One of the main challenges of using wireless sensor networks (WSN) is their power supply. Due to limited charge, environmental concern, and the difficulty of replacing the batteries, energy harvesting is a promising solution to develop self-powered wireless sensor nodes. One of the ambient energy sources is vibration energy, which can be extracted and converted to electrical power by piezoelectric energy harvesters. The main challenge in using these harvesters is their resonant performance; hence these harvesters receive suitable power only at their resonant frequency, and the power drops extremely at other frequencies. Therefore, using the array of piezoelectric energy harvesters with different resonance frequencies can enhance the generated electrical power. Furthermore, it also improves the reliability of the system, especially under some weak vibrations. Having a correct understanding of ambient environmental vibrations and proper resonant frequency selection is essential for extracting maximum power from the array of energy harvesters. Therefore, in the second chapter of this thesis, a criterion for selecting the resonant frequency of an energy harvester based on amplitude and frequency of vibration in a multi-frequency environment is provided. Designing a suitable interface circuit to get power from array of energy harvesters is another important challenge that should be addressed. The limited size of the wireless sensor nodes and finite power density of energy harvesters necessitate that the interface circuit must be as small as possible and implemented as an integrated circuit with low power consumption. Also, because ambient energy sources are often irregular or intermittent, the interface circuit should receive maximum power from all array harvesters in any environmental vibration conditions. In this thesis, a power processing circuit for an array of piezoelectric energy harvesters with different resonant frequencies and time-varying open-circuit voltages is presented. The proposed power processing circuit can receive maximum power for all array elements, independent of the harvester’s open-circuit voltage. The proposed control method only depends on the amount of the cantilever beam capacitance and vibration frequency. Also, in comparison with other interface circuits, all passive capacitive elements are removed, and the amount of shared inductive component is reduced to 100 uH, saving space and fabrication costs. Sharing different parts of the circuit for all transducers in arrays is another advantage of this structure, which reduces the area. The proposed interface circuit extracts 1.57 times more power than a conventional full-bridge rectifier-based harvesting circuit. Another advantage of the proposed interface circuit is that it can be used for all energy harvesters that deliver maximum power at an optimal resistance load. Hence the suggested circuit can be used for a hybrid set that includes several different energy harvesters. The proposed power processing circuit is designed and simulated in 180 nm CMOS technology, and chip layout with a 0.4 mm2 area is also submitted for fabrication. The circuit simulations verify the analytical results consider all parasitic elements, including resistance, capacitance, and coupling capacitance. The self-powered interface circuit’s efficiency is more than 85% for open circuit voltages above 2.7 volts. Wireless Sensor Networks, Array of Piezoelectric Energy Harvesters, Resonance Frequency, Adaptive Selfpowered Interface Circuit, Integrated Circuit