Design of nonlinear springs for wideband magnetic vibration energy harvester

This paper compares four nonlinear springs for the micro power generator (MPG) application which convert low level vibration energy into electrical power. The magnet-spring system decides the generator's resonant frequency, and this work proves that the spring's nonlinearity level influences the width of the operating frequency. 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 were fabricated with lithography, etching, and microelectroplating technology 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 33 Hz.