FINNISH RESEARCHERS CONVERT MECHANICAL VIBRATIONS TO ELECTRICITY

Scientists at the VTT Technical Research Center in Finland have devised a new method for converting mechanical vibrations to electricity

The surface of any given material has a property called a work function, which is defined as the difference between the energy of an electron at rest and the minimum thermodynamic work required to remove it from the material. The researchers discovered that the vibrational energy produced when two surfaces with different work functions are connected via electrodes can be “harvested” and potentially used to power wearables and other low-power electronics. Photoelectric devices, cathode-ray tubes and electronic circuits involving different metals often employ this same principle, though never before has it been used in energy harvesting.

The team first created a parallel-plate capacitor with copper and aluminum that was hooked up to an external circuit, with the plates’ respective work functions providing an initial one volt charge as electrons bounced from one surface to the other. Higher voltages could in theory result from different electrode materials – over 3 V with wide band-gap semiconductors or over 5 V with n and p-type diamond. With the copper plate fixed in place, a motor vibrated the aluminum plate perpendicular to both plates, either continuously or in pulses. Running simulations of their work function energy harvester in realistic microelectromechanical systems (MEMS) scenarios helped the scientists to determine that the built-in voltage could lead to output power over one order of magnitude higher when the vibration frequency is matched with the mechanical resonance frequency of the device.

One advantage of work function energy harvesters over the piezoelectric and electrostatic devices that generate electricity from mechanical vibrations to power many sensors and medical implants is that they don’t require an external power source or electret materials (electrostatic magnets) and are able to generate more power in a wider range of operating conditions. Though VTT cautions that MEMS simulations still need to be performed, the researchers predict that this technology should be industrially feasible in the next three to six years.