The left hand of electromagnetism : metamaterials

Ankara : The Department of Physics and the Institute of Engineering and Science of Bilkent University, 2010.Thesis (Ph. D.) -- Bilkent University, 2010.Includes bibliographical references leaves 160-172.Metamaterials are artificial periodic structures whose electromagnetic response is solely dependent on the constituting unit cells. In the present thesis, we studied unit cell characteristics of metamaterials that has negative permeability and permittivity. We investigated negative permeability medium elements, especially in terms of their electrical size and resonance strength. Experimental and numerical study of µ-negative (MNG) materials: multi split ring resonators (MSRRs), spiral resonators (SRs) and multi-spiral resonators are presented. The resonance frequency of the structures is determined by the transmission measurements and minimum electrical size of λ0/17 for the MSRRs and of λ0/82 for the SRs observed. We explain a method for tuning the resonance frequency of the multi-split structures. We investigated scalability of MNG materials and designed a low loss double negative composite metamaterial that operates at the millimeter wave regime. A negative pass-band with a peak transmission value of -2.7 dB was obtained experimentally at 100 GHz. We performed transmission based qualitative effective medium theory analysis numerically and experimentally, in order to prove the double negative nature of the metamaterial. These results were supported by the standard retrieval analysis method. We confirmed that the effective index of the metamaterial was indeed negative by performing far field angular scanning measurements for a metamaterial prism. Moreover, we illuminated the split-ring resonator based metamaterial flat lens with oblique incidence and observed from the scanning experiments, the shifting of the beam to the negative side. The first device was a horn antenna and metamaterial lens composite whose behavior was similar to Yagi-Uda antenna. We numerically and experimentally investigated planar fishnet metamaterials operating at around 20 GHz and 100 GHz and demonstrated that their effective index is negative. The study is extended to include the response of the metamaterial layer when the metamaterial plane normal and the propagation vector are not parallel. We also experimentally studied the transmission response of a one dimensional rectangle prism shaped metamaterial slab for oblique incidence angles and confirmed the insensitivity of split-ring resonator based metamaterials to the angle of incidence. After the demonstration of complete transmission enhancement by using deep subwavelength resonators into periodically arranged subwavelength apertures, we designed and implemented a metamaterial with controllable bandwidth. The metamaterial based devices can be listed under the categories of antennas absorbers and transmission enhancement. We studied electrically small resonant antennas composed of split ring resonators (SRR) and monopoles. The electrical size, gain and efficiency of the antenna were λ0/10, 2.38 and 43.6%, respectively. When we increased the number of SRRs in one dimension, we observed beam steerability property. These achievements provide a way to create rather small steerable resonant antennas. We also demonstrated an electrically small antenna that operates at two modes for two perpendicular polarizations. The antenna was single fed and composed of perpendicularly placed metamaterial elements and a monopole. One of the metamaterial elements was a multi split ring resonator and the other one was a split ring resonator. When the antenna operates for the MSRR mode at 4.72 GHz for one polarization, it simultaneously operates for the SRR mode at 5.76 GHz, but for the perpendicular polarization. The efficiencies of the modes were 15% and 40% with electrical sizes of λ/11.2 and λ/9.5. Finally, we experimentally verified a miniaturization method of circular patch antennas. By loading the space between the patch and ground plane with metamaterial media composed of multi-split ring resonators and spiral resonators, we manufactured two electrically small patch antennas of electrical sizes λ/3.69 and λ/8.26. The antenna efficiency was 40% for the first mode of the multi-split ring resonator antenna with broad far field radiation patterns similar to regular patch antennas. We designed, implemented, and experimentally characterized electrically thin microwave absorbers by using the metamaterial concept. The absorbers consist of i) a metal back plate and an artificial magnetic material layer; ii) metamaterial back plate and a resistive sheet layer. We investigated absorber performance in terms of absorbance, fractional bandwidth and electrical thickness, all of which depend on the dimensions of the metamaterial unit cell and the distance between the back plate and metamaterial layer. As a proof of concept, we demonstrated a λ/4.7 thick absorber of type i), with a 99.8% absorption peak along with a 8% fractional bandwidth. We have also demonstrated experimentally a λ/4.7 and a λ/4.2 thick absorbers of type ii), based on SRR and MSRR magnetic metamaterial back plates, respectively. The absorption peak of the SRR layout is 97.4%, while for the MSRR one the absorption peak is 98.4%. We conveyed these concepts to optical frequencies and demonstrated a metamaterial inspired absorber for solar cell applications. We finalized the study by a detailed study of split ring resonators at the infrared and visible band. We studied i) frequency tuning, ii) effect of resonator density, iii) shifting magnetic resonance frequency by changing the resonator shape, iv) effect of metal loss and plasma frequency and designed a configuration for transmission enhancement at the optical regime. By using subwavelength optical split ring resonator antennas and couplers we achieved a 400-fold enhanced transmission from a subwavelength aperture area of the electrical size λ2 /25. The power was transmitted to the far field with 3.9 dBi directivity at 300 THz.Alıcı, Kamil BoratayPh.D

Compact Antenna with Enhanced Performances Using Artificial Meta-Surfaces

In recent years, artificial meta‐surfaces, with the advantages of smaller physical space and less losses compared with three‐dimensional (3D) metamaterials (MTM), have intrigued a great impetus and been applied widely to cloaks, subwavelength planar lenses, holograms, etc. Typically, one most important part for meta‐surfaces’ applications is to improve the performance of antennas. In this chapter, we discuss our effort in exploring novel mechanisms of enhancing the antenna bandwidth using the magneto‐electro‐dielectric waveguided meta‐surface (MED‐WG‐MS), achieving circular polarization radiation through fractal meta‐surface, and also realizing beam manipulation using cascaded resonator layers, which is demonstrated from aspects of theoretical analysis, numerical calculation, and experimental measurement. The numerical and measured results coincide well with each other. Note that all designed antenna and microwave devices based on compact meta‐surfaces show advantages compared with the conventional cases

Metamaterials for Decoupling Antennas and Electromagnetic Systems

This research focuses on the development of engineered materials, also known as meta- materials, with desirable effective constitutive parameters: electric permittivity (epsilon) and magnetic permeability (mu) to decouple antennas and noise mitigation from electromagnetic systems. An interesting phenomenon of strong relevance to a wide range of problems, where electromagnetic interference is of concern, is the elimination of propagation when one of the constitutive parameters is negative. In such a scenario, transmission of electromagnetic energy would cease, and hence the coupling between radiating systems is reduced. In the first part of this dissertation, novel electromagnetic artificial media have been developed to alleviate the problem of mutual coupling between high-profile and ow-profile antenna systems. The developed design configurations are numerically simulated, and experimentally validated. In the mutual coupling problem between high-profile antennas, a decoupling layer based on artificial magnetic materials (AMM) has been developed and placed between highly-coupled monopole antenna elements spaced by less than Lambda/6, where Lambda is the operating wavelength of the radiating elements. The decoupling layer not only provides high mutual coupling suppression (more than 20-dB) but also maintains good impedance matching and low correlation between the antenna elements suitable for use in Multiple-Input Multiple-Output (MIMO) communication systems. In the mutual coupling problem between low-profile antennas, novel sub-wavelength complementary split-ring resonators (CSRRs) are developed to decouple microstrip patch antenna elements. The proposed design con figuration has the advantage of low-cost production and maintaining the pro file of the antenna system unchanged without the need for extra layers. Using the designed structure, a 10-dB reduction in the mutual coupling between two patch antennas has been achieved. The second part of this dissertation utilizes electromagnetic artificial media for noise mitigation and reduction of undesirable electromagnetic radiation from high-speed printed-circuit boards (PCBs) and modern electronic enclosures with openings (apertures). Numerical results based on the developed design configurations are presented, discussed, and compared with measurements. To alleviate the problem of simultaneous switching noise (SSN) in high-speed microprocessors and personal computers, a novel technique based on cascaded CSRRs has been proposed. The proposed design has achieved a wideband suppression of SSN and maintained a robust signal integrity performance. A novel use of electromagnetic bandgap (EBG) structures has been proposed to mitigate undesirable electromagnetic radiation from enclosures with openings. By using ribbon of EBG surfaces, a significant suppression of electromagnetic radiation from openings has been achieved

Antenna System Design for 5G and Beyond – A Modal Approach

Antennas are one of the key components that empower a new generation of wireless technologies, such as 5G and new radar systems. It has been shown that antenna design strategies based on modal theories represent a powerful systematic approach to design practical antenna systems with high performance. In this thesis, several innovative multi-antenna systems are proposed for wireless applications in different frequency bands: from sub-6 GHz to millimeter-wave (mm-wave) bands. The thesis consists of an overview (Part I) and six scientific papers published in peer-reviewed international journals (Part II). Part I provides the overall framework of the thesis work: It presents the background and motivation for the problems at hand, the fundamental modal theories utilized to address these problems, as well as subject-specific research challenges. Brief conclusions and future outlook are also provided. The included papers of Part II can be divided into two tracks with different 5G and beyond wireless applications, both aiming for higher data rates.In the first track, Papers [I] to [IV] investigate different aspects of antenna system design for smart-phone application. Since Long Term Evolution (LTE) (so-called 3.5G) was deployed in 2009, mobile communication systems have utilized multiple-input multiple-output antenna technology (MIMO) technology to increase the spectral efficiency of the transmission channel and provide higher data rates in existing and new sub-6 GHz bands. However, MIMO requires multi-antennas at both the base stations and the user equipment (mainly smartphones) and it is very challenging to implement sub-6 GHz multi-antennas within the limited space of smartphones. This points to the need for innovative design strategies. The theory of characteristic modes (TCM) is one type of modal theory in the antenna community, which has been shown to be a versatile tool to analyze the inherent resonance properties of an arbitrarily shaped radiating structure. Characteristic modes (CMs) have the useful property of their fields being orthogonal over both the source region and the sphere at infinity. This property makes TCM uniquely suited for electrically compact MIMO antenna design.In the second track, Papers [V]-[VI] investigate new integrated antenna arrays and subarrays for the two wireless applications, which are both implemented in a higher part of the mm-wave frequency range (i.e. E-band). Furthermore, a newly developed high resolution multi-layer “Any-Layer” PCB technology is investigated to realize antenna-in-package solutions for these mmwave antenna system designs. High gain and high efficiency antennas are essential for high-speed wireless point-to-point communication systems. To meet these requirements, Paper [V] proposes directive multilayer substrate integrated waveguide (SIW) cavity-backed slot antenna array and subarray. As a background, the microwave community has already shown the benefits of modal theory in the design and analysis of closed structures like waveguides and cavities. Higher-order cavity modes are used in the antenna array design process to facilitate lower loss, simpler feeding network, and lower sensitivity to fabrication errors, which are favorable for E-band communication systems. However, waveguide/cavity modes are confined to fields within the guided media and can only help to design special types of antennas that contain those structures. As an example of the versatility of TCM, Paper [VI] shows that apart from smartphone antenna designs proposed in Papers [I]-[IV], TCM can alsobe used to find the desirable modes of the linear antenna arrays. Furthermore, apart from E-band communications, the proposed series-fed patch array topology in Paper [VI] is a good candidate for application in 79 GHz MIMO automotive radar due to its low cost, compact size, ability to suppress surface waves, as well as relatively wide impedance and flat-gain bandwidths

Electromagnetic interactions in one-dimensional metamaterials

All data created during this research is available in ORE at https://doi.org/10.24378/exe.630Metamaterials offer the freedom to tune the rich electromagnetic coupling between the constituent meta-atoms to tailor their collective electromagnetic response. Therefore, a comprehensive understanding of the nature of electromagnetic interactions between meta-atoms is necessary for novel metamaterial design, which is provided in the first part of this thesis. The subsequent work in the thesis applies the understanding from the first part to design and demonstrate novel one-dimensional metamaterials that overcome the limitations of metamaterials proposed in literature or exhibit electromagnetic responses not previously observed. Split-ring Resonators (SRRs) are a fundamental building block of many electromagnetic metamaterials. In the first part of the work in this thesis, it is shown that bianisotropic SRRs (with magneto-electric cross-polarisation) when in close proximity to each other, exhibit a rich coupling that involves both electric and magnetic interactions. The strength and nature of the coupling between two identical SRRs are studied experimentally and computationally as a function of their separation and relative orientation. The electric and magnetic couplings are characterised and it is found that, when SRRs are close enough to be in each other's near-field, the electric and magnetic couplings may either reinforce each other or act in opposition. At larger separations retardation effects become important. The findings on the electromagnetic interactions between bianisotropic resonators are next applied to developing a one-dimensional ultra-wideband backward-wave metamaterial waveguide. The key concept on which the metamaterial waveguide is built is electro-inductive wave propagation, which has emerged as an attractive solution for designing backward-wave supporting metamaterials. Stacked metasurfaces etched with complementary SRRs (CSRRs) have also been shown to exhibit a broadband negative dispersion. It is demonstrated through experiment and numerical modeling, that the operational bandwidth of a CSRR metamaterial waveguide can be improved by restricting the cross-polarisation effects in the constituent meta-atoms. The metamaterial waveguide constructed using the modified non-bianisotropic CSRRs are found to have a fractional bandwidth of 56.3\% which, based on a thorough search of relevant literature, is the broadest reported value for an electro-inductive metamaterial. A traditional coupled-dipole toy-model is presented as a tool to understand the field interactions in CSRR based metamaterials, and to explain the origin of their negative dispersion response. This metamaterial waveguide should be of assistance in the design of broadband backward-wave metamaterial devices, with enhanced electro-inductive waveguiding effects. In the final part of the thesis, a one-dimensional metamaterial prototype that permits simultaneous forward- and backward-wave propagation is designed. Such a metamaterial waveguide could act as a microwave analogue of nanoparticle chains that support electromagnetic energy transfer with a positive or a negative dispersion due to the excitation of their longitudinal or transverse dipole modes. The symmetry of the designed hybrid meta-atom permits the co-existence of two non-interfering resonances closely separated in frequency. It is experimentally and computationally shown that the metamaterial waveguide supports simultaneous non-interacting forward- and backward-wave propagation in an overlapping frequency band. The proposed metamaterial design should be suitable for realising bidirectional wireless power transfer applications.EPSRC Centre for Doctoral Training in Electromagnetic Metamaterial

Size reduction of microstrip antennas using left-handed materials realized by complementary split-ring resonators

Recently, metamaterials (MTMs) engineered to have negative values of permittivity and permeability, resulting in a left-handed system, have provided a new frontier for microwave circuits and antennas with possibilities to overcome limitations of the right-handed system. Microwave circuit components such as waveguides, couplers, power dividers and filters, constructed on left-handed materials, have demonstrated properties of backward coupling, phase compensation, reduced sizes, and propagation of evanescent modes. However, there is very limited work to date, on the microstrip antennas with metamaterials. Microstrip antenna is widely used for its low-profile, simplicity of feed and compatibility with planar microstrip circuitry. As the trend towards miniaturization of electronic circuitry continues, antennas remain as the bulkiest part of wireless devices. There are three primary objectives to the present work: 1. Explore the possibility of miniaturizing microstrip patch antennas using left-handed materials through phase-compensation 2. Achieve negative permittivity using Complementary Split-Ring Resonators (CSRR) 3. Implement CSRR in the ground plane of a rectangular patch antenna, and validate through simulation and measurement A rectangular patch antenna with a combined DPS-DNG substrate has been analyzed with the cavity model, from which the condition for mode propagation has been derived. Criteria for ‘electrically small’ patch, using phase-compensation have been developed and propagating modes that satisfy these criteria have been obtained. With an objective to design practically realizable antennas, amongst several available LHM structures, the Complementary Split Ring Resonators (CSRR) has been chosen, primarily for the ease of implementation in the ground plane. CSRRs are periodic structures which alter the bulk effective permittivity of a host medium in which they are embedded. The effective permittivity becomes negative in a certain frequency band defined as a ‘stop-band’. In the present work the frequency response of the CSRR and the ‘stop-band’ has been determined using a full wave solver, from which, effective permittivity of the composite with CSRRs has been obtained by parameter extraction. Finally, several combinations of patch and CSRR in the ground plane have been designed and constructed in the X-band frequency range. Measurements of input characteristics and directivity have been validated through simulation by Ansoft Designer and HFSS. It has been observed that the best designs are achieved when the ‘stop-band’ of the CSRR corresponds to the desired resonant frequency of the antenna. Under these conditions, a size reduction of up to fifty percent has been achieved and it is noted that the back lobe is negligible and the directivity is comparable to that of a right-handed microstrip antenna

Synthesis of Planar Microwave Circuits based on Metamaterial Concepts through Aggressive Space Mapping

RF and microwave applications represent one of the fastest-growing segments of the high performance electronics market, where ongoing innovation is critical. Manufacturers compete intensively to meet market needs with reduced cost, size, weight and many other performance criteria demands. Under this scenario, transmission lines based on metamaterial concepts can be considered a very interesting alternative to the conventional transmission lines. They are more compact (compatible with planar manufacturing processes) and present higher degrees of design flexibility. Furthermore, metamaterial transmission lines can also provide many other unique properties not achievable with ordinary transmission lines, such as dispersion or impedance engineering. Nevertheless, the impact in the industry is still not relevant, mostly due to the complexity of the related synthesis and design procedures. These procedures are mainly based on the engineer’s experience, with the help of costly full-wave electromagnetic (EM) simulators and parameter extraction methods. The aim of this thesis is to contribute to simplify and speed up the synthesis and design procedures of artificial transmission lines. In particular, the lines obtained by periodically loading a conventional transmission line with electrically small resonators, such as split ring resonators (SSRs) or its complementary particle (CSRR). The design procedure is automated by using Space Mapping techniques. In contrast to other alternative methods, real synthesis is found from the circuit schematic (that provides a given target response) and without need of human intervention. Some efforts to make the method practical and useful have been carried out. Given a certain target response, it is determined whether it can be physically implemented with a chosen technology, and hence proceeding next to find the synthesis, or not. For this purpose, a two-step Aggressive Space Mapping approach is successfully proposed. In contrast to other methods, the real synthesis is found from certain target circuit values (corresponding to the equivalent circuit model that characterizes the structure to be synthesized). Different efforts have been carried out in order to implement a useful and practical method. Some of them were focused to determine if, given certain circuit parameters (which determine the target response) and certain given technology specifications (permittivity and height of the substrate, technology limits), that response is physically realizable (convergence region). This technique was successfully formulated and it is known as “Two-Step Aggressive Space Mapping Approach”. In this work, the latest improvements made till date, from the synthesis of basic unit cells until different applications and kinds of metamaterial-based circuits, are presented. The results are promising and prove the validity of the method, as well as its potential application to other basic cells and more complex designs. The general knowledge gained from these cases of study can be considered a good base for a coming implementation in commercial software tools, which can help to improve its competitiveness in markets, and also contribute to a more general use of this technology.Rodríguez Pérez, AM. (2014). Synthesis of Planar Microwave Circuits based on Metamaterial Concepts through Aggressive Space Mapping [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48465TESI

산소 플라즈마 애싱 공정을 이용한 응력 구배 MEMS 외팔보가 있는 Ka밴드 대역 가변형 메타물질 흡수체

학위논문(박사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2022. 8. 김용권.This dissertation proposes and realizes the first Ka-band frequency tunable metamaterial absorber with stress-induced MEMS cantilever with oxygen plasma ashing process. To employ a MEMS-driven actuator for LC resonance frequency tuning method in the GHz regime, the split-ring resonator (SRR) structure of the metamaterial unit cell is designed to have a sub-mm scale cantilever as a capacitor element of the unit cell. To enlarge capacitance change, the MEMS cantilever is released with a large out-of-plane deflection by the plasma ashing process. This MEMS cantilever with stress gradient is arranged at four parts of a symmetrical SRR unit cell, and the two cells compose the absorber sample as an array structure. The overall cantilevers of the absorber actuate from the initial bent upward state to pulled down state when the electrostatic voltage is applied. The decrease of deflection reduces the gap between cantilevers and bottom electrodes to increase capacitance for frequency tuning to lower frequency. To verify and improve the uniformity of the mechanical behavior of the absorber, this research proposes and demonstrates 3 different design types of releasing on stress-induced cantilevers. First, the array design of 12 cantilevers with 400 μm in length and 50 μm widths is modified from a cantilever with 400 μm in length and 800 μm widths. To overcome the limitation on the mechanical behavior of cantilever arrays due to their nonuniformity, further modification on etching hole rearrangement is reflected in the 2nd type of rectangular cantilever. The space length of etch hole varies depending on the position from the open end of cantilevers. This incremental space length between 8 μm etch holes from the open end enables sequential releasing of cantilevers during photoresist oxygen plasma ashing. The cyclic process was performed in the ashing process to lower the distribution of fabrication results. Finally, the last design to have a semicircle shape with incremental space length between etching holes to improve the uniformity of the cantilever to prevent such drawbacks of a wrinkled profile which the previous design shows. Also, our last design is driven by a digital drive creating 5 different reconfiguration states. With full-wave simulations, the performance of the proposed absorber demonstrates experimentally in each of 5 different reconfiguration states. The initially measured deflection of the cantilever beam is 51.8 μm on average. At the initial state, the resonant frequency and the absorptivity are 32.95 GHz and 80.95%. When all the cantilevers are pulled down, the frequency shifts a total of 4.08 GHz from the initial state showing a tuning ratio of 12.29 %. The error between the measured value and the simulation value came within 0.39 GHz in all five states. This dissertation demonstrated the potential of MEMS as a tuning method for Ka-band absorbers.이 논문은 산소 플라즈마 애싱 공정을 사용하여 응력구배 MEMS 외팔보를 사용한 최초의 Ka 대역 주파수 가변 메타물질 흡수체를 제안하고 검증하였다. GHz 영역에서 LC 공진 주파수 가변 방식에 MEMS 액추에이터를 구동하기 위해 메타물질 단위 셀인 분할링공진기 구조는 mm 스케의 외팔보를 정전용량의 요소를 갖도록 설계하였다. 정전용량 변화를 최대화하기 위해 MEMS 외팔보는 플라즈마 애싱 공정에 의해 수직 방향으로 큰 편향차를 갖도록 설계하였다. 응력구배 MEMS 외팔보는 대칭의 분할링 공진기 구조의 단위 셀 4곳에 배열되고 두 셀은 배열구조로 설계되었다. 이 때, 풀인 전압 이상의 높은 전압을 인가 시 외팔보는 바닥전극에 붙게 되어 정전용량을 키우고 LC 공진 주파수를 낮춘다. 흡수체의 기계적 거동에 대한 균일성을 개선하기 위해 총 3가지 다른 모양의 외팔보를 설계하였다. 먼저 길이 400μm, 너비 50μm인 외팔보를 12개의 배열상태로 설계하여 컴퓨터 시뮬레이션과 측정값을 확인하였다. 첫 번째 흡수체의 플라즈마 애싱 공정을 통한 외팔보 구현 공정의 결과, 96개의 외팔보의 평균 값은 41.5 μm이고 표준 편차는 15.4 μm였다. 첫 번째 흡수체의 경우 제작 외팔보의 산포가 상당히 큼에도 불구하고, 15 V까지 아날로그 튜닝을 하여, 초기 상태의 28 GHz의 공진주파수에서 25.5 GHz의 공진주파수 변화하여 총 2.5 GHz의 주파수 가변범위를 도달하였다. 반사계수는 초기 -5.68 dB에서 -33.60 dB까지 변화하였고, 투과 계수의 경우 -40에서 -60 dB를 유지하였다. 흡수율 계산 결과, 각 공진 주파수에서의 흡수율은 0 V일 때 72.9%에서 계속 증가하며 15 V일때 99.9%의 흡수율을 도달하였다. 그럼에도 불구하고, 외팔보 어레이 갖는 넓은 편향값 산포가 컴퓨터 시뮬레이션과의 괴리가 있어 개선된 설계를 다시 시도하였다. 앞선 설계의 단점을 극복하기 위해 점진적으로 증가하는 패턴의 식각 구멍을 외팔보에 적용하였다. 이 두 번째 구조 또한 제작, 컴퓨터 계산 및 실험 검증하였다. 이러한 식각 구멍 패턴은 외팔보를 산소 플라즈마 애싱 공정으로 구현 시, 제작 균일성을 크게 증가시킨다. 나아가 플라즈마 애싱 공정 또한 시간을 분할하여 제작함으로써 균일도를 크게 증가시킨다. 또한 두번째 설계부터는 응력 구배로 인한 큰 편향을 갖는 외팔보가 갖는 비평형 구동 방식의 해석 어려움에 따라 전압을 개별적으로 인가하며 on/off 형태의 디지털 구동방식으로만 구동하게끔 시스템 구동방식을 변경하였다. 2개의 메타물질 단위 구조에 4개의 전극을 분리하여 총 5개의 구조적으로 다른 상태를 구현하였다. 모든 외팔보가 위로 휘어진 상태에서 전극에 전압을 순차적으로 인가하여 2개씩 바닥에 붙게 하여 최종적으로 모든 외팔보가 바닥에 붙게 하였다. 두 번째 흡수체의 경우, 외팔보 구현이 크게 개선됨에도 불구하고 초기 32.24 GHz의 공진 주파수 값에서 2.14 GHz만 변화하여 최종 30.10 GHz의 공진주파수 측정 결과를 보였다. 흡수율의 경우에도 초기 83.59%에서 최종 90.75%의 결과를 보였지만 컴퓨터 계산과 많은 차이를 보였다. 최종적으로 앞선 2개의 설계를 보완한, 최종 진화한 형태인, 반원형 응력 구배 외팔보를 갖는 흡수체를 설계, 제작, 및 실험 검증하였다. 특히, 외팔보가 갖는 불안정한 기계적 거동을 단순화하여 디지털 구동을 하게끔 흡수체를 설계하였다. 식각 패턴의 거리를 2 μm씩 늘리며 반원 형태의 외곽으로부터 설계한 결과 재현성과 균일성이 매우 크게 개선되었다. 특히 반원 형태의 외팔보의 경우 최고점 편향 높이가 항상 반원 중간에서 구현되기 때문에 반원형 외팔보 간의 모양이 균일하게 유지된다. 제작된 18개 흡수체 샘플에서 144개의 외팔보를 측정한 결과 평균 편향 높이의 평균 값이 51.8 μm였으며 표준 편차는 3.1μm였다. 4개의 전극에서 기반한 5개 상태의 서로 다른 구조에 따른 반사 계수와 투과 계수를 도파관 측정으로 실험 값을 얻었다. 상용 유한요소법 컴퓨터 계산과 비교 검증하였다. 초기 상태에서 공진 주파수는 32.95 GHz였고, 모든 외팔보가 풀인 전압 인가로 인해 바닥 전극에 붙으면 하면 주파수 28.87 GHz가 되어 총 4.08GHz 이동하여 12.29%의 주파수 가변율을 갖는다. 측정값과 유한요소 시뮬레이션 값의 오차는 5개 상태 모두에서 0.39GHz 이내였다. 흡수율의 경우 각 상태에서 80.95 %, 88.17 %, 86.29 %, 99.21 %, and 86.51% 값을 보였다. 이 논문은 Ka-대역 흡수체의 튜닝 방법으로서 MEMS의 가능성을 보여주었다.CHAPTER 1. Introduction 1 1.1 Background 1 1.1.1 Advent of metamaterial 1 1.1.2 Application of metamaterial 2 1.1.3 Physics of metamaterial 3 1.1.4 Meta-atom 10 1.1.5 Electromagnetic absorber to metamaterial absorber 14 1.1.6 Reconfigurable metamaterial 17 1.1.7 MEMS reconfigurable metamaterial 21 1.1.8 Tunable metamaterial absorber 24 1.1.9 MEMS reconfigurable metamaterial absorber 27 1.1.10 Tunable metamaterial absorber for Ka-band 29 1.2 Originality and contribution 32 1.3 Document structure 33 CHAPTER 2. Stress-induced sub-mm scale cantilever 34 2.1 Initial design 34 2.2 Cantilever arrays with stress gradient 37 2.2.1 Preliminary experiment 37 2.2.2 Design 38 2.2.2 Fabrication results 39 2.3 Rectangular shape sub-mm scale cantilever with incremental etch hole spacing 40 2.3.1 Preliminary experiment 40 2.3.2 Design 42 2.4 Semicircular sub-mm scale cantilever with incremental etch hole 49 2.4.1 Design of semicircular sub-mm scale cantilever with incremental etch hole 49 2.4.2 Fabrication 52 CHAPTER 3. The 1st design of MEMS tunable metamaterial absorber with cantilever arrays for continuous tuning 57 3.1 General overview 57 3.2 Design 59 3.2.1 Split ring resonator and simulation 61 3.2.2 Capacitance of cantilever with stress gradient 64 3.2.3 Electrostatic driving of cantilever 67 3.2.4 Stress analysis & PR ashing 69 3.3 Fabrication 71 3.3.1 Fabrication process 71 3.3.2 Fabrication results 74 3.4 Simulation 77 3.5 Experiment 81 3.5.1 Experiment setup 81 3.5.2 Experiment results 84 3.6 Summary 86 CHAPTER 4. The 2nd design of MEMS tunable metamaterial absorber with rectangular shape sub-mm scale stress-induced cantilever with an incremental etch hole spacing for digital driving 87 4.1 General overview 87 4.2 Design 90 4.3 Fabrication 93 4.4 Simulation 98 4.5 Experiment 100 4.6 Summary 102 CHAPTER 5. The 3rd design of MEMS tunable metamaterial absorber with semicircular sub-mm scale stress-induced cantilever with an incremental etch hole spacing for digital driving 103 5.1 General overview 103 5.2 Design 107 5.2.1 Electromagnetic properties 107 5.2.2 Design parameter 109 5.3 Fabrication 112 5.4 Simulation 119 5.4.1 Simulation setup 119 5.4.2 Simulation results 122 5.5 Experiment 126 5.5.1 Experiment setup 126 5.5.2 Preliminary experiment 130 5.5.2 Experiment results 133 5.6 Further Analysis 137 5.6.1 The waveguide simulation 137 5.6.2 The periodic metamaterial unit cell simulation 141 5.6.3 Analysis on the surface current 148 5.7 Summary 152 5.7.1 Summary of the 1st, 2nd, and 3rd design 152 5.7.2 Comparison with MEMS tunable metamaterial absorber 155 5.7.3 Comparison with Ka-band tunable metamaterial absorber 157 CHAPTER 6. Conclusion 159 Bibliography 161 초록 (국문) 180박