Acoustic tweezers are a method of using acoustic waves to manipulate small particles in medium such as water or air without touching or contaminating them. Here, we report a water-immersed phase-modulating acoustic holographic lens as kinds of acoustic tweezers. It can be used to generate single-bottle beams or even multi-bottle beams at specific locations. These types of acoustic tweezers can be used to examine single or multiple particle trapping. The concept is based on the highly localized acoustic radiation force induced by the destructive interference of the acoustic waves across the holographic lens, which makes the particles trapped in the center of the bottle beam. Because the proposed system is independent of reflection, it is suitable for studying the interaction between cells in vivo.
We present a water-immersed ultrasound high-efficiency Fresnel lens based on the theory of extraordinary acoustic transmission of plate-wave resonance. We studied, experimentally and numerically, the acoustic pressure gain of the Fresnel lens with and without gratings on the back. We found that the transmission coefficient of the incident acoustic waves through the lens with gratings on the back was much higher than that of the lens without gratings, thus increasing the acoustic pressure gain at the focal point of an impedance-mismatched Fresnel lens by 14.1 dB. We then optimized the grating width in the structure, thereby increasing the acoustic pressure gain by 16.3 dB. This lens has potential applications in acoustic imaging and medical diagnosis.
Focused acoustic vortex (FAV) beams can steadily trap particles in three-dimensions. Previous FAV emitters are mainly based on the active device arrays. Here, we design a passive artificial structure engraved with two sets of discrete Archimedean spiral slits to generate the FAV in water. The acoustic intensity and phase distributions of FAVs are investigated theoretically and demonstrated using the finite element method. The constructive interference between two transmitted acoustic vortices through the inner and outer spiral parts achieves the FAV. It is found that the focal length and depth of the FAV can be modulated by simply changing the initial radius of the Archimedean spiral. Furthermore, we implement the Schlieren imaging experiment to verify the generation of the FAV by the artificial structure. Our design may offer potential applications in particle trapping, biomedical therapy, and medical imaging.
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