How to define a 3D geometry given the contour function f(x, y, z)?

Hi,

I am trying to build a 3D lattice shown in the "geom.png" attachment. As seen, it is a binary composite lattice, where the grey volume is filled with material A, and the rest of the volume is filled with material B. Mathematically, this lattice is defined by the boundary function shown in the "func.png" attachment. When the function f(x, y, z) > 0, it is filled with material A, and material B, otherwise.

Up to now, my desired geometry should be clear (hopefully!). I have being trying to do this for the whole day, but no luck. I believe COMSOL definitely supports user-defined arbitrary geometry, as the built-in geometry primitives are just too limited.

I would appreciate if you could demonstrate how I can create such a geometry.

Thanks in advance!

Regards,
A. Wang