US Patent 8669770 Selectively actuating wireless, passive implantable sensor

A wireless sensor having a primary passive electrical resonant circuit that has an intrinsic electrical property that is variable in response to a characteristic of a patient and a secondary passive electrical resonant circuit. In one aspect, the primary passive resonant circuit can be positioned into a tuned position in response to the actuation of the secondary passive electrical resonant circuit. In a further aspect, in the tuned position, the primary passive electrical resonant circuit, in response to an energizing signal produced by an ex-vivo source of RF energy, is configured to generate a sensor signal characterized by a resonant frequency that is indicative of the characteristic.