Wenlong Lv

Spectroscopic evidence for a high fraction of ferroelectric phase induced in electrospun polyvinylidene fluoride fibers

Effective transformation from paraelectric to a high fraction of ferroelectric phase is crucial to produce piezoelectric materials with a high piezoelectric constant for broad applications. In polyvinylidene fluoride (PVDF) thin films, both mechanical stretching and electric poling processes have been found to be critical in the α → β phase transformation. However, in PVDF fibers fabricated by the electrospinning process, the roles of mechanical stretching and electric poling have not been well explored. Here, the properties of PVDF fibers from electrospinning and forcespinning, a mechanical spinning process without electric poling, have been characterized and analyzed by FTIR and XRD spectroscopic techniques. The results show that pure mechanical stretching in the forcespun fibers can result in a high fraction of the all-trans β-phase, at 95%. Electrospun fibers from the same material system, on the other hand, can also reach a high fraction of β-phase, at approximately 99%. These results preliminarily demonstrate that mechanical stretching is the main reason for β-phase induction in PVDF fibers. Further experiments performed in this work show that higher wt% of PVDF, lower polymer solution supply rate, and more uniformly mixed solvent systems facilitate achieving a higher level of ferroelectric β-phase in electrospun PVDF fibers.

Conductive micro silver wires via aerosol deposition

A novel non-contact micro manufacturing technology of aerosol deposition is presented to fabricate conductive micro silver wires with width of several micrometers from silver inks. The ceramic nozzle with inner diameter of 250 μm is utilized to print the micro silver wires, the width of wires ranges from 15 μm to 70 μm and the thickness ranges from 200 nm to 2 μm. The printed silver wires are cured to decrease the resistance. High curing temperature and long curing time result in better conductivity of deposited wires due to the sufficient melt and combine of sliver particles. The minimum resistivity of 3.32 μΩ·cm is demonstrated for a continuous track cured at 300°C.

Design and simulation of electrostatic inkjet head

A laminated, multi-substrate inkjet head that called “electrostatic inkjet head” has been designed, which consists of three parts: upper layer (Si), middle layer (Si), bottom layer (glass). Middle layer includes nozzles, ink cavity and diaphragms. Ink is jetted out of the ink cavity through the nozzle, and diaphragm defined as the bottom of ink cavity. Charging channels is used for supplying ink to the ink cavity. Electrodes on the bottom layer face to the diaphragm, as to drive the diaphragms by electrostatic force. Theoretical analysis and simulation has been done to optimize the design of the ink jet head. Diaphragm with 380µm width, 6000µm length and 5µm thickness is designed in this work, and the gap between the diaphragm and the ground electrode is 1µm. A displacement of 0.26µm can be achieved under 36V DC voltage according to the simulation. Flat-walled diffuser elements were applied as the charging channels that positioned in the upper layer to eliminate the reflux of ink, by which the voltage can be reduced. Simulation of Fluid Structure Interface (FSI) is carried out in ANSYS to analyze the whole process of printing. When the applied voltage is 36V DC, the velocity in the nozzle is 2.82m/s and Weber Number is 8.5. Simulation results show that Weber Number is between 1 and 12, which can provide sufficient power to eject ink drop out of the nozzle. Furthermore, the new design of inkjet head needs lower driving voltage and easier process, which increases the rate of finished products and reduces the cost. Due to these advantages, this inkjet head would have widespread application prospect.

Biomimetic Beetle-Inspired Flapping Air Vehicle Actuated by Ionic Polymer-Metal Composite Actuator

During the last decades, the ionic polymer-metal composite (IPMC) received much attention because of its potential capabilities, such as large displacement and flexible bending actuation. In this paper, a biomimetic flapping air vehicle was proposed by combining the superiority of ionic polymer metal composite with the bionic beetle flapping principle. The blocking force was compared between casted IPMC and IPMC. The flapping state of the wing was investigated and the maximum displacement and flapping angle were measured. The flapping displacement under different voltage and frequency was tested. The flapping displacement of the wing and the support reaction force were measured under different frequency by experiments. The experimental results indicate that the high voltage and low frequency would get large flapping displacement.

Design and simulation of fully-symmetrical resonant pressure sensor

A fully-symmetrical resonant pressure sensor based upon lateral drive is presented, which can avoid stress concentration that arises from temperature or vacuum packaging. Unlike conventional driving method, resonant structure with laterally driven comb capacitance allows the linear characteristic of driving force and also obtains high quality factor for its slide-film air damping. Furthermore, the detection sensitivity of the device can be improved by using differential capacitance, which will reduce shared-frequency interference phenomenon at the same time. According to the FEM analysis, the structural parameters of resonant pressure sensor are optimized. Meanwhile, the pressure sensitivity of the sensor has designed to be 22.602 Hz/kPa for a 18 μm thick diaphragm over a pressure range of 550 kPa. From temperature simulation, the temperature coefficient of sensor is -1.8233 Hz/°C in the range of -20°C~60°C without any temperature compensation. Finally, the frequency domain characteristics have been confirmed and the quality factors of sensor under different damping ratios are identified, it offers reliable reference for the choice of vacuum in resonant pressure sensor packaging.

A novel electrohydrodynamic printing jet head with retractable needle

This paper presents a novel electrohydrodynamic printing system with a retractable needle, by which both dots and bead-on-string structures can be fabricated. Solution concentration is the key element defining the ejection mode. Dots can be gained when solution concentration is lower, otherwise bead-on-string structures would be fabricated. Experimental results show that the diameter of the deposition dots increases with the increasing of supply rate and the decreasing of polyethylene oxide solution concentration. In addition, the deposition frequency has a fine synchronization with the retractable frequency of the needle.

Improve the Performance of Mechanoelectrical Transduction of Ionic Polymer-Metal Composites Based on Ordered Nafion Nanofibres by Electrospinning

An ionic polymer–metal composite (IPMC) is a kind of soft material. The applications of IPMC in actuators, environmental sensing, and energy harvesting are currently increasing rapidly. In this study, an ordered Nafion nanofibre mat prepared by electrospinning was used to investigate the characteristics of the mechanoelectrical transduction of IPMC. The morphologies of the Nafion nanofibre mat were characterized. The proton conductivity, ion exchange capacities, and water uptake potential of the Nafion nanofibre mat were compared to traditional IPMC, respectively. A novel mechanism of Nafion nanofibre IPMC was designed and the open circuit voltage and short circuit current were measured. The maximum voltage value reached 100 mv. The output power was 3.63 nw and the power density was up to 42.4 μW/Kg under the load resistance. The Nafion nanofibre mat demonstrates excellent mechanoelectrcical transduction behavior compared to traditional IPMC and could be used for the development of self-powered devices in the future.

Comparison of glass etching properties between HCl and HNO 3 solution

A comparison of glass etching properties between HCl and HNO3 solution is presented in this paper, which allows us to predict the etched products shape under a variety of etching conditions, mask compensation and multiple processing steps. Four conclusions could be draw from the experiments. First, the best concentration ratio of the etching solution to protect the mask from damage and get a channel with depth of 40 μm is HF:HCl:NH4F=5.5mol/L:4mol/L:2.5mol/L. Second, as the temperature increases, the longitudinal etching rate increases. However, the temperature has little influence on the lateral erosion ratio when the temperature gets high. Third, HCl has a better surface morphology against HNO3 as an addition to solution. Last, the mask will introduce strain because of sputtering, which is harmful to the glass etching..

Ni-electroplating of double-width micro-cantilever

Micro-electroplating technology has an increasingly wider application in the fabrication of MEMS devices. In order to fabricate a double-width cantilever beam which has three different electroplated areas. The proper composition of the bath solution is obtained through experiments firstly in the paper. Then the effects of the peak of current density, duty cycle and pause time on the surface morphology of the electroplated nickel are studied experimentally to make sure the regulating range of pulsed parameters. And at last the double-width cantilever beam is fabricated using lithographic, micro-electroplating and sacrificial layer releasing processes. The results show that the surface of the beam is bright and smooth, and the nucleation rate increases steadily. But the thickness of the three parts with different width is different which can be modified by increasing the duty cycle and reducing the current density to some extent.