Bohumila Lencova - Academia.edu (original) (raw)

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Papers by Bohumila Lencova

Research paper thumbnail of Computer-aided lens design for electron microscopes

Research paper thumbnail of Comparison of FDM, FEM and BEM for electrostatic charged particle optics

Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 1999

ABSTRACT The accuracy and speed of three programs based on different methods for solving problems... more ABSTRACT The accuracy and speed of three programs based on different methods for solving problems in electrostatic charged particle optics are compared, using a set of benchmark tests. The methods are the Finite Difference, Finite Element and Boundary Element Methods (FDM, FEM and BEM, respectively).

Research paper thumbnail of Linear finite element method in axisymmetric magnetostatic problems

IEEE Transactions on Magnetics, 1992

If there is a long iron cylinder on the axis of rotational symmetry, the FEM with linear shape fu... more If there is a long iron cylinder on the axis of rotational symmetry, the FEM with linear shape function for the computation of the angular component of the vector potential yields an i n c o m t solution. Based on a suitable weight factor in the expression for the z component of the flux density, new formulas for the coefficients of the linear

Research paper thumbnail of Use of the first-order FEM for the computation of magnetic electron lenses

The first order finite element method allows an accurate computation of rotationally symmetric ma... more The first order finite element method allows an accurate computation of rotationally symmetric magnetic electron lenses with saturated materials. The paper gives an overview of six methods for the evaluation of the coefficients of FEM equations. Then we present a study of local and global errors in the axial flux density distribution. These effects are illustrated on computations of a simple magnetic lens, closed magnetic circuit, and an objective lens for 1 MeV microscope. Finally we give a recommendation on the use of meshes with sufficient number of mesh points and with graded mesh size, and provide information on the computation time and memory requirements on a personal computer.

Research paper thumbnail of Accurate computation of higher multipole components of electrostatic and magnetic deflectors with the first-order FEM

The first order finite element method allows an accurate computation of multipole components of e... more The first order finite element method allows an accurate computation of multipole components of electrostatic and magnetic fields. The paper presents an analytical expression of the first, the third and the fifth harmonic component of electrostatic deflectors defined on an electrostatic box and for magnetic deflectors made of straight or tapered saddle coils or straight toroidal coils in air. The axial field functions are compared with those computed with the first order finite element method for the same geometry, with a very good agreement of the results.

Research paper thumbnail of Studies on the asymptotic cardinal elements and aberration coefficients of symmetric unipotential electrostatic lenses

Optik, 2002

Numerical and theoretical evidence is provided to establish the number of independent coefficient... more Numerical and theoretical evidence is provided to establish the number of independent coefficients needed to characterize fully the magnification-dependence of the spherical aberration coefficient of symmetric unipotential electrostatic lenses. Claims that the number is smaller than believed are shown to be unfounded.

Research paper thumbnail of Computer-aided lens design for electron microscopes

Research paper thumbnail of Comparison of FDM, FEM and BEM for electrostatic charged particle optics

Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 1999

ABSTRACT The accuracy and speed of three programs based on different methods for solving problems... more ABSTRACT The accuracy and speed of three programs based on different methods for solving problems in electrostatic charged particle optics are compared, using a set of benchmark tests. The methods are the Finite Difference, Finite Element and Boundary Element Methods (FDM, FEM and BEM, respectively).

Research paper thumbnail of Linear finite element method in axisymmetric magnetostatic problems

IEEE Transactions on Magnetics, 1992

If there is a long iron cylinder on the axis of rotational symmetry, the FEM with linear shape fu... more If there is a long iron cylinder on the axis of rotational symmetry, the FEM with linear shape function for the computation of the angular component of the vector potential yields an i n c o m t solution. Based on a suitable weight factor in the expression for the z component of the flux density, new formulas for the coefficients of the linear

Research paper thumbnail of Use of the first-order FEM for the computation of magnetic electron lenses

The first order finite element method allows an accurate computation of rotationally symmetric ma... more The first order finite element method allows an accurate computation of rotationally symmetric magnetic electron lenses with saturated materials. The paper gives an overview of six methods for the evaluation of the coefficients of FEM equations. Then we present a study of local and global errors in the axial flux density distribution. These effects are illustrated on computations of a simple magnetic lens, closed magnetic circuit, and an objective lens for 1 MeV microscope. Finally we give a recommendation on the use of meshes with sufficient number of mesh points and with graded mesh size, and provide information on the computation time and memory requirements on a personal computer.

Research paper thumbnail of Accurate computation of higher multipole components of electrostatic and magnetic deflectors with the first-order FEM

The first order finite element method allows an accurate computation of multipole components of e... more The first order finite element method allows an accurate computation of multipole components of electrostatic and magnetic fields. The paper presents an analytical expression of the first, the third and the fifth harmonic component of electrostatic deflectors defined on an electrostatic box and for magnetic deflectors made of straight or tapered saddle coils or straight toroidal coils in air. The axial field functions are compared with those computed with the first order finite element method for the same geometry, with a very good agreement of the results.

Research paper thumbnail of Studies on the asymptotic cardinal elements and aberration coefficients of symmetric unipotential electrostatic lenses

Optik, 2002

Numerical and theoretical evidence is provided to establish the number of independent coefficient... more Numerical and theoretical evidence is provided to establish the number of independent coefficients needed to characterize fully the magnification-dependence of the spherical aberration coefficient of symmetric unipotential electrostatic lenses. Claims that the number is smaller than believed are shown to be unfounded.

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