Improvement on frequency response characteristics of the ultra-thin piezoelectric acoustic actuators

This paper proposes a new method to improve the frequency response characteristics of the ultra-thin piezoelectric acoustic actuators. In order to improve the sound quality of the piezoelectric acoustic actuators, we simulated and analyzed the modal vibration characteristics of the piezoelectric acoustic actuator using the finite-element analysis (FEA) method and experimental studies. The ultra-thin piezoelectric acoustic actuator was fabricated by a volume of 23.5×17×0.8 mm³. The fabricated piezoelectric acoustic actuator had the significant dip and peak at 1.32 kHz and 2.24 kHz, respectively. The FEA simulation and laser scanning vibrometer (LSV) measurement results showed that the dip and peak correspond respectively to (1,3) and (3,1) resonant modes of the acoustic diaphragm. By attaching the elastic mass to the acoustic diaphragm, the resonant frequencies corresponded to (1,3) and (3,1) modes shifted to higher frequencies and the vibrational displacements at each mode were quite reduced by about 40 %. These result in a flat and smooth output sound pressure response of the piezoelectric acoustic actuator by improving the significant peak and dip. This paper presents that the optimized elastic masses can allow flat frequency response characteristics for the improved sound quality of the piezoelectric acoustic actuator.

I. Introduction

Recently, piezoelectric acoustic actuators have attracted a great deal of attention for ultra-slim portable electronic devices because of their obvious benefits of being thinner, more powerefficient and lighter than the traditional dynamic speakers [1]–[4]. While the traditional moving-coil speakers are usually thicker than 3 mm, the ultra-thin piezoelectric acoustic actuators can be thinner than 1 mm because they do not need any thick permanent magnet.