High-density stacked microcoils integrated microminiaturized electromagnetic vibration energy harvester for self-powered acceleration sensing

With the rapid development of microelectronics and flexible electronics technology, self-powered sensors have significant application prospects in human-machine interface systems and Internet of Things. However, piezoelectric- and triboelectric-based sensors have low current output and are easily affected, while electromagnetic-based sensors are difficult to miniaturize. This work proposes a high-density stacked microcoil integrated microminiaturized electromagnetic vibration energy harvester (EVEH). The double-layer high-density microcoil is fabricated on both sides of the flexible polyimide substrate interconnected via the central through-hole. Owing to reduced single coil line width, line spacing, and stacked structure, the number of turns can be substantially enhanced. Moreover, the relative position of the coils and magnet has a considerable influence on the performances; due to the huge change rate in magnetic flux when the coil is placed in the radial direction of the magnet than in the axial direction, the open-circuit voltage in the radial direction is 10 times greater. The microcoil can maintain good performance at high, low temperatures and under bending conditions. When the distance between the ends of the coil changes from 2 to 20 mm in 2 mm steps, the bending angle of the coil changes from 45° to 270° in 45° steps; furthermore, when the coil is exposed to −40 and 60°C conditions, the coil resistance is maintained at approximately 447 Ω. The peak open-circuit voltage of three-piece microcoils reaches 0.41 V at 4 Hz under 2g, and the output voltage and current increase with an increasing number of stacked layers. These excellent properties indicate that EVEH can be used for self-powered acceleration sensing. The sensitivity is measured to be 0.016 V/(m/s 2 ) with a correlation coefficient of 0.979 over the acceleration range of 1–18 m/s 2 . Thus, the developed microminiaturized EVEH has enormous potential for self-powered sensing applications in confined spaces and harsh environments.