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How to Apply Electromechanical Forces

Electromechanical devices generate electrostatic fields that can cause structural parts to deflect by design. For example, a MEMS radial comb motor generates an electrostatic field in the air that pushes on its metal parts to precisely move them. Such electromechanical effects can be accurately simulated through a sequential multiphysics analysis:

  1. perform an electrostatic field strength and voltage analysis to calculate the electromechanical (or Coulomb) forces; and
  2. then apply those electromechanical forces as a load in a structural analysis.

The process is illustrated by the following example.

Electrostatic Field Strength and Voltage Analysis

When setting up the model for an electrostatic field strength and voltage analysis in the FEA Editor environment of FEMPRO, use the "Analysis Parameters" dialog to specify that electromechanical forces should be calculated by activating the "Invoke force generator" option on the "Options" tab. In the "Force Output" table, specify the surface(s) where you want the analysis processor to calculate the electromechanical forces. For this example using a MEMS radial comb motor, surface 2 was defined to enclose the air between the static combs and the moving comb, which is the area where electromechanical forces are to be considered (see Figure 1).

Figure 1: On the "Options" tab of the "Analysis Parameters" dialog for an electrostatic field strength and voltage analysis, specify options to output electromechanical forces.

Perform the electrostatic field strength and voltage analysis, which will calculate the electromechanical forces (see Figure 2).

Figure 2: These electrostatic analysis results show the electric field magnitude, which is strongest in the air between the metal parts. Electromechanical forces were calculated within the air.

Structural Analysis

Next, set up and analyze the model for a structural analysis to determine the structural effects caused by the electromechanical forces.

Note: The calculated electromechanical forces can be input as a load to any structural analysis including Mechanical Event Simulation (MES). For this example, a static stress with linear material models analysis was used.

Transfer the model from the FEA Editor environment to Superdraw by using the "Tools:Transfer to Superdraw" command. Then, merge the model with the electromechanical forces that were calculated during the electrostatic analysis by using the "File:Merge..." command (see Figure 3) and specifying the name of the file that contains the electromechanical forces.

Figure 3: In Superdraw, use the "File:Merge..." command to merge the model with the electromechanical forces that were calculated during the electrostatic analysis.

After saving the model, transfer it back to the FEA Editor environment by using the "File:Export to FEMPRO" command. Specify the data needed for the structural analysis including the analysis type, element type, element properties, constraints, additional loads and analysis parameters. For the comb motor model, the air part between the combs was deactivated so that it would not be included in the structural analysis.

Perform the structural analysis and then examine the results in the Superview IV Results environment to see the structural effects caused by the electromechanical forces (see Figure 4).

Figure 4: The effects of the electromechanical forces are shown by the displacement results of a structural analysis. The undisplaced shape is shown as a transparent mesh.

Thus, the multiphysics capability to calculate electromechanical forces in an electrostatic field strength and voltage analysis and then apply them as a load in a structural analysis enables you to accurately simulate electromechanical effects.

For more details about the MEMS radial comb motor example shown here, see the Electrostatic and MEMS Tutorial. For more information about applying electromechanical forces, see the ALGOR User's Guide.



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