Magnetomechanical Coupling Characteristic Of Giant Magnetostrictive Thin Film And Its Application In Swimming Robot

As a new functional material, giant magnetostrictive thin film (GMF) exhibits vastpotential in the field of microactuator and microsensor, which can benefit from the largeMagnetostrictive strains, high energy density, short response time, non-contact driving, andrelatively simple integration. The static and dynamic characteristics and models ofmagnetomechanical coupling of GMF are the basis for developing and designing GMF microdevices. However, it is very difficult to model the characteristics of GMF, due to thenonlinearity and hysteresis of the magnetomechanical coupling relations. The static model ofGMF proposed by researchers with much variables and complex computation can notdescribe the hysteresis characteristic of GMF, and the dynamic characteristic model of GMFis not presented now, which hinder the development of GMF and its devices. Therefore, basedon this new functional material, in this paper, a new way is provided to study themagnetomechanical coupling relations of GMF and microactuator and microsensor, withsome new principles and methods.According to the principle of magnetostriction, the magnetostrictive characteristic ofGMF is introduced, firstly. Then, the effects of material composition, internal stress andheating treatment on the magnetostrictive characteristic of GMF at low magnetic fields areanalyzed. Two kinds of bimorph GMF with good surface quality and small magnetizationhysteresis, TbDyFe-PI-SmFe and TbDyFe-Cu-SmFe, are developed by the magnetronsputtering method. Then, an experiment system for the static and dynamic characteristics ofGMF is established, which consists of a Helmholtz coil and a laser triangulation sensor. Themagnetic field amplitude and uniformity of coil are simulated by ANSYS software andtestified by experimental data. The results indicate that the magnetic field produced by thecoil match the need of magnetic field amplitude and uniformity for driving the GMF.For the "force nonlinearity" of magnetomechanical coupling characteristic of GMF,through analyzing the large magnetostriction, the soft magnetization and the hysteresis underthe prestress, a nonlinear coupling model of GMF at low magnetic fields, which is composedof the modified Rayleigh model and the "butterfly curve" model, is proposed. Experiments onTbDyFe-Polyimide(PI)-SmFe and TbDyFe-Cu-SmFe are conducted, respectively, to verifythe proposed model. Results indicate that the model curve coincides well with theexperimental results of the magnetic polarization and the magnetostriction forTbDyFe-PI-SmFe and TbDyFe-Cu-SmFe at low magnetic fields, especially well with the magnetostriction hysteresis. Besides, the proposed model is also in good conformity with thepublished experimental data of other GMFs.For the geometric nonlinear deformation of GMF, experiments on PI substrate GMF andCu substrate GMF cantilever are conformed, and the results show that the deflection ofcantilever end of is two times, and 0.5 times of these thickness, respectively. Meanwhile, withcombining the nonlinear elastic theory, a nonlinear deformation model and flexure lineequation of bimorph GMF is established. The rationality of deformation model is verified bythe bimorph GMF cantilever data. The nonlinear coupling model and nonlinear deformationmodel will provide a theoretical basis for fabricating effective quasi-static micro devices withGMF.Under quasi-static magnetic field, GMF exhibits the "force nonlinearity" and geometricnonlinearity, while, under the alternative magnetic field, GMF shows bigger nonlinearity.Thus, based on the Hamilton principle, by virtue of the method of separation of variables andthe perturbation method, the nonlinear vibration model is presented. Thereafter, thecomparison of the proposed model with the experimental data indicates that the nonlinearmodel can explain well the main resonance and super harmonic vibration. Then, the drivingproperty of bimorph GMF is measured and analyzed. The experimental data shows that twokinds of bimorph GMF exhibits tenth order superharmonic resonance. Moreover, the effect ofdirect current magnetic field and alternative magnetic field on the resonant frequency and thevibration amplitude is given and analyzed. The nonlinear vibration model and theexperimental conclusion of vibration characteristics can improve the design efficiency andcontrol precision of GMF devices.At last, GMF is employed to design a micro swimming robot for the first time. Accordingto the fish propulsion principle, a swimming micro robot in pipe is developed, whose caudalfin is fabricated by the GMF micro actuator. Experiments on the swimming characteristics ofthis micro robot show that this robot can swim in gasoline, when the driving frequency isclose to the fifth superharmonic resonant frequency of GMF beam. Moreover, the dynamicmodel of the swimming robot is given on the basis of fluid dynamics principle. The effects ofliquid viscosity, mass and rigidity of main body and of the GMF caudal fin on the swimmingperformance are studied with the experiments. The PI substrate GMF micro robot can swim ata maximum velocity of 2.86mm/s.