A sensor for implantation within a living animal and measurement of an analyte in a medium within the living animal, the sensor comprising: an analyte indicator configured to exhibit a detectable property based on the amount or concentration of the analyte in the medium; sensor elements configured to generate an analyte measurement signal based on the detectable property exhibited by the analyte indicator; an inductive element configured to produce a current when in an electrodynamic field generated by an external device ; an input/output circuit configured to wirelessly convey measurement information to the external device via the inductive element; and a measurement controller , wherein the sensor further comprises a charge storage device and a substrate ; one or more of the sensor elements are mounted on or fabricated in the substrate; the inductive element is a coil; and the measurement controller is configured to: (i) control the sensor elements to generate a first analyte measurement signal using power provided by the charge storage device while the inductive element is not in an electrodynamic field generated by the external device; (ii) generate first measurement information based on the first analyte measurement signal; and (iii) control the input/output circuit to wirelessly convey the first measurement information to the external device while the inductive element is in an electrodynamic field generated by the external device, characterised in that the charge storage device and the substrate are located within the coil. an analyte indicator configured to exhibit a detectable property based on the amount or concentration of the analyte in the medium; sensor elements configured to generate an analyte measurement signal based on the detectable property exhibited by the analyte indicator; an inductive element configured to produce a current when in an electrodynamic field generated by an external device ; an input/output circuit configured to wirelessly convey measurement information to the external device via the inductive element; and a measurement controller , wherein the sensor further comprises a charge storage device and a substrate ; one or more of the sensor elements are mounted on or fabricated in the substrate; the inductive element is a coil; and the measurement controller is configured to: (i) control the sensor elements to generate a first analyte measurement signal using power provided by the charge storage device while the inductive element is not in an electrodynamic field generated by the external device; (ii) generate first measurement information based on the first analyte measurement signal; and (iii) control the input/output circuit to wirelessly convey the first measurement information to the external device while the inductive element is in an electrodynamic field generated by the external device, (i) control the sensor elements to generate a first analyte measurement signal using power provided by the charge storage device while the inductive element is not in an electrodynamic field generated by the external device; (ii) generate first measurement information based on the first analyte measurement signal; and (iii) control the input/output circuit to wirelessly convey the first measurement information to the external device while the inductive element is in an electrodynamic field generated by the external device, characterised in that the charge storage device and the substrate are located within the coil. <EOS>