This thesis presents a method for design and characterization of piezoelectric energy harvesters for supplying smart grids self-power wireless sensors. The proposed characterization methods determine the beam parameters including the mechanical damping ratio and electrical coupling coefficient which significantly affect on the performance of energy harvesters. Existing methods often need to measure the beam tip deflection for the characterization of the beam parameters. This requires the accessibility of the tip and advanced measurement tools such as a laser vibrometer. However, the proposed method determines the most of the beam parameters including mechanical damping ratio based on a pure electrical test. The proposed method is useful for the characterization of all types of piezoelectric energy harvesters particularly the vacuum-packed ones in which the tip of the beam is inaccessible. After the characterization, the design optimization of magnetic field energy harvesting platforms is presented. The designed platform can be used with any type of vibration-to-electricity energy conversion schemes including piezoelectric, electromagnetic, and electrostatic energy harvesters. The platform includes a cantilever beam with a miniaturized permanent magnet (PM) at the tip that vibrates due to the interaction with the magnetic field of the ac line. The proposed method analytically determines the optimum geometric orientations of the platform as well as the optimum dimensions of PM to maximize the applied magnetic force to the beam. In the next step a design method for wireless piezoelectric sensors of power lines is presented which includes a detailed method to optimize the piezoelectric energy harvester in order to extract the maximum energy at line frequency by tuning its electrical load and effective mass. Different modes of optimizing the energy harvestercorresponding to various amounts of the damping ratios will be explained and the design guidelines for each mode will be discussed. The validity of the all proposed methods and design procedures are experimentally verified using a few test setups. These tests are performed by designing a vacuum-packed piezoelectric energy harvester and a scaled down ac power line. The measured data and parameters verifies the validity of proposed methods.