μm-thick Pyrex glass substrate with 70% transmission bandwidth of 0.051 THz, which remains nearly constant up to 20° angle of incidence. These designs show that the reflections from samples can be reduced compared to the conventional sample holders used in THz spectroscopy applications, by using single layer FSS structures manufactured through a relatively simple fabrication process. Practically, these structures are achieved on a fabricated 285-μm-thick glass substrate. Taking into account the losses and discrepancies in the substrate thickness, the measured results are in good agreement with the electromagnetic simulations. © 2017, Springer Science+Business Media New York.
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    Transmission and reflection properties of composite double negative metamaterials in free space
    (IEEE, 2003) Özbay, Ekmel; Aydin, K.; Cubukcu, E.; Bayındır, Mehmet
    We report free space transmission and the first reflection measurements of a composite double negative (DNG) metamaterial, also known as a left-handed material (LHM). The metaniaterial composes of the split-ring-resonators and discontinuous thin wires. Very high transmission values of the metamaterial are observed within a frequency range for which both effective permeability and permittivity are expected to be negative.
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    Transmission enhancement through deep subwavelength apertures using connected split ring resonators
    (Optical Society of American (OSA), 2010) Ates, D.; Cakmak, A.O.; Colak, E.; Zhao, R.; Soukoulis, C.M.; Özbay, Ekmel
    We report astonishingly high transmission enhancement factors through a subwavelength aperture at microwave frequencies by placing connected split ring resonators in the vicinity of the aperture. We carried out numerical simulations that are consistent with our experimental conclusions. We experimentally show higher than 70,000-fold extraordinary transmission through a deep subwavelength aperture with an electrical size of λ/31xλ/12 (width x length), in terms of the operational wavelength. We discuss the physical origins of the phenomenon. Our numerical results predict that even more improvements of the enhancement factors are attainable. Theoretically, the approach opens up the possibility for achieving very large enhancement factors by overcoming the physical limitations and thereby minimizes the dependence on the aperture geometries. © 2010 Optical Society of America.