Transducer configurations for enhanced power density in cylindrical electromagnetic vibration energy harvesters

• A systematic comparison of cylindrical electromagnetic VEH transducers is presented. • A novel fully enclosed back iron design is proposed to concentrate the magnetic flux. • Simulations show the novel transducer improves magnetic flux density by 74 percent. • The magnetic flux leakage is reduced by over 99 percent for the novel transducer. • Tests show a max power of 44.50 mW and 4.25m W/cm 3 power density in 1 g vibrations. Vibration energy harvesters (VEHs) convert the mechanical energy of vibrations into electrical energy and can power wireless sensor networks. However, there are challenges to overcome in the development of practical VEHs that include maximizing the converted energy and energy density. This work presents a systematic comparison of cylindrical electromagnetic VEH transducers and a novel transducer configuration to address these challenges. An enclosure and spring system was designed, and a basic single cylindrical magnet transducer was established as a baseline. Multiple transducers were developed to investigate the use of opposing magnets and back irons to concentrate the magnetic flux. A novel transducer was introduced that incorporates a fully enclosed back iron. The transducers were simulated, fabricated, and tested experimentally. Simulations showed that the novel transducer enhanced the magnetic flux density by 74 percent from 0.23 T to 0.40 T over the coil and reduced the magnetic flux leakage by over 99 percent from 0.15 T to 3.6 × 10 −5 T below the transducer. These results show that the novel transducer effectively channels the magnetic flux over the coil and nearly eliminates magnetic flux leakage. Experimental tests in vibrations of 60 Hz and 1 g RMS demonstrated a maximum power generation of 44.50 mW and a power density of 4.25 mW/cm 3 for the novel design, representing an improvement in power density of 103 percent over the basic transducer. This study demonstrates that opposing magnets and back irons can be used to enhance the power density of electromagnetic VEH transducers and improve the overall practicality of VEHs.