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This paper introduces a passive self-tuning energy harvester by applying self-resonating behavior. Under certain operating conditions, self-resonating systems have the capability to passively adjust their dynamical characteristics until the whole system becomes resonant. A clamped-clamped beam with an attached mass sliding freely with a slight gap showed self-resonating behavior. Under a harmonic input excitation and a well-defined operating regime, the mass moved along the beam thus causing a change in the natural frequency of the structure, and then stopped at the position where the natural frequency matched the excitation frequency, resulting in a significant increase in the vibration amplitude. For harvesting energy, a piezoelectric element was glued at one end of the beam. The operating regime of the self-resonating behavior was found experimentally in the two halves of the beam. In the half containing the piezoelectric element, self-resonating behavior was achieved between 126 Hz and 143 Hz. In the other half, it was achieved between 135 Hz and 165 Hz. Maximum power output of 2.5 mW was obtained under an input excitation of 4.92 m/s2 and 148 Hz. It is to be concluded that applying self-resonating behavior on energy harvesting provides a promising broadband technique.

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This paper proposes a non-resonant linear ultrasonic motor utilizing longitudinal traveling waves. The longitudinal traveling waves in the rod type stator are generated by inducing longitudinal vibrations at one end of the waveguide and eliminating reflections at the opposite end by a passive damper. Considering the Poisson’s effect, the stator surface points move on elliptic trajectories and the slider is driven forward by friction. In contrast to many other flexural traveling wave linear ultrasonic motors, the driving direction of the proposed motor is identical to the wave propagation direction. The feasibility of the motor concept is demonstrated theoretically and experimentally. First, the design and operation principle of the motor are presented in detail. Then, the stator is modeled utilizing the transfer matrix method and verified by experimental studies. In addition, experimental parameter studies are carried out to identify the motor characteristics. Finally, the performance of the proposed motor is investigated. Overall, the results indicate very dynamic drive characteristics. The motor prototype achieves a maximum mean velocity of 115 mm s−1 and a maximum load of 0.25 N. Thereby, the start-up and shutdown times from the maximum speed are lower than 5 ms.