Contactless electromagnetic excitation of resonant sensors made of conductive miniaturized structures

An electromagnetic contactless excitation principle is presented to induce mechanical vibrations on miniaturized electrically conductive resonant structures to be used as passive sensors. An external coil arrangement generates a time-varying magnetic field which induces eddy currents on the structure surface. The interaction between the eddy currents and the magnetic field causes forces which can set the structure into vibration. The principle avoids any contact to the resonator structure to inject current and only requires the structure to be electrically conductive, without the need for specific magnetic properties. The principle is attractive for the development of passive sensors operating in environments with limited accessibility or incompatible with active electronics. A mathematical model of the excitation principle has been derived and has been supported by means of finite-element simulations. Experimental demonstration of the excitation principle has been obtained on cantilever and a clamped-clamped beam miniaturized conductive structures used as resonators. The readout of the vibrations has been performed by either piezoelectric and optical methods.