Enhancing output power of rotational electret energy harvester by synchronized switch harvesting on inductor

A nonlinear interface circuit, known as synchronized switch harvesting on inductor (SSHI), for in-plane rotational electret kinetic energy harvesters (EHs) was developed. An explicit generator model is derived to verify the applicability of SSHI, which was originally proposed for the piezoelectric EH, on an in-plane electret EH. Experimentally, 505 μW was harvested with SSHI at a rectified voltage of 142 V for an in-plane rotational electret EH rotating at 1 rps, which is 2.47 times of that with a full-bridge rectifier, and which is in good agreement with the simulation result. The circuit efficiency and criteria for the inductor selection were clarified through circuit analysis based on spice simulation. It is found that the power dissipation of voltage-divider and rectification diodes becomes pronounced as the load voltage increases, constraining the efficiency. The inductor, which usually dominates the circuit volume, can be miniaturized for electret EHs, because the voltage inversion ratio, a benchmark of the SSHI performance, turns out to be insensitive to the series resistance of the inductor. The self-powering ability of the proposed circuit is also presented.

Analytic Elements from Separation of Variables

Separation of variables provides influence functions for analytic elements, which extend the solutions available with complex functions to problems involving the Helmholtz and modified Helmholtz equations. Methods are introduced for one-dimensional problems that provide the background vector field for many problems, and these solutions are extended to finite domains with interconnected rectangle elements in Section 4.3. Circular elements are developed in Section 4.4 using series of Bessel and Fourier functions to model wave propagation around and through collections of elements, and vadose zone solutions are extended to solve the nonlinear interface conditions occurring along circles. Methods are extended to three-dimensional problems for spheres (Section 4.5), and prolate and oblate spheroids in Section 4.6.

Structuring Nonlinear Wavefront Emitted from Monolayer Transition-Metal Dichalcogenides

The growing demand for tailored nonlinearity calls for a structure with unusual phase discontinuity that allows the realization of nonlinear optical chirality, holographic imaging, and nonlinear wavefront control. Transition-metal dichalcogenide (TMDC) monolayers offer giant optical nonlinearity within a few-angstrom thickness, but limitations in optical absorption and domain size impose restriction on wavefront control of nonlinear emissions using classical light sources. In contrast, noble metal-based plasmonic nanosieves support giant field enhancements and precise nonlinear phase control, with hundred-nanometer pixel-level resolution; however, they suffer from intrinsically weak nonlinear susceptibility. Here, we report a multifunctional nonlinear interface by integrating TMDC monolayers with plasmonic nanosieves, yielding drastically different nonlinear functionalities that cannot be accessed by either constituent. Such a hybrid nonlinear interface allows second-harmonic (SH) orbital angular momentum (OAM) generation, beam steering, versatile polarization control, and holograms, with an effective SH nonlinearity χ2 of ~25 nm/V. This designer platform synergizes the TMDC monolayer and plasmonic nanosieves to empower tunable geometric phases and large field enhancement, paving the way toward multifunctional and ultracompact nonlinear optical devices.

A Nonlinear Electromagnetic Energy Harvesting System for Self-Powered Wireless Sensor Nodes

The Internet of things requires long-life wireless sensor nodes powered by the harvested energy from environments. This paper proposes a nonlinear electromagnetic energy harvesting system which may be used to construct fully self-powered wireless sensor nodes. Based on a nonlinear electromagnetic energy harvester (EMEH) with high output voltage, the model of a nonlinear interface circuit is derived and a power management circuit (PMC) is designed. The proposed PMC uses a buck–boost direct current-direct current (DC–DC) converter to match the load resistance of the nonlinear interface circuit. It includes two open-loop branches, which is beneficial to the optimization of the impedance matching. The circuit is able to work even if the stored energy is completely drained. The energy harvesting system successfully powered a wireless sensor node. Experimental results show that, under base excitations of 0.3 g and 0.4 g (where 1 g = 9.8 m·s−2) at 8 Hz, the charging efficiencies of the proposed circuit are 172% and 28.5% higher than that of the classic standard energy-harvesting (SEH) circuit. The experimental efficiency of the PMC is 41.7% under an excitation of 0.3 g at 8 Hz.