Forest fires present a great threat as they can rapidly grow and become large, resulting in tragic loss of life and property when occurring near occupied land. Here a self‐powered fire alarm system based on a novel multilayered cylindrical triboelectric nanogenerator (MC‐TENG) that can produce electrical power for the detection sensors by harvesting the kinetic energy of moving tree branches in a forest is presented. The major parameters for harvesting the kinetic energy using the proposed MC‐TENG are investigated, including the number of triboelectric layers, the frequency, the amplitude of external excitation, and the orientation between motion direction and device configuration. The fabricated MC‐TENG results in a peak power of 2.9 mW and a maximum average power of 1.2 mW at a low frequency of 1.25 Hz. The integrated self‐powered forest fire alarm system, consisting of fire sensors, a carbon‐based micro‐supercapacitor, and the MC‐TENG, is demonstrated to be able to report fire risk or hazard efficiently, accurately, and robustly. This study provides a new solution to reduce the forest fire risk through a portable and sustainable alarm system by effectively harvesting kinetic energies in natural environment with TENG technology.

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SUMMARYAn extension of the material design problem is presented in which the base cell that characterizes the material microgeometry is polygonal. The setting is the familiar inverse homogenization problem as introduced by Sigmund. Using basic concepts in periodic planar tiling it is shown that base cells of very general geometries can be analysed within the standard topology optimization setting with little additional e ort. In particular, the periodic homogenization problem deÿned on polygonal base cells that tile the plane can be replaced and analysed more e ciently by an equivalent problem that uses simple parallelograms as base cells. Di erent material layouts can be obtained by varying just two parameters that a ect the geometry of the parallelogram, namely, the ratio of the lengths of the sides and the internal angle. This is an e cient way to organize the search of the design space for all possible single-scale material arrangements and could result in solutions that may be unreachable using a square or rectangular base cell. Examples illustrate the results.

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In article number 2003598, Changyong Cao and co-workers design a novel high-performance multilayered cylindrical triboelectric nanogenerator (MC-TENG) to harvest the kinetic energy of tree branches for powering a fire sensing system in a forest. The self-powered alarm system can wirelessly send warning messages and fire locations to forest firefighters. Early detection of forest fires can minimize the possible damage and casualties caused by the rapid spread of fires.