An electrostatic springless inertial harvester for converting multi-dimensional low-frequency motion

This paper introduces a new type of energy harvester for converting multi-axial and low-frequency motion from humans and the environment into the electrical domain. An innovative array of electrostatic transducer cells is used to convert the mechanical energy captured from the environment by a freely rolling spherical magnetic proof mass. The magnet never comes in contact with the transducer cells but rather transfers energy via magnetic coupling. The inertial mass attracts a magnetic fluid/ferrofluid and causes it to actuate a variable-gap capacitor. A micromachined prototype is fabricated and used to demonstrate that repeatable capacitance changes are possible from magnet velocities in the range of 2-18 mm/s. A cubic NdFeB magnet of grade N42 with a 5 mm edge length can generate 16 pF capacitance transitions at a distance of 0.5 mm from the surface of the transducer array. An energy density of 9 mJ/mm can be expected with a 100 V pre-bias.