Freely shuttling in complex terrain is a basic skill of multi-legged animals.To make the hexapod robot have omnidirectional motion ability by controlling only one parameter,this paper uses the motion control method ba...Freely shuttling in complex terrain is a basic skill of multi-legged animals.To make the hexapod robot have omnidirectional motion ability by controlling only one parameter,this paper uses the motion control method based on Central Pattern Generator(CPG),maps the output signal of CPG to the foot end trajectory space of the hexapod robot,and proposes an omnidirectional gait controller strategy.In addition,to enable the hexapod robot to adapt to unstructured terrain,an adaptive method based on Dynamic Threshold(DT)is proposed to enable the hexapod robot move in all directions without changing the heading angle in unstructured terrain.Finally,the feasibility of the proposed method is verified by virtual simulation and hexapod robot prototype experiment.Results show that the hexapod robot can omnidirectional motion without changing the heading angle and has good stability in unstructured terrain.展开更多
This paper is concerned with the properties of propagation fax-field patterns corresponding to the scattering of time harmonic acoustic waves by a bounded penetrable obstacle in an ocean waveguide. The sets of solutio...This paper is concerned with the properties of propagation fax-field patterns corresponding to the scattering of time harmonic acoustic waves by a bounded penetrable obstacle in an ocean waveguide. The sets of solutions to the transmission problem are constructed such that the restriction of these solutions to the boundary of the penetrable obstacle is dense in a Hilbert space. Then conditions under which a set of propagation far-field patterns is complete in a Hilbert space are determined. These properties are important in investigating inverse transmission problems in an ocean waveguide.展开更多
The measurement of the far-field radiation pattern is an important factor in describing the character-istics of the antenna.The measurement process is time consuming and expensive.Therefore,this paper proposes a novel...The measurement of the far-field radiation pattern is an important factor in describing the character-istics of the antenna.The measurement process is time consuming and expensive.Therefore,this paper proposes a novel method to reduce the number of samples required for radiation pattern measurement by adopting com-pressed sensing theory.This method reconstructs the radiation pattern from data measured by a few sensors,and the positions of these sensors are generated via the m-sequence.Simulation results demonstrate that the proposed algorithm can effectively reconstruct the complete radiation pattern by using the 50%samples.展开更多
The time-harmonic electromagnetic plane waves incident on a perfectly conducting obstacle in a homogeneous chiral environment are considered. A two-dimensional direct scattering model is established and the existence ...The time-harmonic electromagnetic plane waves incident on a perfectly conducting obstacle in a homogeneous chiral environment are considered. A two-dimensional direct scattering model is established and the existence and uniqueness of solutions to the problem are discussed by an integral equation approach. The inverse scattering problem to find the shape of scatterer with the given far-field data is formulated. Result on the uniqueness of the inverse problem is proved.展开更多
A nonlinear optimization method was developed to solve the inverse problem of determining the shape of a hard target from the knowlegde of the far-field pattern of the acoustic scattering wave,it was achieved by solvi...A nonlinear optimization method was developed to solve the inverse problem of determining the shape of a hard target from the knowlegde of the far-field pattern of the acoustic scattering wave,it was achieved by solving independently an ill-posed linear system and a well-posed minimization problem.Such a separate numerical treatment for the ill-posedness and nonlinearity of the inverse problem makes the numerical implementation of the proposed method very easy and fast since there only involves the solution of a small scale minimization problem with one unknown function in the nonlinear optimization step for determining the shape of the sound-hard obstacle.Another particular feature of the method is that it can reproduce the shape of an unknown hard target efficiently from the knowledge of only one Fourier coefficient of the far-field pattern.Moreover,a two-step adaptive iteration algorithm was presented to implement numerically the nonlinear optimization scheme.Numerical experiments for several two-dimensional sound-hard scatterers having a variety of shapes provide an independent verification of the effectiveness and practicality of the inversion scheme.展开更多
c-plane GaN-based blue laser diodes（LDs） were fabricated with Al-free cladding layers（CLs） and deepened etching depth of mesa structure, so the aspect ratio of the far-field pattern（FFP） of the laser beam can be...c-plane GaN-based blue laser diodes（LDs） were fabricated with Al-free cladding layers（CLs） and deepened etching depth of mesa structure, so the aspect ratio of the far-field pattern（FFP） of the laser beam can be reduced to as low as 1.7, which is nearly the same as conventional AlGa In P-based red LDs. By using GaN CLs,the radiation angle of the laser beam θ⊥ is only 10.1° in the direction perpendicular to the junction plane. After forming a deeply etched mesa, the beam divergence angle parallel to the junction plane of FFP, θ;, increases from4.9° to 5.8°. After using the modified structure, the operation voltage of LD is effectively reduced by 2 V at an injection current of 50 mA, but the threshold current value increases. The etching damage may be one of the main reasons responsible for the increase of the threshold current.展开更多
The system of a true-time delay line for X-band and 8-unit phased array antennas is introduced. Changing the length of a chirp grating with piezotranslator(PZT), the variable delay is obtained. The scheme is applied t...The system of a true-time delay line for X-band and 8-unit phased array antennas is introduced. Changing the length of a chirp grating with piezotranslator(PZT), the variable delay is obtained. The scheme is applied to X-band phased array radar whose searching data rate is 56/s. It is simulated that the beam squinting is influenced by the error of real time delay. The relation between the beamforming mode and its modifying volt is discussed.展开更多
The problem of diffraction of a plane acoustic wave by a finite soft (rigid) cone is investigated. This one is formulated as a mixed boundary value problem for the three-dimensional Helmholtz equation with Dirichlet (...The problem of diffraction of a plane acoustic wave by a finite soft (rigid) cone is investigated. This one is formulated as a mixed boundary value problem for the three-dimensional Helmholtz equation with Dirichlet (Neumann) boundary condition on the cone surface. The diffracted field is sought as expansion of unknown velocity potential in series of eigenfunctions for each region of the existence of sound pressure. The solution of the problem then is reduced to the infinite set of linear algebraic equations (ISLAE) of the first kind by means of mode matching technique and orthogonality properties of the Legendre functions. The main part of asymptotic of ISLAE matrix element determined for large indexes identifies the convolution type operator amenable to explicit inversion. This analytical treatment allows one to transform the initial diffraction problem into the ISLAE of the second kind that can be readily solved by the reduction method with desired accuracy depending on a number of truncation. All these determine the analytical regularization method for solution of wave diffraction problems for conical scatterers. The boundary transition to soft (rigid) disc is considered. The directivity factors, scattering cross sections, and far-field diffraction patterns are investigated in both soft and rigid cases whereas the main attention in the near-field is focused on the rigid case. The numerically obtained results are compared with those known for the disc.展开更多
Conventional periodic structures usually have nontunable refractive indices and thus lead to immutable photonic bandgaps. A periodic structure created in an ultracold atoms ensemble by externally controlled light can ...Conventional periodic structures usually have nontunable refractive indices and thus lead to immutable photonic bandgaps. A periodic structure created in an ultracold atoms ensemble by externally controlled light can overcome this disadvantage and enable lots of promising applications. Here, two novel types of optically induced square lattices, i.e., the amplitude and phase lattices, are proposed in an ultracold atoms ensemble by interfering four ordinary plane waves under different parameter conditions. We demonstrate that in the far-field regime, the atomic amplitude lattice with high transmissivity behaves similarly to an ideal pure sinusoidal amplitude lattice, whereas the atomic phase lattices capable of producing phase excursion across a weak probe beam along with high transmissivity remains equally ideal. Moreover, we identify that the quality of Talbot imaging about a phase lattice is greatly improved when compared with an amplitude lattice. Such an atomic lattice could find applications in alloptical switching at the few photons level and paves the way for imaging ultracold atoms or molecules both in the near-field and in the far-field with a nondestructive and lensless approach.展开更多
基金the National Natural Science Foundation of China No.E1102/52071108National Defense Science and Industry Bureau Stability Support Project No.JCKYS2020SXJQR-04Natural Science Foundation of Heilongjiang Province No.JJ2021JQ0075.
文摘Freely shuttling in complex terrain is a basic skill of multi-legged animals.To make the hexapod robot have omnidirectional motion ability by controlling only one parameter,this paper uses the motion control method based on Central Pattern Generator(CPG),maps the output signal of CPG to the foot end trajectory space of the hexapod robot,and proposes an omnidirectional gait controller strategy.In addition,to enable the hexapod robot to adapt to unstructured terrain,an adaptive method based on Dynamic Threshold(DT)is proposed to enable the hexapod robot move in all directions without changing the heading angle in unstructured terrain.Finally,the feasibility of the proposed method is verified by virtual simulation and hexapod robot prototype experiment.Results show that the hexapod robot can omnidirectional motion without changing the heading angle and has good stability in unstructured terrain.
基金Project supported by the National Natural Science Foundation of China (No.10672128)the Doctor Foundation of Wuhan University of Technology (No.471-38650238)the Undergraduate Innovative Foundation of Wuhan University of Technology (No.A145)
文摘This paper is concerned with the properties of propagation fax-field patterns corresponding to the scattering of time harmonic acoustic waves by a bounded penetrable obstacle in an ocean waveguide. The sets of solutions to the transmission problem are constructed such that the restriction of these solutions to the boundary of the penetrable obstacle is dense in a Hilbert space. Then conditions under which a set of propagation far-field patterns is complete in a Hilbert space are determined. These properties are important in investigating inverse transmission problems in an ocean waveguide.
基金the National Natural Science Founda-tion of China(No.61571146)。
文摘The measurement of the far-field radiation pattern is an important factor in describing the character-istics of the antenna.The measurement process is time consuming and expensive.Therefore,this paper proposes a novel method to reduce the number of samples required for radiation pattern measurement by adopting com-pressed sensing theory.This method reconstructs the radiation pattern from data measured by a few sensors,and the positions of these sensors are generated via the m-sequence.Simulation results demonstrate that the proposed algorithm can effectively reconstruct the complete radiation pattern by using the 50%samples.
基金Supported by the Key Project of Chinese Ministry of Education(102088)the NNSF of China(10431030).
文摘The time-harmonic electromagnetic plane waves incident on a perfectly conducting obstacle in a homogeneous chiral environment are considered. A two-dimensional direct scattering model is established and the existence and uniqueness of solutions to the problem are discussed by an integral equation approach. The inverse scattering problem to find the shape of scatterer with the given far-field data is formulated. Result on the uniqueness of the inverse problem is proved.
文摘A nonlinear optimization method was developed to solve the inverse problem of determining the shape of a hard target from the knowlegde of the far-field pattern of the acoustic scattering wave,it was achieved by solving independently an ill-posed linear system and a well-posed minimization problem.Such a separate numerical treatment for the ill-posedness and nonlinearity of the inverse problem makes the numerical implementation of the proposed method very easy and fast since there only involves the solution of a small scale minimization problem with one unknown function in the nonlinear optimization step for determining the shape of the sound-hard obstacle.Another particular feature of the method is that it can reproduce the shape of an unknown hard target efficiently from the knowledge of only one Fourier coefficient of the far-field pattern.Moreover,a two-step adaptive iteration algorithm was presented to implement numerically the nonlinear optimization scheme.Numerical experiments for several two-dimensional sound-hard scatterers having a variety of shapes provide an independent verification of the effectiveness and practicality of the inversion scheme.
基金supported by the National Key R&D Program(Nos.2017YFB0403100,2017YFB0403101)the National Natural Science Foundation of China(Nos.61534007,61404156,61522407,61604168,61775230)+7 种基金the Key Frontier Scientific Research Program of the Chinese Academy of Sciences(No.QYZDB-SSW-JSC014)the Science and Technology Service Network Initiative of the Chinese Academy of Sciences,the Key R&D Program of Jiangsu Province(No.BE2017079)the Natural Science Foundation of Jiangsu Province(No.BK20160401)the China Postdoctoral Science Foundation(No.2016M591944)supported by the Open Fund of the State Key Laboratory of Luminescence and Applications(No.SKLA-2016-01)the Open Fund of the State Key Laboratory on Integrated Optoelectronics(Nos.IOSKL2016KF04,IOSKL2016KF07)the Seed Fund from SINANO,CAS(No.Y5AAQ51001)supported technically by Nano Fabrication Facility,Platform for Characterization&Test,Nano-X of SINANO,CAS
文摘c-plane GaN-based blue laser diodes（LDs） were fabricated with Al-free cladding layers（CLs） and deepened etching depth of mesa structure, so the aspect ratio of the far-field pattern（FFP） of the laser beam can be reduced to as low as 1.7, which is nearly the same as conventional AlGa In P-based red LDs. By using GaN CLs,the radiation angle of the laser beam θ⊥ is only 10.1° in the direction perpendicular to the junction plane. After forming a deeply etched mesa, the beam divergence angle parallel to the junction plane of FFP, θ;, increases from4.9° to 5.8°. After using the modified structure, the operation voltage of LD is effectively reduced by 2 V at an injection current of 50 mA, but the threshold current value increases. The etching damage may be one of the main reasons responsible for the increase of the threshold current.
基金Natural Science Foundation from Universities in Jiangsu Province(06KJD510034)
文摘The system of a true-time delay line for X-band and 8-unit phased array antennas is introduced. Changing the length of a chirp grating with piezotranslator(PZT), the variable delay is obtained. The scheme is applied to X-band phased array radar whose searching data rate is 56/s. It is simulated that the beam squinting is influenced by the error of real time delay. The relation between the beamforming mode and its modifying volt is discussed.
文摘The problem of diffraction of a plane acoustic wave by a finite soft (rigid) cone is investigated. This one is formulated as a mixed boundary value problem for the three-dimensional Helmholtz equation with Dirichlet (Neumann) boundary condition on the cone surface. The diffracted field is sought as expansion of unknown velocity potential in series of eigenfunctions for each region of the existence of sound pressure. The solution of the problem then is reduced to the infinite set of linear algebraic equations (ISLAE) of the first kind by means of mode matching technique and orthogonality properties of the Legendre functions. The main part of asymptotic of ISLAE matrix element determined for large indexes identifies the convolution type operator amenable to explicit inversion. This analytical treatment allows one to transform the initial diffraction problem into the ISLAE of the second kind that can be readily solved by the reduction method with desired accuracy depending on a number of truncation. All these determine the analytical regularization method for solution of wave diffraction problems for conical scatterers. The boundary transition to soft (rigid) disc is considered. The directivity factors, scattering cross sections, and far-field diffraction patterns are investigated in both soft and rigid cases whereas the main attention in the near-field is focused on the rigid case. The numerically obtained results are compared with those known for the disc.
基金National Natural Science Foundation of China(NSFC)(61605155,61627812)Fundamental Research Funds for the Central Universities
文摘Conventional periodic structures usually have nontunable refractive indices and thus lead to immutable photonic bandgaps. A periodic structure created in an ultracold atoms ensemble by externally controlled light can overcome this disadvantage and enable lots of promising applications. Here, two novel types of optically induced square lattices, i.e., the amplitude and phase lattices, are proposed in an ultracold atoms ensemble by interfering four ordinary plane waves under different parameter conditions. We demonstrate that in the far-field regime, the atomic amplitude lattice with high transmissivity behaves similarly to an ideal pure sinusoidal amplitude lattice, whereas the atomic phase lattices capable of producing phase excursion across a weak probe beam along with high transmissivity remains equally ideal. Moreover, we identify that the quality of Talbot imaging about a phase lattice is greatly improved when compared with an amplitude lattice. Such an atomic lattice could find applications in alloptical switching at the few photons level and paves the way for imaging ultracold atoms or molecules both in the near-field and in the far-field with a nondestructive and lensless approach.
