ON THE RESONANCE/BANDWIDTH-COUPLING RELATIONSHIP OF ELECTROMAGNETIC VIBRATION ENERGY HARVESTER WITH A NON-VARYING MAGNETIC FLUX DENSITY

An investigation on how the degree of coupling determined by the coil size and the magnet spacing affects the bandwidth and or resonance of an electromagnetic vibration energy harvester was presented in this work. The vibration energy harvesting model was realized as a magnet mounted on a linear spring, the response of the magnet was however constrained using a mechanical slider/guiderail. The guiderail introduces another Coulomb damping different from the mechanical and electromagnetic damping into the model. The transduction coil is fixed with the base such that during excitation, the response of the magnet over the guiderail induces field in the coil, thereby generating electrical energy. Six different coil geometries of widths 4.00 mm, 6.00 mm, 8.00 mm, 10.00 mm and 12.00 mm were tested within two different magnet spacing configurations realized as a fixed spacing (14.00 mm) and variable spacing. The variable space corresponds to the coil width added to 2.00 mm clearance spacing. To establish a baseline for effective performance comparison between different models analyzed, the respective mechanical property such as the mechanical damping coefficients, mechanical stiffness and the model inertia masses are fixed The magnetic flux density on each designs were simulated on a Finite Element Magnetic Software (FEMM) software while the actual harvested voltage, power, optimum load capacity, resonance/bandwidth were queried in the MATLAB using relevant analytical governing equations. According to the Ohm's law, the harvested voltage-resistance relationship indicates that using smaller coil in larger magnet spacing is beneficial for realizing vibration harvester model suitable for powering high current, low impedance sensor since such configurations is characterized by low optimum impedance. However, using coil geometries with commensurate spacing will realize capacity for operating low current, high impedance sensor because the optimum impedances are quite higher. Also, comparing similar geometry shows that the power density improved by 30.74 %, 18.06 %, 14.75 %, 7.29 % and 0 %, on coil geometries 4.00 mm, 6.00 mm, 8.00 mm, 10.00 mm and 12.00 mm respectively.