Resonant Piezoelectric Vibrator With High Displacement at Haptic Frequency for Smart Devices

Piezoelectric actuators have been spotlighted as a promising candidate for vibration motors, but their application is limited due to their inherent low output displacement and high operating frequency in small volume. In this paper, a resonant piezoelectric vibrator with a high output displacement of 427 μm at a low haptic frequency of 188.8 Hz was developed within a diameter of 10 mm and a thickness of 3.4 mm for haptic smart device applications. In the proposed resonant piezoelectric vibrator, a circular piezoelectric unimorph excites a mass-spring system on the circular piezoelectric unimorph at a natural frequency to maximize the vibration of the mass-spring system. The thickness ratio of the elastic layer to the piezoelectric layer and the thickness of the piezoelectric layer were theoretically optimized to maximize the displacement of the circular piezoelectric unimorph considering the attachment of the spring. A spiral spring with a low spring constant was utilized to assign the first natural frequency of the mass-spring system within the haptic frequency that humans can sense sensitively. Furthermore, the natural frequencies and output displacement of the proposed resonant piezoelectric vibrator were calculated and verified by using finite-element analyses. Finally, we prototyped the proposed resonant piezoelectric vibrator and confirmed that measured results match well with simulated ones.