I had the opportunity last week to talk to Dr. Xudong Wang from the University of Wisconsin about his research into energy harvesting using nanfibers. By coincidence this came just a week after I talked to Dr. Krupenkin about his energy harvesting technology. They are similar in that they generate energy using the electrostatic force to move current rather than by moving a wire through a magnetic field as in a traditional generator.
Nanofiber energy harvesting uses materials that develop a charge when mechanical compression deforms their crystalline structure. This happens in materials made of atoms with a high disparity of charge. The compression causes one side of the material to have more atoms of a positive charge while the other side has more negatively charged atoms. PVDF is common material with this property. It can develop several volts when compressed.
Dr. Wang is researching ZnO because it can be grown into nanofibers and it is not toxic to the human body, so it may therefore lend itself to powering medical implants. Nanofibers can be located in an assembly in which wires or other nanofibers brush against them, causing them to develop a charge. This charge can be collected and stored in a battery or capacitor.
The ZnO nanofibers typically only develop hundreds of millivolts, which makes it harder to harness than energy from PVDF. How to collect charge efficiently from low-voltage sources is outside Dr. Wang's focus.
The energy from airflow can be harvested from a thin film using this property by allowing the film to oscillate in the wind. This has been demonstrated with PVDF. If researchers can make this work with very thin films using nanotechnology, tiny amounts of power could be harvested from the airflow associated with respiration. It would be good to see a productive use for a phenomenon that has become a metaphor for general engineering failure owing to the case of Galloping Gertie.
This technology touches me personally because my mother-in-law has a pacemaker. Her doctors are monitoring its battery's charge. Replacing the battery requires surgery, which can always be risky in people with health problems. So deciding at which point to change the battery becomes tricky decision. One application Dr. Wang talked about was pacemakers. The heart undergoes a lot of motion from which energy could be harvested. If this technology could provide even some of the power for a pacemaker, it would be a huge benefit to patients.
As with all energy harvesting, my impression is someone needs to find a "killer app" for it. I'm not clear whether enough charge could be collected from nanofibers to put a dent in a pacemaker's energy budget. It will likely find applications that the reasearchers haven't even considered.