Abstract: An RFID memory device includes two arrays of resonant members. A first array extends in a first member direction and a second array extends in a second member direction. The device includes one or more elements for transforming energy associated with vibration of the resonant members into a change in impedance of an electrical equivalent circuit of the memory device. The magnitude of impedance change caused by resonance of the first resonant members is maximized at a different magnetic field direction to that at which the magnitude of the impedance change caused by resonance of the second resonant members is maximized. Thus, different data may be encoded on each array and separately read. The resonant members may form part of a common electrical conductor that forms a coupling element for coupling with an applied excitation signal and causing vibration of the resonant members.

Abstract: The method of interrogating an RFID memory device (14) including one or more vibrating members (16-34) each being able to resonate at a different known resonant frequency uses a ring-up/down interrogation technique which exploits a property of the resonance increments in relation to the background that is not exploited in steady-state interrogation techniques. This ring-up/down interrogation technique operates by application of an electrical stimulus of appropriate band width to which one or more of the resonances can respond and absorb some amount of energy, holding it in (ultimately) mechanical form (“ring-up”) (228). This stimulus is then reduced to zero, and the electrical response appearing across the terminals of the device then recorded (“ring-down”)(230).