Chinese researchers have successfully built an electromagnetic absorbing device for microwave frequencies. The device, made of a thin cylinder comprising 60 concentric rings of metamaterials, is capable of absorbing microwave radiation, and has been compared to an astrophysical black hole (which, in space, soaks up matter and light).
An omnidirectional perfect electromagnetic absorber may have many applications in science and engineering, such as cross-talk reduction in optoelectronic devices or solar light harvesting. However, in reality, few of the actual materials come close to 100 per cent absorption of electromagnetic waves from all directions. It is possible to reach near total absorption based on existing methods, but this is generally limited to a specific range of incidence angles.
Main results. In this work, we realize an omnidirectional electromagnetic absorber for the first time in the microwave frequencies, based on a previous theoretical work using non-magnetic metamaterials. We designed and fabricated the omnidirectional absorbing device using non-resonant metamaterials in the external layer and resonant metamaterials in the internal core, and measured the electric-field distributions using the planar-waveguide near-field scanning apparatus. Experimental results show good agreement with full-wave numerical simulations. Numerical results show that the absorption rate can reach 99 per cent in the microwave frequency.
Wider implications. The designed omnidirectional absorbing device can trap and absorb electromagnetic waves coming from all directions spirally inwards without any reflections due to the local control of electromagnetic fields. Hence it behaves like an 'electromagnetic black body' or an 'electromagnetic black hole' to some extent. Since the lossy core of the device can transfer the electromagnetic energies into heat energies, it is expected that the omnidirectional absorber could find important applications in thermal emitting and electromagnetic-wave harvesting. The more important message is that artificial metamaterials will prove remarkably more helpful and more useful for modern science and engineering.
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