We report a numerical study of a broadband metamaterial absorber in visible light region by utilizing a single layer of metal-dielectric-metal configuration. The absorption bandwidth and absorption performances are tailored by varying the resonator shapes and metal materials. The absorption bandwidth of the proposed metamaterial absorber (MA) structure is enhanced significantly with decreasing the order of rotational symmetry of the resonator shape. Using gold configuration, the twofold symmetry MA structure based on the double-sized axe shaped resonator exhibits the broadband absorption response over the entire visible light and apart of infrared spectrum range from 320 to 982 nm with absorptivity above 90% for both transverse electric and transverse magnetic polarizations. The physical mechanism of broadband absorption is explained by the current, electric, and magnetic distributions, significantly affected by the propagating surface and localized surface plasmon resonances. Furthermore, the high absorber performances of the twofold symmetry MA structure can be obtained over entire visible light region (400-700 nm) for both noble metal of gold and low-cost metal of nickel configurations, indicating the proposed absorber is a promising candidate for low-cost and large-scale fabricate device operated in visible light region.

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We propose a simple and new approach to design the broadband metamaterial absorber (MA) based on FR-4 substrate. The defected resonant patch of symmetry MA unit cell has been conceived to achieve the broadband absorbance. The simulated results demonstrate that the defected absorber structure exhibits the co-polarization broadband absorption response with absorptivity higher than 90% in the range of 4.0 - 6.0 GHz and the relative absorption bandwidth (RAB) of 40% for normal incidence. Furthermore, the defected structure can maintain the absorbance above 80% for oblique incidence up to 50° under both transverse electric (TE) and transverse magnetic (TM) polarizations. The compact structure (unit cell dimension of ∼λ/5.5 and thickness of ∼λ/20.8 with respect to the lower resonant frequency) and co-polarization broadband absorption with wide incident angle insensitivity of the absorber design based on defect make it suitable for defense system applications. Furthermore, this approach can be used to design co-polarization broadband absorbers in the terahertz, infrared and optical frequencies.

Developing a millimeter-wave (mm-wave) antenna that enables wide bandwidth with its operating band covering the entire global 5G spectrum is highly desirable but very challenging for achieving both compact size and high-performance antenna. Herein, the mm-wave microstrip patch antenna (MPA) and its multiple-input multiple-output (MIMO) configuration based on the metasurfaces for 5G system applications are proposed and investigated by the simulation method. To improve performance and keep the low-profile and low-cost MPA antenna, square ring resonator (SQRR) metasurface and radiating patch are printed on a single dielectric layer. With the presence of the metasurfaces that acting as a secondary radiator, the performance of the designed antenna is significantly improved with a wide operating band in the range of 23.9-30.7 GHz, high peak gain of 9.4 dBic, and radiation efficiency of above 87%. Based on this design, four-port MIMO antenna configuration is performed for evaluating a MIMO system that realizes the advantage features such as compact size, wide bandwidth covering the entire global mm-wave 5G spectrum band of 24.25-29.5 GHz, and excellent diversity performance characterized by good isolation between the adjacent elements and low envelope correlation coefficient. Thus, the MIMO antenna design is a very promising candidate for 5G MIMO mm-wave applications, specifically in cellular systems.

The logical structure of clauses indicates the logical connection between experiential events, thus it brings smoothness and coherence to writings. There are two fundamental systems that need to be considered in the analysis of how clauses are related to each other: taxis and logico-semantics (Halliday & Matthiessen, 2014). The theoretical framework used to analyse the logical relations of the clauses employed in academic IELTS sample essays on which the present study is based is the Systemic Functional Theory developed by Halliday & Matthiessen (2014). By focusing on the logical manifestations of the clause complex, particularly the study of taxis and logico-semantics, this paper sheds light on the logical relations demonstrated in IELTS sample essays. This study was designed using descriptive, analytic and inductive research method. Data were 60 IELTS academic essays taken from published books and official IELTS websites with band scores ranging from 7.0 to 7.5. The findings indicate that the writers employ more hypotaxis than parataxis to establish logical connections between states of affairs, proving that the IELTS writers tend to support their arguments using some unequal status. The analysis of logico-semantic relation also reveals that the dominant relationship is expansion. It is expected that the study will enable IELTS candidates to take into account the salient logical features of high-quality essays to produce more effective pieces of writing.