The document discusses experimental investigations of piezoelectric energy harvesting systems. It compares four different piezoelectric materials and configurations: (1) PZT, (2) PZT+IDE, (3) MFC, and (4) different system parameters. Finite element analysis was used to simulate the systems and optimize their designs. Experimental results show that voltage output, power density, and efficiency vary based on the material, configuration, and operating frequency/strain levels. PZT+IDE and MFC generated higher voltage outputs than PZT under similar conditions.