Observation of Ultrabroadband Acoustic Focusing Based on V‐Shaped Meta‐Atoms

Abstract

Acoustic focusing has extensive applications in medical ultrasound and nondestructive detection. The recent rapid development of acoustic metamaterials and metasurfaces has provided various mechanisms for designing advanced focusing lenses. However, the realization of acoustic focusing lenses with ultrabroad bandwidth still remains a challenge. To overcome it, ultrabroadband acoustic focusing lens based on phased unit cells composed of different numbers of same V‐shaped meta‐atoms is theoretically proposed and experimentally realized. By using eight types of unit cells, the fractional bandwidth of the acoustic lens can reach about 1.12 with a high focusing performance. Moreover, based on two types of unit cells with a phase difference of π, the fractional bandwidth of the focusing lens still reaches about 0.76 with the same criteria, showing a high robustness characteristic. The proposed acoustic focusing lenses have the advantages of ultrabroad bandwidths, simple fabrication and assembly, and high robustness, which provide diverse routes to construct ultrabroadband sound devices for medical ultrasound and nondestructive detection.

Microacoustic Metagratings at Ultra‐High Frequencies Fabricated by Two‐Photon Lithography

“…[16][17][18] In the case of the latter two examples, the class of gradient metasurfaces including reflecting [19,20] and refracting [21][22][23][24][25][26][27] designs were proven by experiments to be an effective passive approach for wavefront control, for example, for acoustic Fresnel lenses. [19,22,24,25,27,28] However, the wavelength limits the resolution and therefore for high resolution applications the frequency rises to high or even ultra-high frequency ultrasound requiring scaling of the metasurface geometries. When speaking of airborne ultrasound, the ultra-high frequency range starts from 0.5 MHz, where thermoviscous layers at sound-hard boundaries introduce stronger losses.…”

“…This opened up a wide range of applications, such as acoustic cloaking, [7][8][9] acoustic barriers of subwavelength thickness, [10][11][12] flat acoustic lenses, [13][14][15] and ultrasonic imaging with subwavelength resolution. [16][17][18] In the case of the latter two examples, the class of gradient metasurfaces including reflecting [19,20] and refracting [21][22][23][24][25][26][27] designs were proven by experiments to be an effective passive approach for wavefront control, for example, for acoustic Fresnel lenses. [19,22,24,25,27,28] However, the wavelength limits the resolution and therefore for high resolution applications the frequency rises to high or even ultra-high frequency ultrasound requiring scaling of the metasurface geometries.…”

Microacoustic metagratings at ultra-high frequencies fabricated by two-photon lithography

“…This opened up a wide range of applications, such as acoustic cloaking [7][8][9], acoustic barriers of subwavelength thickness [10][11][12], flat acoustic lenses [13][14][15], and ultrasonic imaging with subwavelength resolution [16][17][18]. In the case of the latter two examples, the class of gradient metasurfaces including reflecting [19,20] and refracting [21][22][23][24][25][26][27] designs were proven by experiments to be an effective passive approach for wavefront control, e.g. for acoustic Fresnel lenses [19,22,24,25,27].…”

“…In the case of the latter two examples, the class of gradient metasurfaces including reflecting [19,20] and refracting [21][22][23][24][25][26][27] designs were proven by experiments to be an effective passive approach for wavefront control, e.g. for acoustic Fresnel lenses [19,22,24,25,27]. However, the wavelength limits the resolution and therefore for high resolution applications the frequency rises to high or even ultra-high frequency ultrasound requiring scaling of the metasurface geometries.…”

Tunable Asymmetric Transmissions via Anisotropic Acoustic Metamaterials

“…[11] Afterward, acoustic metasurfaces, [12,13] which are used to modulate the wave fronts by controlling the wave responses of each meta-atom, have aroused increasing attention from researchers. Indeed, due to their potential application values in many fields, a series of practical works has been reported, including acoustic communication, [14][15][16] acoustic hologram, [17][18][19] acoustic focusing, [20][21][22][23] and anomalous reflection and refraction. [24][25][26][27] Acoustic asymmetric transmission (AAT), in which an incident acoustic wave is permitted to propagate forward while blocked backward, has been investigated since the first prototype of an acoustic diode was proposed due to its potential utility in engineering fields.…”