Research On Key Technology Of Glass-based Piezoelectric Thin Film Ultrasonic Transducer

Multimedia equipment is developing towards a thinner and lighter,full-screen display.The new screen structure design greatly reduces the space of traditional speakers and declines the number of sound reflections and buffers,which leads to poor sound quality.The directional screen speaker solution proposed in this project is a combination of screen sound field technology and audio frequency directional principles,using piezoelectric thin film ultrasonic transducers to make the screen have the dual function of display and speaker,which is an immersive "audio and video" for portable electronic devices.The “one-in-one” function and the implementation of partitioning applications of home multimedia equipment provide a feasible solution.First,based on the basic principles of piezoelectric thin film ultrasonic transducers,according to the basic theory of audio frequency orientation and specific application scenarios,and by comparing the structure of traditional piezoelectric transducers,a multilayer circular piezoelectric film suitable for the application needs of this project is proposed.The structure is an array element structure and a theoretical analysis of its acoustic characteristics is performed.Next,with full transparency as the primary criterion,the corresponding material for each functional layer is select.Aiming at the electrical breakdown as the key inspection indicator,the piezoelectric layer material is determined to be the polyvinylidene fluoride(PVDF)film.Taking high electro-acoustic conversion efficiency as the traction,the upper and lower electrode materials are determined to be indium tin oxide(ITO)and molybdenum(Mo).The remaining auxiliary material layers are mainly matched to the needs of the piezoelectric layer and the electrode layer,and are selected in combination with the existing mature technology.Then,the selected material parameters are used to determine the geometric structure parameters of the single array element,including: the thickness of each material layer and the radius of the array element.Considering the acoustic performance such as sound pressure level and directivity,as well as the actual application requirements,the geometric parameters of the transducer array arrangement are determined,including: array element spacing and arrangement method.The multi-physics simulation software is used to simulate and analyze the main characteristics of the determined model,including: frequency response,directivity and sound field.The working frequency of the transducer is confirmed by the frequency response curve to be 40 kHz,and the maximum sound pressure level can reach 107 dB.The directivity and sound field simulations are carried out at the operating frequency,and the directivity angle is within ±30° with a clear main lobe,accompanied by side lobes whose amplitude is much smaller than the main lobe.The three key indicators of the transducer all meet the requirements,and the feasibility verification of the scheme is completed.Finally,the sample is trial-produced and tests are conducted.Compared with simulation,the consistency and audible test are increased.The test results of frequency response and directivity meet the design specifications.The single-frequency signal demodulation sound pressure level of the audible sound demodulation test is above 60 dB,but the audio signal cannot be demodulated.The main reason for the comparison between the sound field test and the simulation may be that the main lobe range is narrow.After further optimization of the glass-based piezoelectric thin-film ultrasonic transducer,it has feasibility and unique advantages as a screen speaker and "integrated audio and video" solution.