A shear wave electromagnetic acoustic transducer(EMAT)optimized structure is proposed by using circumferential annular Halbach magnet structure.Based on the orthogonal test,the effects of the coil conductor width,the ...A shear wave electromagnetic acoustic transducer(EMAT)optimized structure is proposed by using circumferential annular Halbach magnet structure.Based on the orthogonal test,the effects of the coil conductor width,the spacing between adjacent conductors,the number of turns and the lifting distance on EMAT energy conversion effect are studied,and the optimal parameter combination is given.The structural design of the Halbach magnet is proposed.The cost coefficient S of the Halbach structure is defined,and the optimal thickness of auxiliary magnetic pole is obtained.The optimized EMAT coil diameter is reduced by 35%and the echo signal strength is significantly improved.Finally,C-scan imaging is carried out on the sample to verify the detection ability of EMAT.展开更多
The magnetic field of coaxial permanent magnet Halbach circuit is calculated first using the finite element method SUPERFISH and the approximate expression of the magnet circuit is obtained.The forces acting on IREB&#...The magnetic field of coaxial permanent magnet Halbach circuit is calculated first using the finite element method SUPERFISH and the approximate expression of the magnet circuit is obtained.The forces acting on IREB's electron in such magnetic field are analyzed by the use of fluid model and the radial force equation in modified Mathieu function form is drawn then.At last a 2.5-D particle in-cell(PIC)simulation code is used to investigate the physical process of the IREB's propagation.In the PIC simulation,the electron beam current,thickness,magnet field amplitude and the beam's initial incident angle related to the stable propagation are mainly discussed.The conclusion is made that several kilo-amperes intense annular electron beam could propagate stably,meanwhile the focusing form of such magnet geometry provides action mechanism for the interaction between beam electrons and microwave in the ubitron.展开更多
文摘A shear wave electromagnetic acoustic transducer(EMAT)optimized structure is proposed by using circumferential annular Halbach magnet structure.Based on the orthogonal test,the effects of the coil conductor width,the spacing between adjacent conductors,the number of turns and the lifting distance on EMAT energy conversion effect are studied,and the optimal parameter combination is given.The structural design of the Halbach magnet is proposed.The cost coefficient S of the Halbach structure is defined,and the optimal thickness of auxiliary magnetic pole is obtained.The optimized EMAT coil diameter is reduced by 35%and the echo signal strength is significantly improved.Finally,C-scan imaging is carried out on the sample to verify the detection ability of EMAT.
文摘The magnetic field of coaxial permanent magnet Halbach circuit is calculated first using the finite element method SUPERFISH and the approximate expression of the magnet circuit is obtained.The forces acting on IREB's electron in such magnetic field are analyzed by the use of fluid model and the radial force equation in modified Mathieu function form is drawn then.At last a 2.5-D particle in-cell(PIC)simulation code is used to investigate the physical process of the IREB's propagation.In the PIC simulation,the electron beam current,thickness,magnet field amplitude and the beam's initial incident angle related to the stable propagation are mainly discussed.The conclusion is made that several kilo-amperes intense annular electron beam could propagate stably,meanwhile the focusing form of such magnet geometry provides action mechanism for the interaction between beam electrons and microwave in the ubitron.
