Key Engineering Materials Vols. 306-308

Abstract: This paper presents vibration control of a flexible smart beam structure using a new discrete-time sliding mode controller. After formulating the dynamic model in the space representation, so called the separation principle for equivalent controller is established so that the sliding mode conditions are satisfied. By doing this, undesirable chattering of the flexible structures can be attenuated in the settled phase. In order to demonstrate some benefits of the proposed methodology, an experimental realization is undertaken. Both transient and forced vibration control responses are evaluated in time domain and compared between with and without the separation principle.

Abstract: This paper is addressed to the Love wave propagation in a layered piezoelectric structure immersed in a viscous fluid. The layered piezoelectric structure consists of an isotropic layer and a relatively thicker transversely isotropic piezoelectric substrate. The velocity of the Love waves changes due to the presence of the viscous fluid. The exact theory is accurate but not convenient to apply because it is generally difficult to get an explicit relation between the quantities we interest. In this paper, the perturbation approach is applied to obtain the explicit relations for the phase velocity and attenuation of Love waves. The result is useful for the measurement of the viscosity and mass density in Love wave sensors.

Abstract: This paper presents some useful discussions on the shear horizontal acoustic waves in an inhomogeneous plate that possess coupled piezoelectric, piezomagnetic, and magnetoelectric effects. The magnetoelectroelastic material is of hexagonal symmetry (6mm crystal) and polarized in the shear horizontal direction. It is assumed that the material constants of the magnetoelectric plate vary continuously along the thickness direction. Solutions of the mechanical displacement, electric potential, and magnetic potential are obtained by solving the coupled field equations. The phase velocity equations are obtained and the influence of the inhomogeneity of the material constants on the phase velocity is considered. These findings are significant in the applications of wave propagation in the coupled piezoelectric, piezomagnetic, and magnetoelectric structures.

Abstract: The propagation of Bleustein-Gulyaev (BG) waves in an inhomogeneous layered piezoelectric half-space is investigated in this paper. Application of the Fourier transform method and by solving the electromechanically coupled field equations, solutions to the mechanical displacement and electric potential are obtained for the piezoelectric layer and substrate, respectively. The phase velocity equations for BG waves are obtained for the surface electrically shorted case. When the layer and the substrate are homogenous, the dispersion equations are in agreement with the corresponding results. Numerical calculations are performed for the case that the layer and the substrate are identical LiNbO3 except that they are polarized in opposite directions. Effects of the inhomogeneities induced by either the layer or substrate are discussed in detail.

Abstract: This paper is concerned with developing a mathematical model to describe the scattering of a plane wave obliquely incident on a piezoelectric hexagonal 6mm cylinder in a fluid. The mode is based on the normal-mode expansion method. Far-field form functions are obtained. The sensitivities of Rayleigh, Whispering Gallery, and guided wave resonances to perturbations in elastic and piezoelectric constants are discussed. The resonance scattering theory can be used for characterizing the sample in both transverse and axial directions.

Abstract: Deformable focusing micromirror is one of the important optical MEMS devices. The focusing length is determined by the profile of the micromirror surface. For uniform deformation, based on bulk microfabrication of isotropic etching and wafer bonding, a novel micro electrostatic deformable focusing mirror actuated by hemispherical electrode is designed and analyzed. Due to the coupling between elastic and electrostatic force, numerical method of finite element using ANASYS software is used to analyze the deformations and stresses of different structure sizes. The phenomenon that structures deform abruptly fast due to nonlinear increasing electrostatic force called pull-in is also discussed. Using the least square method, the profile of micro focusing mirror can be curve fitting as a parabola. And the focal length can be obtained. The results show deformation increases nonlinearly as applying voltages increasing. The stresses increase linearly when thickness also increase but nonlinearly when radius of mirror increases. The maximum stress happens in the region of bounded. The focal length decreases quasi-linearly as applying voltage increases. The mirror sizes and gaps have effect on pull-in voltages. Larger gap and smaller mirror radius will cause larger pull-in voltage.

Abstract: This paper presents electro-mechanical characteristics of a micro-machined vibrating silicon ring gyroscope which can measure angular velocity components about three orthogonal axes. The ring gyroscope has a ring connected to the gyroscope main body by support ligaments that are arranged with cyclic symmetry. The natural modes of its vibration can be distinguished into the in-plane motion and the out-of-motion that are coupled by the gyro-effect due to the rotation of the gyroscope main body. The motions of the ring are electro-statically driven, sensed and balanced by electrodes. The equations of motion are formulated with considering the electrostatic effects of electrodes. The measuring method of angular velocities of the gyroscope main body by force-torebalance is proposed. The dynamic characteristics of the ring gyroscope are discussed.

Abstract: In this paper, a methodology of modeling and simulating the electro-statically driven micro-electromechanical systems (MEMS) is presented, utilizing topography data with an arbitrary structure. In the methodology, the mask layout and process recipe of a device are first generated and the model then discretized by an auto-mesh generation for the finite element analysis. Finally the analysis is performed to solve the Laplace and the dynamic equation at a time. The methodology is applied to an electro-statically driven comb-drive as a test vehicle for verification.

Abstract: This paper presents a surface micro-machined differential resonant accelerometer (DRXL) by using the epitaxially grown thick polysilicon process. The proposed DRXL utilizes the electrostatic stiffness changing effect of an electrostatic torsional actuator. This device produces a differential digital output proportional to an applied acceleration. For a self-generated and self-sustained oscillation of the resonator, a feedback oscillation loop is designed, implemented, and applied to the DRXL chip. The oscillation loop is designed using an analytical result based on the describing function method. Using the implemented self-sustaining oscillation loop, pecifications of sensor performance are obtained by various performance tests. These results show quite an improved quality factor and resolution compared to that of the sensing device only. And we obtained more stable output frequency responses.

Abstract: In this paper, presented are the design and the fabrication of the novel bulk-micromachined gyroscope with its detection and control circuit. The proposed structure is designed to have good properties such as heavy proof mass, a large movement and high moving velocity of the proof mass at an operating frequency. Despite of an appropriate design of the proof mass and comb electrodes, the high-Q property and the capacitance measurement scheme inevitably bring on nonlinear property and limited bandwidth of the system. Moreover, temperature variation degrades the stability of the performance. In this paper, we adopt a feedback control scheme to achieve a linear output and a less sensitive operation to the temperature variation. Through experiments, it is confirmed that the designed gyroscope and the control circuit achieve performances of wide input range of 1,000 deg/sec and bandwidth of 80 Hz.