Abstract
In this paper, a broadband metamaterial (MM) absorber is presented for X-band applications. A novel eight-resistive-arm (ERA) cell is proposed as an MM unit cell to achieve both broadband absorption and wide incidence angles. The proposed ERA cell is designed using equivalent circuit model and full-wave analysis in order to achieve an absorption ratio higher than 90% in the range of 8.2–13.4 GHz. The experimental results indicate that the absorptivity was greater than 90% in the range of 8–13 GHz for all polarization angles under normal incidence. Under oblique incidence, the measured absorptivity was greater than 90% in the range of 8.2–12.2 GHz up to 60° and in the range of 9.2–12 GHz up to 65° in the transverse electric (TE) mode. In the transverse magnetic (TM) mode, the measured absorptivity was higher than 90% in the range of 9.5–12.4 GHz when the incidence angle was varied from 0° to 60° and remaining a 90% absorption bandwidth in the range of 10–12 GHz up to 65°. Compared to other broadband MM absorbers, the proposed MM absorber exhibited the widest incidence angles in both TE and TM modes.
Highlights
Electromagnetic (EM) wave absorbers are applicable in various applications, including electromagnetic cloaking[1], low-radar-cross-section materials[2], sensing[3], photovoltaic and thermal photovoltaic applications[4], metal–insulator–metal[5], and perfect absorber[6,7,8]
The previous broadband MM absorbers are mostly operated under normal incidence and their bandwidth becomes narrower under wider oblique incidence
The design of the ERA unit cell can be understood by an equivalent circuit and its circuit parameters are calculated to realise broadband impedance matching based on the substrate and ERA pattern
Summary
Under normal and x-polarized incidence, the electric field and electric current density are plotted on the XY plane of the ERA unit cells at three frequencies—9 GHz, 11 GHz, and 13 GHz. At low frequencies, the electric resonance is generated from the outer rings and resistors, whereas the electric resonance is generated from the inner ring and the vertical axis (x-axis in Fig. 4(c) at high frequencies. This is because the direction of the magnetic field is parallel to the resistive surface layer; the electric field cannot be parallel to the layer.
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