Fig. 2 – Piezoelectric schematic symbol (top) and theoretical equivalent circuit. Piezoelectric transducers can be modeled such that the voltage source V is directly proportional to the compression that is applied to the piezoelectric device. (Credit: en.wikipedia.org)
Fortunately, the human body has the remarkable capacity to regulate to a fairly constant core temperature even as the ambient temperature changes. Thermoelectric harvesting technologies take advantage of human body heat, and are now able to produce a few hundred microwatts. This amount of power is suitable for minimal power applications such as implanted nerve and muscle stimulators or cochlear hearing implants.

Piezoelectric materials provide another promising approach to energy harvesting for implanted devices, as reported by mechanical engineers at the University of Buffalo in IEEE Spectrum. These materials respond with an electrical polarization that is proportional to an applied mechanical strain, and are thus used to convert mechanical motion to electrical energy. The movements of a beating heart are apparently sufficient. Earlier this year, and published in the Proceedings of the National Academy of Sciences of the United States of America, researchers at the University of Illinois at Urbana-Champaign reported on a new harvesting device that can be surgically applied onto the heart to generate power from the moving organ. The flexible device, roughly the size of a postage stamp, incorporates a piezoelectric material called lead zirconate titanate onto an ultrathin compound. The energy produced when the device flexes with each pulse is stored in a miniaturized battery, and is enough to power a pacemaker. (See Figures 2 and 3)

Other energy harvesting options include electrostatic transduction, magnetic induction, and blood sugar oxidation. With the great potential that energy harvesting brings to consumer electronics and wearable technology as well as the medical market, many exciting developments in these and other harvesting techniques are guaranteed.

Summary

Fig. 3 –Lead zirconate titanate (PZT) shows a marked piezoelectric effect. “Perovskite structure of PZT” by Pinin. (Licensed under Public Domain via Wikimedia Commons)

As the world waits for the next generation of batteries, wireless charging and energy harvesting are the low power technologies that are propelling the implantable medical device industry forward. Releasing the designs of future medical implants from the size and lifespan constraints caused by the battery, new product innovations in these areas will transform the medical industry for years to come.

This article was written by Landa Culbertson, Technical Writer, Mouser Electronics, Mansfield, TX. For more information, Click Here.