Miniature Audio Directional Transducer Sound Field Modeling And Verification

Micro-directional loudspeaker generates audible sound with high directivity which is based on non-linear interaction of ultrasound in the air. Basing on the acoustic theory of the finite element method (FEM) and boundary element method (BEM), the micro-directional transducer model is built in this thesis, and the accuracy of the model is verified by the experimental test of impedance, directional pattern and SPL (Sound Pressure Level).The working principle of micro-directional loudspeaker, non-linear interaction of ultrasound and parametric acoustics array principle are respectively elaborated. The relationship of the SPL of the ultrasound, propagating distance and emitting area of the transducer with the SPL of the audible sound is studied. The main content of this thesis is as following: according to the directivity theory of the single circular piston transducer, linear uniform array and multiplication theorem, the directivity function and pattern of micro-directional transducer array are deduced and obtained. Meanwhile the investigation on the directivity pattern of micro-directional transducer array affected by different radius, number and spacing among elements is made.The acoustic FEM model of micro-directional transducer element is created, and the important parametric of resonant frequency and sound transmitting volt level (SVL) about micro-directional transducer is obtained. The acoustic BEM models of micro-directional transducer element and array are created and the sound pressure frequency response of micro-directional transducer element and array in certain frequency range are respectively analyzed. The consistency of the calculated SPL about the transducer element by two methods is analyzed. Also the comparison of SPL between transducer element and transducer array is given, meanwhile the mutual radiation impedance is introduced to illustrate the difference. For micro-directional transducer array the parametric acoustic array conversion efficiency from ultrasound SPL to audio SPL is discussed, and the reason is illustrated.Finally, the acoustic parametric of micro-directional transducer array is obtained in this thesis: the resonant frequency, the directional angle of -3dB and the SPL under the condition of far field. The results between simulation and testing are compared, and why the discrepancy exists is explained.