Cantilever resonance induced in situ by magnetostriction for active flow control

Air flow separation can be actively controlled by blowing air jets through submillimetric holes on a surface. To achieve such pulsed jets, a microvalve composed of an internal resonant cantilever actuated by a magnetostrictive film was designed, fabricated and characterized. The microvalve is fed by a pressurized source of air and the resonating cantilever acts as a deflector on the internal fluid flow addressed alternatively to the output hole on the wing's surface or to a recycling output. Magnetostrictive films were chosen as actuating means for they can provide high induced stress compared to other kinds of active materials, and also because of their remote actuation capability. In this device, artificially nanostructured TbCo/FeCo multilayers were used,making possible the induction of a Spin Transition Reorientation (SRT) state in the layer. This technique increases dramatically the magnetoelastic sensitivity and make magnetostrictive actuation compatible with Microsystems: thus, the field produced by two microcoils is sufficient for the dynamic actuation. Characterization of the resonance frequency, amplitude and magnetoelastic coefficient are achieved by interferometric means. Outcoming flow is visualized by conventional strioscopy method using He / Air optical index difference. The design and fabrication process of the microsystem, and the results of these characterizations are presented in this paper.