Piezoelectric energy harvesters are devices capable of converting the kinetic energy present in vibration-based motion into electrical energy using piezoelectric transducers. This kind of device has its maximum efficiency when the exciting frequency matches its natural frequency. In the past years, some authors have explored the use of human motion as a vibration source, and harvesting energy in this situation is not trivial because the low-frequency characteristics of the motion are not compatible with small, light-weight transducers, which have relatively high natural frequencies. To overcome this problem, a method known as frequency up-conversion is used; it consists of a nonlinear vibration-based, magnetically excited harvester that exhibits frequency-independent performance, allowing the device to be efficient in a wide band of frequencies. In this work, the power output of a piezoelectric energy harvesting with frequency up-conversion submitted to walking and running vibrations is analyzed. Data are collected using an accelerometer located on the front pocket of each subject and then used in simulations. The model used consists of a cantilever beam with a permanent magnetic tip at the free end; this tip interacts with a magnetized structure that adds a nonlinear interaction to the model. A pure resistance matching the device’s impedance at its fundamental frequency is used to account for the output power. To verify the advantages of using the frequency up-conversion method for vibration-based energy harvesters regarding the power output and frequency band, a comparison with the linear cantilever model is analyzed. Also, in order to confirm the simulation results, a prototype of the device is built and submitted to vibration tests using a horizontally oriented motor-driven cart that recreates the motions recorded by the accelerometer; it is tested with and without the magnetic force in order to experimentally determine the nonlinearity’s effects on the power harvesting performance.

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