Research On Sub-wavelength Resolution Of Photoacoustic Microscopy Imaging Based On Acoustic Metamaterial Lens

Implementation of the photoacoustic microscopy imaging with subwavelength ultra-high resolution is one of the most important targets of the research area of the super-resolution image processing, and it’s also the research focus of many scholars currently. Thus, the main work of this paper is also focused on the key technologies of subwavelength ultra-high resolution for the photoacoustic microscopy imaging. The research field of this disseration belongs to the frontier physics- an expansion application of acoustic materials research technology specifically.One the one aspect, for the detection object of biological tissue with the characteristic of rich and complex microstructure, the method of photoacoustic signal acquisition of the current photoacoustic imaging processing has a great limitation, as the "diffraction limit" could not be broken through the far field imaging. On the other aspect, the lens based on the acoustic metamaterial could achieve a subwavelength resolution during the process of the near field imaging for tiny structures, which has been proved by many authoritative research results at home and abroad. Besides, for the demand of subwavelength resolution, there are many similarities between the photoacoustic microscopy imaging and the lens imaging based on the acoustic metamaterial. Therefore, the technology of the acoustic metamaterials is one of the preferred solutions for overcoming the problem of the "diffraction limit" undoubtedly. For meeting the special demand of photoacoustic imaging, and for satisfing the size and standard requirements of photoacoustic signal acquisition, the author take a hard effect work on the technologies of the subwavelength ultra-high resolution of photoacoustic imaging during of the doctoral period. Such work is mainly based on the novel acoustic metamaterials. Several fruits are also attained during the doctoral period as follows.Firstly, Based on analyzing of the influence of photoacoustic signal transmission mediumto the imaging resolution, this dissertation try to introduce the novel concept of photonic crystal negative refractive index of physical frontiers into the research area of photoacoustic imaging. By means of using the acoustic metamaterial lens in the field of photoacoustic imaging, and using the negative index characteristics of acoustic metamaterial, the evanescent wave that contain the image detail could contribute to the imaging process, which may change the far field imaging method in the process of photoacoustic imaging currently. Thus, a subwavelength resolution in the near field imaging process is hopeful, and this study is expected to develop a new way of realizing super-resolution imaging technology.Secondly, using of the knowledge of geometrical acoustics and wave acoustics, and combined with the band gap theory of lattice plane wave, the transmission/sound distribution characteristics and nature of the evanescent wave in medium that carry the detail information of the photoacoustic image are studied, which provides a reference for the construction of ultra-high resolution photoacoustic image processing theory that using the evanescent wave.Based on analyzing the characteristic of subwavelength resolution photoacoustic microscopy imaging, this dissertation focus on the source of imaging signal, and the signal propagation process is considered. This dissertation proposes to use the metamaterials lens in the acoustic signal acquisition process of the photoacoustic microscopy imaging. A new scheme, which using the metamaterial lens in the acoustic signal acquisition, is also proposed. This metamaterial lens is expected to guarantee the evanescent wave transmission without large loss in the photoacoustic imaging process, which contain the information of image detail. This dissertation also put forward a new kind of miniature acoustic superlen-tubular structure,which is suitable for the photoacoustic microscopy imagings. The lens imaging performance of this superlen is also analyzed successfully by using the horizontal, vertical axis two-dimensional profile sound field transmission analysis methods. The analyzed result is coincided with the result of three-dimensional method.Then, for meeting the demand of photoacoustic microscopy energy concentrating in the center shaft during the transmitting process, this dissertation also proposes to use the photoacoustic lens to solve the problem of photoacoustic evanescent wave transmission. Theminiature lens with ‘special structure’ is designed for the photoacoustic microscopy.Theoretical analysis and experimental simulation show that a ‘funnel’ axisymmetric structure forms is also proposed in this dissertation, and a good subwavelength resolution imaging effect is attained finally.Finally, the realization method of subwavelength resolution for the acoustic metamaterial lens constituted photoacoustic microscopy imaging is studied too. Preliminary experiment results have been achieved. But it should be noted that the work of parameters optimization of acoustic superlens and the practical application of photoacoustic microscopy imaging research need to be perfected furtherly.