Design and optimization of cantilever based piezoelectric micro power generator for cardiac pacemaker

Abstract

Piezoelectric micro-power generator (PMPG) converts mechanical vibration energy into electric energy via piezoelectric effects. In cardiac pace makers, the use of PMPG eliminates the need for a traditional lithium iodide battery replacement. In this paper we design and optimize PMPG that is able to harvest the mechanical movement of the heart beat to be converted into usable electrical power in frequency range 1---1.7 Hz. Eight control parameters are selected: which are proof mass material, piezoelectric material, proof mass length, proof mass thickness, piezoelectric layer width, piezoelectric layer thickness, silicon nitride layer width, silicon nitride layer thickness. Orthogonal arrays of Taguchi method for these eight parameters mentioned with three levels and signal-to-noise (S/N) ratio, and ANOVA analysis is studied to determine the optimum design. COMSOL Multiphysics ver. 4.2 is used in 18 different simulations. The maximum output power and highest efficiency designed at 1.2 Hz is equivalent to 72 beat per min. Both Taguchi and ANOVA confirms the same results of determining the parameter of having the most influence on the generated output power at 1.2 Hz in descending order: which are piezoelectric material of PZT-5A, proof mass length of 5 mm, piezoelectric layer thickness of 30 µm, proof mass thickness of 4 mm, piezoelectric layer width of 0.12 mm, silicon nitride layer width of 0.16 mm, silicon nitride layer thickness of 30 µm, and proof mass material of aluminum. Eigen frequency analysis for the first six modes of operation for PMPG frequencies are: 1.2 HZ, 5.4 Hz, 6.9 Hz, 29,7 Hz, 694.8 Hz, 708.3 Hz. The first mode of operation is selected as operation mode and shows that 93 % of PMPG's total displacement and output power was produced in the range of 1---1.4 Hz, therefore PMPG can work when the heart rate between 60 and 84 bpm. Transient analysis performed at 1.2 Hz reaches the steady state before the first 10 cycles with output power density of 23.13 µW/cm3, which is suitable for powering cardiac pace maker.