Parametric Frequency Increased Generators harvest vibrations

There are many power sources today as wind power, hydro-power, tidal, geothermal, solar power as well as the power used in wristwatches, where oscillations that occur while we move our hand power the watch. Researchers from the University of Michigan are developing a similar, more sensitive, technology. Their small generators could produce enough electricity from random, ambient vibrations.

The energy-harvesting devices, created at U-M’s Engineering Research Center for Wireless Integrated Microsystems, are highly efficient at providing renewable electrical power from arbitrary, non-periodic vibrations. This type of vibration is a byproduct of traffic driving on bridges, machinery operating in factories and humans moving their limbs, or noise, for example.

The Parametric Frequency Increased Generators (PFIGs) are being developed by Khalil Najafi, Schlumberger Professor of Engineering and also a professor in the Department of Biomedical Engineering., and Tzeno Galchev, a doctoral student in the same department.

“The vast majority of environmental kinetic energy surrounding us everyday does not occur in periodic, repeatable patterns. Energy from traffic on a busy street or bridge or in a tunnel, and people walking up and down stairs, for example, cause vibrations that are non-periodic and occur at low frequencies,” Najafi said. “Our parametric generators are more efficient in these environments.”

The researchers have built three prototypes and a fourth is under development. In two of the generators, the energy conversion is performed through electromagnetic induction, in which a coil is subjected to a varying magnetic field. This is a process similar to how large-scale generators in big power plants operate.

The latest and smallest device, which measures one cubic centimeter, uses a piezoelectric material, which is a type of material that produces charge when it is stressed. This version has applications in infrastructure health monitoring. The generators could one day power bridge sensors that would warn inspectors of cracks or corrosion before human eyes could discern problems.

The generators have demonstrated that they can produce up to 0.5 milliwatts from typical vibration amplitudes found on the human body. That’s more than enough energy to run a wristwatch, which needs between one and 10 microwatts, or a pacemaker, which needs between 10 and 50.

“The ultimate goal is to enable various applications like remote wireless sensors and surgically implanted medical devices,” Galchev said. “These are long lifetime applications where it is very costly to replace depleted batteries or, worse, to have to wire the sensors to a power source.”

These generators could also power wireless sensors deployed in buildings to make them more energy efficient, or throughout large public spaces to monitor for toxins or pollutants.

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