March 22, 2012
ANN ARBOR, Mich. - Tiny generators developed at the University of
Michigan could produce enough electricity from random, ambient
vibrations to power a wristwatch, pacemaker or wireless sensor.
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, for example.
The Parametric Frequency Increased Generators (PFIGs) were
created by Khalil
Najafi, chair of electrical and computer engineering, 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, said Najafi, who is
the Schlumberger Professor of Engineering and also a professor
in the Department of Biomedical Engineering.
"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
The researchers have built three prototypes 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. 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
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
"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."
Batteries are often an inefficient way to power the growing
array of wireless sensors being created today, Najafi said.
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 said.
"There is plenty of energy surrounding these systems in the form
of vibrations, heat, solar, and wind."
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.
The research is funded by the National Science Foundation,
Sandia National Laboratories, and the National Institute of
Standards and Technology.
The university is pursuing patent protection for the
intellectual property. Galchev and a team of engineering and
business students are working to commercialize the technology
through their company, Enertia. Enertia recently won first place
in the DTE/U-M Clean Energy Prize business plan competition and
second place in the U-M Zell Lurie Institute for Entrepreneurial
Studies' Michigan Business Challenge. Other members of the team
are Erkan Aktakka, and Adam Carver. Aktakka is an electrical
engineering doctoral student. Carver is an MBA student at the
Ross School of Business.
U-M Press Release (by Nicole Casal-Moore)
Related Topics: Energy Energy Scavenging MEMS and microsystems Najafi, Khalil Sensors