Sir- I too remember seeing this article a few years ago. At that time I believe Lucent Technologies/AT&T/Bell Labs or some subgroup of theirs was doing this. You're right in that all it relied upon was a "smashing" of one part with studs into another mating part with holes sized to...
How about dipping them in Plastisol (which is the coating used on handles of pliers, cutters, etc.)? This is available at hardware stores in the USA but I don't know about Spain.
If you are referring to damage at the nodal point of the plastics component, i.e., away from the "anti-node" where the ultra sonics is introduced (horn contact)then I would try these-
mechanical dampening (via fixture)of the effected area, clamp around the piece
lower amplitude at...
