This project investigates continuous powering of leadless cardiac pacemakers by conversion of mechanical energyofthehearttoelectricalenergy.Thisenergyconversionprocessiscalledvibrationenergyharvesting. The central element in piezoelectric vibration energy harvesters (EHs) is a piezoelectric structure. The structure resonates in response to the ambient oscillations, and its mechanical oscillations are converted to electricalenergythroughthepiezoelectricphenomenon.Theamountsofenergyproducedbyvibrationenergy harvestingaretypicallyintheorderofmicrowatts.IfEHsareusedinsteadofbatteriestopowerasystem,they willbepermanentregenerativepowersourcesandwillnotneedreplacement.ThefactthatEHsarepermanent power sources is instrumental for leadless pacemakers. Unlike conventional pacemakers, leadless pacemakerscannotbeextractedfromtheheartwhentheirbatteriesdeplete.Thusafteraboutsevenyearsa new leadless pacemaker must be implanted in the heart which occupies even further ventricular space. We haveshownthatanEHcanbedevelopedtoregenerativelypowertheconventionalpacemakersbyconversion of heart beat induced vibrations to electricity. This could eliminate the need for periodic pacemaker replacement surgeries. Leadless pacemakers are implanted in the heart and are thus substantially smaller thanconventionalpacemakers.ThissizelimitdemandedminiatureEHs. Our preliminary studies show that vibration EHs can have larger power density than the leadless pacemaker batteries. Using an EH instead of a battery will not only result in potentially permanent leadless pacemakers butalsoenablesaddingmorefunctionstothepacemaker.Thisprojectinvolvessystematicmodeling,design, optimization, fabrication, and testing of a number of EH designs for leadless pacemakers. Since the typical shapeofaleadlesspacemakeriscylindrical,theshapeoftheEHelementshouldbethree-dimensional.This sets the EH designs in this project aside from the majority of the EH in the literature, which are 2D. The investigated EHs are divided into two large categories of linear and nonlinear EHs. Nonlinear EHs are more advanced and more complicated. If properly designed, nonlinear EHs can be very robust to heart rate variations. The proposed linear EH is a fan-folded structure composed of multiple linked beams clamped at one end and free at the other end. We use thermal and magnetic buckling to induce nonlinearity in the nonlinear EH. Development of electromechanical models that can accurately predict the response of the EH designs is a major goal of this project. These models will be used to optimally design the miniature EHs. Fabrication and experimental testing of each EH design (through in vitro and animal tests) will both evaluate themodelsandcalibratetheperformanceoftheEHs.Theprojectalsoincludesextensivereliabilityanalysesto ensurethelonglifetimeoftheEHandtoascertainsufficientpowerproductionoftheEHdespitevariationsof heartrateandheartcontractilityamongpatients.
Development of energy harvesters for powering leadless pacemakers from myocardial motion Leadless pacemakers are the new generation of cardiac pacemakers that are implanted in the heart. This project investigates continuous powering of leadless cardiac pacemakers by conversion of mechanical energy of the heart to electrical energy. We design, study, and fabricate novel piezoelectric devices that are integrated into the pacemaker and generate power when the heart motion shakes the device.