Multi-functional microwave metamaterials offer a great solution for active components and modules that are potentially applicable in stealth, energy, and wireless communication systems/devices. However, it is challenging to realize a multi-functional behavior in a cost-effective and simple metamaterial system. This paper proposes and demonstrates a metamaterial inspired by origami building blocks that can be controlled by mechanical stimuli. By mechanically changing folding states, the proposed metamaterial can be switched from an ultra-broadband absorber to a reflector. In the compressed mode, the structure exhibits an absorption of more than 90% in a broad frequency range of 6–16 GHz. The absorption characteristic is insensitive to polarization angles and works with a wide range of incident angles. In the stretched mode, the absorption function is turned off and all the incident waves become reflected. Such origami-inspired metamaterials behave in multiple figures of merit involving bandwidth, frequency of operation, angle of polarization, and incidence.

In this work, we proposed a flexible broadband metamaterial perfect absorber (FBMPA) by exploiting a pasted conductive-graphene ink on a polyimide substrate. For the flat FBMPA, an absorption over 90% was found to cover a wide frequency range (from 7.88 to 18.01 GHz). The high-absorption feature was polarization-insensitive and regarded as stable with respect to the oblique incidence up to 30 degrees of electromagnetic wave. The high absorption was maintained well even when the absorber was wrapped. That is, the FBMPA was attached to cylindrical surfaces (with the varying radius from 4 to 50 cm). For both flat and curved states, the absorption mechanism was explained by the perfect impedance matching and the dielectric loss of the proposed absorber. Our work provides the groundwork for the commercialization of future meta-devices such as sensors, optical filters/switchers, photodetectors, and energy converters.

The structural, optical, and photocatalytic properties of TiO2 and Ag–TiO2 thin films grown by a hydrothermal method were studied by using an x-ray diffractometer, scanning electron microscope, energy-dispersive x ray, and UV–vis spectroscopy. The results indicated that all films were of single-phase and the Ag presence enhanced catalytic and water-splitting performances in the visible light region. In particular, the methylene blue solution was disintegrated up to 99% after 12 and 8 h for TiO2 and Ag–TiO2 films, respectively. Meanwhile, the splitting efficiency increased from 0.3% for TiO2 to 1% for Ag–TiO2. These performances demonstrate the great potential of Ag–TiO2 films in photocatalytic and water-splitting applications.

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