Metamaterials and phononic crystals (PCs) with artificially designed periodic microstructures have attracted increasing research interests due to their unique properties that cannot be easily realized in natural materials. In recent years, the applications of metamaterials and PCs have been extended into the field of energy harvesting. A direct integration design strategy can yield a multifunctional system to suppress undesired vibrations/noise and convert them into electrical energy for providing power supply to widely distributed micro-electromechanical systems. Moreover, the defect state mode of metamaterials/PCs can localize the energy with an amplification effect, which has a great potential for improving energy harvesting efficiency. In addition, through tailoring the refractive index profile of metamaterials/PCs, the wave focusing phenomenon can be realized to boost the energy harvesting efficiency over a wide frequency range. This paper presents a comprehensive overview of the state-of-the-art advances in this direction over the past decade. According to the design strategies and working mechanisms, the existing studies in the literature on this topic are outlined and classified into three different categories. The advantages and disadvantages of various configurations are compared. The potential solutions to the existing drawbacks are discussed. An outlook on future prospects in this area is provided.

Mobile communication standards were developed for enhancing transmission and network performance by using more radio resources and improving spectrum and energy efficiency. How to effectively address diverse user requirements and guarantee everyone's Quality of Experience (QoE) remains an open problem. The Sixth Generation (6G) mobile systems will solve this problem by utilizing heterogenous network resources and pervasive intelligence to support everyone-centric customized services anywhere and anytime. In this article, we first coin the concept of Service Requirement Zone (SRZ) on the user side to characterize and visualize the integrated service requirements and preferences of specific tasks of individual users. On the system side, we further introduce the concept of User Satisfaction Ratio (USR) to evaluate the system's overall service ability of satisfying a variety of tasks with different SRZs. Then, we propose a network Artificial Intelligence (AI) architecture with integrated network resources and pervasive AI capabilities for supporting customized services with guaranteed QoEs. Finally, extensive simulations show that the proposed network AI architecture can consistently offer a higher USR performance than the cloud AI and edge AI architectures with respect to different task scheduling algorithms, random service requirements, and dynamic network conditions.

Conventional frequency-modulated LLC topology is unsuitable for ultra-wide voltage range applications and suffers from poor voltage regulation performance at light load conditions. To cope with those issues, this manuscript proposes a novel two-phase dual LLC resonant converter. The primary side of the proposed converter is two parallelled half-bridges LLC, and the transformers' secondary sides are in reverse series with shared full bridge rectifier. Both resonant tanks are driven by two fixed-frequency square waves, whose frequencies are always tuned at the optimal resonant frequency. A phaseshift is introduced between those two square waves to regulate the output voltage. The proposed topology demonstrates good voltage regulation performance, which is weakly dependent on the load condition. Zero-voltage switching and zero-current switching are well realized on the power MOSFETs and diodes in a wide range. A 1 kW rated laboratory prototype is designed to convert 390 V input to 10-420 V output. The prototype demonstrates a 98.1% peak efficiency and good voltage regulation capability. The experimental results agree well with the theoretical analysis.

The power conditioning interface circuit plays a crucial role in the energy harvesting (EH) capability enhancement in piezoelectric EH (PEH) systems. The principle of most existing synchronized switch circuits for PEH enhancement was summarized under the recently introduced synchronized multiple bias-flip (SMBF) model. The optimal bias-flip strategy derived from SMBF provides valuable insights for future circuit development. Based on such theoretical foundation, this paper implements a new interface circuit called the parallel synchronized triple bias-flip (P-S3BF) for further boosting the harvesting capability beyond the state-of-the-art solutions. By sophisticatedly allocating more bias-flip actions, it makes the best compromise between higher extracted power and lower dissipated power for power conditioning, toward maximum net harvested power. Moreover, the bias voltage reference in P-S3BF is self-contained and self-adaptive. Compared to the other existing solutions involving active voltage manipulations, these two conveniences brought in by P-S3BF are the most significant and necessary features, which facilitate the practical stand-alone implementation of P-S3BF under different periodic vibrations. Experimental result shows that, with the piezoelectric cantilever in use, which vibrates at a constant deflection magnitude, the P-S3BF circuit harvests 24.5% more power than its single bias-flip counterpart, the extensively studied parallel synchronized switch harvesting on inductor; and 287.6% more power than its null bias-flip counterpart, the standard EH bridge rectifier.

In this article, we introduce a vibration-powered sensing node (ViPSN), a programmable Internet-of-Things (IoT) platform for the development of vibration-powered or motion-powered sensing and transmitting systems. It leverages the exploitation and utilization of ambient vibration energy by using a piezoelectric transducer. The roles and relations of six necessary modules, including energy generation unit (EGU), energy transduction unit (ETU), energy enhancement unit (EEU), energy management unit (EMU), energy user unit (EUU), and edge demonstration unit (EDU) are discussed in detail. In particular, an enhanced EMU is proposed by making necessary complements to an extensively used off-the-shelf integrated circuit (IC) solution for piezoelectric transducers. It provides more comprehensive energy storage indicating signals, such that the sensing, computing, and transmitting tasks can be carried out more robustly by keeping a good awareness of the remaining energy. Owing to the enhanced EMU design, vibration energy in various forms, such as intermittent and transient ones, can be more effectively harvested and utilized. The performance of ViPSN is evaluated, in terms of its lifetime and Quality of Service (QoS), under different vibration scenarios. The inclusive design and affiliated opensource project of ViPSN help build a new ecosystem for the research and development of vibration- or motion-powered IoT systems.