Provided is a remote sensing apparatus comprising: (a) an electromagnetic field detector and (b) an acoustic resonator comprising an electromagnetic field generator and a sensing material in wireless communication with the generator; wherein the sensing material is in wireless communication with the detector, and an acoustic property of the sensing material is responsive to a change in state of an environment to which the sensing material is exposed, and wherein the sensing material is in the form of one or more particles and/or fragments.
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