An underwater directional acoustic emitter is conceived with a highly anisotropic lattice material,whose acoustic characteristics manifest strong dependence on the orientation of the lattice material’s principal axis...An underwater directional acoustic emitter is conceived with a highly anisotropic lattice material,whose acoustic characteristics manifest strong dependence on the orientation of the lattice material’s principal axis.Exploiting these features,a cylindrical structure made of such anisotropic lattice material is engineered to possess distinct impedance values in different directions,thereby facilitating wave emission along the principal axis while inducing reflection in other directions.Notably,through numerical simulations,it is demonstrated that the emission direction can be effectively manipulated by adjusting the principal axis orientation,concurrently enhancing the emitted power.In contrast to previous directional acoustic structures,the compact emitter presented in this study can get rid of the size-wavelength constraint,enabling effective control of low-frequency waves.展开更多
An underwater acoustic metasurface with sub-wavelength thickness is designed for acoustic wavefront manipulation.In this paper,a pentamode lattice and a frequency-independent generalized acoustic Snell's law are i...An underwater acoustic metasurface with sub-wavelength thickness is designed for acoustic wavefront manipulation.In this paper,a pentamode lattice and a frequency-independent generalized acoustic Snell's law are introduced to overcome the limitations of narrow bandwidth and low transmittance.The bulk modulus and effective density of each unit cell can be tuned simultaneously,which are modulated to guarantee the achievement of refractive index profile and high transmission.Here,we actualize anomalous refraction,generation of non-diffracting Bessel beam,sub-wavelength flat focusing,and surface wave conversion by constructing inhomogeneous acoustic metasurface.This design approach has potential applications in medical ultrasound imaging and underwater acoustic communications.展开更多
Metamaterials have been receiving an increasing amount of interest in recent years. As a type of metamaterial, pentamode materials (PMs) approximate the elastic properties of liquids. In this study, a finite-element a...Metamaterials have been receiving an increasing amount of interest in recent years. As a type of metamaterial, pentamode materials (PMs) approximate the elastic properties of liquids. In this study, a finite-element analysis was conducted to predict the mechanical properties of PM structures by altering the thin wall thicknesses and layer numbers to obtain an outstanding load-bearing capacity. It was found that as the thin wall thickness increased from 0.15 to 0.45 mm, the compressive modulus of the PM structures increased and the Poisson’s ratio decreased. As the layer number increased, the Poisson’s ratio of the PM structures increased rapidly and reaches a stable value ranging from 0.50 to 0.55. Simulation results of the stress distribution in the PM structures confirmed that stress concentrations exist at the junctions of the thin walls and weights. For validation, Ti–6Al–4V specimens were fabricated by selective laser melting (SLM), and the mechanical properties of these specimens (i.e., Poisson’s ratio and elastic modulus) were experimentally studied. Good consistency was achieved between the numerical and experimental results. This work is beneficial for the design and development of PM structures with simultaneous load-bearing capacity and pentamodal properties.展开更多
The acoustic scattering is theoretically studied in this paper for three-dimensional spherical cloak composed of unideal pentamode material,for which small shear rigidity is always inevitable for a real designed micro...The acoustic scattering is theoretically studied in this paper for three-dimensional spherical cloak composed of unideal pentamode material,for which small shear rigidity is always inevitable for a real designed microstructure.A theoretical formulation is developed to efficiently evaluate the cloaking performance.The generic scattering feature of the cloak and the efTects of material imperfectness and inner cloak boundary constraints are systematically examined.The preferable constraint type and the critical imperfectness parameter of the material are identified for possible broadband invisibility.In addition,a very practical lining shell scheme is proposed to tune the constraint strength on the inner boundary.By combining the theoretical model with optimization algorithm,it is further proved that the cloak can be reduced by several piecewiseuniform layers and optimized to achieve excellent invisibility in targeted frequency bands.The study will provide valuable guidance for the future microstructural design of cloaks.展开更多
Pentamode acoustic cloak is promising for underwater sound control due to its solid nature and broadband efficiency,however its realization is only limited to simple cylindrical shape.In this work,we established a set...Pentamode acoustic cloak is promising for underwater sound control due to its solid nature and broadband efficiency,however its realization is only limited to simple cylindrical shape.In this work,we established a set of techniques for the microstructure design of elliptical pentamode acoustic cloak based on truss lattice model,including the inverse design of unit cell and algorithms for latticed cloak assembly.The designed cloak was numerically validated by the well wave concealing performance.The work proves that more general pentamode acoustic wave devices beyond simple cylindrical geometry are theoretically feasible,and sheds light on more practical design for waterborne sound manipulation.展开更多
<div style="text-align:justify;"> Coding metasurface draws amounts of research interests due to its potential for achieving sophisticated functions in wave manipulation by using simple logical unit cel...<div style="text-align:justify;"> Coding metasurface draws amounts of research interests due to its potential for achieving sophisticated functions in wave manipulation by using simple logical unit cells with out-of-phase responses. In this paper, we present a novel acoustic coding metasurface structure for underwater sound scattering reduction based on pentamode metamaterials. The metasurface is composed of two types of hexagonal pentamode unit cells with phase responses of 0 and π respectively. The units are arranged in random 1-bit coding sequence to achieve low-scattering underwater acoustic stealth effect. Full-wave simulation results are in good accordance with the theoretical expectation. The optimized arrangement resulted in the distribution of scattered underwater acoustic waves and suppression of the far field scattering coefficient over a wide range of incident angles. We show that pentamode-based coding metasurface provides an efficient scheme to achieve underwater acoustic stealth by ultrathin structures. </div>展开更多
Biomimetic metallic biomaterials prepared for bone scaffolds have drawn more and more attention in recent years.However,the topological design of scaffolds is critical to cater to multi-physical requirements for effic...Biomimetic metallic biomaterials prepared for bone scaffolds have drawn more and more attention in recent years.However,the topological design of scaffolds is critical to cater to multi-physical requirements for efficient cell seeding and bone regeneration,yet remains a big scientific challenge owing to the coupling of mechanical and mass-transport properties in conventional scaffolds that lead to poor control towards favorable modulus and permeability combinations.Herein,inspired by the microstructure of natural sea urchin spines,biomimetic scaffolds constructed by pentamode metamaterials(PMs)with hierarchical structural tunability were additively manufactured via selective laser melting.The mechanical and mass-transport properties of scaffolds could be simultaneously tuned by the graded porosity(B/T ratio)and the tapering level(D/d ratio).Compared with traditional metallic biomaterials,our biomimetic PM scaffolds possess graded pore distribution,suitable strength,and significant improvements to cell seeding efficiency,permeability,and impact-tolerant capacity,and they also promote in vivo osteogenesis,indicating promising application for cell proliferation and bone regeneration using a structural innovation.展开更多
基金supported by the National Natural Science Foundation of China(Grants No.11991030,No.11991033,No.12202054,and No.11802017).
文摘An underwater directional acoustic emitter is conceived with a highly anisotropic lattice material,whose acoustic characteristics manifest strong dependence on the orientation of the lattice material’s principal axis.Exploiting these features,a cylindrical structure made of such anisotropic lattice material is engineered to possess distinct impedance values in different directions,thereby facilitating wave emission along the principal axis while inducing reflection in other directions.Notably,through numerical simulations,it is demonstrated that the emission direction can be effectively manipulated by adjusting the principal axis orientation,concurrently enhancing the emitted power.In contrast to previous directional acoustic structures,the compact emitter presented in this study can get rid of the size-wavelength constraint,enabling effective control of low-frequency waves.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61571222 and 11474160)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20161009)the Six-Talent Peaks Project of Jiangsu Province,China
文摘An underwater acoustic metasurface with sub-wavelength thickness is designed for acoustic wavefront manipulation.In this paper,a pentamode lattice and a frequency-independent generalized acoustic Snell's law are introduced to overcome the limitations of narrow bandwidth and low transmittance.The bulk modulus and effective density of each unit cell can be tuned simultaneously,which are modulated to guarantee the achievement of refractive index profile and high transmission.Here,we actualize anomalous refraction,generation of non-diffracting Bessel beam,sub-wavelength flat focusing,and surface wave conversion by constructing inhomogeneous acoustic metasurface.This design approach has potential applications in medical ultrasound imaging and underwater acoustic communications.
文摘Metamaterials have been receiving an increasing amount of interest in recent years. As a type of metamaterial, pentamode materials (PMs) approximate the elastic properties of liquids. In this study, a finite-element analysis was conducted to predict the mechanical properties of PM structures by altering the thin wall thicknesses and layer numbers to obtain an outstanding load-bearing capacity. It was found that as the thin wall thickness increased from 0.15 to 0.45 mm, the compressive modulus of the PM structures increased and the Poisson’s ratio decreased. As the layer number increased, the Poisson’s ratio of the PM structures increased rapidly and reaches a stable value ranging from 0.50 to 0.55. Simulation results of the stress distribution in the PM structures confirmed that stress concentrations exist at the junctions of the thin walls and weights. For validation, Ti–6Al–4V specimens were fabricated by selective laser melting (SLM), and the mechanical properties of these specimens (i.e., Poisson’s ratio and elastic modulus) were experimentally studied. Good consistency was achieved between the numerical and experimental results. This work is beneficial for the design and development of PM structures with simultaneous load-bearing capacity and pentamodal properties.
基金the National Natural Science Foundatio nof China(Grant Nos.11372035,11632003,11472044,11802017)the Postdoctoral Innovation Talent Support Program(No.BX20180040).
文摘The acoustic scattering is theoretically studied in this paper for three-dimensional spherical cloak composed of unideal pentamode material,for which small shear rigidity is always inevitable for a real designed microstructure.A theoretical formulation is developed to efficiently evaluate the cloaking performance.The generic scattering feature of the cloak and the efTects of material imperfectness and inner cloak boundary constraints are systematically examined.The preferable constraint type and the critical imperfectness parameter of the material are identified for possible broadband invisibility.In addition,a very practical lining shell scheme is proposed to tune the constraint strength on the inner boundary.By combining the theoretical model with optimization algorithm,it is further proved that the cloak can be reduced by several piecewiseuniform layers and optimized to achieve excellent invisibility in targeted frequency bands.The study will provide valuable guidance for the future microstructural design of cloaks.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972080,11972083 and 11991030)the Innovation Foundation of Maritime Defense Technologies Innovation Center(Grant No.JJ-2021-719-06).
文摘Pentamode acoustic cloak is promising for underwater sound control due to its solid nature and broadband efficiency,however its realization is only limited to simple cylindrical shape.In this work,we established a set of techniques for the microstructure design of elliptical pentamode acoustic cloak based on truss lattice model,including the inverse design of unit cell and algorithms for latticed cloak assembly.The designed cloak was numerically validated by the well wave concealing performance.The work proves that more general pentamode acoustic wave devices beyond simple cylindrical geometry are theoretically feasible,and sheds light on more practical design for waterborne sound manipulation.
文摘<div style="text-align:justify;"> Coding metasurface draws amounts of research interests due to its potential for achieving sophisticated functions in wave manipulation by using simple logical unit cells with out-of-phase responses. In this paper, we present a novel acoustic coding metasurface structure for underwater sound scattering reduction based on pentamode metamaterials. The metasurface is composed of two types of hexagonal pentamode unit cells with phase responses of 0 and π respectively. The units are arranged in random 1-bit coding sequence to achieve low-scattering underwater acoustic stealth effect. Full-wave simulation results are in good accordance with the theoretical expectation. The optimized arrangement resulted in the distribution of scattered underwater acoustic waves and suppression of the far field scattering coefficient over a wide range of incident angles. We show that pentamode-based coding metasurface provides an efficient scheme to achieve underwater acoustic stealth by ultrathin structures. </div>
基金This work was sponsored by the National Natural Science Foundation of China(Grant No.51922044)the Key Area Research and Development Program of Guangdong Province(No.2020B090923001)the Academic frontier youth team at Huazhong University of Science and Technology(HUST)(2018QYTD04).
文摘Biomimetic metallic biomaterials prepared for bone scaffolds have drawn more and more attention in recent years.However,the topological design of scaffolds is critical to cater to multi-physical requirements for efficient cell seeding and bone regeneration,yet remains a big scientific challenge owing to the coupling of mechanical and mass-transport properties in conventional scaffolds that lead to poor control towards favorable modulus and permeability combinations.Herein,inspired by the microstructure of natural sea urchin spines,biomimetic scaffolds constructed by pentamode metamaterials(PMs)with hierarchical structural tunability were additively manufactured via selective laser melting.The mechanical and mass-transport properties of scaffolds could be simultaneously tuned by the graded porosity(B/T ratio)and the tapering level(D/d ratio).Compared with traditional metallic biomaterials,our biomimetic PM scaffolds possess graded pore distribution,suitable strength,and significant improvements to cell seeding efficiency,permeability,and impact-tolerant capacity,and they also promote in vivo osteogenesis,indicating promising application for cell proliferation and bone regeneration using a structural innovation.
