Study On Wideband Micro Electro Magnetic Vibration Energy Harvester Based On MEMS Technology

The recent advances in microelectronics technology and the design of ultra low power VLSI systems have been making various electronic devices smaller, wireless, portable and low power consumption, and led to many new applications such as medical implants, embedded sensors and wireless sensor networks. How to power these micro devices effectively is becoming a key question while they are often used in very bad environment inaccessible to mankind or completely embedded in the structures without any physical connection to the outside world. So they have very high requirements for the volume, cost, lifetime and performance of power supply. Energy scavenging which transform light, heat and kinetic energy available in ambient environment into electrical energy is a very attractive alternation to batteries, where power source replacement or recharging is impractical. Mechanical vibrations seem to be the most promising energy source since they are abundant in many environments.This dissertation mainly focuses on electromagnetic vibration energy harvester based on MEMS technology. A novel wideband electromagnetic vibration energy harvester is presented in this work; the energy harvester prototype is fabricated by MEMS technique, and the performance of the prototype is measured and analyzed in detail. The main work and the conclusion of this dissertation are in the following:The physical model of the electromagnetic vibration energy harvester was build including the physical model of vibration harvesting system and that of energy conversion system. The dynamic response of vibration harvesting system under different vibration excitation was solved and used to analyze the influence of damping ratio and vibration frequency on the amplitude- frequency and phase-frequency characteristics. A micro electromagnetic vibration energy harvester based on MEMS technology was presented which includes a double-layer copper coil and a planar nickel spring with an NdFeB permanent magnet suspended on the SU-8 frame. Structure static analysis, modal analysis and harmonic analysis of the magnet-spring system were carried out using finite element analysis software--ANSYS. The four different planar springs have the same outer/inner dimensions and the same linear stiffness calculated by ANSYS. The minimum nonlinear deflection of the springs is 0.372mm at the load of 15mN, while the maxim result is 0.693mm and the linear result is supposed to be 0.870mm. The spring samples and prototypes were fabricated and were tested to compare their nonlinearity in both static elasticity coefficient and dynamic response including amplitude-frequency curve, peak-peak output voltage and the bandwidth for above 30mV output voltage, which demonstrated that the energy harvester output bandwidth could be improved by careful consideration of the nonlinearity of the spring and the largest bandwidth frequency was 33Hz.