The Static And Dynamic Characteristics And Key Control Techniques Of The Positive/Negative Giant Magnetostrictive Composite Thin Films

Micro-systems are more and more widely applied in iatrology, biology, semiconductor, and other science and technology fields having played an important role. The functions of micro actuation and micro sensing are the core of the micro-systems technology. The material of the micro-systems is required to produce sensitive response to an outside signal and to output a greater stress and strain. Thulium giant magnetostrictive thin film(GMF) is a new smart material developed recently, which shows many advantages such as large magnetostriction, short response time, high energy density, low anisotropy, soft magnetization and high frequency driving, etc., being able to realize microminiaturization, intellectualization and integration. So, GMF has become a potential material for micro-systems, such as the cantilever driver, the probe of the atomic force microscope, the ultrasonic micro motor. and the micro pump. However, the performance of GMF as a new smart material, especially that of the positive/negative GMF specially suitable for making micro driver, is not yet completely cognized. In this paper, the magnetostriction mechanism, the static and dynamic characteristics and control techniques are studied by combining theoretical analysis with experimental verification. The project is funded by the National Natural Science Foundation of China and the theoretical and experimental achievement will provide a basis for advancing application of GMFs in micro-systems area.Firstly, based on the theory of small elastic deformation and microcosmic quantum mechanics, the static and dynamic magnetostrictive equations are established, and the positive/negative GMF with steady performance, great magnetostrictive strain, high energy density and fast response is formulated. There are two kinds of substrates for positive/negative GMFs made of polyimide (PI) and Cu, respectively. The initial magnetization curve, the magnetic hysteresis loop, the saturation magnetization intensity, the coercive force and the demagnetizing field are measured and analyzed, with the relationship among the performance parameters and relevant physical quantities such as the saturated magnetization intensity, the coercive force and the recessional magnetization, etc. for making positive/negative GMF are obtained.Then, based on the research and analysis of the calculation theory and design method for hollow cylindrical magnetic field, aiming at the requirement for driving, with the intensity of magnetic field and the uniformity of distribution as the objective, two kinds ofHelmholtz combined coils with and without iron core are designed. The internal magnetic field and the uniformity of distribution in these two magnetic fields are studied and analyzed. The measured results show that, the exciting magnetic filed of the two magnetic fields is strong enough to drive GMFs for large magnetostriction; the uniformity of the exciting magnetic field is high enough to make GMFs under a relatively uniform magnetic field. During the magnetostriction, the internal magnetic field of GMFs is very uniform, with identical magnitude but opposite direction with the exciting magnetic field. As a result, in the process of establishing and solution of the magnetomechanical coupling model, it is feasible and applicable that the internal magnetic field of GMFs is substituted by the external exciting one.According to the magnetoelastic energy theory and the first thermodynamic law, the magneto- mechanical coupling model of GMFs is established and solved. Hence, the measurement system of positive/negative GMFs cantilever is established based on the measurement principle and method of GMFs beam. Through the force analysis of positive/negative GMFs, the flexibility curve equation of GMFs cantilever is deduced. The theoretical flexibility curve is compared with the experimental observations and the results show that the former basically coincide with the latter. Furthermore, based on the static equation, the calculation method for resonant frequency and the vibration equation of positive/negative GMFs are proposed. After studying the vibrating waves of GMFs cantilever, it can be concluded that the vibration equation of GMFs cantilever agrees basically with the harmonic equation of the exciting magnetic field. Finally, with the designed measurement system, the static and dynamic characteristics of the two kinds of GMFs with PI and Cu substrate, respectively, are measured, and the influences of Young modulus of the substrate, the exciting magnetic field and the sizes of GMFs on the static and dynamic characteristics are studied.For the study of control theory and method of GMFs, the control model of GMFs based on Preisach hysteresis model is constituted and the adaptive control arithmetic based on PID controller is also proposed. The static and dynamic control variables are chosen among the exciting current and the magnetic flux density. The experimental results show that, in comparison with the control method based on the exciting current, the control method based on the magnetic flux density exhibits lower magnetic hysteresis and nonlinearity, higher control precision, better repeatability and independence of the change of magnetic field for both static deflection and dynamic vibration magnitude. In order to satisfy the need for short response time, the control theory and method of GMFs based on the vibration frequency are presented. The experimental observations illustrate that with the control methods based on frequency, the vibration responds fast with a higher control precision, which is suitable for control of the vibration response velocity near the resonance frequency of the GMFs micro feed system.Finally, systemic experiments on the magnetostriction of positive/negative. GMFs cantilever and the static-dynamic response properties of two kinds of experimental system...