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In the wide field of tumor treatment, thermal ablation procedures are very promising. Alternating magnetic fields are used to transfer the energy from outside the patient to the tumor area located anywhere in the body. This energy is converted to heat by implanted devices located in the tumor area. In this paper, the spatial distribution of the magnetic field of different circular coil configurations is analyzed and optimized with focus on patients' safety and on coil configuration performance. The analysis is based on several performance criteria and is conducted with respect to the worst case scenario of a contactless thermal tumor ablation of deep-seated tumors, in which the energy has to be transferred over a considerably large distance. The magnetic field and the specific absorption rate (SAR) are calculated numerically and the performance criteria are evaluated based on a model of a human body including a tumor area. The most suitable coil configurations for different application scenarios are presented and a thermal analysis is done. Based on this, the minimum required heating power, coil current and number of coil windings, and the corresponding maximum SAR to achieve an adequate rise of tissue temperature are evaluated. For a heating power of 1.45 W, a minimum SAR of 130 mW/kg, a maximum power transfer efficiency of 1.05%, and a maximum coupling coefficient of 0.00695 is achieved. This paper shows the potential to enhance the safety of the patients significantly by choosing the appropriate coil configuration for a specific application scenario.

This article focuses on increasing the computational efficiency of 3D multi-static magnetic finite element analysis (FEA) for electrical machines (EMs), which have a magnetic field evolving in 3D space. Although 3D FEA is crucial for analyzing these machines and their operational behavior, it is computationally expensive. A novel approach is proposed in order to solve the magnetic field equations by exclusively using the magnetic scalar potential. For this purpose, virtual variable permanent magnets (vPMs) are introduced to model the impact of the machine's coils. The effect on which this approach is based is derived from and explained by Maxwell's equations. To validate the new approach, an axial flux machine (AFM) is simulated using both 2D and 3D FEA with the magnetic vector potential and current-carrying coils as a reference. The results demonstrate a high level of agreement between the new approach and the reference simulations as well as an acceleration of the computation by a factor of 15 or even more. Additionally, the research provides valuable insights into meshing techniques and torque calculation for EMs in FEA. [ABSTRACT FROM AUTHOR]

• Analytic approximation by multiple Taylor series expansions. • Unlimited spatial area with high accuracy is achieved. • A fast evaluation of the magnetic field for every point in space can be done. • Accuracy depends on the distance of the evaluation point to the current loop. In the wide field of contactless energy transfer over a large distance, e.g. for charging electric vehicles or for supplying energy to implanted medical devices in the human body, different types of coils are used. For being able to determine the properties of the path of energy transfer, the spatial distribution of the generated magnetic field is very important. An analytic expression has several advantages for determining the spatial distribution of the magnetic field in an efficient way. In this paper, an analytic approximation for the vector potential and the magnetic flux density of a filamentary circular current loop is proposed. The derivation of the fundamental equations and the concept of the approximation is presented and the range of parameters, in which an analytic solution with sufficient precision is obtained, is determined and evaluated dependent on the parameters of the design and the approximation. The results of the analytic approximation for the magnetic flux density are presented based on an exemplary filamentary circular current loop. Finally, the results are verified by a FEM simulation. The analytic approximation shows a sufficient accuracy at large distances as well as in the close vicinity of the current loop and turns out to be a fast and efficient option to evaluate the magnetic field of one or more circular coils. [ABSTRACT FROM AUTHOR]