The first demonstration of an optofluidic metamaterial is reported where resonant properties of every individual metamolecule can be continuously tuned at will using a microfluidic system. This is called a random-access reconfigurable metamaterial, which is used to provide the first demonstration of a tunable flat lens with wavefront-reshaping capabilities.

Abstract. The sensor data collection satellite (SDCS) system, as a part of the Internet of Things (IoT), enables data transmission in areas without Internet and mobile communication coverage. A novel technology named LoRa for Low power wide area network (LPWAN) enables energy-efficient communication over long distances, which can meet the requirement of energy-constraint in SDCS system. However, the LoRaWAN as the MAC protocol of LoRa has the problem of initial channel allocation and power selection if directly used in SDCS system. In this paper, we propose a SA-LoRaWAN protocol for power adaptation based on position information of sensors and satellite, and sensors can dynamically access channel according to the packet buffer size. We use OPNET to model SDCS system based on SA-LoRaWAN protocol, and the simulation results demonstrate that the proposed protocol can reduce the energy consumption and improve the packet delivery rate.

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In this work, an innovative vibration energy harvester is designed by using the point defect effect of two-dimensional (2D) magneto-elastic phononic crystals (PCs) and the piezoelectric effect of piezoelectric material. A point defect is formed by removing the central Tenfenol-D rod to confine and enhance vibration energy into a spot, after which the vibration energy is electromechanically converted into electrical energy by attaching a piezoelectric patch into the area of the point defect. Numerical analysis of the point defect can be carried out by the finite element method in combination with the supercell technique. A 3D Zheng-Liu (Z-L) model which accurately describes the magneto-mechanical coupling constitutive behavior of magnetostrictive material is adopted to obtain variable band structures by applied magnetic field and pre-stress along the z direction. The piezoelectric material is utilized to predict the output voltage and power based on the capacity to convert vibration energy into electrical energy. For the proposed tunable vibration energy harvesting system, numerical results illuminate that band gaps (BGs) and defect bands of the in-plane mixed wave modes (XY modes) can be adjusted to a great extent by applied magnetic field and pre-stress, and thus a much larger range of vibration frequency and more broad-distributed energy can be obtained. The defect bands in the anti-plane wave mode (Z mode), however, have a slight change with applied magnetic field, which leads to a certain frequency range of energy harvesting. These results can provide guidance for the intelligent control of vibration insulation and the active design of continuous power supply for low power devices in engineering.

The present study investigated the intelligent control of both band gaps (BGs) and energy harvesting based on the point defect of magneto-elastic acoustic metamaterial and piezoelectric effect. The numerical results obtained by the finite element method indicate that band structures and frequency range of acoustic energy harvesting can be modulated significantly by an applied magnetic field, which leads to broadband BGs and promotes the electromechanical energy conversion efficiency. Consequently, the proposed structure can provide new avenues for designing of both tunable acoustic insulator and a broad-distributed energy harvester in engineering fields.