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What’s New in Depth: Planar Isotropic Conductivity Normal to Surface

26 May, 2017


‘Planar Isotropic’ implies that a material property is the same in two directions, i.e. across a plane, but different in the third direction, the normal. This can be true of a wide range of material properties but from the perspective of 6SigmaET, the most important is thermal conductivity.

Typically, composite materials exhibit this type of behavior. Examples include:

-PCB’s

-Graphite sheets

-Carbon nanotubes

Previous versions of 6SigmaET can handle planar isotropic thermal conductivities on flat surfaces with the user able to specify the ‘material normal’ direction using an objects local coordinates.

But what if a surface isn’t flat? Flexible PCB’s used to join other PCB’s are becoming increasingly commonplace. Curved planar isotropic materials are also being used to create complex enclosures for automotive, lighting and medical applications. In previous versions of 6SigmaET, the thermal conductivity of such objects would become more and more approximate as the severity of the curvature increased.

In Release 11 we have recognized this growing trend and introduced a new feature to ensure the software can handle planar isotropy across a curved surface. When ‘Material Normal’ is set to ‘Surface’ under the ‘Cooling’ node of a solid’s property sheet, the material normal is calculated on a cell by cell basis by determining the nearest point on the surface for each cell centre. This ensures that the thermal conductivity is adjusted accordingly to follow the contours of the material. 

Property Sheet.PNG

This setting is primarily used on solid obstructions.

Modeling tip: As the 6SigmaET PCB object is always flat, to provide the complex options needed to model most PCB’s, the best way to model flexible ‘connecting’ PCB’s is to use the solid obstruction object with the geometry imported from CAD.

Flexible PCB.PNG


By: Matt Evans, Product Engineer