The Modulation Of Multiple Acoustic Field Information Based On The Design Of Functional Acoustic Metamaterials

With the continuous development and progress of modern science and technology,people have higher and higher requirements for acoustic structure design.Traditional natural materials can not fully meet the structural functional properties required by military and industrial production.As an artificial micro-structure with sub-wavelength scale,the emergence of acoustic metamaterials(including phononic crystals,acoustic metasurfaces and other related artificial functional structures)breaks through the performance limitations of conventional acoustic structures/materials,presents a novel design concept of composite structures/materials,and meets the needs of people to design and build functional artificial acoustic devices according to their own will,which provides a new means for arbitrary modulation of various acoustic field information.Nevertheless,there are still some challenges in the realization of high-performance acoustic functional devices: For the modulation of the transmission/reflection acoustic field information,the traditional acoustic metamaterials are limited by the working bandwidth and design complexity,which affects their engineering applications;For the asymmetric modulation of transmission acoustic field information,the singleness of functional response and the large size of structure thickness lead to the low utilization rate and cost performance of the device,which is not conducive to its industrial promotion;For the modulation of the coupling acoustic field information,the existing resonant coupling design strategy needs high structural dimension accuracy and is sensitive to the change of the incident wavelength,which cannot meet the application requirements of strong robustness and broad spectral response of the device.To overcome the above challenges,in this dissertation,the optimization designs of various functional acoustic metamaterials are utilized to realize the flexible manipulation and shaping of the transmission wavefront,and then obtain the acoustic information modulation of the reflection field,transmission field and coupling field.The main research contents of this dissertation are as follows:(1)The modulation of reflected acoustic field information based on resonator-type acoustic functional metamaterial: To solve the problem of bandwidth limitation in the modulation of reflected acoustic field information,a reflective acoustic Helmholtz resonator with subwavelength scale is proposed to serve as a basic unit for the construction of acoustic metamaterial,which can obtain high-precision reflected phase modulations by changing the height of its internal air cavity.Then,the broadband acoustic stealth and patterned acoustic field customization of the reflected acoustic field information are realized by the construction of gradient phase.In addition,in view of the complex design of traditional reflective acoustic metamaterials,a binary coding method is proposed to further optimize the design of the metamaterial by reducing the phase discrete level.Different coding sequences are adopted to realize and verify the modulation of multiple functional metamaterials on the reflected acoustic field information.The results show that the proposed design method effectively simplifies the construction of reflective metamaterial and broadens the working band of modulation for reflective acoustic field information.(2)The modulation of transmitted acoustic field information based on labyrinth-type acoustic functional metamaterial: In view of the impedance mismatch problem in the broadband information modulation of the transmitted acoustic field,an acoustic labyrinth cavity with mirror symmetry configuration is proposed,which obtains the impedance matching between the structure and the air background in a broadband range by changing the length of its internal interdigital plate,thus realizing the full phase modulation of the transmitted acoustic wave at high transmittance.Taking acoustic stealth and patterned acoustic field customization as examples,the feasibility of the labyrinth cavity for the design of the transmission acoustic functional device is verified.At the same time,in order to further broaden the available frequency band of transmission acoustic field modulation,functional acoustic metamaterials are constructed by using binary coding method,and thus the relative operating bandwidth is up to 0.66.The results illustrate that the proposed design method shows good applicability in the modulation of ultra-broadband transmission field with impedance matching property.(3)Asymmetric modulation of transmission acoustic field information based on coding acoustic functional metamaterial: To solve the problem of single functional response and poor adjustability in the asymmetric modulation of transmission acoustic field information,two layers of functional coding metamaterials that can generate transmitted beam shaping and excite surface acoustic waves are constructed.By integrating them into the same plane through the existence of air gap,the acoustic field modulation function with asymmetric transmission and beam shaping is obtained simultaneously.In addition,the distance between the layers of the air cavity can be served as a tunable degree of freedom to realize the flexible switching of the device from asymmetric transmission to symmetric transmission.The results show that the proposed design method gives multi-function response to the acoustic device with asymmetric field modulation,increases its overall tunability,and provides a solution for the design of highcost performance device for asymmetric field modulation.(4)The modulation of coupling acoustic field information based on slit-type acoustic functional metamaterial: To overcome the problem of being sensitive to the change of incident wavelength and structural parameters in the information modulation of the coupled acoustic field,a method of introducing stimulated Raman adiabatic passage into the acoustic system is proposed.By using the height change of the coupling slit between two adjacent acoustic cavities,the continuous modulation of the acoustic coupling strength is obtained,and then the efficient acoustic energy transport process that can follow the quantum state transfer passage is realized.The influence of structural parameter and incident wavelength on the coupled acoustic field is reduced.At the same time,aiming at the problem of large size of acoustic adiabatic devices,the driving form of multi-cavity acoustic coupling pulse is optimized by using the shortcut to adiabatic passage,which further shortens the transfer path of acoustic energy and device length,and constructs an acoustic multi-cavity coupler with compact configuration.The results show that the proposed design method enhances the robustness of the coupling acoustic field modulation to the changes of structural parameter and incident wavelength,and effectively shortens the length of the device while broadening the operating band of the device.