**EMTGEN**,
* Ncomp*,

`Ecomp`

`PNcomp`

`DOF`

`GAP`

`GAPMIN`

`FKN`

`EPZERO`

`--`

`Smethod`

Compatible Products: – | – | – | Enterprise | Ent PP | Ent Solver | –

`Ncomp`

Component name of the surface nodes of a structure which attach to the TRANS126 elements. You must enclose name-strings in single quotes in the

**EMTGEN**command line.`Ecomp`

Component name of the TRANS126 elements generated. You must enclose name-strings in single quotes in the

**EMTGEN**command line. Defaults to EMTELM.`PNcomp`

Component name of the plane nodes generated by the command at an offset (

) from the surface nodes. You must enclose name-strings in single quotes in the`GAP`

**EMTGEN**command line. Defaults to EMTPNO.`DOF`

Active structural degree of freedom (DOF) for TRANS126 elements in the Cartesian coordinate system. You must enclose the DOF label in single quotes:

**UX**—

Displacement in X direction.

**UY**—

Displacement in Y direction.

**UZ**—

Displacement in Z direction.

`GAP`

Initial gap distance from the surface nodes to the plane. Be sure to use the correct sign with respect to Ncomp node location.

`GAPMIN`

Minimum gap distance allowed (GAPMIN real constant) for TRANS126 elements. Defaults to the absolute value of (

)*0.05.`GAP`

`FKN`

Contact stiffness factor used as a multiplier for a contact stiffness appropriate for bulk deformation. Defaults to 0.1. A negative value is interpreted as the modulus of elasticity on which the contact stiffness will be based.

`EPZERO`

Free-space permittivity. Defaults to 8.854e-6 (μMKS units).

`--`

Unused field.

`Smethod`

Stiffness method for TRANS126 elements (KEYOPT(6) setting). You must enclose the following labels in single quotes:

**AUGM**—

Augmented stiffness method (default).

**FULL**—

Full stiffness method. This method must be used in a linear perturbation harmonic analysis.

The **EMTGEN** command generates a set of
TRANS126 elements between the surface nodes of a moveable
structure and a plane of nodes, typically representing a ground plane. The plane of
nodes is created by the command at a specified offset (* GAP*).
Each element attaches to a surface node and to a corresponding node representing the
plane. The generated plane nodes should be constrained appropriately for the analysis.

By default, the created elements use the augmented stiffness
method (KEYOPT(6) = 1), which can help convergence. You can change to the full stiffness
method (KEYOPT(6) = 0) by setting * Smethod* = FULL. The full
stiffness method is required for a linear perturbation harmonic analysis.

You can use TRANS126 elements for simulating fully coupled
electrostatic structural coupling between a MEMS device and a plane, if the gap distance
between the device and the plane is small compared to the overall surface area
dimensions of the device. This assumption allows for a point-wise closed-form solution
of capacitance between the surface nodes and the plane; i.e. CAP = EPZERO*AREA/GAP,
where EPZERO if the free-space permittivity, AREA is the area associated with the node,
and GAP is the gap between the node and the plane. The area for each node is computed
using the ARNODE function. See the ***GET** command description for more
information on the ARNODE function.

With a distributed set of TRANS126 elements attached directly to the structure and a plane (such as a ground plane), you can perform a full range of coupled electrostatic-structural simulations, including:

Static analysis (due to a DC voltage or a mechanical load)

Prestressed modal analysis (eigenfrequencies, including frequency-shift effects of a DC bias voltage)

Prestressed harmonic analysis (system response to a small-signal AC excitation with a DC bias voltage or mechanical load)

Large signal transient analysis (time-transient solution due to an arbitrary time-varying voltage or mechanical excitation)

The TRANS126 element also employs a node-to-node gap feature so you can perform contact-type simulations where the structure contacts a plane (such as a ground plane). The contact stiffness factor, FKN, is used to control contact penetration once contact is initiated. A smaller value provides for easier convergence, but with more penetration.