Key Engineering Materials Vols. 645-646

Abstract: Piezoelectric actuator (PEA) is widely applied in micro/nanopositioning system. However, its inherent hysteresis limits its application. Modeling of hysteresis plays an important role in solving this problem. Linear play operators (LPO) adaptive hysteresis model is introduced in this paper. LPO operators are used to replace delay operators of adaptive transversal filter to compose a new serial structure of adaptive transversal filter model, and LMS (Least Mean Square) algorithm is used to adjust the weight values. As hysteresis loop of piezoelectric actuator is asymmetric and LPO operator is symmetric, a modified LPO (MLPO) adaptive filter is proposed for asymmetric hysteresis effect. At last, the two LPO filters are applied to model hysteresis characteristic of Piezoelectric actuator, and the modeling effect is verified via a micro-positioning system experiment platform based on Piezoelectric actuator. Experimental results show that the modified LPO filters can achieve better accurate hysteresis modeling.

Abstract: Traditional MEMS V-shaped electrothermal actuator is always fabricated with doping polysilicon, which always need a big voltage due to high resistivity of material. A new structure of actuator is proposed, which embeds heating layer, AL, into structural layer, SiO₂. Using the surface silicon technology, the fabrication process of new actuator is built and verified by simulation in Coventorware. Besides, through multiphysics dynamic simulation in Comsol Multiphysics, which takes some material property change with temperature into consideration, effect of structure parameter and input voltage on displacement is studied. The result proves that the new actuator structure can obtain a big displacement under a lower voltage in short time.

Abstract: In this paper, a mechanical MEMS S&A device has been proposed. The size of the device is 10mm×13mm×0.5mm. The role of the threshold value judging mechanism is to determine the environment suffered by centrifugal force and control the sub-centrifugal slider not movement under the threshold, so as to effectively guarantee the time of long-distance arming. Through establishing the three-dimensional model of threshold value judging mechanism, establishing the force and the parameters of locking-releasing mechanism, deriving the mathematical model according to the rigid dynamic mechanics theory and establishing the finite element model by using ANSYS/LS-DYNA, appropriate threshold value judging mechanism is designed to meet two items, one item is the deformation of threshold value rod is not enough to release sub-centrifugal slider when the speed is less than 60000r/min; the other item is deformation of threshold value rod can release sub-centrifugal slider when the speed is more than 60000r/min.

Abstract: In this article the micro flow self-sensing actuator has carried on the theoretical analysis and experimental research. Using output micro-displacement generated by the first inverse piezoelectric effect to realize cell micro flow injection, using output voltage generated by secondary direct piezoelectric effect of piezoelectric ceramic to self-sensing the output displacement in the process of the micro flow injection. The experimental results show that the micro-displacement of micro-flow self-sensing actuator has nonlinear error, error is 5.03%. The error between measured micro-displacement and self-sensing micro-displacement is 63.13%. In this paper, the error causes analysis of micro-flow self-sensing actuator is from non-linearity and hysteresis, external factors, it lay the foundation for the further study of micro-flow self-sensing actuator.

Abstract: In this paper, the harmonic distortion of fourth-order sigma-delta modulator is analyzed. Based on the analysis non-ideal models are established and simulation results demonstrated the validity of these models. The non-linear capacitors introduce harmonic distortion and the non-linear on-resistance nearly only introduce second order harmonic distortion. The non-ideal integrators can increase the noise floor of the modulator.The fully-differential topology can be adopted to eliminate even order harmonic distortion and the operational amplifier with high performance can also be used to decrease noise floor of the modulator.

Abstract: In this paper, a mechanical MEMS S&A device has been proposed. The size of the device is 10mm×13mm×0.5mm. The role of the lock-releasing mechanism is to amplify the moving distance of two times, so as to effectively guarantee the time of long-distance arming. Through establishing the three-dimensional model of without optimized lock-releasing mechanism, establishing the force and the parameters of locking-releasing mechanism, deriving the mathematical model according to the rigid dynamic mechanics theory and establishing the finite element model by using ANSYS/LS-DYNA, appropriate lock-releasing mechanism is designed to meet two items, one item is that the lock-releasing rod locks the main centrifugal slider before sub-centrifugal slider movement in place; the other item is that sub-centrifugal slider will hit the lock-releasing rod when it movement in place, so the lock-releasing rod rotates around rotational positioning block and releases the main centrifugal slider.

Abstract: Theoretical investigation of BN nanowires have been performed by density functional theory (DFT). The energy gap and electronic properties of BN nanowires (BNNWs) in the direction of growth [001] and [111] have been calculated. The calculations show that both nanowires exhibit a wide band gap at center of Brillouin zone, and the calculated band gaps are 1.90eV and 2.40eV, respectively. Noticeably, in the absence of any bias voltage, the transmission spectrum exhibit a region of zero transmission and a step-like behavior.

Abstract: For effectively harvesting the broadband and low-frequency vibration energies in real environment, a micro bistable piezoelectric generator, without containing magnet, is designed. On the basis of analysis the nonlinear behavior of the stiffness, damping and the electromechanical coupling coefficient about the bistable vibration system, a precise mechanical-electric transfer model is built. The output characteristic of the piezoelectric generator is simulated and tested. The results showed that the piezoelectric generator can effectively harvest the broadband and low frequency vibration energies. And the output voltage can meet the electricity demand of a wireless sensor network node. The structure of the piezoelectric generator does not contain magnets, and it is easy to realize miniaturization and integration.

Abstract: In this article, impact of cross-section and size on vibration of silicon nanowires is simulated by the molecular dynamics method based on molecular dynamics software Material Studio. The comparison of fundamental frequencies of the silicon nanowires with triangle, diamond, and hexagon cross sections is carried out. The orientations of these silicon nanowires are all in <111> direction. Then we change the length and the width of silicon nanowires to investigate the impact of size on vibration of silicon nanowires. The results show that with the influence of surface effect, the vibration frequency of silicon nanowires strongly depends on cross-section and size.

Abstract: Loading drops with discrete objects, such as particles and cells, is often necessary when performing chemical and biological assays in microfluidic devices. The vast majority of reported encapsulating methods of particles into monodisperse picolitre droplets are based on micro-fluidic chip using the standard soft lithography technique are necessary. This paper presents a new approach, not based on micro-fluidic chip, for encapsulating particles into droplets actuated by microfluidic pulse inertia force. The polystyrene bead suspension can be ejected out of a tapered glass capillary in mineral oil drop by drop actuated by an enough pulse inertia force which is produced by a hollow PZT stack. The polystyrene beads will be randomly encapsulated in monodisperse picolitre droplets. The tapered glass capillary has the advantages of good chemical resistance, low friction, easy to manufacture and low cost and is suitable for chemical and biological analysis. The minimum size of the spherical droplets can reach 12 μm in diameter and about 1 picolitre in volume. The percentage of the droplets with single 5 μm-diameter polystyrene bead can reach 40% when the droplet size is 40 μm and the concentration of the bead suspension is 1×10⁷ beads per milliliter. The experiment result can be applied in droplet-based single cell encapsulating and analyzing.