Chipless RFID "Tags"
It took a bit longer than I thought it would, but it appears as if a company has finally put together all the right "ideas" to get a patent on chipless-RFID tags. I first mentioned the physical possibility of these in a position paper I wrote back in 2000.
The basic idea here is to use the natural resonanting properties of a conductive antenna to do the "id" part. This operates in reverse from a normal RFID tag. The reader sends a series of psudo-unique "id pulses" and only the tags with the correct RF ressonance will respond. This bypasses the tag having to have any on-board Aloha protocol anti-interference logic (the chip). Essentially the 'tag' is nothing more than a RF resonant cavity reflector and will only have significant backscatter (i.e. return signal) if hit by the right analog waveform at the correct series of frequencies.
These tags will never have the mass-bulk-reading capabilities of their 5-10 cent relatives, any kind of read/write security, or EPC-sized unique identity namespace.
The read process itself is also much slower, since the reader has to cycle through the various ID classification signals (in a similar fashion to how some univeral remotes work). Nevertheless, their ultra-cheap cost would enable automated product authentication/classification--though typically not a unique enough identity to support holonic systems. Think of these aa RF-Classifiers rather than true IDs. Also, the typical coke-can application wouldn't stand a chance here--way too much interferance from that OTHER nearby resonator (the can) and that RF energy sink (the cola).Of coarse, a patent is not a product and I have yet to finish reviewing the literature enough to determine how/if they've addressed the "resonance-creep" issues (think out-of-tune) with the manufacturing process and over the anticipated useful lifetime of the tags. This is your classic sword-based patent so the details are extremely, uh, detailed.