You can't protect function through means of copyright. You can only protect form.
If he took your design or was inspired by it and simply re-designed it, there is nothing you can do about it. The only way you could have prevented him from doing this is two fold;
1. Trademark; You can also get a trademark on a very specific look, as long as it's unique for a brand. Monique Dekkers (who designs underwear) won a court case over this at some point.
2. Patent; You have a novel (technical) solution for a problem. However, one could argue that in this case the solution is obvious, so a patent is not valid.
Legally speaking see no fault here.