Miniature Audio Directional Transducer Electrical Properties And Drive Circuit Design

Audio beam system can emit high directional audible sound due to the nonlinear interaction of ultrasound in air. The main target of this thesis is to produce a micro audio beam system used in mobile multimedia for portable communication equipments. As piezoelectric Micromachined Ultrasonic Transducer (pMUT) is the key part of audio beam system, it is necessary to analyze its equivalent circuit and to calculate its electrical parameters. Meanwhile, based on the electrical analysis of transducer array, the driving circuit of system was devised.The theoretical basis of audio beam technology originates from directivity principle and ultrasound nonlinear theory. According to these, the scheme of micro audio beam system is proposed. Then, based on energy equivalent theory, the electromechanical equivalent model of pMUT could be built and the value of elements in this model may be calculated by introducing effective electro-mechanical coupling coefficient, electro-elastic constants and structure size of pMUT. In this case, the relationship between frequency and admittance is easy to established, whose accuracy would be verified by experiment. In order to actuating the transducer to vibration and sound production, a driving circuit with functions of power amplifier, filter and impedance matching is designed. In addition, considered that the transducer appears capacitance in working, the driving circuit should be able to drive big capacitance load.With the purpose of testing the performance of driving circuit and the directivity of system, a series of experiments are performed. Based on the analysis of testing results, it is concluded that the circuit is capable of driving load with high efficiency and low distortion, and the directivity of micro audio beam system is ideal with no obvious side lobes.