Power output of the nonlinear bistable energy harvester, conceived as a way to use heartbeats to power a pacemaker device . X-axis is the thickness of the piezoelectric layer. Credit Karami and Inman, Univ. of Mich.; Applied Physics Letters.
A heart-powered pacemaker? Although the concept may seem novel, the goal of eliminating a pacemaker’s battery (and the subsequent need to surgically replace the battery) via a piezoelectric device has been around for a while, and it appears that a group from the University of Michigan has solved some of the remaining problems and may be several steps closer to actually creating a working prototype of such a device.
First some background. As recently as 2008, United Kingdom researchers presented a paper at the American Heart Association’s Scientific Sessions 2008 describing some proof-of-concept successes related to a pacemaker based on heart energy-harvesting. At the time, the group’s microgenerator could generate only 17 percent of power needed for a pacemaker. (The group proposed that such a microgenerator could supplement the battery so that either a more elaborate electronic unit could be installed with no additional weight or extend the life of the battery in a standard pacemaker.) These researchers and a group of investors launched a start-up company, InVivo Technology, to continue the R&D and commercialize the product. However, little has been heard from InVivo since 2008 and the project website seems to be dead.
On the other side of the Atlantic Ocean, a group of researchers in the University of Michigan’s Department of Aerospace Engineering (which initially struck me as an unlikely location for this type of project) liked the idea of a self-powered pacemaker and decided to see if they could capture more heartbeat power than the UKgroup. Their idea was to engineer a ceramic “broadband” piezoelectric device, i.e., made to be sensitive to a larger range of frequencies delivering higher voltages through a combination of linear, nonlinear, monostable and bistable effects.
According to a UM news release, Amin Karami, a research fellow in the aerospace engineering and Daniel Inman, chair of the department, “have precisely engineered the ceramic layer to a [zigzag] shape that can harvest vibrations across a broad range of frequencies. They also incorporated magnets, whose additional force field can drastically boost the electric signal that results from the vibrations.”
No prototype exists, but Karami and Inman have run simulations demonstrating that a nonlinear, bistable harvester with a piezoelectric layer 80 µm thick should easily be able to power or recharge a pacemaker.
According to the release, “[T]he new device could generate 10 microwatts of power, which is about eight times the amount a pacemaker needs to operate, Karami said. It always generates more energy than the pacemaker requires, and it performs at heart rates from 7 to 700 beats per minute. That’s well below and above the normal range.” (The paper actually says the 80 µm device would generate 8 microwatts, but that would still be enough to accomplish their goals.)
So what is the connection between aerospace engineering and the pacemaker idea? Apparently Karami and Inman started creating designs and running simulations for broadband energy harvesting devices that would be built into lightweight drone airplanes, scavenging power from wing vibrations. Karami, Inman and Alper Erturk published an interesting paper for the UK’s Energy Harvesting Network in 2011, “Nonlinear Considerations in Energy Harvesting” (pdf) that describes some of the science and engineering behind the pacemaker concept.
Karami and Inman’s pacemaker concept is explained in more depth in a new paper, “Powering Pacemakers from Heartbeat Vibrations Using Linear and Nonlinear Energy Harvesters,” (doi:10.1063/1.3679102), which appears in Applied Physics Letters.
Their research is funded by the National Institute of Standards and Technology and the Institute for Critical Technology and Applied Science at Virginia Tech.