A strain sensor comprises a transmitting element; a receiving element wirelessly coupled to the transmitting element; and a modulating element located on a rotating component, wherein the modulating element modulates the wireless coupling between the transmitting element and the receiving element, wherein the modulation of the wireless coupling is indicative of strain on the rotating component. A method of detecting strain in a rotating component of a rotary machine comprises wirelessly coupling a transmitting element and a receiving element; modulating the coupling with a modulating element located on the rotating component; and calculating the strain in the rotating component based on the modulation of the coupling.