Identification tag

DETAILED DESCRIPTION What is claimed is: 1.
An identification tag, comprising: a) transponding means for receiving interrogating radiation and for emitting modulated radiation in response; and b) modulating means for modulating the received interrogating radiation in a manner indicative of tag identity to generate the modulated radiation, the transponding means including first and second structures for receiving first and second radiation components of the interrogating radiation and generating corresponding first and second signals respectively, said first and second components being at mutually different frequencies, the modulating means including a coupling structure operative for receiving the second signal and generating corresponding acoustic radiation, and for coupling the acoustic radiation to the first structure, the acoustic radiation modulating the first signal in the first structure to generate the modulated radiation, the coupling structure comprising a piezo-electric film for generating the acoustic radiation in response to the second signal, the first and second structures comprising radio antennas for receiving the interrogating radiation and emitting the modulated radiation, and the antennas comprising conductive regions formed onto the piezo-electric film on a surface of the tag, the film being operative to generate the acoustic radiation in response to the second signal.
2.
The tag according to claim 1, wherein the film is of piezo-electric polyvinyl difluoride (PVDF) material.
3.
The tag according to claim 1, wherein the film is in a range of 100 .
mu.
m to 250 .
mu.
m thick.
4.
The tag according to claim 1, wherein the first structure includes one of a dipole antenna and a circular electrode region, and wherein the second structure includes a loop antenna.
5.
The tag according to claim 1, wherein the first structure is spatially within the second structure.
6.
The tag according to claim 1, wherein the first structure comprises a plurality of electrically interconnected and radially disposed elongate conducting segment tracks, each track being operative to function as an acoustic resonator having an associated modal vibrational response and to modulate the first component with a modal response corresponding to a segment track stimulated into resonance by acoustic vibrations, thereby providing the tag with a signature code modulated onto the modulated radiation