Researchers at the Frederick Seitz Materials Research Laboratory at Illinois have achieved something never before accomplished: printing an electronic antenna onto a curved surface. Why would you want to do this? According to electrical and computer engineering professor Jennifer T. Bernhard:
These antennas are electrically small relative to a wavelength (typically a twelfth of a wavelength or less) and exhibit performance metrics that are an order of magnitude better than those realized by monopole antenna designs.
Printing in this way is quite different than the layer-by-layer approach typically used in 3D printing. Instead the print head must scurry along the curved surface so precisely that it doesn't mess up the smooth and uniform deposition of the electrically conductive material. The very short video is quite interesting to watch.
However, this raises an interesting idea: does 3D printing really need to be done layer-by-layer? Or can print heads move up and down as necessary to permit more printable object geometries? Obviously, extremely precise motion is required, but the Illinois team's work demonstrates this is possible.