Atomic Battery Could Power Medical Implants

Originally Published MDDI December 2002

R&D DIGEST

The trend for some time in the development of medical devices has been to make them smaller, yet more complex and powerful. But development of smaller electronic circuits and nanoscale components has not been matched by similar advances in power supply technologies. Batteries have generally remained huge by comparison, and have been limited by short life spans. Now, a tiny device developed by researchers at Cornell University (Ithaca, NY) may be capable of supplying power to remote sensors or implantable medical devices for decades by drawing energy from a minute amount of a radioisotope.

The group has already constructed a prototype device that can convert energy from the radioactive material directly into mechanical motion. They speculate that such a power system eventually could directly move the parts of a tiny machine. It could also generate electricity in a form that is more useful for small-scale electronic circuits than is now possible with conventional methods.

According to Amit Lal, PhD, assistant professor of electrical and computer engineering at Cornell, the approach being developed creates a high-impedance source that he believes is better suited to powering many types of circuits. The prototype is the first microelectromechanical version of a larger device that Lal designed and built while a faculty member at the University of Wisconsin, Madison. Lal developed the earlier device with nuclear engineering professors James P. Blanchard, PhD, and Douglas L. Henderson, PhD, and created the prototype in collaboration with Cornell doctoral candidate Hui Li.

The prototype comprises a 1 mm ¥ 2 cm ¥ 60-µm copper strip that is cantilevered above a thin film of radioactive nickel-63. As the isotope decays, it emits beta particles—but not hazardous alpha particles or gamma rays. Lal chose this isotope because beta particles do not penetrate human skin. As the emitted electrons collect on the copper strip, a negative charge builds. At the same time, the isotope film, losing electrons, becomes positively charged. The attraction between positive and negative bends the copper strip down. When the strip gets close enough to the isotope, a current flows, equalizing the charge. The strip then springs up, and the process repeats.

Because the half-life of nickel-63 is more than 100 years, Lal believes that a battery using this isotope could supply usable energy for at least half that time. Other isotopes would offer various combinations of energy level versus battery life span. Unlike chemical batteries, the devices will work in a wide range of temperatures and could be left unattended for long periods. This would make them well suited for use in medical devices implanted inside the body, the researcher says.

Aside from use as a power supply, the design may have other novel applications. The moving cantilever could actuate a linear device directly, or produce rotary motion using a cam or ratcheted wheel. Electricity could also be generated by attaching a magnetized piece of material to the strip and moving it through a tiny coil.

Lal explains that in other versions of the design, the cantilever is made of a piezoelectric material. In these devices, the cantilever generates electricity when deformed and releases a current pulse as it snaps up. This also generates a radio-frequency pulse that could be used to transmit information, says Lal. The electrical pulse could also drive a light-emitting diode to generate an optical signal.

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