A closed-loop wide-range tunable mechanical resonator for energy harvesting systems

This paper presents a novel electrically tunable structure which can be used as a resonator for vibration-based energy harvesters. The adjustment of the resonance frequency is provided by mechanical stiffening of the structure using piezoelectric actuators. This concept can easily be stand-alone integrated to realize an autonomous, tunable harvester. The resonator was simulated using ANSYS to find the optimum operation point concerning tuning range. The scalability of this tuning concept is also investigated in this work. A phase shift control circuit was developed for very efficient autonomous closed-loop control of the resonance frequency. Prototypes of the resonators were fabricated and measured with and without the control circuit. The tuning voltage can be kept as low as +/- 5 V leading to a measured resonance shift of +/- 15% for the larger resonator (40 mm) and around +/- 8% for the smaller resonator (27 mm). This tuning range can be simply enhanced by increasing the tuning voltage.