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.

Non-resonant vibration energy harvesters (VEHs) attract much attention for the excellent performance in scavenging ambient low-frequency and broadband vibrations. In this paper, effects of the mild steel sheets, thicknesses of the magnets and coils, wire diameter of coils, and inner dimension of the coils on the outputs of a non-resonant electromagnetic vibration energy harvester (EMVEH) were simulated and the optimized geometries was obtained. Numerical simulations show that the mild steel sheets can enlarge the magnetic flux density about 25.0%, agreeing well with the experimental result that the output voltage increased about 29.3%. Under a base excitation of 0.3 g (where 1g = 9.8 m s−2) at 8.3 Hz, the RMS voltage across a 10.4 kΩ resistor of an EMVEH prototype, with the inner volume of 76.26 cm3, is about 15.53 V. The power density is about 304 µW cm−3, about 18.7% higher than the previous device.