Modeling And Testing Of The Directional Micro-transducer Based On Pzt Materials, Sound Frequency

Audio beam loudspeaker can generate high directional audible sound due to the nonlinear interaction of ultrasound in air. In this thesis, the main target is to produce the audio beam system used in mobile multimedia for portable communication equipments. As piezoelectric Micromachined Ultrasonic Transducer (pMUT) is one of the most important parts in audio beam system, it is necessary to analyze its vibration characteristics and to optimize its structure parameters. Meanwhile, based on the directivity analysis of transducer array, number of elements and interspacing between elements are optimized. Finally, audio beam micro-transducer array with high output pressure level, high direction and stable performance is fabricated due to the theoretical analysis results.According to classical piezoelectric shell theory, a theoretical model of a circular thin-film piezoelectric actuator on a clamped elastic plate, with consideration of coupled extension and flexure, is cited to predict the performance of piezoelectric micromachined ultrasonic transducer. Then the vibration characteristic of low-frequency is analyzed to optimize the radius of the top electrode on the deflection of the elastic plate, to optimize the thickness of PZT layer, Si layer, adhesive layer and etc on the effective electromechanical coupling coefficient, to optimize the radius of transducer on proper resonant frequency. To improve the directivity pattern and increase radiation acoustic power, transducer array is proposed. Considering off-axis effect and rapid ultrasonic attenuation in air, directivity function of acoustic parametric array is introduced to optimize the transducer array on number of elements and interspacing between elements. Finally, beam width becomes narrow and side-lobe is withdrawed.Based on the optimal results above, pMUT is fabricated. To verify the accuracy of theoretical analysis results, impedance measurement, frequency response measurement, Sound Pressure Level (SPL) measurement and directivity measurement are carried on in an anechoic chamber. However, the test results are not so perfect. Due to the immature MEMS process, transducer elements show some inconsistency on resonant frequency, which distribute between 35 kHz and 60 kHz (designed 40 kHz). Audible SPL is 30 dB at 20 cm, which is not large enough. The -3 dB beam width is about±30°and the side-lobe is about 12 dB when the carrier frequency is 36.24kHz, and signal frequency is about 8 kHz.