AC/DC Module Updates
For users of the AC/DC Module, COMSOL Multiphysics® version 5.5 offers updated Electric Currents in Shells and Electric Currents in Layered Shells interfaces, a Lorentz Coupling multiphysics coupling for modeling electroacoustic transducers, and a hard magnetic materials library with about 50 sintered NdFeB grades (Chinese standard). Learn about all of the AC/DC Module updates in more detail below.
Electric Currents in Shells and Electric Currents in Layered Shells Interfaces
The new (layered) shell interfaces are an evolution of the previously available Electric Currents, Layered Shell and Electric Currents, Shell interfaces, with a focus on better usability and robustness. Modeling of both nonlayered shells, as well as layered shells, has become more streamlined with improved integration to other physics (multiphysics).
For layered shells, the physics interface models the shell’s boundary selection in 3D, as well as an extra dimension that points in the shell’s normal direction. This way, you can model both tangential and normal electric fields inside the shell, and as a result, you can use the interface to model conductors and dielectrics for Stationary, Time Dependent, and Frequency Domain studies. Combining either the MEMS Module or Structural Mechanics Module with the Composite Materials Module, this allows for modeling piezoelectric materials in layered shells.
You can see these new interfaces in the following models:
- piezoelectricity_layered_shell (new model)
- heating_circuit
- planar_pcb_coil
- solid_multilayer_shell_comparison
Lorentz Coupling Multiphysics for Electroacoustic Transducers
The Lorentz Coupling multiphysics coupling supports a two-way coupling between the Magnetic Fields and the Solid Mechanics interfaces. The Lorentz force is determined by computing the cross product of the current density (J) and the magnetic flux (B) inside of a domain. This force is then applied as a volumetric force on the mechanics side. At the same time, the velocity is taken from Solid Mechanics and applied in the Magnetic Fields interface as a Lorentz velocity term. This type of multiphysics coupling has been available in earlier versions of the AC/DC Module but is now much easier to define. The feature is intended for conductive, nonmagnetizable domains, such as copper coils. When combined with the Acoustic-Structure Boundary multiphysics coupling, this allows for easier modeling of electroacoustic transducers. It is available in 2D and 3D, for Time Dependent, Frequency Domain (Perturbation), and Eigenfrequency analyses.
You can see this feature demonstrated in the following models:
Hard Magnetic Materials Library for Permanent Magnets
About 50 sintered NdFeB grades, adhering to the Chinese standard, have been added to the AC/DC Module material library. The materials include N, M, H, SH, UH, EH, and TH grades, and are characterized by a typical value for the remanent magnetic flux density norm 
and the recoil permeability 
. The remanent flux density constitutive relation has been updated to support these new materials. Now, the magnitude of the remanent flux density is provided by the material, while the direction is specified in the physics settings. This allows for quick and easy modeling of devices with permanent magnets. By combining the materials together with a Material Switch feature, you can sweep over different grades to investigate the corresponding performance.
You can see these materials used in the following models:
- pm_motor_3d
- rotating_machinery_3d_tutorial
- loudspeaker_driver
- loudspeaker_driver_transient
- generator_3d
- static_field_halbach_rotor_3d
- falling_magnet
Material Property Enhancements
In addition to the new materials, numerous improvements have been added to the Constitutive Relations, material models governing magnetic, conductive, or dielectric properties. A utility application, B-H Curve Checker, allows you to investigate the quality, smoothness, and physical correctness of nonlinear magnetic curves. Imported data can be corrected and saved before use in a numerical model. The entire Nonlinear Magnetic materials library has been processed through this application to make sure that they are smooth, cross the zero point (that is, B equals zero when H is zero), and approach the physically correct asymptotic value for the incremental relative permeability (the relative permeability should approach 1 when the material becomes saturated). The user interface and section naming of the material models have also been improved and made more consistent across all interfaces within the AC/DC Module.
Coil Improvements
Numerous small improvements have been added to the Coil feature. Support for spatially dependent conductivity has been added to the Domains > Coil feature when operating in single-conductor mode. The Accurate coil voltage calculation feature is now available for the Time Dependent study and has been made available for boundary coils in Frequency Domain and Time Dependent studies. The method to calculate the coil length for a circular coil has been improved with volumetric averaging for computing the coil length. It is no longer necessary to select a set of edges with the correct average length; only the edge directions matter.
New AC/DC Model Wizard Tree
The physics interfaces in the AC/DC branch of the Model Wizard tree have been reorganized to allow for easier navigation. Important multiphysics interfaces that involve the AC/DC Module, but that have previously been available in other branches of the Model Wizard tree, have been included as well.
Extended Support for Jiles–Atherton Hysteresis
The nonlinear Magnetostrictive Material has been extended to include the Jiles–Atherton model of magnetic hysteresis. The model is suitable for investigating the hysteretic loss effects in applications such as power transformers and rotating electric machines. The model parameters are related to microscopic physical effects in magnetic materials and they can also be estimated based on experimental data.
Additionally, the Jiles–Atherton material model for magnetic hysteresis has been extended to support parametric stationary studies (in addition to the previously available Time Dependent analysis). Ferromagnetic hysteresis is for low-to-moderate frequencies, rate-independent, and can be analyzed using a parametric stationary study, for example when studying magnetization and demagnetization.
Surface Current Density for the Transition Boundary Condition
With the Transition boundary condition, you can now add an explicit surface current density contribution on the up and down side, by means of a Surface Current Density attribute. This is useful when studying the shielding of electromagnetic fields in the context of EMC and EMI.
Static Gauge for Time-Dependent and Frequency Domain Studies
The Gauge Fixing for A-field feature has added support for using a magnetostatic approximation (with Coulomb gauge) in nonconducting domains for the Frequency Domain and Time Dependent studies. It can be used to stabilize models with poorly conducting or nonconducting domains that are excited at low frequencies. You can see this feature in the E-Core Transformer model.
New and Updated Tutorial Models and Applications
Version 5.5 brings new and updated tutorial models and applications.
Induction Heating of a Steel Billet
Application Library Title:
billet_induction_heating
Piezoelectricity in a Layered Shell
Application Library Title:
piezoelectric_layered