# AC magnetic analysis overview

AC magnetic analysis is used to analyze magnetic field caused by alternating currents and, vice versa, electric currents induced by alternating magnetic field (eddy currents). This kind of analysis is useful for designing inductor devices, solenoids, electric motors, and so forth. Generally the quantities of interest in harmonic magnetic analysis are electric current (and its source and induced component), voltage, generated Joule heat, magnetic flux density, field intensity, forces, torques, impedance and inductance.

The AC magnetic field simulation can be coupled with electric circuit. The circuit can contain arbitrarily connected resistors, capacitors, inductances, and solid conductors located in the magnetic field region.

A special type of AC magnetic is nonlinear analysis. It allows estimating with certain precision the behavior of a system with ferromagnets, which otherwise would require much lengthier transient analysis.

Following options are available for harmonic magnetic analysis:

• Material properties: air, orthotropic materials with constant permeability, isotropic soft ferromagnets, current-carrying conductors with known current or voltage.
Electrical conductivity can depend on temperature. The dependency of conductivity on temperature is given in tabular form using the curve editor. The temperature can be specified separately for each block by a number or a formula of coordinates. In addition, the temperature distribution can be imported from the coupled problem of heat transfer analysis.

To a certain degree, AC Harmonic Magnetics formulation takes the saturation of ferromagnetic cores into account. You can define DC-based magnetization curves in the curve editing window. With AC, QuickField uses the equivalent magnetic permeability value for every field point. Calculating this value, it aims to maintain the average magnetic field energy for the period unchanged. QuickField automatically recalculates materials' magnetization curves for the problem-defined frequency.
Although this simplified formulation can only provide a rough estimate for the local field values, the integral results (e.g., energy, force, flux linkage) are reasonably accurate. For highest accuracy, both in local and integral field quantities, please refer to the Transient Magnetic analysis.

• Loading sources: voltage, total current, current density or uniform external field.

• Boundary conditions: Prescribed potential values (Dirichlet condition), prescribed values for tangential flux density (Neumann condition), constant potential constraint for zero normal flux conditions on the surface of superconductor.

• Postprocessing results: magnetic potential, current density, voltage, flux density, field intensity, forces, torques, Joule heat, magnetic energy, impedances, self and mutual inductances as well as current and voltage drop in each branch of connected electric circuit.

• Special features: A postprocessing calculator is available for evaluating user-defined integrals on given curves and surfaces. The magnetic forces can be used for stress analysis on any existing part (magneto-structural coupling); and power losses can be used as heat sources for thermal analysis (electro-thermal coupling).