IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2000
One of the most important steps in pre-surgical diagnosis of medically intractable epilepsy is to... more One of the most important steps in pre-surgical diagnosis of medically intractable epilepsy is to find the precise lo- cation of the epileptogenic foci. Electroencephalography (EEG) is a non-invasive tool commonly used at epilepsy surgery centers for pre-surgical diagnosis. In this paper, a modified particle swarm optimization (MPSO) method is used to solve the EEG source localization problem. The method is applied to non-invasive EEG recording of somatosensory evoked potentials (SEPs) for a healthy subject. A 1 mm hexahedra finite element volume conductor model of the subject's head was generated using T1- weighted magnetic resonance imaging data. Special consideration was made to accurately model the skull and cerebrospinal fluid (CSF). An exhaustive search pattern and the MPSO method were then applied to the peak of the averaged SEP data and both identified the same region of the somatosensory cortex as the location of the SEP source. A clinical expert independently identified the expected source location, further corroborating the source analysis methods. The MPSO converged to the global minima with significantly lower computational complexity compared to the exhaustive search method that required almost 3 700 times more evaluations.
Gradient-based aerodynamic shape optimization using computational fluid dynamics (CFD), and time ... more Gradient-based aerodynamic shape optimization using computational fluid dynamics (CFD), and time dependent problems in aero-elasticity, that is, coupled calculations between computational structural mechanics (CSM) and CFD, require repeated deformations of the CFD mesh. An interpolation scheme, based on radial basis functions (RBF), is devised in order to propagate the deformations from the boundaries to the interior of the CFD mesh. This method can lower the computational costs due to the deformation of the mesh, in comparison with the usual Laplace smoothing. Moreover, the algorithm is independent of the mesh connectivities. Therefore, structured and unstruc-tured meshes are equally treated as well as hybrid meshes. The application of this interpolation scheme in problems of aerodynamic shape optimization is also carefully investigated. When the optimization is executed by a gradient-based algorithm the cost function is differentiated with respect to the design parameters in order to obtain the gradient. The gradient is most efficiently and accurately calculated by solving a certain adjoint equation derived from the dis-cretized flow equations. The calculation of the gradient, which is detailed in this presentation, involves the Jacobian matrix of the mesh deformation. Finally, we present the results of an optimization of the ONERA M6 wing at transonic speed using the interpolation algorithm. The results are used for comparison with another technique of mesh deformation. The quality of the mesh obtained by the new algorithm, and the interpolation error, are analyzed with respect to the parameters of the interpolation scheme: the type of RBF, the RBF's shape parameter, and the sets of control points.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2012
One of the most important steps of pre-surgical diagnosis in patients with medically intractable ... more One of the most important steps of pre-surgical diagnosis in patients with medically intractable epilepsy is to find the precise location of the epileptogenic foci. An Electroencephalography (EEG) is a non-invasive standard tool used at epilepsy surgery center for pre-surgical diagnosis. In this paper a modified particle swarm optimization (MPSO) method is applied to a real EEG data, i.e., a somatosensory evoked potentials (SEPs) measured from a healthy subject, to solve the EEG source localization problem. A high resolution 1 mm hexahedra finite element volume conductor model of the subject's head was generated using T1-weighted magnetic resonance imaging data. An exhaustive search pattern and the MPSO method were then applied to the peak of the averaged SEPs data. The non-invasive EEG source analysis methods localized the somatosensory cortex area where our clinical expert expected the received SEPs. The proposed inverse problem solver found the global minima with acceptable a...
To simulate the physical and chemical processes inside combustion engines is possible by appropri... more To simulate the physical and chemical processes inside combustion engines is possible by appropriate software and high performance computers. For combustion engines a good design is such that it combines a low fuel consumption with low emissions of soot and nitrogen oxides. These are however partly conflicting requirements. In this paper we approach this problem in a multi-criteria setting which
In this paper we show how multiobjective optimization can be applied to elec- tromagnetic problem... more In this paper we show how multiobjective optimization can be applied to elec- tromagnetic problems. The optimization algorithms are combined with CAD and mesh generation software, and electromagnetic solvers. Three dieren t multiobjective optimization methods are applied: one evolutionary method, one method based on scalarizing of the objectives combined with a method for single objective optimization and a multiobjective respond surface method. To demonstrate the procedure we study the optimization of the return loss of a patch antennas at two dieren t frequencies.
ABSTRACT Purpose The aim of this paper is to evaluate the performance of an EEG source localizati... more ABSTRACT Purpose The aim of this paper is to evaluate the performance of an EEG source localization method that combines a finite element method (FEM) and the reciprocity theorem. Methods The reciprocity method is applied to solve the forward problem in a four-layer spherical head model for a large number of test dipoles. To benchmark the proposed method, the results are compared with an analytical solution and two state-of-the-art methods from the literature. Moreover, the dipole localization error resulting from utilizing the method in the inverse procedure for a realistic head model is investigated with respect to EEG signal noise and electrode misplacement. Results The results show approximately 3% relative error between numerically calculated potentials done by the reciprocity theorem and the analytical solutions. When adding EEG noise with SNR between 5 and 10, the mean localization error is approximately 4.3 mm. For the case with 10 mm electrode misplacement the localization error is 4.8 mm. The reciprocity EEG source localization speeds up the solution of the inverse problem with more than three orders of magnitude compared to the state-of-the-art methods. Conclusions The reciprocity method has high accuracy for modeling the dipole in EEG source localization, is robust with respect to noise, and faster than alternative methods.
2011 IEEE International Symposium on Antennas and Propagation (APSURSI), 2011
ABSTRACT This paper discusses the use of multi-objective optimization in the context of designing... more ABSTRACT This paper discusses the use of multi-objective optimization in the context of designing a dual antenna system for diversity reception or MIMO communication on a mobile platform in the recently released communication band 750-800 MHz. The performance of such systems is highly dependent on the received signal levels and also on the correlation between the signals. Also, from a radio-engineering point of view, there are limitations on the S-parameters of the design. Further, the antennas also need to share space with other devices on the platform, which adds requirements on the size of the antennas. All these aspects often lead to conflicting requirements, which traditionally are dealt with in the optimization by weighting the different requirements into a single requirement. That approach has several disadvantages including that no trade-off discussion between the different requirements can be made. Multi-objective optimization avoids these disadvantages and has the benefit that the decision of optimal design is made by the antenna engineer then all possibilities and limitations are known.
ABSTRACT In this paper multiobjective optimization is applied to antenna design. The optimization... more ABSTRACT In this paper multiobjective optimization is applied to antenna design. The optimization algorithm is a novel response surface method based on approximation with radial basis functions. It is combined with CAD and mesh generation software, and electromagnetic solvers. To demonstrate the procedure we optimize the geometric design and feed position of a PIFA antenna located on a ground plane.
ABSTRACT We present a recently developed method to interpolate functions with poles by quotients ... more ABSTRACT We present a recently developed method to interpolate functions with poles by quotients of two radial basis functions (RBF) expansions. This method combines rational function's ability to approximate function with poles with RBF interpolation's flexibility for scattered data interpolation in any space dimension. The method is tested on an approximation problem for antenna data.
IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2000
One of the most important steps in pre-surgical diagnosis of medically intractable epilepsy is to... more One of the most important steps in pre-surgical diagnosis of medically intractable epilepsy is to find the precise lo- cation of the epileptogenic foci. Electroencephalography (EEG) is a non-invasive tool commonly used at epilepsy surgery centers for pre-surgical diagnosis. In this paper, a modified particle swarm optimization (MPSO) method is used to solve the EEG source localization problem. The method is applied to non-invasive EEG recording of somatosensory evoked potentials (SEPs) for a healthy subject. A 1 mm hexahedra finite element volume conductor model of the subject's head was generated using T1- weighted magnetic resonance imaging data. Special consideration was made to accurately model the skull and cerebrospinal fluid (CSF). An exhaustive search pattern and the MPSO method were then applied to the peak of the averaged SEP data and both identified the same region of the somatosensory cortex as the location of the SEP source. A clinical expert independently identified the expected source location, further corroborating the source analysis methods. The MPSO converged to the global minima with significantly lower computational complexity compared to the exhaustive search method that required almost 3 700 times more evaluations.
Gradient-based aerodynamic shape optimization using computational fluid dynamics (CFD), and time ... more Gradient-based aerodynamic shape optimization using computational fluid dynamics (CFD), and time dependent problems in aero-elasticity, that is, coupled calculations between computational structural mechanics (CSM) and CFD, require repeated deformations of the CFD mesh. An interpolation scheme, based on radial basis functions (RBF), is devised in order to propagate the deformations from the boundaries to the interior of the CFD mesh. This method can lower the computational costs due to the deformation of the mesh, in comparison with the usual Laplace smoothing. Moreover, the algorithm is independent of the mesh connectivities. Therefore, structured and unstruc-tured meshes are equally treated as well as hybrid meshes. The application of this interpolation scheme in problems of aerodynamic shape optimization is also carefully investigated. When the optimization is executed by a gradient-based algorithm the cost function is differentiated with respect to the design parameters in order to obtain the gradient. The gradient is most efficiently and accurately calculated by solving a certain adjoint equation derived from the dis-cretized flow equations. The calculation of the gradient, which is detailed in this presentation, involves the Jacobian matrix of the mesh deformation. Finally, we present the results of an optimization of the ONERA M6 wing at transonic speed using the interpolation algorithm. The results are used for comparison with another technique of mesh deformation. The quality of the mesh obtained by the new algorithm, and the interpolation error, are analyzed with respect to the parameters of the interpolation scheme: the type of RBF, the RBF's shape parameter, and the sets of control points.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2012
One of the most important steps of pre-surgical diagnosis in patients with medically intractable ... more One of the most important steps of pre-surgical diagnosis in patients with medically intractable epilepsy is to find the precise location of the epileptogenic foci. An Electroencephalography (EEG) is a non-invasive standard tool used at epilepsy surgery center for pre-surgical diagnosis. In this paper a modified particle swarm optimization (MPSO) method is applied to a real EEG data, i.e., a somatosensory evoked potentials (SEPs) measured from a healthy subject, to solve the EEG source localization problem. A high resolution 1 mm hexahedra finite element volume conductor model of the subject's head was generated using T1-weighted magnetic resonance imaging data. An exhaustive search pattern and the MPSO method were then applied to the peak of the averaged SEPs data. The non-invasive EEG source analysis methods localized the somatosensory cortex area where our clinical expert expected the received SEPs. The proposed inverse problem solver found the global minima with acceptable a...
To simulate the physical and chemical processes inside combustion engines is possible by appropri... more To simulate the physical and chemical processes inside combustion engines is possible by appropriate software and high performance computers. For combustion engines a good design is such that it combines a low fuel consumption with low emissions of soot and nitrogen oxides. These are however partly conflicting requirements. In this paper we approach this problem in a multi-criteria setting which
In this paper we show how multiobjective optimization can be applied to elec- tromagnetic problem... more In this paper we show how multiobjective optimization can be applied to elec- tromagnetic problems. The optimization algorithms are combined with CAD and mesh generation software, and electromagnetic solvers. Three dieren t multiobjective optimization methods are applied: one evolutionary method, one method based on scalarizing of the objectives combined with a method for single objective optimization and a multiobjective respond surface method. To demonstrate the procedure we study the optimization of the return loss of a patch antennas at two dieren t frequencies.
ABSTRACT Purpose The aim of this paper is to evaluate the performance of an EEG source localizati... more ABSTRACT Purpose The aim of this paper is to evaluate the performance of an EEG source localization method that combines a finite element method (FEM) and the reciprocity theorem. Methods The reciprocity method is applied to solve the forward problem in a four-layer spherical head model for a large number of test dipoles. To benchmark the proposed method, the results are compared with an analytical solution and two state-of-the-art methods from the literature. Moreover, the dipole localization error resulting from utilizing the method in the inverse procedure for a realistic head model is investigated with respect to EEG signal noise and electrode misplacement. Results The results show approximately 3% relative error between numerically calculated potentials done by the reciprocity theorem and the analytical solutions. When adding EEG noise with SNR between 5 and 10, the mean localization error is approximately 4.3 mm. For the case with 10 mm electrode misplacement the localization error is 4.8 mm. The reciprocity EEG source localization speeds up the solution of the inverse problem with more than three orders of magnitude compared to the state-of-the-art methods. Conclusions The reciprocity method has high accuracy for modeling the dipole in EEG source localization, is robust with respect to noise, and faster than alternative methods.
2011 IEEE International Symposium on Antennas and Propagation (APSURSI), 2011
ABSTRACT This paper discusses the use of multi-objective optimization in the context of designing... more ABSTRACT This paper discusses the use of multi-objective optimization in the context of designing a dual antenna system for diversity reception or MIMO communication on a mobile platform in the recently released communication band 750-800 MHz. The performance of such systems is highly dependent on the received signal levels and also on the correlation between the signals. Also, from a radio-engineering point of view, there are limitations on the S-parameters of the design. Further, the antennas also need to share space with other devices on the platform, which adds requirements on the size of the antennas. All these aspects often lead to conflicting requirements, which traditionally are dealt with in the optimization by weighting the different requirements into a single requirement. That approach has several disadvantages including that no trade-off discussion between the different requirements can be made. Multi-objective optimization avoids these disadvantages and has the benefit that the decision of optimal design is made by the antenna engineer then all possibilities and limitations are known.
ABSTRACT In this paper multiobjective optimization is applied to antenna design. The optimization... more ABSTRACT In this paper multiobjective optimization is applied to antenna design. The optimization algorithm is a novel response surface method based on approximation with radial basis functions. It is combined with CAD and mesh generation software, and electromagnetic solvers. To demonstrate the procedure we optimize the geometric design and feed position of a PIFA antenna located on a ground plane.
ABSTRACT We present a recently developed method to interpolate functions with poles by quotients ... more ABSTRACT We present a recently developed method to interpolate functions with poles by quotients of two radial basis functions (RBF) expansions. This method combines rational function's ability to approximate function with poles with RBF interpolation's flexibility for scattered data interpolation in any space dimension. The method is tested on an approximation problem for antenna data.
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Papers by Stefan Jakobsson