Broadband Acoustic Metaveils for Configurable Camouflage

We theoretically propose and experimentally demonstrate acoustic metasurfaces that exhibit undistorted transmission and configurable reflection, therefore serving as remarkable veil structures with camouflage effects for sonars, hereby denoted as acoustic metaveils. The metaveil is composed of a configurable array of two acoustic meta-atoms, which are the flipped counterparts of each other. Reciprocity and space inversion guarantee distortion-free transmission in an ultrabroad spectrum, irrespective of the arrangement of the array, while the reflection can be conveniently manipulated by changing the arrangement to produce the desired acoustic camouflage. Three types of unusual reflection behaviors are demonstrated, including diffuse reflection, multibeam reflection, and reflective focusing. The acoustic metaveils open a way to independently manipulate the reflection without influencing the acoustic transmission wave front, which is a crucial step for sonar stealth and camouflage.

Figure 1

Acoustic metaveil with flipped meta-atoms. (a) Schematic diagram of an acoustic metaveil that exhibits configurable reflection and undistorted transmission. (b)–(d) Schematic diagrams of reciprocity and transmission invariance under space inversion.

Figure 2

Acoustic metaveil for camouflage. (a) Three-dimensional (3D) illustration of the designed metaveil. Bottom-right inset shows a magnified view of the edge of the metaveil. White arrow shows the incident direction. (b) Detailed structures of the head and tail. (c) Transmittance and transmission phase spectra of the head and tail. (d) Reflectance and reflection phase spectra of the head and tail. (e) Transmittance at the condition of reflection phase difference, Δφ = 180°, as a function of the inner radius of the ring-shaped block.

Figure 3

Acoustic metaveils with diffuse reflection and undistorted transmission. Simulated far-field radiation-power patterns of the designed metaveil (a) and a reference metasurface (b) under normal incidence at 5400, 5900, and 6200 Hz. (c) Simulated near-field distributions of the reflected (lower) and transmitted (upper) acoustic fields of the metaveil under normal incidence in the x-z plane at 5400, 5900, and 6200 Hz, respectively. (d) Simulated far-field radiation-power patterns of the designed metaveil under the irradiation of incident waves with incident angles of 10°, 25°, and 40° at 5900 Hz.

Figure 4

Acoustic metaveils with two-beam reflection and undistorted transmission. (a) Simulated far-field radiation-power patterns of the designed metaveil under normal incidence at 5200, 5900, and 6200 Hz. (b) Simulated far-field radiation-power patterns of the designed metaveil under the irradiation of incident waves with incident angles of 10°, 25°, and 40° at 5900 Hz. (c) Schematic diagram of the experimental setup. (d) Photograph of the experimental setup. (e) Simulated near-field distribution of the reflected (lower) and transmitted (upper) acoustic fields of the metaveil under normal incidence in the x-z plane at 5900 Hz. Measured acoustic field distributions of transmitted (f) and reflected (g) waves under normal incidence at 5900 Hz.

Figure 5

Acoustic metaveils with reflective-wave focusing and undistorted transmission. (a) Schematic diagram for the design of the metaveil. (b) Photograph of a real sample fabricated by the 3D printing method. Simulated (c) and measured (d) transmitted acoustic field distributions (upper) and reflected intensity profiles (lower) of the proposed metaveil under normal incidence in the x-z plane at 5900 Hz.