Flexible perfect metamaterial absorbers for electromagnetic wave

The flexible metamaterials (MMs) provide a new field in controlling electromagnetic waves. This paper comprises the MMs made on flexible and elastic substrates, together with the relevant techniques and approaches. The perspective is also described, which includes the possible conversion of investigated MMs into practical devices. For an example of the research and development so far in this fascinating area, by using a planar and flexible MM, the low-frequency perfect absorption has been obtained even with very small unit-cell size in snake-shape structure. These shrunken, deep-sub-wavelength and thin MM absorbers were numerically and experimentally investigated by increasing the inductance. The absorbers are specially designed for absorption peaks around 2 GHz and 400 MHz, which can be used for depressing the EM noise from everyday electronic devices and mobile phones. It has been reported new concept of water droplet-based MM perfect absorber absorbing perfectly electromagnetic wave with water, an eco-friendly material which is very ordinary and plentiful on the earth. If arranging water droplets with particular height and diameter on material surface, meta-properties absorbing electromagnetic wave perfectly in GHz broadband were shown. It was possible to control absorption ratio and absorption wavelength band of electromagnetic wave according to the shape of water droplet and apply to various flexible and/or transparent substrates such as plastic, glass, and paper. These results can lead wide applications to variously civilian and military products in the future by providing perfect absorber of broadband in all products including bendable and transparent materials.