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We propose a single low-profile skin metasurface carpet cloak to hide objects with arbitrary shape and size under three different waves, i.e., electromagnetic (EM) waves, acoustic waves and water waves. We first present a metasurface which can control the local reflection phase of these three waves. By taking advantage of this metasurface, we then design a metasurface carpet cloak which provides an additional phase to compensate the phase distortion introduced by a bump, thus restoring the reflection waves as if the incident waves impinge onto a flat mirror. The finite element simulation results demonstrate that an object can be hidden under these three kinds of waves with a single metasurface cloak.

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Energy and the environment are two of the main issues facing the world today. As a consequence abundant renewable green energy sources such as wave energy, have become hot topics. Here, a multiple‐frequency triboelectric nanogenerator based on the water balloon (WB‐TENG) is proposed for harvesting water wave energy in any direction. Owing to the high elasticity of the water balloon, the WB‐TENG can realize a multiple‐frequency response to low‐frequency external mechanical simulations to generate high‐frequency electrical output. In addition, the water balloon can achieve self‐support without any additional supporting structure because of its tension, to make WB‐TENG still produce electrical output under slight vibration, which can also bring high energy conversion efficiency. Moreover, the fabricated WB‐TENG generates a maximum instantaneous short‐circuit current and an open‐circuit voltage of 147 µA and 1221 V, respectively. Most noteworthy, under the same conditions, the total transferred charge of WB‐TENG is 28 times than that of traditional TENG based on double plate structure during one working cycle. Therefore, this design can provide an effective way to promote the development of TENGs in blue energy.

Plug-in electric vehicle (PEV) technology has drawn increasing amounts of attention in the last decade. As the world's largest automotive market, China has recently made the electrification of transportation central to its national strategic plan. Because of the unique nature of the vertically regulated power industry, China's massive deployment of PEVs has to face unique challenges that may not be encountered by any other country/region. Therefore, a comprehensive coordinated PEV charging scheme is urgently needed to facilitate the smooth grid integration of PEVs at all levels (e.g., transmission systems, distribution systems, and charging stations). This paper presents detailed mathematical modeling of a novel hierarchical framework for coordinated PEV charging at multiple timescales (i.e., day-ahead and real-time). The proposed three-level (e.g., provincial level, municipal level, and charging station level) PEV charging strategy jointly optimizes system load profile and charging costs while satisfying customer charging requirements. The interrelationships between various levels in terms of energy transaction and information exchange are clearly identified. Case studies on Guangdong Province, China, are carried out and simulation results demonstrate the effectiveness of our proposed hierarchical control framework in reducing system peak demand and charging costs.

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