Scalable Metagrating for Efficient Ultrasonic Focusing

Acoustic metalenses have been pursued over the past decades due to their pivotal role in a wide variety of applications. Recent research efforts demonstrated that, at ultrasonic regimes, acoustic levitation can be realized with standing waves, which are created by interference between incoming and reflected focused waves. However, conventional gradient-metasurface approach focus waves is complex, leading poor scalability. In this work, we propose design principle for metalenses, based on metagratings---arrays discrete scatters coarser features than gradient metasurfaces. We achieve beam focusing locally controlling excitation single diffraction order use metagratings, geometry adiabatically varying lens aperture. show that our metalens effectively impinging focal point full width half maximum 0.364 wavelength. The performance experimentally, validating proposed approach. This metagrating adopted different operating frequencies scaling size structure, has coarse suitable high-frequency designs, potential applications ranging from biomedical science nondestructive testing.