Electromagnetic Vibrational Energy Harvesters and Power Management

Abstract

The interest in scavenging various energy sources from the environment is rapidly increasing. Thanks to the advances in developing effective energy harvesters researches. Kinetic energy is a renewable source and it can be found numerously in the environment. One of the most popular class of the kinetic energy harvesters in this field is vibration energy harvesters (VEH). It is an electrical source that converts the vibrational energy into usable electrical energy to power up low-power portable or unreachable devices. The harvesting system can be self-powered as stand-alone or as alternative power source depending on the application.

In this thesis, we have studied and developed two architectures for electromagnetic VEHs: a baseline VEH and a springless VEH. We introduced and studied power management circuits consisting of a full-wave bridge rectifier and a smoothing capacitor. Moreover, electromechanical model was developed and validated by the comparison to the experimental data.

The basic electromagnetic VEH uses a mechanical mass-damper-spring oscillator to capture kinetic energy from vibrations. It has an electrical transducer using induction between a moving coil and a fixed magnets. It uses a cantilever suspension and operates at a frequency range of 57-59 Hz. We re-designed it using 80 turns coil-chip instead of 30-turns. The springless VEH works in a frequency range of 13-18 Hz. It was redesigned to carry 60-turns coil-chip. The re-design of the VEHs successfully increased the output voltage and power. The maximum power experimentally measured were 14.3mW and 12.27mW at optimal loads RL of 40 ohm and 3 ohm, respectively.

The power management circuits introduced is consist of a MOSFET-based full-wave bridge rectifier and a smoothing capacitor to convert the VEH AC output waveform into a DC signal. We found that this rectifier can effectively convert the VEHs output with high voltage and power efficiencies > 93 %. The smoothing capacitor trades-in the signal ripples for lower voltage and power e efficiencies > 79 %.

We identified the model parameters for the cantilever VEH, namely the natural frequency, mechanical Qm and total Qt quality factors, and effective average magnetic field density B. We solved the model equations numerically and analytically to find the eigenvalues, frequency response, output voltage and power. The model results agree with the obtained experimental results.