Design Of Following Audio Directional System Based On P(VDF-TrFE) Ultrasonic Transducer

Noise pollution seriously affects people’s living and working conditions,and even endangers human health.Solving the problem of noise pollution has attracted more and more attention.The audio directional system has the advantages of small pointing angle,long propagation distance and acoustic energy concentration.It can produce independent audio space like flashlight beam,which reduces the generation and propagation of noise from the source.In this thesis,a following audio directional system based on P(VDF-TrFE)ultrasonic transducer is designed,which can generate high directivity audible sound that follows the face.The system is expected to be widely used in such fields as solving noise pollution,sound guidance and acoustic weapons.The main work of this thesis is as follows:Firstly,the nonlinear acoustic theory is analyzed.According to the Westervelt equation and the "Berktay far-field solution",the low-frequency audible sound is made into the envelope of the high-frequency carrier by using the signal modulation technology.Then it is emitted into the air by the ultrasonic transducer,and the high directivity audible sound is selfdemodulated by the nonlinear effect of the air.Secondly,a following audio directional system is designed,which is mainly composed of three parts:audio directional signal processing,ultrasonic transducer,face detection and tracking.The signal processing module is designed and manufactured to realize the signal modulation function.A wavy piezoelectric ultrasonic transducer with high electro-acoustic conversion efficiency,high power and low cost is designed by using P(VDF-TrFE)piezoelectric film which has the advantage of excellent piezoelectric performance,good toughness and easy impedance matching.Based on the open source OpenCV library and aduino microcontroller,the face detection and tracking algorithm is designed and implemented,which provides the hardware and software basis for the subsequent research.Thirdly,according to the design requirements of the ultrasonic transducer,the structural parameters and material properties of the transducer are analyzed theoretically,and a wavy P(VDF-TrFE)piezoelectric film ultrasonic transducer is designed.The frequency response,directivity and sound field distribution of the transducer are simulated by COMSOL software.The results show that the resonant frequency of the transducer is near the theoretical value of 40 kHz,and the beam width is less than ± 30° when the directivity decreases by 3dB.The sound field distribution shows obvious directivity,and the directivity becomes better with the increase of arc width.According to the simulation results,P(VDF-TrFE)piezoelectric film ultrasonic transducers with different structural parameters are fabricated.Finally,a following audio directional experimental system based on P(VDF-TrFE)ultrasonic transducer is established.The directivity experiment results show that the pointing angle decreases with the increase of the transducer width and the number of arcs.When the sound pressure level decreases by 3dB,the pointing angle is between ± 3° and ± 10°.The results of sound pressure level attenuation test show that the emission sound pressure level increases with the increase of transducer width and arc number.The sound pressure level and sound pressure attenuation speed at different angles of the transducer are different,and the larger the angle of deviation from the central axis,the faster the attenuation is.The sound pressure level emitted by the system is in the range of 40 dB～80 dB.According to the ultrasonic safety use guide,it can be considered that it will not cause harm to the human body.The system can detect,mark and follow the face rotation,and the tracking accuracy is 0.27°.The system could emit high directional audible sound with simple structure,low cost and wide application scenarios.It is expected to promote the development of audio directional equipment in fields of social life,industry and military.