The lower Yarlung Tsangpo River basin of the Qinghai-Tibet Plateau frequently experiences geo-hazardous occurrences such as landslides,ice/rock avalanches and debris flows,causing loss of human lives and damage to inf...The lower Yarlung Tsangpo River basin of the Qinghai-Tibet Plateau frequently experiences geo-hazardous occurrences such as landslides,ice/rock avalanches and debris flows,causing loss of human lives and damage to infrastructure.However,a comprehensive inventory map of geohazards is lacking for this region,due to the extreme challenges of the geomorphological and environmental conditions(i.e.,steep terrain,dense vegetation cover,and the presence of ice and snow).To this end,we propose a novel approach for mapping active geohazards in complex mountainous regions through InSAR phase gradient measurements based on a deep learning algorithm,which is then applied to the lower Yarlung Tsangpo River basin for the first time,in order to prepare an inventory map of active geohazards using ascending and descending Sentinel-1 SAR images acquired between March 2017 and July 2023.First,the InSAR phase gradient stacking method was introduced to estimate ground deformation,which offers significant advantages in minimizing the influence of InSAR decorrelation and effectively suppressing topographic residuals and atmospheric delays.InSAR phase gradient rates effectively retrieve patterns of localized ground deformation associated with geohazard activity.Then,a DeepLabv3 deep learning model was established and trained with phase gradient rate maps of manually labeled geohazards,in order to achieve the automatic identification of active geohazards.Our results show that there are 277 active geohazards within the lower Yarlung Tsangpo River basin,encompassing an area of~25600 km^(2).The DeepLabv3 model achieved good precision,recall rate and F1 scores at 92,86 and 90%,respectively.The distribution of detected geohazards is closely correlated with the topographic factors,faults and river system.Compared to the results derived from Small Baseline Subset InSAR(SBAS-InSAR)and optical images,the proposed approach can obtain high density pixels of InSAR measurement in low-coherence scenarios,thus enabling high-accuracy mapping of active geohazards in complex mountainous areas.展开更多
A new method to design an ultra-thin high-gain circularly-polarized antenna system with high efficiency is proposed based on the geometrical phase gradient metasurface（GPGM）.With an accuracy control of the transmiss...A new method to design an ultra-thin high-gain circularly-polarized antenna system with high efficiency is proposed based on the geometrical phase gradient metasurface（GPGM）.With an accuracy control of the transmission phase and also the high transmission amplitude,the GPGM is capable of manipulating an electromagnetic wave arbitrarily.A focusing transmission lens working at Ku band is well optimized with the F /D of 0.32.A good focusing effect is demonstrated clearly by theoretical calculation and electromagnetic simulation.For further application,an ultra-thin single-layer transmissive lens antenna based on the proposed focusing metasurface operating at 13 GHz is implemented and launched by an original patch antenna from the perspective of high integration,simple structure,and low cost.Numerical and experimental results coincide well,indicating the advantages of the antenna system,such as a high gain of 17.6 d B,the axis ratio better than 2 d B,a high aperture efficiency of 41%,and also a simple fabrication process based on the convenient print circuit board technology.The good performance of the proposed antenna indicates promising applications in portable communication systems.展开更多
Optical phase-gradient metasurfaces have garnered significant attention for enabling flexible light manipulation,with applications across diverse domains.In this work,we will demonstrate that the metasurfaces with pha...Optical phase-gradient metasurfaces have garnered significant attention for enabling flexible light manipulation,with applications across diverse domains.In this work,we will demonstrate that the metasurfaces with phase gradient modulation can be used to achieve illusion optics,featuring the advantages of simple geometric structure and feasible implementation compared with the well-known transformation optics method.The underlying mechanism is the anomalous diffraction law caused by the phase gradient,which provides a theoretical basis for freely manipulating the propagation path of light.By considering a specific example,we will demonstrate that the phase gradient can transform spatial coordinates in real space into illusion space,thereby converting a plane in real space into a curved surface structure in illusion space to achieve the illusion effect.This approach provides a viable alternative to transformation optics for designing illusion devices.展开更多
Perfect anomalous reflections have been demonstrated in optical phase gradient metasurfaces(PGMs),but they suffer from single-frequency(narrow-band)response due to the intrinsic limitation of natural geometric periodi...Perfect anomalous reflections have been demonstrated in optical phase gradient metasurfaces(PGMs),but they suffer from single-frequency(narrow-band)response due to the intrinsic limitation of natural geometric periodicity.Here,we provide both numerical and analytical evidence that a depth gradient metasurface can achieve discrete ultra-broadband perfect anomalous reflection in the microwave range in the absence of geometric periodicity.Remarkably,by adjusting the operating frequency of the incident wave,the same effect can be steadily obtained via a physically equivalent phase periodicity in the PGM.Based on this mechanism,a perfect retroreflector with a broadband response ranging from 1 GHz to 40 GHz is realized.Our work has promising applications in communication,source tracking,and military satellites.展开更多
The phase error estimated by phase gradient autofocus(PGA) is not based on a finite order polynomial mode, so PGA has a good autofocus property for arbitrary order phase error and is fit for high resolution airborne S...The phase error estimated by phase gradient autofocus(PGA) is not based on a finite order polynomial mode, so PGA has a good autofocus property for arbitrary order phase error and is fit for high resolution airborne SAR. But PGA has two shortcomings: first, it has a worse estimation property for fast changing phase error; second, there exists a section of linear phase in the phase error estimated by this algorithm. This paper introduces the idea of rank one phase estimate (ROPE) autofocus technique, and improves PGA. The improved PGA(IPGA) can successfully overcome both these shortcomings of PGA.展开更多
A new type of power-exponent-phase vortex-like beams with both quadratic and cubic azimuthal phase gradients is investigated in this work.The intensity and orbital angular momentum(OAM)density distributions are notice...A new type of power-exponent-phase vortex-like beams with both quadratic and cubic azimuthal phase gradients is investigated in this work.The intensity and orbital angular momentum(OAM)density distributions are noticeably different when the phase gradient increases or decreases along the azimuth angle,while the orthogonality and total OAM remain constant.The characteristics of the optical field undergo a significant change when the phase shifts from linear to nonlinear,with the variation of the power index having little impact on the beam characteristics under nonlinear phase conditions.These characteristics provide new ideas for applications such as particle manipulation,optical communications,and OAM encryption.展开更多
The temporal interface microstructures and diffusions in the diffusion couples with the mutual interactions of the temperature gradient, concentration difference and initial aging time of the alloys are studied by pha...The temporal interface microstructures and diffusions in the diffusion couples with the mutual interactions of the temperature gradient, concentration difference and initial aging time of the alloys are studied by phase-field simulation, and the diffusion couples are produced by the initial aged spinodal alloys with different compositions. Temporal composition evolution and volume fraction of the separated phase indicate the element diffusion direction through the interface under the temperature gradient. The increased temperature gradient induces a wide single-phase region on two sides of the interface.The uphill diffusion proceeds through the interface, no matter whether the diffusion direction is up or down with respect to the temperature gradient. For an alloy with short initial aging time, phase transformation accompanying the interdiffusion results in the straight interface with the single-phase regions on both sides. Compared with the temperature gradient,composition difference of diffusion couple and initial aging time of the alloy show greater effects on diffusion and interface microstructure.展开更多
By applying phase-only technique in array antenna pattern synthesis, antenna arrays can form desired patterns with the use of phase shifters only. A novel phase-only pattern synthesis algorithm is proposed for the pas...By applying phase-only technique in array antenna pattern synthesis, antenna arrays can form desired patterns with the use of phase shifters only. A novel phase-only pattern synthesis algorithm is proposed for the passive phased array seeker. This algorithm synthesizes the main beam of the antenna pattern through least-squares approximation, thus minimizing the errors between the actual and the desired main beams. The synthesis problem can be solved by applying gradient-descent optimization. The item for suppressing side lobes is added to the above synthesis problem. To obtain a side lobe level as low as possible, the algorithm assigns different weights to different directions in the side lobe region. The algorithm is run repeatedly and the weights are adjusted adaptively according to the normalized power in the side lobe directions. Detailed examples are presented to demonstrate the accuracy and effectiveness of the proposed approach.展开更多
This study developed a method to perform the simultaneous concentration and selective separation of 66 （ultra） trace persistent toxic substances in Antarctic waters. The substances included 30 polychlorinated biphen...This study developed a method to perform the simultaneous concentration and selective separation of 66 （ultra） trace persistent toxic substances in Antarctic waters. The substances included 30 polychlorinated biphenyls, 17 organochlorine pesticides, 16 polycyclic aromatic hydrocarbons, 3 hexabromocyclododecanes. Solid phase extraction was performed using a C18 membrane and silica gel column. Gradient elution was conducted using organic solvents with different polarities; as a result, the efficiency of the C18 film is improved and the interferences from impurities and target compounds are eliminated. Extracts were subsequently analyzed through gas chromatography or liquid and gas chromatography coupled to tandem mass spectrometry. Method validation yielded the following values： recoveries of all target analytes in the Antarctic water ranged from 87.3% to 117.6% and reproducibility as percent relative standard deviation was lower than 5%. Quantification limits ranged from 0.004 μg L^-1 to 0.030 μg L^-1. The established method improved the recoveries and reduced the limits of detection. Results indicated the method exhibited good performance in the simultaneous concentration and selective separation of 66 （ultra） trace organic pollutants; Therefore, the proposed sample pretreatment can potentially eliminate the effects of various classes of impurities to some extent.展开更多
In this paper, we proposed a spectral gradient-Newton two phase method for constrained semismooth equations. In the first stage, we use the spectral projected gradient to obtain the global convergence of the algorithm...In this paper, we proposed a spectral gradient-Newton two phase method for constrained semismooth equations. In the first stage, we use the spectral projected gradient to obtain the global convergence of the algorithm, and then use the final point in the first stage as a new initial point to turn to a projected semismooth asymptotically newton method for fast convergence.展开更多
This paper presents an enhanced multi-baseline phase unwrapping algorithm by combining an unscented Kalman filter with an enhanced joint phase gradient estimator based on the amended matrix pencil model, and an optima...This paper presents an enhanced multi-baseline phase unwrapping algorithm by combining an unscented Kalman filter with an enhanced joint phase gradient estimator based on the amended matrix pencil model, and an optimal path-following strategy based on phase quality estimate function. The enhanced joint phase gradient estimator can accurately and effectively extract the phase gradient information of wrapped pixels from noisy interferograms, which greatly increases the performances of the proposed method. The optimal path-following strategy ensures that the proposed algorithm simultaneously performs noise suppression and phase unwrapping along the pixels with high-reliance to the pixels with low-reliance. Accordingly, the proposed algorithm can be predicted to obtain better results, with respect to some other algorithms, as will be demonstrated by the results obtained from synthetic data.展开更多
A new approach to phase averaging in phase gradient algorithm (PGA) is proposed, which is based on the fundamental fact that the information of translational phase error is widely contained in every defocused scattere...A new approach to phase averaging in phase gradient algorithm (PGA) is proposed, which is based on the fundamental fact that the information of translational phase error is widely contained in every defocused scatterer in ISAR image. The new approach aims to choose strong scatterers for error phase averaging with a threshold rather than just simply to pick out the strongest point in each range cell, which is not necessarily real strong scatterers if in some range cells consists more than one strong scatterer and whereas in other range cells no scatterer at all. The results of processing real data are presented to confirm the validity of the proposed approach.展开更多
Acoustic metasurface has attracted increasing attention due to the ability of manipulating the transmitted and reflected phase of waves to generate various acoustic functionalities with planar layer of sub-wavelength ...Acoustic metasurface has attracted increasing attention due to the ability of manipulating the transmitted and reflected phase of waves to generate various acoustic functionalities with planar layer of sub-wavelength structure.We design an acoustic metasurface with a semi-closed and nested slotted tube array,and it possesses the capacity of modulating the reflected phase with sub-wavelength thickness (about λ/23).The reflected phase shifts can be obtained from 0 to 2π by different rotation angles of internal slotted tubes.The theoretical results agree well with the numerical results by a finite element method.The results show that some excellent wavefront manipulations are demonstrated with the phase array by using acoustic metasurface such as anomalous reflection and sub-wavelength flat focusing.The design may offer a path for acoustic manipulation and promote the potential applications of acoustic metasurface in low frequency noise control,acoustic imaging and cloaking.展开更多
基金financially supported by the Joint Funds of the National Natural Science Foundation of China(Grant No.U2244226)the National Key R&D Program of China(No.2022YFC3004302)+7 种基金Chinese Geological Survey Project(No.DD20230538)the Science Foundation of Gansu Province(No.23JRRA830)the Science and Technology Major Project of Gansu Province(No.23ZDFA007)the Foundation for Innovation Groups of Basic Research in Gansu Province(24JRRA169)Power China Project(No.CD2C20230228)the Lanzhou Youth Science and Technology Talent Innovation Project(No.2024-QN-170)supported by the ESA-MOST China DRAGON-5(Grant No.59339)DRAGON-6 project(Grant No.95355).
文摘The lower Yarlung Tsangpo River basin of the Qinghai-Tibet Plateau frequently experiences geo-hazardous occurrences such as landslides,ice/rock avalanches and debris flows,causing loss of human lives and damage to infrastructure.However,a comprehensive inventory map of geohazards is lacking for this region,due to the extreme challenges of the geomorphological and environmental conditions(i.e.,steep terrain,dense vegetation cover,and the presence of ice and snow).To this end,we propose a novel approach for mapping active geohazards in complex mountainous regions through InSAR phase gradient measurements based on a deep learning algorithm,which is then applied to the lower Yarlung Tsangpo River basin for the first time,in order to prepare an inventory map of active geohazards using ascending and descending Sentinel-1 SAR images acquired between March 2017 and July 2023.First,the InSAR phase gradient stacking method was introduced to estimate ground deformation,which offers significant advantages in minimizing the influence of InSAR decorrelation and effectively suppressing topographic residuals and atmospheric delays.InSAR phase gradient rates effectively retrieve patterns of localized ground deformation associated with geohazard activity.Then,a DeepLabv3 deep learning model was established and trained with phase gradient rate maps of manually labeled geohazards,in order to achieve the automatic identification of active geohazards.Our results show that there are 277 active geohazards within the lower Yarlung Tsangpo River basin,encompassing an area of~25600 km^(2).The DeepLabv3 model achieved good precision,recall rate and F1 scores at 92,86 and 90%,respectively.The distribution of detected geohazards is closely correlated with the topographic factors,faults and river system.Compared to the results derived from Small Baseline Subset InSAR(SBAS-InSAR)and optical images,the proposed approach can obtain high density pixels of InSAR measurement in low-coherence scenarios,thus enabling high-accuracy mapping of active geohazards in complex mountainous areas.
基金Project supported by the National Natural Science Foundation of China(Grant No.61372034)
文摘A new method to design an ultra-thin high-gain circularly-polarized antenna system with high efficiency is proposed based on the geometrical phase gradient metasurface（GPGM）.With an accuracy control of the transmission phase and also the high transmission amplitude,the GPGM is capable of manipulating an electromagnetic wave arbitrarily.A focusing transmission lens working at Ku band is well optimized with the F /D of 0.32.A good focusing effect is demonstrated clearly by theoretical calculation and electromagnetic simulation.For further application,an ultra-thin single-layer transmissive lens antenna based on the proposed focusing metasurface operating at 13 GHz is implemented and launched by an original patch antenna from the perspective of high integration,simple structure,and low cost.Numerical and experimental results coincide well,indicating the advantages of the antenna system,such as a high gain of 17.6 d B,the axis ratio better than 2 d B,a high aperture efficiency of 41%,and also a simple fabrication process based on the convenient print circuit board technology.The good performance of the proposed antenna indicates promising applications in portable communication systems.
基金supported by the National Natural Science Foundation of China (Grant Nos.12274313 and 62375234)the Gusu Leading Talent Plan for Scientific and Technological Innovation and Entrepreneurship (Grant No.ZXL2024400)。
文摘Optical phase-gradient metasurfaces have garnered significant attention for enabling flexible light manipulation,with applications across diverse domains.In this work,we will demonstrate that the metasurfaces with phase gradient modulation can be used to achieve illusion optics,featuring the advantages of simple geometric structure and feasible implementation compared with the well-known transformation optics method.The underlying mechanism is the anomalous diffraction law caused by the phase gradient,which provides a theoretical basis for freely manipulating the propagation path of light.By considering a specific example,we will demonstrate that the phase gradient can transform spatial coordinates in real space into illusion space,thereby converting a plane in real space into a curved surface structure in illusion space to achieve the illusion effect.This approach provides a viable alternative to transformation optics for designing illusion devices.
基金supported by the National Natural Science Foundation of China(Grant Nos.12274313,62275184,and 62411540033)Collaborative Innovation Center of Suzhou Nano Science and Technology,Suzhou Basic Research Project(Grant No.SJC2023003)+1 种基金the Gusu Leading Talent Plan for Scientific and Technological Innovation and Entrepreneurship(Grant No.ZXL2024400)the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘Perfect anomalous reflections have been demonstrated in optical phase gradient metasurfaces(PGMs),but they suffer from single-frequency(narrow-band)response due to the intrinsic limitation of natural geometric periodicity.Here,we provide both numerical and analytical evidence that a depth gradient metasurface can achieve discrete ultra-broadband perfect anomalous reflection in the microwave range in the absence of geometric periodicity.Remarkably,by adjusting the operating frequency of the incident wave,the same effect can be steadily obtained via a physically equivalent phase periodicity in the PGM.Based on this mechanism,a perfect retroreflector with a broadband response ranging from 1 GHz to 40 GHz is realized.Our work has promising applications in communication,source tracking,and military satellites.
文摘The phase error estimated by phase gradient autofocus(PGA) is not based on a finite order polynomial mode, so PGA has a good autofocus property for arbitrary order phase error and is fit for high resolution airborne SAR. But PGA has two shortcomings: first, it has a worse estimation property for fast changing phase error; second, there exists a section of linear phase in the phase error estimated by this algorithm. This paper introduces the idea of rank one phase estimate (ROPE) autofocus technique, and improves PGA. The improved PGA(IPGA) can successfully overcome both these shortcomings of PGA.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research(No.2020B0301030009)National Natural Science Foundation of China(Nos.61935013,62375181,and 61975133)+1 种基金Science and Technology Innovation Commission of Shenzhen,Shenzhen Peacock Plan(Nos.KQTD20170330110444030 and JCYJ20200109114018750)Shenzhen University(No.2019075)。
文摘A new type of power-exponent-phase vortex-like beams with both quadratic and cubic azimuthal phase gradients is investigated in this work.The intensity and orbital angular momentum(OAM)density distributions are noticeably different when the phase gradient increases or decreases along the azimuth angle,while the orthogonality and total OAM remain constant.The characteristics of the optical field undergo a significant change when the phase shifts from linear to nonlinear,with the variation of the power index having little impact on the beam characteristics under nonlinear phase conditions.These characteristics provide new ideas for applications such as particle manipulation,optical communications,and OAM encryption.
基金Project supported by the National Natural Science Foundation of China(Grant No.51571122)the Fundamental Research Funds for the Central UniversitiesChina(Grant No.30920130121012)
文摘The temporal interface microstructures and diffusions in the diffusion couples with the mutual interactions of the temperature gradient, concentration difference and initial aging time of the alloys are studied by phase-field simulation, and the diffusion couples are produced by the initial aged spinodal alloys with different compositions. Temporal composition evolution and volume fraction of the separated phase indicate the element diffusion direction through the interface under the temperature gradient. The increased temperature gradient induces a wide single-phase region on two sides of the interface.The uphill diffusion proceeds through the interface, no matter whether the diffusion direction is up or down with respect to the temperature gradient. For an alloy with short initial aging time, phase transformation accompanying the interdiffusion results in the straight interface with the single-phase regions on both sides. Compared with the temperature gradient,composition difference of diffusion couple and initial aging time of the alloy show greater effects on diffusion and interface microstructure.
基金supported by the National Natural Science Foundation of China(1127301761471196)
文摘By applying phase-only technique in array antenna pattern synthesis, antenna arrays can form desired patterns with the use of phase shifters only. A novel phase-only pattern synthesis algorithm is proposed for the passive phased array seeker. This algorithm synthesizes the main beam of the antenna pattern through least-squares approximation, thus minimizing the errors between the actual and the desired main beams. The synthesis problem can be solved by applying gradient-descent optimization. The item for suppressing side lobes is added to the above synthesis problem. To obtain a side lobe level as low as possible, the algorithm assigns different weights to different directions in the side lobe region. The algorithm is run repeatedly and the weights are adjusted adaptively according to the normalized power in the side lobe directions. Detailed examples are presented to demonstrate the accuracy and effectiveness of the proposed approach.
基金financially supported by the National Natural Science Foundation of China(No.21377032)the Chinese Polar Environment Comprehensive Investigation and Assessment Program(Nos.2014-02-01,2014-03-04,2014-04-01,2014-04-03)+1 种基金the Marine Public Welfare Scientific Research Projects(No.201105013)the Foundation of Polar Science Key Laboratory,SOA,China(No.KP201208)
文摘This study developed a method to perform the simultaneous concentration and selective separation of 66 （ultra） trace persistent toxic substances in Antarctic waters. The substances included 30 polychlorinated biphenyls, 17 organochlorine pesticides, 16 polycyclic aromatic hydrocarbons, 3 hexabromocyclododecanes. Solid phase extraction was performed using a C18 membrane and silica gel column. Gradient elution was conducted using organic solvents with different polarities; as a result, the efficiency of the C18 film is improved and the interferences from impurities and target compounds are eliminated. Extracts were subsequently analyzed through gas chromatography or liquid and gas chromatography coupled to tandem mass spectrometry. Method validation yielded the following values： recoveries of all target analytes in the Antarctic water ranged from 87.3% to 117.6% and reproducibility as percent relative standard deviation was lower than 5%. Quantification limits ranged from 0.004 μg L^-1 to 0.030 μg L^-1. The established method improved the recoveries and reduced the limits of detection. Results indicated the method exhibited good performance in the simultaneous concentration and selective separation of 66 （ultra） trace organic pollutants; Therefore, the proposed sample pretreatment can potentially eliminate the effects of various classes of impurities to some extent.
文摘In this paper, we proposed a spectral gradient-Newton two phase method for constrained semismooth equations. In the first stage, we use the spectral projected gradient to obtain the global convergence of the algorithm, and then use the final point in the first stage as a new initial point to turn to a projected semismooth asymptotically newton method for fast convergence.
基金supported by the National Natural Science Foundation of China(4120147961261033+2 种基金61461011)the Guangxi Natural Science Foundation(2014GXNSFBA118273)the Dean Project of Guangxi Key Laboratory of Wireless Broadband Communication and Signal Processing(GXKL061503)
文摘This paper presents an enhanced multi-baseline phase unwrapping algorithm by combining an unscented Kalman filter with an enhanced joint phase gradient estimator based on the amended matrix pencil model, and an optimal path-following strategy based on phase quality estimate function. The enhanced joint phase gradient estimator can accurately and effectively extract the phase gradient information of wrapped pixels from noisy interferograms, which greatly increases the performances of the proposed method. The optimal path-following strategy ensures that the proposed algorithm simultaneously performs noise suppression and phase unwrapping along the pixels with high-reliance to the pixels with low-reliance. Accordingly, the proposed algorithm can be predicted to obtain better results, with respect to some other algorithms, as will be demonstrated by the results obtained from synthetic data.
文摘A new approach to phase averaging in phase gradient algorithm (PGA) is proposed, which is based on the fundamental fact that the information of translational phase error is widely contained in every defocused scatterer in ISAR image. The new approach aims to choose strong scatterers for error phase averaging with a threshold rather than just simply to pick out the strongest point in each range cell, which is not necessarily real strong scatterers if in some range cells consists more than one strong scatterer and whereas in other range cells no scatterer at all. The results of processing real data are presented to confirm the validity of the proposed approach.
基金supported by the National Natural Science Foundation of China (No.51575431)the China Postdoctoral Science Foundation Funded Project (Nos. 2014M550485, 2015T81019)+1 种基金the Fundamental Research Funds for the Central Universities (No.xjj2015098)the Shaanxi Province Postdoctoral Science Foundation Funded Project
文摘Acoustic metasurface has attracted increasing attention due to the ability of manipulating the transmitted and reflected phase of waves to generate various acoustic functionalities with planar layer of sub-wavelength structure.We design an acoustic metasurface with a semi-closed and nested slotted tube array,and it possesses the capacity of modulating the reflected phase with sub-wavelength thickness (about λ/23).The reflected phase shifts can be obtained from 0 to 2π by different rotation angles of internal slotted tubes.The theoretical results agree well with the numerical results by a finite element method.The results show that some excellent wavefront manipulations are demonstrated with the phase array by using acoustic metasurface such as anomalous reflection and sub-wavelength flat focusing.The design may offer a path for acoustic manipulation and promote the potential applications of acoustic metasurface in low frequency noise control,acoustic imaging and cloaking.
