Design, fabrication and characterization of a very low frequency piezoelectric energy harvester designed for heart beat vibration scavenging

International audienceCurrent version of implatable cardioverter defibrillators (ICDs) and pacemakers consists of a battery-powered pulse generator connected onto the heart though electrical leads inserted through the veins. However, it is known that the long-term lead failure may occur and cause the dysfunction of the device. When required, the removal of the failed leads is a complex procedure associated with a potential risk of mortality. As a consequence, the main players in the field of intracardiac implants are preparing the next generation of devices: miniaturized and autonomous leadless implants, which could be directly placed inside the heart. The idea of a stand-alone cardiac implant is not new and several approaches for powering the device have been suggested. More recently, Karami presented the simulation results of a piezoelectric energy harvester based on and operating at 40Hz that could in theory power a cardiac implant with heart-induced vibrations. Deterre presented an acceleration spectrum of the heart obtained by placing accelerometers inside several heart cavities. It appears that the heart vibration energy is rather localized at lower frequencies in the 15-30Hz-frequency band. In this paper, we will discuss the frequency content of the heart vibration spectrum, and the dimensional restrictions in the case of a leadless pacemaker. In combination with the requirements in terms of useable energy, we will present a design study of a resonant piezoelectric scavenger aimed at powering such a device. In particular, we will show how the frequency-volume-energy requirement leads to new challenges in terms of power densities, which are to be addressed through implementation of innovative piezoelectric thick films fabrication processes. This paper also presents the simulation, fabrication and the testing of an ultralow frequency (15Hz) resonant piezoelectric energy harvester prototype. Using both harmonic (50mg) and actual heart-induced vibrations, we obtained an output power of 60µW and 10µW respectively. Finally, we will place emphasis on the new constraint represented by the gravitational (orientation) sensitivity inherent to these ultra low frequency resonant energy harvesters