A frequency sensor, comprising: a magnetoresistive nano-oscillator (110, 210) including a magnetic heterostructure of at least a magnetic free layer (120, 220), a magnetic reference layer (122, 222) and a non-magnetic intermediate layer (124, 224) arranged between the magnetic free layer (120, 220) and the magnetic reference layer (122, 222), wherein the magnetoresistive nano-oscillator (110, 210) is a magnetic tunnel junction, MTJ, wherein the magnetic free layer (120, 220) is configurable in a state having at least one magnetic vortex core; a coupling arrangement arranged to couple an incoming signal to at least one magnetic mode of said magnetic free layer (120, 220), wherein the at least one magnetic mode includes a gyrotropic mode of the magnetic vortex core, and a frequency estimator; characterized in that: the frequency estimator is configured to: perform a plurality of voltage measurements across said magnetoresistive nano-oscillator (110, 210) over a time interval spanning several oscillations of said at least one magnetic vortex core; calculate, based on said plurality of voltage measurements, a time averaged voltage across said magnetoresistive nano-oscillator (110, 210); estimate, over a finite range of frequencies, a frequency of the incoming signal as a one-to-one function of the calculated time averaged voltage, and output a signal representative of said estimated frequency; and in that the coupling arrangement comprises at least one field line adjacent to the MTJ for passing the incoming signal through as current to generate a magnetic field, said magnetic field being usable to excite said at least one gyrotropic mode of the magnetic vortex core using the incoming signal or at least one conductor for passing the incoming signal as current through the MTJ. a magnetoresistive nano-oscillator (110, 210) including a magnetic heterostructure of at least a magnetic free layer (120, 220), a magnetic reference layer (122, 222) and a non-magnetic intermediate layer (124, 224) arranged between the magnetic free layer (120, 220) and the magnetic reference layer (122, 222), wherein the magnetoresistive nano-oscillator (110, 210) is a magnetic tunnel junction, MTJ, wherein the magnetic free layer (120, 220) is configurable in a state having at least one magnetic vortex core; a coupling arrangement arranged to couple an incoming signal to at least one magnetic mode of said magnetic free layer (120, 220), wherein the at least one magnetic mode includes a gyrotropic mode of the magnetic vortex core, and a frequency estimator; characterized in that: the frequency estimator is configured to: perform a plurality of voltage measurements across said magnetoresistive nano-oscillator (110, 210) over a time interval spanning several oscillations of said at least one magnetic vortex core; calculate, based on said plurality of voltage measurements, a time averaged voltage across said magnetoresistive nano-oscillator (110, 210); estimate, over a finite range of frequencies, a frequency of the incoming signal as a one-to-one function of the calculated time averaged voltage, and output a signal representative of said estimated frequency; and in that the coupling arrangement comprises at least one field line adjacent to the MTJ for passing the incoming signal through as current to generate a magnetic field, said magnetic field being usable to excite said at least one gyrotropic mode of the magnetic vortex core using the incoming signal or at least one conductor for passing the incoming signal as current through the MTJ. perform a plurality of voltage measurements across said magnetoresistive nano-oscillator (110, 210) over a time interval spanning several oscillations of said at least one magnetic vortex core; calculate, based on said plurality of voltage measurements, a time averaged voltage across said magnetoresistive nano-oscillator (110, 210); estimate, over a finite range of frequencies, a frequency of the incoming signal as a one-to-one function of the calculated time averaged voltage, and output a signal representative of said estimated frequency; and in that the coupling arrangement comprises at least one field line adjacent to the MTJ for passing the incoming signal through as current to generate a magnetic field, said magnetic field being usable to excite said at least one gyrotropic mode of the magnetic vortex core using the incoming signal or at least one conductor for passing the incoming signal as current through the MTJ.