Hollow‐Out Patterning Ultrathin Acoustic Metasurfaces for Multifunctionalities Using Soft fiber/Rigid Bead Networks

Abstract

Acoustic metasurfaces that can manipulate and control sound waves at 2D subwavelength scales open new avenues to unusual applications, such as asymmetric transmission, super-resolution imaging, and particle manipulation. However, the long-standing goals of pushing frontier metamaterials research into real practice are still severely constrained by cumbersome configuration, large acoustic loss, and rigid structure of the existing metamaterials. An ultrathin metasurface (10-300 µm in thickness, up to ≈λ/650, λ the wavelength) that is capable of imparting sound wave with a nontrivial phase shift with high transmittance (>80%) in the range of 5-30 kHz is fabricated here. The metasurface is comprised of a porous network of soft polymer fiber/rigid beads that are physically equivalent to crosslinked spring-mass resonators. Moreover, the traditional paper-cutting art to carve the ultrathin metasurface into hollow-out patterns is incorporated, resulting in a variety of remarkable functions, including acoustic vortex, focusing, and super-resolution. The hollow-out patterning approach innovates the traditional one-step metadevice fabrication process into two separated steps: 1) fabrication of ultrathin metasurfaces; 2) hollow-out patterning of metasurfaces. The strategy opens an avenue to mass production of acoustic metadevices, shedding light on the applications of the metamaterials in acoustic cloaking, acoustic positioning, and particle manipulation.

Meta-neural-network for real-time and passive deep-learning-based object recognition

“…It is apparent, however, that such equivalence between the mathematical model and practical physical system requires effective connection between each meta-neuron and all the meta-neurons on the neighboring layer, which would be difficult for bulky diffractive components modulating phase continuously when the system has a compact size or the object has a complicated pattern. In contrast, meta-neurons' unique capability of metamaterials to offer arbitrary and abrupt phase shift [41][42][43][44][45][46] validates the monopole approximation required by Eq. (1) which is the hinge of the physical analogy of a standard neural network (see Supplementary Note 1 for details).…”

“…To be specific, the holistic performance of the current meta-neural-network can be further improved by modifying the design and training of meta-neurons. For example, one can easily enhance its compactness and efficiency by replacing the simple metamaterial unit cell used here with some recently-emerged designs such as hollow-out-type metamaterial with thinner than 1/600 wavelength 46 , and allows programmable meta-neural-network by using reconfigurable meta-neurons. Our scheme also applies to more realistic applications such as ultrasound imaging by employing waterborne metamaterials such as with soft graded-porous media 58 and including non-planar incident wave and inhomogeneous medium in the training process.…”

Sharkskin-Inspired Magnetoactive Reconfigurable Acoustic Metamaterials

“…This study highlights a unique paradigm for applying stimuli-responsive smart materials to acoustic metamaterials and metadevices to enable active control of their acoustic properties [32,33]. This paradigm may promote the integration between various smart or soft materials and acoustic metamaterials to achieve unprecedented functionalities [53,54]. The unique paradigm may also promote the study of active acoustic metamaterials in switching of acoustic properties via other untethered stimuli, such as electric field, light, and temperature.…”

Scalable additive manufacturing via integral image formation

“…Herein, the use of compressive integral projection to decompose the high-frequency spatial component of the initial target image can provide a solution restoring the desired target image (Fig. S7B-ii Therefore, the structures are a promising tool for exploring the physics of wave transport and controlling the properties of wave patterns, which are relevant to several areas of acoustic metasurfaces [34], wave localisation [39,40], tunable multiband responses of quasilattice metasurfaces [41], and chiral structures [35]. Considering an exposure area of several square milimetres and a lateral feature size similar to that of the single-aperture imaging-based PµSL configuration [11,12], the areal ratio (~10 2 ) of printing scales demonstrates that this imaging approach can be scaled without reducing optical resolution.…”

“…1G-I) with different degrees of periodicity. Aperiodic microstructures can be used to create exotic metasurfaces or woodpile structures for wave engineering[34][35][36].…”