ANSYS Composite Beams can model arbitrary beam cross sections with multiple materials. This is an efficient way of modeling the multi-layered nature of many surface micro-machined MEMS devices. The complex high aspect ratio geometry of many devices such as linear resonators can be represented by connected beams. Use of the beams eliminates the need to mesh the volume of a complex geometry for a structural analysis, and thus the model size and computational solution times are dramatically reduced.
The multiple material ability allows additional process layers to be included in the model, for example: oxide or nitride layers on a Polysilicon core. Beam element formulations can be used to efficiently & accurately characterize the eigenfrequencies and dynamic response of the structure. Note that the composite beams are only applicable to structural analysis.
Top view of the beam model. Orange symbols show the anchors points. The beam are dashed because they have been meshed. This model has about 100 beam elements
View of composite beam section. The shape is defined, material properties assigned and meshed in a separate window. The section can then be saved in a library for use later. Multiple cross section can be referenced in the same beam model allowing for complex geometry representations.
Beam cross section showing materials allocation: Polysilicon structural base with a thin oxide layer deposited on top.
Meshed beam cross section
The folowing image shows that ANSYS correctly interprets the beam section when viewing the full 3-D beam model. This graphics plot is achieved by using the /ESHAPE command.
The results for a simple static displacement are shown in this contour plot, but the beams can be used for time transient and modal solutions also.
