The resolution and accuracy of the positional stages in the present
system can be upgraded with commercially available stages. However,
one of the principal limitations to extending this technology to
terahertz waveguides is the requirement for small tools. For example,
the dimensions of a half-height 2.5 THz waveguide are
m. To fabricate such a waveguide, one would need a cutter
smaller than 1 mil in diameter. Grinding down saws to small
thicknesses should be feasible by using the high-speed spindles as a
microgrinder. Only straight sections of waveguide can be fabricated
with these tools. The
rigidity of a tool is inversely proportional to the third power of its
thickness. In order to prevent breakage of thin saws, the toolholder
will need to clamp the tool closer to the cutting edge, which in turn
causes the maximum cutting depths to become shallower. One
alternative is to make custom endmills, which when used in the high
speed spindle does not suffer the rigidity problems of stationary
tools.
Another challenge in the fabrication of terahertz structures is maintaining the temperature of the workpiece and toolholders. Enclosing the entire machine in a closed chamber and using a closed loop system with less than 0.1 K of absolute change in temperature will result in higher dimensional accuracy of the parts produced.
The features that are produced with the micro NC machine are extremely tiny and stretch the limit of metrology tools associated with conventional microscopes. One of the limitations of the current system is the difficulty of measurement of test target features to identify tool coordinates with respect to the workpiece. Good relative tool registration between tools and the work is crucial in the production of useful terahertz components. A metrology system with a high resolution digital camera attached to high magnification scopes and coupled with an image processing software package will be required to improve the accuracy of measurement and thus correction of relative tool positions.