We study wave splitting procedures for acoustic or electromagnetic scattering problems. The idea of these procedures is to split some scattered field into a sum of fields coming from different spatial regions such tha...We study wave splitting procedures for acoustic or electromagnetic scattering problems. The idea of these procedures is to split some scattered field into a sum of fields coming from different spatial regions such that this information can be used either for inversion algo- rithms or for active noise control. Splitting algorithms can be based on general boundary layer potential representation or Green＇s representation formula. We will prove the unique decomposition of scattered wave outside the specified reference domain G and the unique decomposition of far-field pattern with respect to different reference domain G. Further, we employ the splitting technique for field reconstruction for a scatterer with two or more separate components, by combining it with the point source method for wave recovery. Us-ing the decomposition of scattered wave as well as its far-field pattern, the wave splitting procedure proposed in this paper gives an efficient way to the computation of scattered wave near the obstacle, from which the multiple obstacles which cause the far-field pattern can be reconstructed separately. This considerably extends the range of the decomposition methods in the area of inverse scattering. Finally, we will provide numerical examples to demonstrate the feasibility of the splitting method.展开更多
A novel modified physical optics algorithm is proposed to overcome the difficulties of near field scattering prediction for classical physical optics. The method is applied to calculating the near field radar cross se...A novel modified physical optics algorithm is proposed to overcome the difficulties of near field scattering prediction for classical physical optics. The method is applied to calculating the near field radar cross section of electrically large objects by taking into account the influence of the distinct wave propagation vector, the near field Green function, and the antenna radiation pattern. By setting up local reference coordinates, each partitioned facet has its own distinct wave front curvature. The radiation gain for every surface element is taken into consideration based on the modulation of the antenna radiation pattern. The Green function is refined both in amplitude and phase terms and allows for near field calculation. The scattered characteristics of the near field targets are studied by numerical simulations. The results show that the approach can achieve a satisfactory accuracy.展开更多
Ths paper introduces a transducer for measuring suspended sand particles, and a shading principle to eliminate the blind point in the near field of sound source axis. By adopting the front matching layer and back line...Ths paper introduces a transducer for measuring suspended sand particles, and a shading principle to eliminate the blind point in the near field of sound source axis. By adopting the front matching layer and back liner, the transducer’s fraquency band becomes 2. 1 times wider and the sensitivity 1. 6 times higher. The transducer is characterized by simple structure and portability.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
文摘We study wave splitting procedures for acoustic or electromagnetic scattering problems. The idea of these procedures is to split some scattered field into a sum of fields coming from different spatial regions such that this information can be used either for inversion algo- rithms or for active noise control. Splitting algorithms can be based on general boundary layer potential representation or Green＇s representation formula. We will prove the unique decomposition of scattered wave outside the specified reference domain G and the unique decomposition of far-field pattern with respect to different reference domain G. Further, we employ the splitting technique for field reconstruction for a scatterer with two or more separate components, by combining it with the point source method for wave recovery. Us-ing the decomposition of scattered wave as well as its far-field pattern, the wave splitting procedure proposed in this paper gives an efficient way to the computation of scattered wave near the obstacle, from which the multiple obstacles which cause the far-field pattern can be reconstructed separately. This considerably extends the range of the decomposition methods in the area of inverse scattering. Finally, we will provide numerical examples to demonstrate the feasibility of the splitting method.
文摘A novel modified physical optics algorithm is proposed to overcome the difficulties of near field scattering prediction for classical physical optics. The method is applied to calculating the near field radar cross section of electrically large objects by taking into account the influence of the distinct wave propagation vector, the near field Green function, and the antenna radiation pattern. By setting up local reference coordinates, each partitioned facet has its own distinct wave front curvature. The radiation gain for every surface element is taken into consideration based on the modulation of the antenna radiation pattern. The Green function is refined both in amplitude and phase terms and allows for near field calculation. The scattered characteristics of the near field targets are studied by numerical simulations. The results show that the approach can achieve a satisfactory accuracy.
文摘Ths paper introduces a transducer for measuring suspended sand particles, and a shading principle to eliminate the blind point in the near field of sound source axis. By adopting the front matching layer and back liner, the transducer’s fraquency band becomes 2. 1 times wider and the sensitivity 1. 6 times higher. The transducer is characterized by simple structure and portability.
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.
