中文摘要：

提出了一种用于手机的微型声频定向扬声器实现方法,该新型扬声器可将声音控制在发声单元正前方轴向传播,能为使用者提供免提的局部声音服务。4只直径为10mm的锆钛酸铅（PZT）压电陶瓷超声换能器组阵作为发声部件,换能器阵列谐振频率作为超声载波频率,数字信号处理器（DSP）芯片作为声频定向调制算法实现平台,D类超声功率放大器为阵列驱动器,诺基亚N73手机作为外壳,制作出了样机。对换能器单元及阵列阻抗、声压级频率响应等特性进行了测试和分析,对样机作了自解调可听声指向性测试和整机功耗测试。实验结果表明,样机尺寸、功率和声压级基本满足手机中的应用需求,为微型声频定向扬声器在便携式多媒体设备中的应用提供了实践依据。

英文摘要：

A method for realizing the micro audio directional loudspeaker in mobile phone is investigated to examine a novel auditory experience in this paper.This novel directional loudspeaker can provide private listening service by emitting the audible sound with high directivity along propagating axis.A prototype using Nokia N73 mobile phone as the package is constructed in which the emitter array is assembled by four PZT ceramic ultrasonic transducers with the diameter of 10mm.The emitter array is driven by a class D amplifier.The modulation algorithm is realized on a DSP platform on which the carrier frequency is equal to the resonant frequency of the emitter array.The testing results of impedance,frequency response and sound pressure level characteristics are described and analyzed.The directivity angle and power consumption of the prototype are measured.The experiment result indicates that the prototype size,power and the acoustic pressure level can satisfy the requirements for the mobile phone,thus the micro audio directional loudspeaker can be used for the portable multimedia devices.