Patent ID: 7608978

Claim:
A sensing system including a detector and an oscillating circuit comprising a coupling device, an amplifier, and a plurality of resonators, wherein: each resonator comprises: (i) a body of piezoelectric material; (ii) an input electrode assembly mounted on the body of piezoelectric material whereby the input electrode assembly when activated produces an acoustic wave across the body of piezoelectric material; and (iii) an output electrode assembly mounted on the body of piezoelectric material and being in contact with a sensitive area that is sensitive to a supplied stimulus so that the acoustic velocity of the acoustic wave across the sensitive area is modified when a supplied stimulus binds to the sensitive area in sufficient quantity, whereby the output electrode assembly receives the acoustic wave after the acoustic wave has passed across the sensitive area; and wherein for each resonator, when the input electrode assembly is activated, the input electrode assembly and the output electrode assembly cooperate to produce a frequency response representative of one of presence or absence of a sufficient quantity of the stimulus; wherein the resonators are coupled in series from 1 to n; and wherein: the n th resonator has an output connected to an amplifier input of the amplifier; the amplifier has an amplifier output connected to a coupling device input of the coupling device; the coupling device has a first coupling device output connected to an input of the first resonator; the coupling device has a second coupling device output connected to the detector; and the amplifier has a gain that is insufficient to cause the oscillator circuit to meet Barkhausen criteria when at least one of the n resonators produces a frequency response representative of absence of a sufficient quantity of its respective stimulus and that is sufficient to cause the oscillator circuit to meet Barkhausen criteria when all of the n resonators produce a frequency response representative of presence of a sufficient quantity of their respective stimulus, so that the detector emits a detection signal only when all of the n resonators produce a frequency response representative of presence of a sufficient quantity of their respective stimulus.