Key Engineering Materials Vols. 336-338

Abstract: Silicon nitride materials with low dielectric properties were prepared using nano and micron silicon nitride powders as raw materials and the green bodies were sintered with cordierite as sintering additive in flowing nitrogen. The additives of cordierite powders prepared by sol-gel method and solidstate reaction method could greatly decrease the sintering temperature. The dielectric constant of materials decreased as sintering temperature fell, whereas the strength showed relatively low as the low sintering temperature. XRD analysis showed the main phase of material was Si2N2O, which indicated that the Si3N4 could be integrated with SiO2. Porous structures were observed by SEM, showing compact sintering cannot be achieved at these temperatures, explaining the low strength.

Abstract: The sintering dynamics, microstructures and microwave dielectric properties of Bi2O3 and MnO2 co-doped [(Pb,Ca) La](Fe,Nb)O3 (PCLFN) ceramics were investigated. Bi2O3 and MnO2 dopants effectively enhanced bulk densities and reduced sintering temperatures by about 100~140°C. Sintering procedure had significant effect on grain size and porosities of ceramics. Investigation of microstructures revealed that the grain growth was controlled by either volume diffusion or second-order interface mechanism in present ceramics. The potential microwave dielectric properties of εr=91.1,Qf=4870GHz and τf=18.5ppm/°C could be obtained when the mass ratio of Bi2O3/MnO2 (k) was 1, the doping content w=1wt% and sintered at 1050°C for 4h.

Abstract: A novel piezoelectric actuator used for transporting some living cells in micro fluidic systems is presented. The mechanism of the living cell transportation is studied based on the acoustics principles. The structural resonant model and a solid-liquid coupling analysis are obtained by FEM. The works will be useful for design optimization of some corresponding actuators and their applications.

Abstract: This study dealt with the Maxwell stress effect of waterborne polyurethane (WPU)/ conductive filler nanocomposite, which was a promising candidate for a material to be used in dielectric elastomer actuator electrode. Conductive nanocomposites were produced by using three types of conductive filler such as carbon black (CB), vapor grown carbon fiber (VGCF), and silver powder (Ag). Among them, conductive nanocomposite containing VGCF exhibited the lowest threshold concentration. And the blend of CB and VGCF (CB/VGCF) filler had a synergistic effect to electrical conductivity. Actuation test showed that CB/VGCF nanocomposite electrode had the largest displacement. Then it could be stated that the improvement of the displacement in CB/VGCF nanocomposite electrode was originated from the increase in relative dielectric constant. In addition, a unique feature of the hysteresis in the bending deformation was described. The feature is that the prior application of an electric field significantly improves the bending speed in the successive application.

Abstract: The influence of electro-mechanical operation conditions on the actuation capabilities of the piezoelectric bimorph is investigated in this paper. The objective is to compare the performance of the piezoelectric bimorph in different operation conditions and to determine the optimum operating conditions. An experimental set-up is built, and a series of experiments are presented to investigate the static and dynamic characteristics of the bimorph, including tip displacements of the bimorph under different preloads, dynamic response at different drive frequencies, step response and creep. Some properties such as displacement output, force output and hysteresis of the piezoelectric bimorph under different operating conditions are evaluated. Experimental results indicate strong dependence of both elastic and piezoelectric properties of the bimorph on the operating conditions.

Abstract: The responses of the piezoelectric stack actuator under electro-mechanical loading are investigated. Two types of tests are performed: influences of the preload on characteristics of the stack and dynamic test. Experimental results indicate strong dependence of the stack properties on the electro-mechanical loading conditions. The displacement output is initially enhanced with an increase of the mechanical preload, and the maximum value is obtained at the preload of about 0.4 kN. But much higher preload will cause the decrease of the displacement output. The effective piezoelectric coefficient and the hysteresis degree are employed to describe the variations of the stack’s performances caused by the mechanical preload. The effective piezoelectric coefficient under different preloads can be calculated by using experimental results of the displacement output and input voltage. Within low frequency band of about 400 Hz, the displacement magnitude of the stack is nearly constant, and the phase lag increases with the increase of the driving frequency at the applied sine sweep voltage with the amplitude of 150V.

Abstract: The dynamic behavior of a vibration converter of an ultrasonic motor is described using finite element method. Tetrahedral finite elements with three dimensions are formulated with the effects of piezoelectric coupling. And the solution of the coupled electroelastic equations of dynamic motion is presented. The simulated response of the vibration converter is calculated, and shows excellent consistency with experimental results, which proved that finite element modeling is a good approach to optimize piezoelectric apparatus design. A gradual optimized method is employed to ascertain the most compatible structure.

Abstract: The paper presents a novel structure cylinder driving USM (ultrasonic motor). Through development and experimentation, the torque and rotational speed of the prototype were tested, which proves that this type of USM has a very simple structure, self-adjusting pre-tightening force and compensation for wear. The results verify the theoretical feasibility and provide instructions for the industrialization of this type of USM.

Abstract: Conducting polymer (CP) actuators undergo volumetric changes due to the movement of dopant ions into the film during the electrical oxidation process. However, it may be an impediment for practical use of polypyrrole actuator that polypyrrole usually requires electrolyte solution for actuation. To solve this problem, solid polymer electrolyte(SPE) was introduced in CP actuator instead of electrolyte solution. And PPy/SPE/PPy electroactive tri-layer actuator was prepared by the electrochemical polymerization of pyrrole and the actuation characteristics were studied. An all-solid actuator, consisting of two polypyrrole films and a solid polymer electrolyte based on polyurethane, clearly showed a reversible displacement in an atmosphere when a voltage was applied.

Abstract: This article describes out-of-plane resonant modes of a piezoelectric disc structure. A new type of micro ultrasonic motor using the resonant mode B11 (Bmn, where m is the number of nodal circles, n is the number of nodal diameters) has been studied. The motor is a wobble-type motor. The stator of the motor uses this structure, consisting of a hollow metal cylinder and a piezoelectric ceramic disc bonded with a metal one, which is excited in the vibration mode by two electrical signals. The stator exhibits wobble displacement and transfers rotation to a rod rotor by the cylinder. The behavior of the stator has been simulated by the finite element analysis. The simulation results have been checked with laser scanning by a laser scanning vibrometer. The article closes with the introduction of the new micro ultrasonic motors based on this vibration mode with high rotation speed.