Theoretical and experimental investigation of magnet and coil arrays optimization for power density improvement in electromagnetic vibration energy harvesters

Abstract

Power density is a critical evaluation indicator of electromagnetic vibration energy harvesters and has become one of the research hotspots. Therefore, it is of great significance to establish a simple and accurate theory to optimize and guide the design of an energy harvester for power density enhancement. Indeed, an alternating magnet array has a high flux gradient, which is one of the key factors for power enhancement. Under volume constraints, the coil output power is highly related to the magnet configuration, as the latter determines the magnitude of the flux gradient as well as the total flux mutation. Motivated by this, in this paper, an electromagnetic vibration energy harvester based on a coil array and a magnet array is proposed. The magnetic field distribution of rectangular magnets is analyzed. Then, a theoretical model based on Faraday's law of electromagnetic induction is derived to efficiently calculate the open-circuit voltage of coils with different numbers of magnets. After that, the optimal magnetic configuration is obtained based on the developed model without the need of measuring the parasitic damping of the energy harvester. Simulations and experiments verify the correctness of the theory. The results show that at an acceleration of 1 g and frequency of 41.2 Hz, the output power and power density reach a maximum of 3.71 mW and 106.68 μW/cm3, respectively, when the number of magnets m = 6, which is 2.58 times higher than the case of m = 3 and 2.06 times higher than the case of m = 12. The model proposed in this paper applies to the optimization of magnet array configurations of any volume, demonstrating the great benefits of power density enhancement.