Conceptual 3D model of a bio-mechanically driven microgenerator for medical implants.

I joined the MEMS community at the University of Windsor in 2006 in the field of energy harvesting. Within this field the most fascinating developments are those that target the production of electrical energy inside the human body. That is the path that I followed, aiming to make people’s life healthier and happier.

Historically the service life of implantable electronic devices has been restricted to the energy content of their batteries. Conventional batteries in implants need to be recharged periodically by means of an external electromagnetic induction device or have to be replaced through a surgery. The effective lifespan of modern pacemaker batteries ranges from 5 to 7 years. Inevitably, when the battery is exhausted, a new surgery must be carried out to replace the implant. Rechargeable batteries have a limited number of charge cycles, therefore implants powered with this kind of batteries eventually need to be replaced too.

I proposed a new approach to produce electrical power for medical implants that takes advantage of the natural movements of the human body to drive an electromagnetic induction MEMS generator. The device was designed for use in cardiac pacemakers to replace conventional batteries. In the system, an asymmetrical planar rotor with embedded NdFeB micromagnets in alternate-polarities oscillates around a shaft due to the motion of the body. The oscillation induces a voltage in two microfabricated coils embedded in two stators. The microgenerator did not required any external supply of fluid, as needed by some other types of microgenerators.

Close-up view of the 3D model of the microgenerator.

Operating principle of the microgenerator

With a 1 x 1 mm footprint microgeneratorwas designed to generate 397 μW RMS power with 1.0 V open circuit RMS voltage per stator, which is sufficient to meet the power requirements of a typical cardiac pacemaker. A novel magnetization method to produce alternate polarity thin film micromagnets in close proximity was developed and verified through simulation. A nanoparticle based thin film solid lubrication system was identified as a suitable means to minimize wear and energy losses due to friction between the rotor and the shaft, thereby improving the efficiency and extending the lifetime of the microgenerator. A detailed fabrication process sequence was developed to fabricate the device. The developed process sequence was verified by simulation. A biocompatible mounting and actuation system that enables the thorax muscles to drive the proposed microgenerator from breathing was presented and designed to ensure power generation for the pacemaker even when the recipient is at rest.

One of the major challenges of this technology is the deposition and patterning of high-coercivity magnetic thin films to produce high-energy permanent micro-magnets. Micro-energy storage solutions also need to be developed to ensure power availability when the person is at rest. Some solutions to this problem are nanotube-based supercapacitors, which have much higher power storage density than conventional batteries. These challenges need to be addressed before the fabrication of a prototype, however the comprensive design work has established a solid basis for the future development of in-body energy harvesting devices of this kind.