Analysis of how compliant layers and encapsulation affect power generated from piezoelectric stacked composites for bone healing medical devices

Use of piezoelectric materials to harvest energy from human motion is commonly investigated. Traditional piezoelectric materials are inefficient at low frequencies but composite structures can increase efficiency at these frequencies. Compliant layer adaptive composite stack (CLACS) is a new piezoelectric PZT (lead zirconate titanate) structure designed for orthopedic implants to use loads generated during walking to provide electrical stimulation for bone healing. The CLACS structure increases power efficiency and structural properties as compared to PZT alone. The purpose of this study was to investigate the effects of compliant layer and encapsulation thicknesses on strain-related parameters for CLACS predicted by finite element models. Percent changes in strain as compliant layer thickness increased were compared to percent changes in power experimentally produced by CLACS given similar geometries and loading conditions. Percent changes in PZT z-strain matched the trends for increases in experimental power, but was not directly proportional. PZT z-strain and radial strain increased as compliant layer and top and bottom encapsulation thickness increased. PZT z-strain and radial strain decreased as side encapsulation thickness increased for a normalized distributed force on the PZT. The overall goal of this study was to inform future design decisions regarding CLACS structures specifically for use in orthopedic implants.