Analysis of Inhomogeneous Stress Distribution in the Piezoelectric Ceramics of Unimorph Cantilever for Energy Harvesting

Energy harvesting from the vibration through the piezoelectric effect has been studied for powering the wireless sensor node. As piezoelectric unimorph transducer structure can transfer low vibration to large displacement, this structure was commonly deployed to harvest electric energy from vibrations. Piezoelectric unimorph structure was composed of small stiff piezoelectric ceramic on the large flexible substrate. As there is the large Young´s modulus difference between the flexible substrate and stiff piezoelectric ceramic, flexible substrate could not homogeneously transfer the vibration to the stiff piezoelectric ceramic. As a result, most piezoelectric ceramics had been broken at the certain point. Even though the same stress was applied to unimorph cantilever at the end of the unimorph cantilever, there was the difference in output voltages depending on the potion of ceramics. The ratio of the lowest and highest voltage was around 2.4, which reveals the inhomogeneous stress distribution in ceramics.