Abstract: An identification tag is provided comprising a multilayer assembly incorporating, in sequence, a metal backing layer, a bulk structural layer, a piezo-electric layer and an electrode layer. The electrode layer incorporates antennas structures for receiving interrogating radiation comprising a first radiation component at a relatively lower frequency and a second radiation component at a relatively higher frequency. The electrode layer also incorporates a structure for modulating a second signal generated in response to receiving the second component by a first signal generated in response to receiving the first component to generate a modulated signal which is re-emitted as reflected radiation from the tag. The presence of the tag is determinable from modulation components present in the reflected radiation, thereby distinguishing the tag from other objects capable of reflecting radiation, but not modulating it.

Abstract: An amplifier circuit for amplifying an input signal to generate an amplifier output signal incorporates a cascaded series of reflection amplifiers arranged along a signal path and operative to amplify signals propagating in a forward direction along the signal path. The circuit is operative to counteract signal propagation in a reverse direction along the signal path, thereby hindering spontaneous oscillation from arising within the circuit. Incorporation of reflection amplifiers into the circuit enables it to provide high gain, for example 50 dB, while consuming low currents, for example, tens of microamperes. The circuit is especially suitable for use at intermediate frequencies in radio receivers such as mobile telephones.