Micromachined piezoelectric spirals and ultra-compliant packaging for blood pressure energy harvesters powering medical implants

This paper introduces a novel energy harvesting technique and an associated packaged device aimed at powering intracardiac active medical devices by scavenging energy from ordinary blood pressure variations. We present the innovative concept of a micro-bellows packaged implant that deforms due to cyclic blood pressure variations in the cardiac cavities. This bellows transmits stresses on a spiral-shaped piezoelectric transducer that converts mechanical deformations into electric energy. The particular shapes of the different components (bellows and spiral) are designed to dramatically increase the mechanical energy that is harvested. The miniature bellows design, fabrication through electrodeposition for high compliance and hermeticity, and experimental characterization are presented. The specific challenges that arise in spiral shapes piezoelectric harvesters working in bending mode are discussed and we present a method to predict the non-trivial optimal electrode placements for maximum efficiency. This design process is completed by an associated microfabrication method and three types of piezoelectric bimorph spiral samples with doubled-sided microstructured electrode patterns are presented. The experimental performances of these prototypes are confronted to numerical simulation. A power of 4.15 μW/cm³ at 1.5 Hz has been obtained for the best design and we predict that tens of micro-Watts per cubic centimeter could be obtained using similar design process and material.