Bui Son Tung

Perfect and broad absorption by the active control of electric resonance in metamaterial

Anti-oscillating plasmas have been the key to perfect absorption induced by magnetic resonance. This is an achievement in recent research on metamaterials (MMs), especially in GHz and the lower-frequency regions of electromagnetic waves. Here, a comprehensive view of perfect absorption is introduced by means of both magnetic resonance and electric resonance in meta molecules. A conventional metal-dielectric-metal MM absorber is proposed to obtain dual-band perfect absorption. It is clarified that the mechanism of dual-band absorption is due to fundamental (at 7.2 GHz) and third-order (at 18.7 GHz) magnetic resonances. Finally, we develop triple-band absorption by integrating resistors in to the MM absorber. The electric resonance, under the presence of resistors, matches the impedance of the MM absorber with the air at 13 GHz and gives rise to the new absorption band, with absorption higher than 90%.

Simple metamaterial structure enabling triple-band perfect absorber

Two resonators in metamaterial usually correspond only to two absorption peaks. In this report, by breaking the symmetry, we could create multi-fundamental resonances at GHz frequencies in both simulation and experiment. First, a dual-band metamaterial absorber (MA) was achieved for 4.6 and 10.6 GHz. Next, by modifying the relative position of inner square, the triple-band MA was obtained with enhanced absorption properties. In addition, dependence on the polarization of the incident electromagnetic (EM) wave was clarified. The mechanism is elucidated to be an alteration of the coupling strength, which is made by changing the geometrical configuration of the inner square and the outer ring. It is shown that our structural configuration can be applied to the fields where the interaction with a wide range of EM waves exists or is needed.

Polarization-independent, wide-incident-angle and dual-band perfect absorption, based on near-field coupling in a symmetric metamaterial

We numerically and experimentally investigated a dual-band metamaterial perfect absorber (MPA), utilizing the near-field coupling of double split-ring resonators (DSRRs). Owing to the near-field coupling between resonators, two arms in each DSRR resonate in different phases, leading to a dual-band perfect absorption. The proposed MPA also exhibits polarization-insensitive behavior and maintains the high absorption above 90% up to a wide range of incident angle more than 45°. Finally, to further consolidate our approach, a multi-band absorption is also studied by exploiting the near-field coupling among a larger number of DSRRs. Our work is expected to be applied to future broadband devices using MPA.

Ultra-subwavelength thickness for dual/triple-band metamaterial absorber at very low frequency

An integrated model utilizing external parasitic capacitors for a dual-band metamaterial perfect absorber (DMPA) is proposed and demonstrated in the UHF radio band. By adjusting the lumped capacitors on a simple meta-surface, the thickness of absorber is reduced to be only 1/378 and 1/320 with respect to the operating wavelength at 305 and 360.5u2009MHz, respectively. The simulations and the experiments confirm that the DMPA can maintain an absorption over 91% in a wide range of incident angle (up to 55°) and independent of the polarization of incident radiation. Additionally, we examine the integrated model for smaller dual-band absorber and absorption performance at higher frequencies (LTE band). Finally, we consolidate our approach by fabricating an ultrathin triple-band perfect absorber miniaturized to be only 1/591 of the longest operating wavelength. Our work is expected to contribute to the actualization of metamaterial-based devices working at radio frequency.

Flexible ultrathin metamaterial absorber for wide frequency band, based on conductive fibers

ABSTRACT Flexible and ultrathin wide-band metamaterial absorbers are suggested and demonstrated in the microwave-frequency range. By using resonators of different sizes and conductive fibers on metallic-pattern layer, the total thickness of metamaterial absorber is reduced to be only 1/349 with respect to the operating wavelength at 0.97 GHz. We present the absorption mechanism in terms of the impedance matching with the free space, the distributions of surface current and the three-dimensional distributions for power loss. In simulation, the absorption was over 97% at 0.97–6.12 GHz, and the corresponding experimental absorption band over 97% was 0.87–6.11 GHz. Furthermore, the dielectric substrate of metamaterial absorbers was replaced with flexible substrate in order to have the flexibility and the broadband absorption properties. The absorption band is expanded and the high-absorption performance maintains at the same time. The total thickness of metamaterial absorber comes to be only 1/5194 of the operating wavelength at 0.75 GHz. Our work is expected to contribute to the flexible microwave/electronic devices in the near future. Graphical Abstract

Reversibly-propagational metamaterial absorber for sensing application

We investigated a reversibly-propagational metamaterial perfect absorber (MPA) for X band using two separated identically-patterned copper layers, which were deposited on continuous dielectric FR-4...