| BackgroundThe flat-top sound field with uniform energy distribution has potential application value in improving imaging quality and ultrasound dose control.At present,the near-field area of planar ultrasound is used to approximately replace the uniform sound field,and there is a lack of research on devices that generate a flat-top sound field.In the field of acoustics,phased array transducers can theoretically achieve arbitrary sound pressure distribution,but they require a complex and expensive phase shift system,which cannot be widely used for the time being.Acoustic phase elements,such as acoustic lenses,Fresnel lenses,holographic lenses,etc.,have the convenience and low cost of combining with planar piezoelectric ceramics,and have become our main research methods for achieving flat-top sound fields.However,the sound field distribution regulatory functions involved in the existing acoustic phase elements are mainly focused on ultrasonic focusing and beam steering.The design research is biased towards the use of various equivalent models to achieve the construction of new materials,and there is a lack of acoustic phase elements designed for generating flat-top sound fields.The phase element design method in the optical field can artificially realize the amplitude control of the output surface,so the design ideas can be used for reference in the design of the acoustic phase element that generates the flat-top sound field.PurposeConstructed an acoustic phase element design method for producing a flat-top sound field.Method1.Through the study of phase recovery methods used in the design of phase elements in the optical field,learn from the processing method of restoring the phase distribution of the optical field on the input surface from the known optical field amplitudes of the input surface and output surface,analogous to the design of the acoustic phase element.2.Establishment of the transmission matrix between the input surface and the output surface of the sound field according to the principle of Rayleigh integration,combine the swarm intelligent optimization algorithm to achieve the phase optimization of the input surface sound field,and use the relationship between the sound path difference and the phase delay to construct the geometric size of the acoustic phase element.3.Perform theoretical simulation and experimental testing on the designed acoustic phase element to verify the correctness of the design.Result1.Designed an acoustic phase element for generating a flat-top sound field.2.Use the simulated annealing particle swarm algorithm,genetic algorithm and seeker search algorithm in the swarm intelligence optimization algorithm to optimize the phase of the input surface sound field of the phase element,and the minimum error values respectively converge to: 5.61,8.36,6.68.Compared with the expected ideal flat-top sound pressure,the mean square errors are: 0.0053,0.0099,and 0.0045,respectively.3.The processing of the acoustic phase element is completed,and the ultrasonic transducer is prepared for the sound field scanning test.The sum of squared errors between the experimental results and the theoretical simulation is 15%.ConclusionIn this paper,the phase recovery method used in the design of optical elements is used for reference,analogy is applied to the design of acoustic phase elements,combined with the swarm intelligence optimization algorithm,an acoustic phase element used to generate a flat-top sound field is designed.Through theoretical simulation and experimental testing,the feasibility of the design is verified.Acoustic phase elements that generate a flat-top sound field have the potential to accelerate the expansion of ultrasonic applications,and to a certain extent can promote the development of multi-functional planar acoustic equipment. |
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