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• A new method of coding is proposed based on a four-mode coding acoustic metasurface of simple structure. • The frequency-selective modulation of reflected waves is realized. • The equivalent circuit principle and decoupling effect of the meta-atom are theoretically and numerically analyzed. • We also filter and suppress the redundant diffraction orders of the reflected waves to eliminate side lobes. • The frequency degree of freedom plays a key role in the metasurface performs. Designing a multiplexing metasurface to exhibit diverse functionalities has been a trend in electromagnetics, acoustics, and mechanics. Here, we report a simple method to design the 2-bit coding acoustic metasurface by combining the Helmholtz resonator-like structures. Each meta-atom has four coding modes to independently modulate the wave fronts at two different frequencies. The equivalent circuit principle and decoupling effect are theoretically and numerically analyzed to clarify the underlying physical mechanism of our design. We filter and suppress the redundant diffraction beams to realize perfect negative reflection by controlling the number of outgoing diffraction modes. Considering the impact of loss, we simulate the scattered pressure and directivity of far field radiation for oblique illumination at two predesigned frequencies, the results of which show good agreement with the predicted ones. Our work may have potential in the design of multiplexing, frequency-selective, and programmable acoustic devices. [ABSTRACT FROM AUTHOR]

The artificially periodic structures with the bandgap (BG) features provide a fantastic way for elastic wave manipulation. However, omnidirectional control of elastic waves at low-frequency remains a challenge, especially in the engineering application, due to the great different material parameters of the structure's components. In this work, we present the design of a three-dimensional syndiotactic metastructure (STM) and isotactic metastructure (ITM) composed of a single material with the same density and stiffness. A low-frequency broad bandgap occurs in the global band structure of STM. Meanwhile, it also retains the same high-frequency ultra-wide BG as that of ITM. The formation of the low-frequency BG of STM is attributed to the simultaneous activation of rotation and translation modes. The static deformation analysis indicates that STM has a unique translational and rotational coupling mechanism. The frequency response results reveal that the coupling mechanism can also enhance the attenuation of high-frequency BG. • Three-dimensional syndiotactic elastic metastructure with single-phase material. • Realization of ultra-low frequency band gap with the same stiffness and density. • High-frequency broad bandgap is realized by modal separation. • The attenuation of high-frequency bandgap in syndiotactic metastructure is enhanced. [ABSTRACT FROM AUTHOR]

Optical excitation of mechanical resonators has long been a research interest, since it has great applications in the physical and engineering field. Previous optomechanical methods rely on the wavelength-dependent, optical anti-damping effects, with the working range limited to the blue-detuning range. In this study, we experimentally demonstrated the excitation of optomechanical resonators by periodical modulation. The wavelength working range was extended from the blue-detuning to red-detuning range. This demonstration will provide a new way to excite mechanical resonators and benefit practical applications, such as optical mass sensors and gyroscopes with an extended working range. [ABSTRACT FROM AUTHOR]

Low-frequency vibration-bandgaps in elastic metamaterials open new possibilities to minimize low-frequency vibration and noise. Unfortunately, fabricating a complete vibration bandgap for low frequencies still represents a challenging engineering task. In this paper, a new type of a low-frequency complete vibration bandgap in a thin non-metal elastic metamaterial plate is introduced and investigated numerically. The proposed elastic metamaterial plate consists of decoupling-resonators, which are deposited on a 2D, locally resonant phononic-crystal plate, made of an array of rubber fillers, which are embedded in a nonmetallic plate. The dispersion relationship, the power-transmission spectrum, and the displacement fields for the eigenmode are calculated using the finite element method. It is shown that coupling between the local resonance mode of the decoupling-resonators and the Lamb-wave mode of the epoxy plate, consistent with the modal superposition principle, is responsible for the formation of vibration bandgaps. Moreover, the equivalent spring-mass system for the coupling-resonators can be decoupled by introducing a rubber filler. In addition, both longitudinal and the transverse elastic wave bandgaps can be tuned to the same low-frequency range. As a result, a novel kind of low-frequency complete vibration bandgap, which can damp a low-frequency elastic wave, is produced. Furthermore, the effects of the decoupling-resonators on the vibration bandgap are investigated. It is now possible that an elastic metamaterial plate can be dampen with complete low-frequency vibration bandgaps, which can potentially be used for commercial noise and vibration reduction. [ABSTRACT FROM AUTHOR]

• An innovative 3D auxetic structure (3D CATS) was proposed based on the coupling connection of the tube and auxetic units. • The force responses exhibit multiple stages, and the tube and auxetic units played different roles during different stages. • The interaction between the auxetic units and the tube completely changes the deformation modes of the tube. • The SEA of the structure was significantly superior to most existing 2D and 3D auxetic structures. • Two sets of parameters were introduced to vary the compression displacement and force in the plateau stage. In this paper, a novel 3D composite auxetic tubular structure (3D CATS) connected by a thin-walled (TW) circular tube was proposed, and two sets of parameters h 1 , h 2 , and β , n were introduced to construct structural families with various geometries and mechanical properties. The mechanical responses of the 3D CATS were preliminarily explored through the quasi-static experiment. The good agreement between the experimental results and the finite element (FE) simulation verified the accuracy of the FE model. Subsequently, the coupling mechanism between the tube and auxetic units was revealed by analyzing the deformation modes and force responses. The results indicated that the deformation of auxetic units caused more plastic hinges in the tube to enhance the contact force seriously. Then, the 3D CATS was proved to exhibit better specific energy absorption (SEA) compared with other auxetic structures. Furthermore, the influence of h 1 , h 2 , and β , n on the responses was also discussed. The results showed that h 1 , h 2 can change the compression displacement points and forces, while β , n can adjust the stiffness and forces. The results can provide an important reference for the design and study of variable mechanical properties for innovative 3D auxetic structures with enhanced performance. [ABSTRACT FROM AUTHOR]

Shear wave splitting (SWS) is currently considered to be the most robust seismic attribute to characterize fractures in geological formations. Despite its importance, the influence of fluid pressure communication between connected fractures on SWS remains largely unexplored. Using a 3-D numerical upscaling procedure based on the theory of poroelasticity, we show that fracture connectivity has a significant impact on SWS magnitude and can produce a 90° rotation in the polarization of the fast quasi-shear wave. The simulations also indicate that SWS can become insensitive to the type of fluid located within connected fractures. These effects are due to changes of fracture compliance in response to wave-induced fluid pressure diffusion. Our results improve the understanding of SWS in fractured formations and have important implications for the detection and monitoring of fracture connectivity in hydrocarbon and geothermal reservoirs as well as for the use of SWS as a forecasting tool for earthquakes and volcanic eruptions. [ABSTRACT FROM AUTHOR]

In this letter, we propose a theoretical description of double nonuniform cross-section (DNUCS) channels, which can achieve the designed absorption coefficient with a shorter channel overall. Introducing channels with a nonuniform cross section changes the period of the surface acoustic impedance, which has a significant impact on the dominant operating frequencies. In this paper, we give the relation between the absorption peak position and the geometric parameters, which can be used to design DNUCS channels with a specific operating frequency. Furthermore, multiple nonuniform cross-section channels can be studied in the same way. Based on the above theory, we reduce the operating absorption frequency range of a new type of Fabry–Pérot absorbers to a lower regime in a constant volume. Our theoretical framework may be important in designing absorption metasurfaces and for further research. [ABSTRACT FROM AUTHOR]

Although the auxetic structure exhibits excellent mechanical properties, the low stiffness, and strength still limit its development. Considering the high stiffness and strength of the sandwich structure, a novel sandwich beam with an enhanced auxetic core (SCH SWB) was proposed in this paper. The accuracy of the finite element (FE) modeling was first verified by quasi-static bending experiments. Then, based on FE simulation, the deformation modes and energy absorption were explored. The results showed that local indentation and global bending deformation coexisted under the mid-span loading, and the core can absorb the most energy. Furthermore, using the analogy method, and based on the yield criterion and indentation response of the foam sandwich beam, a theoretical model was established to predict the force response, which considered the influence of local indentation on the overall bending, and the double-plateau characteristic of the auxetic core. The theoretical results were basically consistent with the simulation. Subsequently, the influence of the key parameters of the core and faces on the mechanical responses was discussed in depth, and it was found that changing the key geometric parameters and the material combination of the faces and the core can significantly vary the energy absorption capacity. Finally, several sandwich beams with different auxetic cores were compared, and the results proved that SCH SWB exhibited superior bending resistance and higher energy absorption. This paper presents a new idea and theoretical basis for studying the mechanical response of auxetic sandwich beams. The results show that the auxetic sandwich beam has great potential in aerospace, automobile crash, impact protection of key engineering structures, etc. • A novel sandwich beam with an enhanced SCH auxetic core was proposed and investigated. • The global bending and local indentation were co-exist under quasi-static concentrated loading. • A theoretical analytical model was firstly established to predict the mechanical response of the beam under fixed boundary. • The contribution of the core on the energy absorption was higher than the top/bottom faces. • The SCH sandwich beam exhibited better bending resistance TEA and SEA capacity compared other common auxetic sandwich beam. [ABSTRACT FROM AUTHOR]

Low-frequency sound-absorbing meta-surface is an eye-catching topic in scientific and engineering community. Numerous studies of low-frequency sound-absorbing meta-surface have been explored. However, an acoustic meta-surface with simultaneous low-frequency sound absorption and reversible shape changing property remains absent up till now. In this paper, we propose an acoustic meta-surface by coupling 15 sub-units to realize a desired low-frequency sound absorption. The measured energy attenuation of acoustic meta-surface is average up to 90% from 300 to 1000 Hz, well agreed with stimulated results. The sound absorption band of the designed structure can be customized through flexibly adjusting the sub-units. More surprisingly, the proposed acoustic meta-surface is capable of withstanding large loads and possesses a reversible shape changing property. The unique low-frequency sound absorption and the mechanical properties open interesting perspectives for the use of acoustic meta-surface in low-frequency noise control applications. [ABSTRACT FROM AUTHOR]

To better suppress the structural vibration in the micro vibration and harsh environment, a new type of damper, tuned particle damper (TPD), was designed by combining the advantage of classical dynamic vibration absorber (DVA) and particle damper (PD). An equivalent theoretical model was established to describe the dynamic behavior of a cantilever system treated with TPD. By means of a series of sine sweep tests, the dynamic characteristic of TPD under different excitation intensity was explored and the damping performance of TPD was investigated by comparing with classical DVA and PD with the same mass ratio. Experimental results show that with the increasing of excitation intensity TPD shows two different dynamic characteristics successively, i.e., PD-like and DVA-like. TPD shows a wider suppression frequency band than classical DVA and better practicability than PD in the micro vibration environment. Moreover, to characterize the dynamic characteristic of TPD, a simple evaluation of the equivalent dynamic mass and equivalent dynamic damping of the cantilever system treated with TPD was performed by fitting the experimental data to the presented theoretical model. Finally, based on the rheology behaviors of damping particles reported by the previous research results, an approximate phase diagram which shows the motion states of damping particles in TPD was employed to analyze the dynamic characteristic of TPD and several motion states of damping particles in TPD were presented via a high-speed camera. [ABSTRACT FROM AUTHOR]

In this paper, we numerically and experimentally demonstrate the low-frequency broadband elastic wave attenuation and vibration suppression by using plate-type elastic metamaterial, which is constituted of periodic double-sides stepped resonators deposited on a two-dimensional phononic plate with steel matrix. The dispersion relations, the power transmission spectra, and the displacement fields of the eigenmodes are calculated by using the finite element method. In contrast to the typical phononic plates consisting of periodic stepped resonators deposited on a homogeneous steel plate, the proposed elastic metamaterial can yield large band gap in the low-frequency range, resulting in the low-frequency broadband elastic wave attenuation. The formation mechanisms of the band gap as well as the effects of material and geometrical parameters on the band gap are further explored numerically. Numerical results show that, the formation mechanism of opening the low-frequency band gap is attributed to the coupling between the local resonant Lamb modes of two-dimensional phononic plate and the resonant modes of the stepped resonators. The band gap can be significantly modulated by the material and geometrical parameters. The properties of broadband gaps of the proposed subwavelength scale elastic metamaterials can potentially be applied to vibration and noise reduction in the audio regime as well as broadband elastic wave confinement and modulation in ultrasonic region. [ABSTRACT FROM AUTHOR]

Utilizing absorbers with sub-wavelength thickness for low-frequency broadband noise control is a challenging problem, and rapid on-demand design of structures based on target noise frequency has received continuous attention. In this work, nested cavities are introduced into the typical neck-embedded Helmholtz resonator (NEHR) to obtain the nested neck-embedded Helmholtz resonator (NNEHR), which exhibits better cavity partitioning volume fraction and covers wider sound absorption band. Both theoretical analysis and simulations demonstrate that NNEHR possesses superior acoustic properties: generating an additional absorption peak, lowering the position of the first absorption peak by 11 %, and increasing the absorption coefficient by 4.7 %. Instantaneous velocity fields and thermal-viscous energy dissipation density illustrate that the efficient sound absorption of NNEHR originates from resonant dissipation in the neck and surrounding areas. Furthermore, by combining the theoretical model with genetic algorithms, three sets of NNEHR metasurfaces are optimized. The optimized structures achieve average absorption coefficients of 0.831, 0.913, and 0.885 in the range of 250–550 Hz, 400–1000 Hz, and 500–2000 Hz, with a thickness of only 50 mm, reflecting sub-wavelength, low-frequency broadband sound absorption characteristics. The excellent absorption stems from synergistic coupled weak resonances and higher-order absorption peaks of constituent units, and the overdamping characteristic ensures the realization of the optimal structure with minimal thickness. The contribution of weak resonant units to the total sound absorption performance can be measured by the surface admittance normalized by the total incident area, and the essence of the coupling effect is the strong interaction between units with adjacent absorbing frequencies. The proposed structure exhibits good sound absorption performance and great adjustability, while the genetic algorithm optimization based on the theoretical model demonstrates high efficiency and robustness, providing a methodology for the design and on-demand optimization of low-frequency broadband structures. • Nested neck-embedded Helmholtz resonator for low-frequency sound absorption. • Broadband sound absorber based on higher-order peak and synergistic coupled weak resonances. • Efficient on-demand design based on analytical model and genetic algorithm. • Low-frequency broadband from 250 to 550 Hz. [ABSTRACT FROM AUTHOR]

• Chiral resonator-based metastructure for low-frequency bandgap opening. • Double attenuation notches in coupling metastructure. • Lower-frequency bandgap metastructure under equal mass and equal stiffness. Isolating low-frequency vibrations is a challenge in engineering due to their long wavelength. The bandgap within inertial amplification metastructures has proven to be an effective solution for isolating low-frequency vibrations. In this study, a chiral local resonator is proposed and integrated into a syndiotactic chiral inertial amplification metastructure (SCM) to create a low-frequency bandgap. Under equal mass and stiffness conditions, SCM-CR exhibits a bandgap starting frequency 32.3 % lower than that of traditional metastructures with traditional local resonators (TM-TR), and the normalized width of the bandgap is 31.7 % wider than TM-TR. The low-frequency bandgap is attributed to the presence of chiral local resonators. The inertial amplification effect induced by the chiral structure results in a resonance frequency lower than that of local resonators with equivalent mass and stiffness. Within the low-frequency bandgap, the transmission of the SCM-CR proposed in this study exhibits double attenuation notches over a specific number of periods, leading to the normalized width of the deep attenuation region 45.8 % broader than that of traditional metastructures with chiral local resonators (TM-CR). The tunability of the bandgap has also been investigated. Experimental results verified the double attenuation notches and the tunability of the bandgap. This work provides a promising solution for low-frequency vibration isolation. [Display omitted] [ABSTRACT FROM AUTHOR]

The negative Poisson's ratio (NPR) mechanical metamaterials exhibit excellent mechanical properties, whereas their low stiffness limits the development. In this paper, we investigated an NPR mechanical metamaterial: star-circle honeycomb (SCH), which possesses enhanced stiffness compared to the classical star-shaped honeycomb (SH). Based on the Castigliano's second theorem and the principle of virtual work, a theoretical model was built to calculate the effective elastic properties of the SCH, and validated by the finite element method (FEM). The comparison with the SH showed that the SCH possessed a significantly enhanced elastic modulus. Also, we find that the elastic properties can be adjusted broadly and tailored to meet the engineering needs by selecting parameters reasonably. Subsequently, the anisotropic quasi-static compression responses of the SCH were studied. The results showed that the plateau stress and energy absorption capacity in the y -direction load were both better than that in the x -direction load. The parameter study indicated that θ and ψ produced a greater impact on the quasi-static responses. A reasonable combination of parameters can give full play to the mechanical properties of the structure. This work provided a new design idea for improving the stiffness and choosing the optimal in-plane loading direction of metamaterials. • The theoretical enclosed formulas of effective elastic properties for the SCH are derived. • The coupling between thin-walled circle and corner point strongly enhances the effective Young's modulus. • The SCH exhibits two plateau stages in the y direction, while three plateau stages in the x direction. • The energy absorption of the SCH in the y direction is greatly better than that in the x direction. [ABSTRACT FROM AUTHOR]

• A composite structure RSCS is proposed combining the re-entrant structure with the rotated square structure. • The deformation is uniform and ordered and there are three-step deformation and three plateau stages. • The geometric configuration has a significant effect on the deformation modes and energy absorption. • A general design method is proposed to constructing more innovative structures with multi-step deformation and multi-plateau stages. To solve the problems that the existing negative Poisson's ratio (NPR) structures only exhibit single plateau stage and irregular deformation modes, a novel hierarchical NPR structure called rotating star-circle structure (RSCS) was proposed. We respectively replaced the hinges and the rigid solid square in the classical rotational rigid square with the beam-like links and star-circle substructure. Through the quasi-static experiment, the FE modeling was validated. According to energy conservation, a theoretical model was established to predict the equivalent elastic modulus. The FE analysis was carried out to verify the theoretical model. The deformation modes and compression responses were studied by the FE method. It was found that there were three-step deformation and three plateau stages. Further, the deformation mechanisms were revealed based on the deformation modes and mechanical responses. Additionally, the parameters study showed that the geometric configuration significantly affected the deformation modes and mechanical responses. Compared with other auextic structures in the SEA, the RSCS exhibited better energy absorption. Lastly, we proposed a general design method based on the equal chord division to construct the multi-plateau structure. This research was a reference for the multi-functional application of the NPR structure and improving their energy absorption. [ABSTRACT FROM AUTHOR]

Dissipated power and motion state of granular balls in a quasi-2D closed container subjected to vertical fixed-frequency excitation are investigated by comparing discrete element simulation with experiment test. The verified DEM (Discrete Element Method) model is employed to further study the dissipation characteristics and dynamical behaviors of granular balls under the conditions of different excitation amplitude A and excitation frequency f. Damping contour and phase diagram of vibrated granular balls in the A- f plane of external excitation are obtained respectively, which indicate nine different damping phases of vibrated granular balls. An unknown high damping granular phase that we call as Wave-solid state is revealed and the dissipation behaviors of three high damping granular phases including the Wave-solid state are analyzed based on the velocity profile, density profile and loss profile of vibrated granular balls. Further, the dynamical characteristics of the Wave-solid state and the commonality of the three high damping granular phases are preliminary discussed respectively. Finally, based on the previous and present research results, two solutions by controlling the jamming transition of vibrated granular materials in granular dampers for the universal design of granular dampers are presented. [ABSTRACT FROM AUTHOR]

Low-frequency noise control has aroused continuous interests owing to the intolerant structural thickness of traditional sound absorbing materials comparable to the working wavelength. The low-frequency sound absorbing materials remain challenging in scientific and engineering communities until now. Herein, a controllable broadband sound absorbing metasurface is designed and fabricated successfully by combining micro-perforated panel, coiled channel and embedded partition boards with the thickness of only 7 cm. The proposed metasurface possesses an average absorption coefficient over 0.8 within 0°–75° wide incident angle. Most importantly, the frequency of the absorption peak could be tuned flexibly by changing the number of partition boards in the cavity, providing an effective way for sound absorption on-demand design. The proposed acoustic metasurface opens the possibility of real-life application in low-frequency noise control engineering field. [ABSTRACT FROM AUTHOR]

In order to improve the energy absorption capacity of the honeycomb, a combined auxetic honeycomb is designed in this paper. By using the double-inclined walls replacing the horizontal walls of the star-shaped honeycomb (SSH), and introducing a thin-walled circle contacting with the four concave corners of the SSH, the star-circle honeycomb (SCH) is designed. The in-plane dynamic crushing behaviors was explored based on finite element method (FEM). There are three types of deformation modes observed with different impact velocity, including low-, medium- and high-velocity loading modes and the stress-strain curve exhibits two plateau stress stages. Based on the deformation characteristics of the representative unit, theoretical calculation models were established to estimate the plateau stress of the SCH under low- and high-velocity loading according the conservation of energy and the theoretical calculation was in keep well with the numerical simulation. A deformation modes map was summarized to investigate the effects of the impact velocity and the relative density on the deformation modes and the energy absorption capability and the dynamic Poisson's ratio were studied. The result shows that the SCH presents better energy absorption compared with SSH as well as retaining the negative Poisson's ratio property. The deformation mechanism was revealed form the structural design and plastic hinge dissipation. This work presents a different design strategy for the auxetic honeycomb, expected to guide the design of more novel auxetic with better energy absorption and mechanical property. • A combined auxetic honeycomb is designed through the intracellular common-node contact between the star and the circle. • Two plateau stages for the honeycomb appears under low-velocity loading with enhanced crushing strength and energy absorption. • Two theoretical calculation models are established for the plateau stress under low velocity and high velocity. • The thin-walled circle can dissipate more energy owing to the lateral compression caused by the transverse contraction. [ABSTRACT FROM AUTHOR]

Conventional sound shielding structures is difficult to meet the requirements of low-to-middle frequency broadband sound insulation and free ventilation. In this paper, we propose a ventilated metamaterial silencer based on Fano-like interference, which can achieve the sound transmission loss (STL) of more than 10 dB in the range of 516–970 Hz with subwavelength thickness (0.11 λ) while remains an opening area ratio of 23%. The designed silencer is composed of a large central orifice and four surrounding coiling channels, making the sound waves passing through the two areas generate Fano-like asymmetric transmission spectrum and form efficient reflection to insulate sound coming from various directions. The parametric studies are also carried out to investigate the tunable acoustic performance. Experiment measurement matches well with the simulation results. In the future, the proposed silencer may have potential applications in practical environments requiring broadband sound insulation and free air flows. [ABSTRACT FROM AUTHOR]

We present here the design, fabrication and experimental demonstration of a composite woodpile structure for integral imaging and invisibility cloaking. The structure composed of two layers of 3D-printed woodpile structure and a designed screen beneath it. The 3D display capability is first demonstrated by projecting a real 3D image from the screen. An invisibility carpet cloak is then demonstrated to hide an object on the ground in the visible regime by projecting a 3D virtual image of the ground from a pyramidal-shape screen. Comparing to transformation-optics-based or metasurface-based carpet cloaks, the current cloak can be both easily fabricated in large-scale simply using 3D printing and has an ultra-thin thickness with only 1.4 mm comparing to the height of the object of 4.7 mm. A polar viewing angle up to 20° with an arbitrary azimuthal viewing angle can be obtained with the present cloak. Our approach enables a cost-effective way towards practical 3D-printed optical components using the straight-forward fused deposition modeling method, leading to potential applications in 3D displays, integral microscopy, smart windows and augmented reality. Unlabelled Image • 3D display and invisibility based on woodpile-type lens array are achieved by projecting real and virtual 3D images. • The cloaking effect can span a range of viewing angles while the cloak can be much thinner than the size of object. • The extrusion-based 3D printing enables low-cost and large-scale fabrication for integral imaging. [ABSTRACT FROM AUTHOR]

The multi-ceramic coupling diamond-structured photonic crystals containing alumina and yttria simultaneously were successfully fabricated by rapid prototyping based on stereolithography and multi-step gel-casting process. The lattice constant of the photonic crystal structures was chosen as 7 mm and the measured forbidden gap range lies between 27.2 GHz and 34.9 GHz. The gradually varied solid loading in volume of Al 2 O 3 powder and its controllable electromagnetic forbidden gap properties were investigated in such photonic crystals. It was found that, as the solid loading of Al 2 O 3 powder increased, the electromagnetic forbidden gap width gradually increased and the center frequency shifted to a lower frequency when electromagnetic waves transmitted along the coupling direction of photonic crystals. When the solid loading reached 60 vol%, electromagnetic forbidden gap of the photonic crystals was observed from 27.2 GHz to 34 GHz, and the forbidden gap width was 6.8 GHz which was 126.4% of that of the yttria photonic crystal (the forbidden gap from 30.9 GHz to 35.9 GHz) and 115.3% of that of the alumina photonic crystal (60 vol%, the forbidden gap from 26.4 GHz to 32.3 GHz). These results indicate that a diamond-structured photonic crystal with multi-ceramic coupling could effectively expand the electromagnetic forbidden gap width and may be beneficial for applications of photonic crystals in device. Moreover, this work offers a rapid prototyping technology to three-dimensional photonic crystals with considerable flexibility of materials choice. [ABSTRACT FROM AUTHOR]

The negative Poisson's ratio behavior of metastructures is usually achieved through the uneven structural stiffness distribution caused by the artificial pores in the material. However, the large porosity causes the poor stiffness and lowers the load capacity. The previous stiffness enhancement method inevitably caused a great reduction of negative Poisson's ratio. In this paper, a hierarchical embedded strengthening method is proposed to enhance the stiffness greatly in Honeycomb Metastructure while it still maintain the large negative Poisson's ratio. Both simulations and experiments demonstrate that our proposed design method can increase the normalized elastic modulus by 3.62 times despite the small negative Poisson's ratio reduction of 13.79%. This result is far superior to the negative Poisson's ratio reduction of 66.38% of the traditional strengthening method while the normalized elastic modulus increases by only 2 times. The hierarchical embedded strengthening method provides a new path for applications requiring larger negative Poisson's ratio and higher elastic modulus simultaneously. • A hierarchical embedded strengthening method of honeycomb metastructure for simultaneous the larger negative Poisson's ratio and higher stiffness is proposed. • The embedding of homogeneous negative Poisson's ratio metastructure is the key to maintain the larger negative Poisson's ratio. • In terms of controlling negative Poisson's reduction, the hierarchical embedded strengthening method (13.79% reduction) is far superior to the traditional strengthening method (66.38% reduction). [ABSTRACT FROM AUTHOR]

• A kind of tunable subunit named nested resonant rings (NRRs) is proposed. • The NRRs has a broadband bandwidth which can realize 2π phase range covering from 1000 Hz −8000 Hz. • Tunable acoustic metasurface is realized by 19 NRRs and can work in a broadband. • The proposed tunable acoustic metasurface has been demonstrated in abnormal reflection, illusion and focusing. The capability of a metasurface to freely engineer the wavefronts of phase and amplitude shows great prospect in acoustics. However, current designs generally have a fixed function such as wave focusing, wave trapping, cloaking, etc. To break these traditional restrictions, a tunable acoustic metasurface comprising an array of subwavelength unit cells has been proposed to achieve versatile functions. Each sub-unit contains two concentric resonant rings. The reflected phase of the sub-unit can be regulated by dynamically tuning the relative angle of the two nested resonant rings. According to the principle of phase compensation, versatile wavefronts can be realized in a subwavelength scale. Both simulation and experimental results of the sound fields reveal that the proposed metasurface has various functions, including acoustic wave direction control, acoustic illusion and acoustic focusing. Further, the multi-functions can be observed at multiple frequencies, indicating that the design is effective in a broad frequency range. This work presents a novel metasurface for a wide range of applications such as focusing, imaging and concealing. [ABSTRACT FROM AUTHOR]

• An update finger coiling-up method that can be used to design deep-subwavelength broadband sound absorbing metasurfaces is proposed. • The finger coiling-up method can improve the sound absorption coefficient and working bandwidth of the unit without increasing the thickness. • Compared with classic coiling-up method, the proposed method can simplify the complexity of the metasurface structures to facilitate fabrication. The bulky structure of traditional sound-absorbing materials limits its application to control low-frequency noise, and new deep-subwavelength low-frequency broadband acoustic materials have an urgent need. This paper proposes an update finger coiling-up method, which can improve the sound absorption coefficient and working bandwidth of the unit without increasing the thickness. In addition, the complexity of the structure can be simplified to facilitate manufacturing. The influence of the typical parameters of the unit on the sound absorption performance and the coupling performance of the unit are also studied. Finally, by combining 16 finger coiled-up units, a metasurface with continuous broadband sound absorption in the range of 375 Hz to 855 Hz is obtained, and the average sound absorption coefficient is above 0.85. In particular, the thickness of the metasurface is only 38 mm, which is 1/24 of the corresponding operating wavelength at 375 Hz. The proposed update finger coiling-up method provides a new idea for reducing the thickness of sound-absorbing materials, which will have good application prospects in noise control field. [ABSTRACT FROM AUTHOR]

In the field of low-frequency noise control, the locally resonant membrane and plate-type acoustic metamaterials (PAMMs) have received extensive attention from researchers due to its sub-wavelength thickness and low surface density properties. However, the existing research works mainly focus on the sound transmission loss (STL) of small-sized unit cells with the fixed boundary, resulting in that the sound insulation performances are great different from those of the large-scale structures used in engineering applications. For this reason, a square large-scale PAMM panel with side length of 0.704 m, which consists of a periodic array of square unit cells, is numerically studied under the normal incidence condition. The results show that the large-scale PAMM panels appear the obvious STL peak (~38 dB) in the low-frequency range. Moreover, the goal of broadband sound insulation based on the multi-cells synergetic coupling is realized by reasonably arranging the masses on the metamaterial panels. Numerical results indicate that a broadband insulation with average STL higher than 20 dB is obtained in the range of 300–900 Hz. Finally, a simplified experimental setup based on the box and semi-anechoic chamber is designed to verify the sound insulation performance, and the experiment under standard reverberation chamber and semi-anechoic chamber is performed in order to evaluate the sound insulation capability in the actual reverberation noise environment. The ideal periodic boundary is used in the numerical calculations, which is obviously different from the boundary condition in experiments. Therefore, the influence of the boundary condition on the STL is discussed and analyzed by calculating the STL of the metamaterial panels with different number of cells. The proposed design methods and results can provide some guidance for the application of the PAMM panels in practical engineering. [ABSTRACT FROM AUTHOR]

Postmenopausal osteoporosis (PMOP) seriously endangers the bone health of older women. Although there are currently indicators to diagnose PMOP, early diagnostic biomarkers are lacking. Circular ribonucleic acid (circRNA) has a stable structure, regulates gene expression, participates in the pathological process of disease, and has the potential to become a biomarker. The purpose of this study was to investigate circRNAs that could be used to predict patients with early PMOP. Ribonucleic acid (RNA) sequencing was performed on peripheral blood leukocytes from 15 female patients to identify differential circRNAs between different groups. Using bioinformatics analysis, enrichment analysis was performed to discover relevant functions and pathways. CircRNA-micro ribonucleic acid (miRNA) interaction analysis and messenger ribonucleic acid (mRNA) prediction and network construction help us to understand the relationship between circRNA, miRNA, and mRNA. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to validate the gene expression of candidate circRNAs. We screened out 2 co-expressed differential circRNAs, namely hsa_circ_0060849 and hsa_circ_0001394. By analyzing the regulatory network, a total of 54 miRNAs and 57 osteoporosis-related mRNAs were identified, which, as potential downstream target genes of hsa_circ_0060849 and hsa_circ_0001394, may play a key role in the occurrence and development of PMOP. The occurrence and development of PMOP is regulated by circRNAs, and hsa_circ_0060849 and hsa_circ_0001394 can be used as new diagnostic markers and therapeutic targets for early PMOP., Competing Interests: The authors have no conflicts of interest to disclose., (Copyright © 2024 the Author(s). Published by Wolters Kluwer Health, Inc.)

To explore the role of plasma miRNAs in exosomes in early postmenopausal women. Small RNA sequencing was implemented to clarify the expression of miRNA in plasma exosomes obtained from 15 postmenopausal women, divided into groups of osteoporosis, osteopenia, and normal bone mass based on bone mineral density. Differentially expressed miRNAs (DEMs) were identified by comparing miRNA expression profiles. Five putative miRNAs, miR-224-3p, miR-25-5p, miR-302a-3p, miR-642a-3p, and miR-766-5p were confirmed by real-time PCR; miRNA target genes were obtained from 4 databases: miRWalk, miRDB, RNA22, and TargetScan. The miRNA-mRNA- Kyoto Encyclopedia of Genes and Genomes (KEGG) networks were analyzed, and the DEMs' potential role was investigated by gene ontology terms and KEGG pathway annotation. The results suggest that characterizing plasma exosomal miRNA profiles of early postmenopausal women by small RNA sequencing could identify novel exo-miRNAs involved in bone remodeling, and miR-642a-3p maybe contribute to the prediction and diagnosis of early postmenopausal osteoporosis., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)