Lotus Metasurface for Wide-Angle Intermediate-Frequency Water-Air Acoustic Transmission

Preparation of Long-Range Ordered 1D Nanowire Arrays on PVP-Modified Hydrophobic Highly Adhesive Templates Using Conical Fiber Arrays

Suspended nanoscale one-dimensional (1D) arrays have attracted substantial interest due to their promising applications in nanodevice fabrication. In this study, we propose a novel strategy for fabricating precisely positioned, long-range ordered nanowire arrays by controlling the directional liquid transport of conical fiber arrays (CFAs) on asymmetrically modified silicon templates patterned with periodic spindle-shaped micropillars. The intrinsic properties of CFAs and the tailored wettability of silicon templates play critical roles in nanowire fabrication. CFAs generates quasi-unidirectional surface tension (Fγ), facilitating precise control over the retraction of liquid films and ensuring strict nanowire alignment in the dewetting direction. Meanwhile, high-adhesion hydrophobic surfaces effectively enhance the pinning behavior of the three-phase contact line during the retraction process, thereby improving the liquid bridge stability. It is noteworthy that the method developed for preparing high-yield arrays of ultralong nanowires exhibits remarkable universality. This approach can be widely applied to the synthesis of suspended nanowires using diverse polymers such as polystyrene sulfonic acid, poly(vinyl alcohol), polyvinylpyrrolidone, polyethylene glycol, and sodium alginate as solutes, achieving a robust formation rate exceeding 80% for nanowires that surpass 16 μm in length. These findings contribute valuable knowledge for the scalable production of suspended 1D nanostructures, furthering advancements in nanoscale device development.

Patterned Surface Energy for Modulating Solid-Liquid Interfacial Properties

Surface energy, as an intrinsic property of solids, plays a crucial role in modulating the characteristics of solid surfaces, especially of the solid-liquid interface. Due to inevitable processes such as surface adsorption or contamination, the surface energy of practical solids is usually nonuniform. However, if this nonuniformity is rationally designed and effectively utilized, it is capable of endowing great potential for liquid manipulation. With the rapid development of microfabrication and surface modification techniques, a variety of artificial patterned surface energy surfaces (PSESs) have been fabricated, which extend the diversity, tunability, and precision of liquid-based applications. In this review, we discuss the regulation of solid-liquid interface properties with PSESs from a relatively macroscopic perspective, particularly focusing on how to control matter and energy through rational design. First, we provide a brief introduction about the definition and significance of PSESs. Then, matter selective adhesion by PSESs is summarized, including liquid dynamics regulation, crystallization inducement, and biosample self-distribution. In the following, we discuss how PSESs regulate physical fields, including the thermal field, electric field, and acoustic field, with an explanation centered on discontinuous solid-liquid contact on PSESs. Finally, associated challenges of surface energy regulation for liquid-based scenarios are included.

Study on the discoloration phenomenon caused by iron ion oxidation in Boston ivy pads and its effect on adhesion force

Boston ivy has received much attention from researchers owing to its exceptional climbing abilities. However, many aspects of their adhesion behavior remain unresolved. Our research has discovered a phenomenon of oxidation and discoloration in Boston ivy pads, which leads to a significant decrease in adhesion force. In this study, we conducted a comprehensive investigation into the oxidation discoloration phenomenon. Through XPS analysis, we confirmed that the transition from Fe2+ to Fe3+ in the pad is the primary cause of the oxidation discoloration reaction. Furthermore, by conducting in situ adhesion testing using AFM, we observed a decrease in adhesion during the oxidation of iron ions. The magnitude of adhesion is closely related to the amount of pyrocatechol. Following the oxidation reaction, iron ions chelate with more pyrocatechol, resulting in a decrease in the available pyrocatechol content for adhesion. To validate this mechanism, we designed and prepared a biomimetic composite adhesion surface of a PDMS hydrogel. This composite surface improved oxidation resistance through the hydrogel, demonstrating improved adhesion performance. These findings offer promising prospects for the application of bionic materials in various fields.

Deep Learning-Based Design Method for Acoustic Metasurface Dual-Feature Fusion

Existing research in metasurface design was based on trial-and-error high-intensity iterations and requires deep acoustic expertise from the researcher, which severely hampered the development of the metasurface field. Using deep learning enabled the fast and accurate design of hypersurfaces. Based on this, in this paper, an integrated learning approach was first utilized to construct a model of the forward mapping relationship between the hypersurface physical structure parameters and the acoustic field, which was intended to be used for data enhancement. Then a dual-feature fusion model (DFCNN) based on a convolutional neural network was proposed, in which the first feature was the high-dimensional nonlinear features extracted using a data-driven approach, and the second feature was the physical feature information of the acoustic field mined using the model. A convolutional neural network was used for feature fusion. A genetic algorithm was used for network parameter optimization. Finally, generalization ability verification was performed to prove the validity of the network model. The results showed that 90% of the integrated learning models had an error of less than 3 dB between the real and predicted sound field data, and 93% of the DFCNN models could achieve an error of less than 5 dB in the local sound field intensity.

Ultrasonic barrier-through imaging by Fabry-Perot resonance-tailoring panel

Imaging technologies that provide detailed information on intricate shapes and states of an object play critical roles in nanoscale dynamics, bio-organ and cell studies, medical diagnostics, and underwater detection. However, ultrasonic imaging of an object hidden by a nearly impenetrable metal barrier remains intractable. Here, we present the experimental results of ultrasonic imaging of an object in water behind a metal barrier of a high impedance mismatch. In comparison to direct ultrasonic images, our method yields sufficient object information on the shapes and locations with minimal errors. While our imaging principle is based on the Fabry-Perot (FP) resonance, our strategy for reducing attenuation in our experiments focuses on customising the resonance at any desired frequency. To tailor the resonance frequency, we placed an elaborately engineered panel of a specific material and thickness, called the FP resonance-tailoring panel (RTP), and installed the panel in front of a barrier at a controlled distance. Since our RTP-based imaging technique is readily compatible with conventional ultrasound devices, it can realise underwater barrier-through imaging and communication and enhance skull-through ultrasonic brain imaging.

Hybrid Metasurfaces for Perfect Transmission and Customized Manipulation of Sound Across Water-Air Interface

Extreme impedance mismatch causes sound insulation at water-air interfaces, limiting numerous cross-media applications such as ocean-air wireless acoustic communication. Although quarter-wave impedance transformers can improve transmission, they are not readily available for acoustics and are restricted by the fixed phase shift at full transmission. Here, this limitation is broken through impedance-matched hybrid metasurfaces assisted by topology optimization. Sound transmission enhancement and phase modulation across the water-air interface are achieved independently. Compared to the bare water-air interface, it is experimentally observed that the average transmitted amplitude through an impedance-matched metasurface at the peak frequency is enhanced by ≈25.9 dB, close to the limit of the perfect transmission 30 dB. And nearly 42 dB amplitude enhancement is measured by the hybrid metasurfaces with axial focusing function. Various customized vortex beams are experimentally realized to promote applications in ocean-air communication. The physical mechanisms of sound transmission enhancement for broadband and wide-angle incidences are revealed. The proposed concept has potential applications in efficient transmission and free communication across dissimilar media.

Designing Versatile Superhydrophilic Structures via an Alginate-Based Hydrophilic Plasticene

The rational design of superhydrophilic materials with a controllable structure is a critical component in various applications, including solar steam generation, liquid spontaneous transport, etc. The arbitrary manipulation of the 2D, 3D, and hierarchical structures of superhydrophilic substrates is highly desirable for smart liquid manipulation in both research and application fields. To design versatile superhydrophilic interfaces with various structures, here we introduce a hydrophilic plasticene that possesses high flexibility, deformability, water absorption, and crosslinking capabilities. Through a pattern-pressing process with a specific template, 2D prior fast spreading of liquids at speeds up to 600 mm/s was achieved on the superhydrophilic surface with designed channels. Additionally, 3D superhydrophilic structures can be facilely designed by combining the hydrophilic plasticene with a 3D-printed template. The assembly of 3D superhydrophilic microstructure arrays were explored, providing a promising route to facilitate the continuous and spontaneous liquid transport. The further modification of superhydrophilic 3D structures with pyrrole can promote the applications of solar steam generation. The optimal evaporation rate of an as-prepared superhydrophilic evaporator reached ~1.60 kg·m^-2·h^-1 with a conversion efficiency of approximately 92.96%. Overall, we envision that the hydrophilic plasticene should satisfy a wide range of requirements for superhydrophilic structures and update our understanding of superhydrophilic materials in both fabrication and application.

Remote Water-to-Air Eavesdropping with a Phase-Engineered Impedance Matching Metasurface

Efficiently receiving underwater sound remotely from air is a long-standing challenge in acoustics hindered by the large impedance mismatch at the water-air interface. Here, a phase-engineered water-air impedance matching metasurface is proposed and experimentally demonstrated for remote and efficient water-to-air eavesdropping. The judiciously designed metasurface with near-unity transmission efficiency, long monitoring distance, and high mechanical stiffness is capable of making the water-air interface acoustically transparent and, at the same time, freewheelingly patterning the transmitted wavefront. This enables efficient control over the effective spatial location of a distant airborne sensor such that it can measure underwater signals with large signal-to-noise ratios as if placed close to the physical underwater source. Such airborne eavesdropping of underwater sound is experimentally demonstrated with a measured sensitivity enhancement of nearly 10⁴ at 8 kHz, far from achievable with the current state-of-the-art methods. Moreover, the opportunities of using the proposed metasurface for cross-media orbital-angular-momentum-multiplexed communication and underwater acoustic window are also demonstrated. This metasurface opens new avenues for communication and sensing in inhomogeneities with totally reflective interfaces, which may be translated to nano-optics and radio frequencies.