BoingBoing blogs on instructions for how to kill an RFID chip. It includes methods such as microwaving and hammering. Some methods leave a mark, others do not readily display the tampering. For example, hammering is touted:
The last (and most covert) method for destroying a RFID tag is to hit it with a hammer. Just pick up any ordinary hammer and give the chip a few swift hard whacks. This will destroy the chip, and leave no evidence that the tag has been tampered with. This method is suitable for destroying the tags in passports, because there will be no proof that you intentionally destroyed the chip
However, don’t rush to smash your passport just yet. The E-passport regulations say this about a passport with a defective RFID chip:
Any passport which has been materially changed in physical appearance or composition, or contains a damaged, defective or otherwise nonfunctioning electronic chip, or which includes unauthorized changes, obliterations, entries or photographs, or has observable wear and tear that renders it unfit for further use as a travel document may be invalidated.
So even though your destruction of the RFID chip leaves you with a perfectly normal old-style passport, that’s not how the State Department sees it. You have a mutilated passport which may be invalidated, leaving you without travel papers until they give you a new one. You’d think you had the right to control how electronic your passport will be, but that’s not quite the case.