Determination of capacitances in a twelve column MR-birdcage resonator using finite elements

Simulating the operation of a birdcage resonator numerically requires an accurate knowledge of its inductances and of the capacitances as well. In this paper, a way to determine these capacitances is shown for a twelve column birdcage resonator. For known resonator geometries, the self- and the mutual inductances can be calculated analytically using filaments. For a given frequency, the capacitances are estimated subsequently by solving an eigenvalue problem. In a second approach, the inductances will be computed with a 2D-FEM multiconductor code, which takes the real current density distribution in the conductors into account in order to improve the accuracy of the eigenvalue solution. Once the capacitances are known, a 3D-FEM model of the birdcage resonator can be generated. Varying the capacitance values and comparing the resulting maxima of the magnetic field density is show the correct capacitance value at resonance, as well. The 3D finite element computation uses the A&oarr; v formulation based on edge elements