Piezo-electric tag

DETAILED DESCRIPTION The inventor has devised a tag which addresses this principal problem and which is operable, for example, from moderate levels of incident radiation thereupon in the order of 10 μW.
Such moderate levels of radiation rarely represent any health and safety risk.
According to a first aspect of the present invention, there is provided a piezoelectric tag including receiving means for receiving input radiation and generating a corresponding received signal, piezo-electric vibrating means for increasing voltage magnitude of the received signal to generate a supply potential and electronic circuit means powerable by the supply potential.
The invention provides the advantage that the vibrating means is capable of providing voltage magnification, thereby enabling the tag to be powered from radiation incident thereupon.
For the purpose of describing the invention, microwave frequencies means frequencies substantially in a range of 1 GHz to 30 GHz.
Advantageously, the vibrating means comprises a piezo-electric transformer incorporating mutually vibrationally coupled primary and secondary regions, the transformer operable to be excited into vibration by the received signal at the primary region and to generate a corresponding output signal at the secondary region for use in generating the supply potential.
The piezo-electric transformer provides the advantage that it is capable of being compact, inexpensive and providing a considerable increase in signal voltage amplitude from its primary region to its secondary region, the increase approaching 100 times or more.
Alternatively, the vibrating means comprises a piezoelectric bi-morph operable to be excited into vibration by the received signal and to generate a corresponding output signal for use in generating the supply potential.
As a further alternative, the vibrating means conveniently comprises a silicon micromachined device comprising an array of one or more resonant elements, each element incorporating an associated piezo-electric transducer operable to generate an element signal in response to vibration of its associated element, the transducers connected in series to add their element signals to provide an overall output from which the supply potential is generated, and driving means operable to be driven by the received signal for stimulating the one or more elements into vibration and thereby generating the supply potential