Tiny generators harvest energy from natural motions

The Parametic Frequenzy increased Generators (PFIGs)  could produce enough electricity from random, ambient vibrations to power a wristwatch, pacemaker or wireless sensor. They are highly efficient  at providing renewable power from arbitrary, nonperiodic vibrations. The generators have demonstrated that they can produce up to  0,5 miliwatts ( or 500 microwatts) from typical vibration amplitudes found on the human body. That is 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 energy-harvesting devices were  created by Khalil Najafi,  and Tzeno Galchev, experts of electrical and computer engineering. They have built three prototypes and a forth is forthcoming. 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.

 ‘Batteries are often an inefficient way to power the growing array of wireless sensors being created today’ said Najafi. ‘ They  have more limited abillities, because the rely on regular, predictable energy sources.  But these tiny generators  are working  in environments of traffic driving, on  a busy street or bridge or in a tunnel, machinery operating and people walkin up and down stairs, for example.  This kinetic energy surrounding us every day does not occur in periodic, repeatable patterns.

The ultimate goal is to enable various applications like remote wireless sensors and surgically  implanted medical devices. 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.



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