[ Instrument Network Instrument Research and Development ] Recently, Zheng Hairong and Cai Feiyan, researcher of the Ultrasound Team of the Routberg Biomedical Imaging Research Center of the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, and Zhu Xuefeng, professor of Huazhong University of Science and Technology, and Qiu Chengwei, professor of the National University of Singapore, collaborated on super-oscillation beams and acoustic hyperlenses. Progress has been made in the research. The related research results were published in "Nature Communications" on July 30th under the title of Ultrasonic super-oscillation wave-packets with an acoustic meta-lens.
Waves are accompanied by diffraction during the propagation process. When the wave encounters an obstacle, part of it will wrap around the obstacle and continue to propagate forward. Due to the existence of the diffraction effect, an image formed by an ideal object point through the imaging system cannot be an ideal point with no size, but a sized diffuse spot, ie, Airy disk. When the two diffuse spots overlap each other to a certain extent, the imaging system cannot be distinguished. Therefore, the resolution of the imaging system is directly related to the size of the speckle, and the larger the speckle size, the lower the resolution of the imaging system. In the past few decades, breaking the diffraction limit has been a long-term goal in the field of optics and acoustics. Since the introduction of autorefractive and hyperbolic refractive metamaterials, evanescent waves carrying super-resolution information have been obtained in these metamaterials. However, due to dielectric loss, super-resolution focusing and imaging can only be achieved in the near field. In the 1990s, Aharonov et al. first proposed the existence of super-oscillation of the frequency band-limit function. After careful design, the local band vibration function local vibration frequency can be much larger than its overall maximum vibration frequency component, which is called the super-oscillation wave function. After that, the research on super-oscillation has aroused widespread concern in the academic world. However, how to construct a super-oscillation focusing field in the ultrasound system and break the diffraction limit of the wave in the far field is still an urgent problem to be solved.
Based on this, the researchers firstly constructed the acoustic super-oscillation function with time-period characteristics from the acoustic wave equation; then mapped the time frequency to the spatial frequency, and designed the thickness less than one-fifth of the wavelength by the free optimization algorithm. Planar acoustic lens; further, by superimposing ultrasonic components of different spatial frequencies, far-field super-resolution acoustic focusing is realized, and this phenomenon is observed experimentally. In addition, using the effect of acoustic radiation force, the research work will be visualized by the "captured" particle ring to size the spot size, which proves that it breaks the diffraction limit; in order to test the imaging resolution of the super-oscillation acoustic lens, the research work is still three Ultrasonic imaging experiments were carried out on different patterns of microstructures. Compared with conventional acoustic lens imaging results, the imaging resolution of acoustic superlens based on super-oscillation effect was significantly improved. The ultrasonic superlens has potential applications in biomedical ultrasound imaging, biomedical applications, and general far field ultrasound control.
The work was supported by the National Natural Science Foundation of China, the National Major R&D Program, and the basic research business fees of the central universities.
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