The Lorentz Coupling (
) is a multiphysics coupling feature between the
Magnetic Fields interface and the
Solid Mechanics interface. It passes the Lorentz force
F = J × B from the
Magnetic Fields interface to the
Solid Mechanics interface and, passes the induced electric field
E = v × B from the
Solid Mechanics interface to the
Magnetic Fields interface. The Lorentz force effect on a moving structure is similar to that of the Rayleigh alpha-damping, where the damping coefficient is proportional to the background magnetic field and the material electric conductivity.
The Lorentz force and induced electric field can also be added separately from the interfaces, for instance, by using the Body Load feature from the
Solid Mechanics interface and the
Velocity (Lorentz term) feature (in 2D and 2D axisymmetric) from the
Magnetic Fields interface. Once the
Lorentz Coupling feature is applied, those interface features with the same purpose should not be used to avoid double counting. When modeling electroacoustic transducers, like loudspeakers, the coupling is typically added in the voice coil domain.
The Lorentz Coupling feature is available in 2D, 2D axisymmetric, and 3D geometries and is allowed for both time-dependent and frequency-domain studies (including frequency domain perturbation and eigenfrequency studies). The coupling feature handles frames as well as the correct formulation for transient and frequency domain problems. For time-dependent studies, it only accounts for the Lorentz force contribution when the
Include geometric nonlinearity check box (in Study settings) is selected. When the displacement of the vibrating or moving part of the model cannot be neglected (when topology changes are important), the
Moving Mesh feature (added from the
Definitions) is usually used together with the
Lorentz Coupling feature.
The Label is the multiphysics coupling feature name. The default
Label (for the first multiphysics coupling feature in the model) is
Lorentz Coupling 1.
The Name is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern
<name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or physics interfaces, the
name string must be unique. Only letters, numbers, and underscores (_) are permitted in the
Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling feature in the model) is
ltzc1.
This section defines the physics involved in the multiphysics coupling. The Magnetic fields and
Solid mechanics lists include all applicable physics interfaces.
When the Lorentz Coupling node is added from the Physics ribbon (Windows users),
Physics contextual toolbar (macOS and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.
You can also select None from either list to uncouple the Lorentz Coupling node from a physics interface. If the physics interface is removed from the
Model Builder, for example
Solid Mechanics is deleted, then the list defaults to
None as there is nothing to couple to.
In models where the Lorentz Coupling is not applicable, for example, for magnetizable armatures in transducers, the
Magnetomechanical Forces multiphysics coupling should be used. For details see the
Magnetomechanical Forces and the
The Magnetomechanics Interface documentation of the
Structural Mechanics User’s Guide.
) can be used for modeling deformation of magnetically actuated structures, which includes interaction of magnetic fields with magnetic materials and current carrying elements such as coils and wires. 
