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We present a novel coupled fluid‐poroelastic model and an associated numerical upscaling procedure to calculate seismic attenuation and velocity dispersion in porous rocks induced by fluid pressure diffusion (FPD) in the presence of mesoscopic fluid‐saturated voids, such as, for example, vugs or factures. By applying appropriate interface conditions, the proposed model couples the Navier‐Stokes equations for viscous fluids with Biot's equations of poroelasticity to model the mesoscopic voids and the embedding background, respectively. A finite element method is employed to solve the coupled problem for a set of three relaxation tests, which enables us to compute the complex‐valued and frequency‐dependent equivalent stiffness matrix of the considered synthetic sample. The newly proposed fluid‐poroelastic approach is compared with a purely poroelastic one as well as a fluid‐elastic approach in a benchmark model containing interconnected mesoscopic fractures embedded in a poroelastic background. We obtain excellent agreement for the proposed approach and the purely poroelastic model by optimizing the material properties of the fractures for the latter, which demonstrates both the correctness and advantages of our method over the purely poroelastic approach for modeling fluid‐saturated mesoscopic voids. We also observe that, while the coupled fluid‐elastic approach and the proposed method provide consistent results with regard to seismic attenuation due to the fracture‐to‐fracture FPD, the latter also allows to account for the effects of fracture‐to‐background FPD. Finally, we employ the proposed methodology to explore the seismic characteristics of a synthetic "vuggy" carbonate‐type sample, for which we visualize and interpret the resulting seismic attenuation in terms of FPD between the microscopic and mesoscopic pores. Plain Language Summary: Seismic waves are commonly employed to study porous and/or fractured geological formations in the Earth's upper crust. In the presence of relatively small heterogeneities, such as fluid‐saturated fractures or vugs, seismic waves may exhibit velocity variation and amplitude decay due to fluid pressure diffusion processes, which are important characteristics of seismic waves. To date, it remains difficult to understand how complex and fluid‐saturated voids impact these seismic characteristics. To address this problem, we propose a novel coupled fluid‐poroelastic model and develop a corresponding numerical upscaling procedure to calculate seismic characteristics of porous media containing mesoscopic heterogeneities. Our results demonstrate that the proposed approach is more accurate and flexible than previous related models, which, in turn, opens new and interesting perspectives for the seismic exploration of corresponding geological environments. Key Points: We develop a numerical upscaling procedure to calculate seismic signatures based on a novel coupled fluid‐poroelastic modelIn the presence of fluid‐saturated mesoscopic voids, the newly proposed coupled approach is more flexible and more accurate than existing methodologiesApplication to a synthetic "vuggy" carbonate‐type rock sample provides new insights into seismic energy dissipation related to fluid pressure diffusion between microscale and mesoscale pores [ABSTRACT FROM AUTHOR]

To date, high‐efficiency low‐frequency broadband noise control remains a great challenge in the scientific and engineering community. Herein, a composite acoustic metasurface is proposed that is composed of gradient hybrid unit structure with a perforated panel, coiled‐up cavities, and a separating plate. By controlling the position of the separating plate, a series of broader multistage sound‐absorbing peaks corresponding to different resonant frequencies can be achieved. A highly efficient low‐frequency broadband sound‐absorbing metasurface by combining the multiple unit structures with different absorbing peaks is realized successfully, possessing an average sound absorption coefficient above 0.94 in the range from 470 to 3130 Hz with a subwavelength thickness of only 89.8 mm. Furthermore, the proposed structure maintains a good mechanical performance with the compression elastic modulus of 375.57 MPa due to the designed honeycomb structures. Compared with the traditional sound‐absorbing materials, the composite hybrid honeycomb metasurface can achieve an excellent absorption performance with a simple and stable structure for practical application of low‐frequency noise control. [ABSTRACT FROM AUTHOR]

Metasurfaces have opened up a new era of manipulating electromagnetic waves including the implementation of invisibility cloaks, based on their simple design and ultrathin thickness. However, a perfect design of metasurface structures, such as the carpet cloak on non‐Euclidean geometries independent of the state of polarization and the azimuthal angle of wave incidence, remains unrealized in practice. Herein, a new design and fabrication approach which annihilates current defects of metasurface structures is proposed and illustrated by using a rapid prototyping of a 3D spherical carpet cloak. Benefited from its perfectly symmetric distribution of meta‐atoms, the carpet cloak is demonstrated to be fully insensitive to all polarizations and azimuthal angles of incident waves from both simulated and experimental results. The proposed cloak is also electrically large with 7λ0 in length and 1.2λ0 in height, which opens up the possibility of practical applications in areas governed by wave physics. [ABSTRACT FROM AUTHOR]

Herein, a new method for steering liquid metals (LMs) using only a magnetic field in open 3D space is proposed. The magnetic LM is composed of the alloy Galinstan and iron particles. The 3D horizontal and vertical manipulation of a magnetic LM can be realized via an external magnetic field. The magnetically actuated LM is not only manipulated on various complex pathways in the horizontal plane, but also vertically in 3D space without the use of electrolytes and electrodes. As a proof‐of‐principle, an intelligent delivery vehicle that can avoid obstacles and traps horizontally and overcome gravity vertically to offload a cargo is designed and implemented successfully. Furthermore, a biomimetic soft robotics that can realize both in‐plane and out‐of‐plane locomotion is demonstrated using only magnetic field. The novel 3D motion of the demonstrated system facilitates the development of practical LM‐based smart structures and devices. [ABSTRACT FROM AUTHOR]

To investigate the changing rules between sound absorbing performance and geometrical parameters of porous fibrous metal materials (PFMMs), this paper presents a fractal acoustic model by incorporating the static flow resistivity based on Biot-Allard model. Static flow resistivity is essential for an accurate assessment of the acoustic performance of the PFMM. However, it is quite difficult to evaluate the static flow resistivity from the microstructure of the PFMM because of a large number of disordered pores. In order to overcome this difficulty, we firstly established a static flow resistivity formula for the PFMM based on fractal theory. Secondly, a fractal acoustic model was derived on the basis of the static flow resistivity formula. The sound absorption coefficients calculated by the presented acoustic model were validated by the values of Biot-Allard model and experimental data. Finally, the variation of the surface acoustic impedance, the complex wave number, and the sound absorption coefficient with the fractal dimensions were discussed. The research results can reveal the relationship between sound absorption and geometrical parameters and provide a basis for improving the sound absorption capability of the PFMMs. [ABSTRACT FROM AUTHOR]

The microstructures were fabricated by hot embossing method using biodegradable material PLGA poly(lactic-co-glycolic acid), to serve as the drug carriers in the drug delivery system. The embossing process was studied in a combination of simulations and experiments. Firstly, the viscoelastic model of PLGA was built after testing the material properties. Secondly, the hot embossing process was simulated by ABAQUS finite element software. The deformation rules of PLGA during hot embossing were then achieved. The pressures inside the PLGA materials were different at various places during hot embossing, which lead to the differences of the filling speeds. As a result, the inner structures were easier to get formed than the outer structures. And the fluidity of PGLA would increase with the raising temperature, which however caused serious material overflow. Finally the hot embossing experiments were presented to verify the simulation results. Agreed with the filling rules of the simulation, enough duration was necessary to let the outer corners of the microstructures be formed completely. Moreover the trapped air in the grooves was compressed into small bubbles at the corners. It was also found that the material overflow could be prevented in the use of nonisothermal hot embossing method. [ABSTRACT FROM AUTHOR]

According to the low temperature and high effective bonding problem of microdevices made of degradable polymer PLGA, chemical, plasma, and UV irradiation method are used to study the experimental surface treatment of PLGA films and microdevices bonding process. The results show that all three methods can reduce the surface contact angle of PLGA films, the contact angle increases with time at room temperature, and the PLGA films contact angle is almost unchanged under refrigeration. The PLGA film bonding temperature is significantly reduced after UV irradiation, and the bonding interfaces also generate diffusion cross linking layer are dense and uniform. [ABSTRACT FROM AUTHOR]

High speed motorized spindle has become a key functional unit of high speed machine tools and effectively promotes the development of machine tool technology. The development of higher speed and more power puts forward the stricter requirement for the performance of motorized spindle, especially the dynamic performance which affects the machining accuracy, reliability, and production efficiency. To overcome the problems of ineffective loading and dynamic performance measurement of motorized spindle, a noncontact electromagnetic loading device is developed. The cutting load can be simulated by using electromagnetic force. A new method of measuring force by force sensors is presented, and the steady and transient loading force could be measured exactly. After the high speed machine spindle is tested, the frequency response curves of the spindle relative to machine table are collected at 0~12000 rpm; then the relationships between stiffness and speeds as well as between damping ratio and speeds are obtained. The result shows that not only the static and dynamic stiffness but also the damping ratio declined with the increase of speed. [ABSTRACT FROM AUTHOR]

Metasurfaces have an extraordinary wavefront manipulation capability to generate various functionalities with ultrathin planar structures and provide an unprecedented means of easily achieving invisibility carpet cloaks in practice. However, due to the limitation of the fabrication method, great challenges exist in the implementation of curved or spherical metasurface‐based cloaks with good performance. Here, a novel fabrication method that combines 3D printing via stereolithography and injection molding of liquid metal is proposed, and an arched metasurface carpet cloak operating in the microwave domain is realized successfully as a demonstration. Experiments show that the proposed ultrathin and polarization‐independent cloak has good stealth performance in terms of bandwidth and angular span. Notably, the fabrication method is also suitable for obtaining other metasurfaces and metamaterials with arbitrary shapes, which may greatly promote the practical application of artificial electromagnetic structures. [ABSTRACT FROM AUTHOR]