Magnetically induced oscillations on a conductive cantilever for resonant microsensors

In some specific applications, the measuring environment can have characteristics unsuitable for the correct working of the electronics, because it is not possible to connect the sensitive element to the conditioning electronics by standard cables or by a radiofrequency link. A possible solution can be a contact-less activation of a passive sensor through a magnetic field. The technique proposed here can be applied to resonant microsensors obtained through a microelectromechanical-system (MEMS) technology based, for example, on a standard CMOS process without any magnetic layers required. A conductive and non-magnetic cantilever, located in a time-variable magnetic field, is brought into resonance thanks to the interaction between the eddy currents in the cantilever and the external magnetic field. In order to test this effect for resonant sensors, an experimental set-up has been built. A piezoelectric bimorph covered by two aluminium sheets is used as cantilever: the aluminium sheets are conductive and non-magnetic layers, while the piezoelectric is only used to detect the induced vibrations. Experimental results demonstrate that, when the time-variable magnetic field is applied, resonant vibrations are induced and measured by the piezoelectric cantilever