Studies On The Piezoelectric Vibrating Membranes Used In Electroacoustic Components

Piezoelectric ceramic is one of the functional ceramic materials which can facilitate theconversion between mechanical and electric energies by piezoelectric effect. With thedevelopment of portable devices, piezoelectric ceramic membranes with the thicknessbetween1μm and100μm are widely applied to the electroacoustic components. In thisdissertation, PZT piezoelectric ceramic membranes with the thickness ranging from10μm to40μm are fabricated and analyzed on the micro level. And the effect of membrane thicknesson the dielectric, piezoelectric and ferroelectric properties is investigated. In addition, apiezoelectric loudspeaker based on the PZT piezoelectric ceramic membrane with thickness of50μm is fabricated, and its electroacoustic performance is tested.In order to obtain the membranes with a thin thickness (10~50μm) and good electricalproperties, the experimental samples are fabricated by a tape-casting technique. Themicrostructure analysis shows that the samples possess a single perovskite phase withtetragonal structure near the morphotropic phase boundary (MPB), uniform grain size, lesspores, and high volume density. Much importantly, the chemical composition is the same asthe formula designed.To modify the performance of electroacoustic components at low frequency, the PZTpiezoelectric ceramic membranes are thinned to lower the resonant frequency. Theexperimental results show that the resonant frequency is indeed reduced with the decrease ofsample thickness. However, unfortunately, the dielectric, piezoelectric and ferroelectricproperties also deteriorate. By introducing the "Dead layer" model used widely inpiezoelectric thin film to analyze the results, it is found that the existence of space charge isthe key resulting in the effect of thickness on the properties.PZT piezoelectric membrane with thickness of50μm, special driver circuit, plexiglass,professional sound vibration plate, damping ring and damping rubber are used to design andprepare a piezoelectric loudspeaker. The volume and mass of piezoelectric loudspeaker areminished as possible as we can. To test the acoustic frequency response, we find thatcompared with the reported piezoelectric loudspeakers only achieving1KHz at low frequency, the as-prepared piezoelectric loudspeaker make a great progress in low frequencyperformance. The as-prepared piezoelectric loudspeaker can demonstrate good vocalperformance in the frequency range from600Hz to12000Hz.