U. MICHIGAN (US)—Mini-generators could eventually produce enough electricity from random, ambient vibrations to power a wristwatch, pacemaker, or wireless sensor.
The energy-harvesting devices are highly efficient at providing renewable electrical power from arbitrary, non-periodic vibrations—a byproduct of traffic driving on bridges, machinery operating in factories, and humans moving their limbs, for example.
The Parametric Frequency Increased Generators (PFIGs) were created by Khalil Najafi, Schlumberger Professor of Engineering and a professor of biomedical engineering at the University of Michigan, and Tzeno Galchev, a doctoral student in the same department.
Most similar devices have more limited abilities because they rely on regular, predictable energy sources, says Najafi.
“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 downstairs, for example, cause vibrations that are non-periodic and occur at low frequencies,” Najafi says. “Our parametric generators are more efficient in these environments.”
Three prototypes have been built and a fourth 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, 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 produces charge when it is stressed.
This version has applications in infrastructure health monitoring and 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 (or 500 microwatts) 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. A milliwatt is 1,000 microwatts.
“The ultimate goal is to enable various applications like remote wireless sensors and surgically implanted medical devices,” Galchev says.
“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.”
Batteries are often an inefficient way to power the growing array of wireless sensors being created today, Najafi says. Energy scavenging can provide a better option.
“There is a fundamental question that needs to be answered about how to power wireless electronic devices, which are becoming ubiquitous and at the same time very efficient,” Najafi explains. “There is plenty of energy surrounding these systems in the form of vibrations, heat, solar, and wind.”
The research is funded by the National Science Foundation, Sandia National Laboratories, and the National Institute of Standards and Technology.
University of Michigan news: www.ns.umich.edu/