The Electromechanics (emi) interface (), found under the Structural Mechanics branch () when adding a physics interface, combines Solid Mechanics and Electrostatics with a Moving Mesh to model the deformation of electrostatically actuated structures. The physics interface is also compatible with piezoelectric materials.

The full functionality of the Solid Mechanics and Electrostatics interfaces is accessible under the Structural and Electrical submenus, at the domain, boundary line, or point level in the geometry. Similarly, boundary conditions for the moving mesh are available under the Deformed Mesh submenu.

When this physics interface is added, the following default nodes are also added to the Model Builder— Electrical Material Model, Linear Elastic Dielectric, and Free Deformation (for the Electrostatics interface and the mesh movement) in the domains; Zero Charge (for the Electrostatics interface), Electromechanical Interface (which applies the exterior electrical forces on the surfaces of the dielectric) Free (for the Solid Mechanics interface, initially with no selection) as default boundary conditions; and Initial Value.Then, from the Physics toolbar, add other nodes that implement, for example, loads, constraints, and material models for the solid domain. You can also right-click Electromechanics to select physics features from the context menu.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different 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 physics interface in the model) is emi.

From the Structural transient behavior list, select Include inertial terms (the default) or Quasi-static. Use Quasi-static to treat the elastic behavior as quasi-static (with no mass effects; that is, no second-order time derivatives). Selecting this option gives a more efficient solution for problems where the variation in time is slow when compared to the natural frequencies of the system. The default solver for the time stepping is changed from Generalized alpha to BDF when Quasi-static is selected.

Enter the coordinates for the Reference point for moment computation, xref (SI unit: m). The resulting moments (applied or as reactions) are then computed relative to this reference point. During the results and analysis stage, the coordinates can be changed in the Parameters section in the result nodes.

The typical wave speed cref (SI unit: m/s) is used as an input parameter for the perfectly matched layers (PMLs) which are frequently used to model solid wave propagation. The default value of the pressure-wave speed is emi.cp. For anisotropic materials, it is advisable to use the correct wave velocity for the mode of interest, rather than the approximate value provided. To do this, enter a value or expression in the Typical wave speed for perfectly matched layers field.

Select the Activate terminal sweep check box to switch on the sweep and invoke a parametric sweep over the terminals. Enter a Sweep parameter name to assign a specific name to the variable that controls the terminal number solved for during the sweep. The generated lumped parameters are in the form of capacitance matrix elements. The terminal settings must consistently be of either fixed voltage or fixed charge type.

The lumped parameters are subject to Touchstone file export. Enter a file path or Browse for a file.

Select a Mesh smoothing type—Hyperelastic (the default), Laplace, Winslow, or Yeoh. For the Yeoh mesh smoothing type, also specify a Stiffening factor (default: 100). See Smoothing Methods in the COMSOL Multiphysics Reference Manual for more information.

Select the variable names for the Material frame coordinates (the default is X, Y, and Z) and select the Geometry shape order—1 (linear), 2 (quadratic—the default), 3 (cubic), 4 (quartic), or 5 (quintic, 2D only).

The dependent variable (field variables) are the Displacement field u (SI unit: m), and its components, and the Electric Potential V (SI unit: V). Their names can be changed but the names of fields and dependent variables must be unique within a model.

To display this section, click the Show button () and select Discretization. See Common Physics Interface and Feature Settings and Nodes for links to more information.