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تعداد صفحات این فایل: ۲۹ صفحه

به طور خلاصه یک LHM جدید الگو برداری شده از فراکتال درختی با  رزونانس های الکترریکی و مغناطیسی  چند رزونانس  به طور ازمایشی و عددی مشاهده شده است. شناسایی رزونانس  های چند گانه از طریق  انالزیز میدانی علاوه بر انالیز مدل مدار انجام گردید. MB یک گذر دهی منفی  را نشان داد زیرا سلول  LHM به طور همزمان از  یک  واکنش پلاسما و رزونانس الکتریکی سیمی استفاده می کند در حالی که ۳ رزونانس مغناطیسی که تراوایی منفی MB را در اختیار می گذارند به ۳ حلقه ی جریان با گشتاور های دو قطبی مغناطیسی  تنظیم شده در  DSR نسبت داده شده است یکی از خصوصیات  مهم این موارد رزونانس های  مغناطیسی قوی و باند های عبوری  اصلی است که  ایجاد  می شوند صرف نظر از این که ثابت های شبکه متغیر  باشند با نباشد .رفتار LH هم توسط هم منشور و هم اسلب (صفحه)ارزیابی شده است. 

عنوان انگلیسی:Multi-band left-handed metamaterial inspired by tree-shaped fractal geometry~~en~~

 Introduction Left-handed (LH) metamaterials (LHMs) with abundant exotic electromagnetic (EM) properties are termed and envisioned by Veselago decades ago [1] because the electric field (E), magnetic field (H) and wavevector (k) subject to an LH coordinate system. They are made of a periodic collection of subwavelength unit cells and have undergone a burgeoning interest since the first experimental demonstration of negative refractive index (NRI) n [2] inspired by Pendry’s encouraging proposal of using split ring resonators(SRRs) [3] and conductor wires[4]. With the explosive development of LHMsin recent years, ample proofs for the existence of NRI with simultaneous negative permeability meff and negative permittivity eeff have been extensively reported in GHz, THz and even visible frequency range [5 21]. Moreover, the potential application of them to build invisibility cloaks[22 24], super lens [25,26] and absorbers [27,28] also become a reality and gain a great impetus. Despite these progressive advancements, most of the LHMs are confined to a single frequency operation exceptfor [13 17], which is evidently a considerable drawback and a challenge to practical applications of present LHMs. Furthermore, the acquisition of a negative permeability response over multi-frequency bands is still challenging although the magnetic constituent has been extended from original SRRs and its variations such as V-shaped [5] and S-shaped [13] structures to cutwire pairs [8,18] and fishnet structures [9]. As exposed to fractal geometry, it has been widely adopted by physics and engineering communities due to its two critical natures of space-filling and selfsimilarity which can be engineered for compact and multifunctional microwave devices and antennas. In spite of this, the application of it to metamaterial is a fresh issue in recent years because sub-wavelength fractal structures exhibit the potential of making metamaterials present interesting resonant properties that are not achievable in conventional metamaterials. A review of literature indicates that only a few LHMs have been available by using this concept [17,29] although many electric resonant [30,31] or magnetic resonant [32,33] single negative metamaterials have been reported. Moreover, most of them were limited to utilizing the H-shaped fractal, making an alternative, improved and simplified fractal LHM that can be easily fabricated and experimentally characterized a pressing task. Most recently, the fractal-perturbed composite right/left handed transmission line (CRLH TL) has been thoroughly studied by the authors [34] to miniaturize the dimensions of cells, making them more appropriate to be described by homogenized effective mediums [35]. In this paper, we propose a completely new multiband (MB) LHM using tree-shaped fractal to overcome this pressing obstacle. Quite different from previously reported MB LHMs by cascading a chain of subwavelength unit cells or by combining individual electric and magnetic resonators owning scaled geometrical dimensions [13 16], the current multiple magnetic resonances and resultant LH transmission bands are synthesized by using a single-sided integrated planar fractal structure. Multiple magnetic resonances with occurred negative meff are introduced by the structure and they can be tuned into the negative eeff band produced by its plasma and electric resonance response. The paper is organized as follows: in Section 2, the magnetic and electric resonances together with LH bands of one-layer LHM are identified first by material parameters retrieval and then examined by closing gaps of different rings. The balanced condition is also illustrated by the constant equivalence of electric and magnetic plasma frequencies, followed by the mechanisms and controllability of these resonances that are investigated in depth through circuit model analysis, field distribution analysis and lattice constant analysis. In Section 3, both the numerical and experimental results of a multi-layer LHM prism and an LHM slab are provided to confirm the MB negative permittivity, permeability and resultant LH behavior. Section 4 concludes the whole paper. 2. DNG behavior of the balanced one-layer LHM 2.1. LHM cell structure and configuration Fig. 1 shows the topology and illustrative simulation setup of proposed one-layer (single cell in propagation direction) LHM by etching third-order three-branch tree-shaped fractal metal on one side of a dielectric substrate. The engineered structure built in three iterations is inspired by tree-shaped fractal [36] which was initially exploited for a MB antenna design.

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