Yucheng Ding

Anisotropic wetting on microstrips surface fabricated by femtosecond laser.

In this paper, we present a new method to realize anisotropy by restricting a droplet on an unstructured Si hydrophobic domain between two superhydrophobic strips fabricated by femtosecond laser. The water contact angles and corresponding water baseline length were investigated. The results showed that anisotropy would vary with the volume-induced pinning-depinning-repinning behavior of the droplet. Furthermore, through the observation of water response on small Si domain, the adhesive force of the structure is proven to be the key factor giving rise to the anisotropy wetting. This phenomenon could potentially be used as a model for fundamental research, and such structures could be utilized to control large volume in microfluidic devices, lab-on-chip system, microreactors, and self-cleaning surfaces.

A web-based manufacturing service system for rapid product development

This paper proposes a novel integrated system of rapid product development based on rapid prototyping, and develops a networked manufacturing service system which offers better support for the rapid product development in small and medium sized enterprises by taking full advantage of the quickly evolving computer network and information technologies. The architecture of the networked manufacturing service system is presented. Furthermore, some of the key issues, including modelling and planning a manufacturing chain, selecting feasible collaborative manufacturers, queuing a manufacturing task, using the synchronously collaborative work environment, and constructing a suitable running platform, are described in detail. Java-enabled solution, together with web techniques, is employed for building such a networked service system. Finally, an actual example is provided illustrating the application of this service system.

A motor-piezo actuator for nano-scale positioning based on dual servo loop and nonlinearity compensation

This paper presents the design of an ultra precision positioning system, which consists of a coarse stage and a fine stage. Two servo motors moving on recirculating ball screw are used to drive the coarse stage and three piezo actuators are used to provide the nanoscale positioning. The static and dynamic performances of the positioning system are formulated for designing the micro stage. Based on an evaluation of the systems natural frequency, a dual sever loop approach is used as the control mechanism. The main noise caused by the ambient environment is reduced by a vibration-suppressing table, and in the system control software, a digital Chebyshev filter is used to remove the noise caused by the magnetic chuck on the table. To correct the hysteresis and nonlinearity of PZT, Exact Model Matching (EMM) control law has been used, and therefore repeatability of the fine stages motion can be improved considerably, the positive and negative movement can follow exactly the same path. A positioning accuracy of 8 nm is achieved over a traveling range of 200 mm with this system.

Self-powered flexible pressure sensors with vertically well-aligned piezoelectric nanowire arrays for monitoring vital signs

Human vital signs such as the heartbeat and respiration are important physiological parameters for public health care. Precisely monitoring these very minute and complex time-dependent signals in a simple, low-cost way is still a challenge. This study shows a novel fabrication of vertically well-aligned piezoelectric nanowire arrays with preferential polarization orientation as highly sensitive self-powered sensors for monitoring vital signs. The process realizes in situ poling of the P(VDF-TrFE) nanowires within the nanopores of the anodized aluminium oxide (AAO) template to yield a preferential alignment of both nanowires and the polymer chains required for superior sensitivity in one step. The resulting self-powered flexible sensor shows high sensitivity, good stability and strong power-generating performance. Under bending conditions, the device exhibits a maximum voltage of ∼4.8 V and a current density of ∼0.11 μA cm−2. The fabricated self-powered sensor shows a linear relationship of output voltage versus compressive force with a high sensitivity, and the piezoelectric voltage of the P(VDF-TrFE) nanowire array is enhanced 9 times that of conventional spin-coated bulk films. Furthermore, the highly sensitive vertically well-aligned nanowire array can be applied as a self-powered sensor for detecting some tiny human activities including breath, heartbeat pulse, and finger movements, which may possibly serve for medical diagnostics as sensors, robotics and smart electronic devices.

High-performance ZnO/Ag Nanowire/ZnO composite film UV photodetectors with large area and low operating voltage

A simple and low-cost solution-processed method is used to fabricate ZnO/Ag nanowire/ZnO composite UV photodetectors with a large area of 4 × 5 mm2, low operating voltage of 1 V and high visible transmittance of 75%. Due to the low-dimensionality confinement ability and small persistent photoconductivity effect in polycrystalline ZnO nanoparticle thin films and excellent conductivity of Ag nanowire networks, composite UV photodetectors exhibit a high on/off ratio and short response time under high light illumination, while exhibiting large detectivity and responsivity under low light illumination. Compared with traditional polycrystalline ZnO thin films, the formation of a large number of Ohmic contacts between ZnO nanoparticles and Ag nanowires in a composite structure greatly improves the extraction number and shortens the extraction time of photoelectrons. Additionally, both Schottky contact and Ohmic contact at the electrode interface can obtain a high on/off ratio and short response time. Our composite structure device is regarded as a compromise between high-performance with large-area, low-voltage and low-cost. It has many advantages compared with its counterparts include ZnO nanowires, and other ZnO composites, which is very promising in UV photodetective applications.

Numerical Characterization of Electrohydrodynamic Micro- or Nanopatterning Processes Based on a Phase-Field Formulation of Liquid Dielectrophoresis

The electrohydrodynamic patterning of polymer is a unique technique for micro- and nanostructuring where an electric voltage is applied to an electrode pair consisting of a patterned template and a polymer-coated substrate either in contact or separated by an air gap to actuate the deformation of the rheological polymer. Depending on the template composition, three processes were proposed for implementing the EHDP technique and have received a great amount of attention (i.e., electrostatic force-assisted nanoimprint, dielectrophoresis-electrocapillary force-driven imprint, and electrically induced structure formation). A numerical approach, which is versatile for visualizing the full evolution of micro- or nanostructures in these patterning processes or their variants, is a desirable critical tool for optimizing the process variables in industrial applications of this structuring technique. Considering the fact that all of these processes use a dielectric and viscous polymer (behaving mechanically as a liquid) and are carried out in ambient air, this Article presents a generalized formulation for the numerical characterization of the EHDP processes by coupling liquid dielectrophoresis (L-DEP) and the phase field of the air-liquid dual phase. More importantly, some major scale effects, such as the surface tension, contact angle, liquid-solid interface slip, and non-Newtonian viscosity law are introduced, which can impact the accuracy of the numerical results, as shown experimentally by our electrical actuation of a dielectric microdroplet as a test problem. The numerical results are in good agreement with or are well explained by experimental observations published for the three EHDP processes.

Fabrication of Well-Defined Mushroom-Shaped Structures for Biomimetic Dry Adhesive by Conventional Photolithography and Molding

Biomimetic dry adhesives have many attractive features, such as reversible and repeatable adhesion against various surfaces. This paper presents a method for the simple fabrication of biomimetic dry adhesives composed of a mushroom-shaped structure, which is based on conventional photolithography and molding. Firstly a masked and a maskless exposure are performed on the top and bottom of a photoresist, respectively, that generates microholes with an undercut after development. This structured photoresist is then used for molding, leading to mushroom-shaped structural features after sacrificing the photoresist. Because of the convenience of photolithography, the proposed method has the potential to fabricate various dry adhesives cost-efficiently.

A theoretical and numerical investigation of travelling wave induction microfluidic pumping in a temperature gradient

The phenomenon of induction electrohydrodynamics (EHD) has recently received great attention as a promising driving mechanism for microfluidic pumping due to its miniaturization capability. To obtain a high working efficiency of induction micropumps, a vertical temperature gradient can be imposed along the depth of a pump channel. A travelling wave (TW) potential signal propagating along an electrode array at the channel substrate interacts with this conductive heat flux, resulting in a local free charge distribution inside the bulk fluid. The induced charge wave lags behind the voltage wave in the spatial phase, and this out-of-phase polarization based pumping effect exhibits a single structural dispersion at charge relaxation frequency of the dielectric system. The classical model of electrothermal flow has always been used to numerically obtain the flow field of TW pumps, but the effect of its small temperature gradient approximation has rarely been investigated. In this study, an enhanced treatment for induction EHD modelling is developed, in which the deflection of potential contour lines caused by large temperature gradients is successfully characterized by an advection–diffusion equation, and a more accurate expression of electrothermal body force is derived and introduced to fluid dynamics as a source term of electrical origin. For the calculation of a repulsion-type induction micropump, although both models present similar results in a small thermal gradient, the enhanced one can provide more exact frequency-dependence of the pump performance and spatial distribution of electrostatic force as well as the resulting velocity profile in an excessive heat flux. Furthermore, a model extension for Joule heating induced TW pumping is also presented, and surprisingly matches the unexpected nonlinear fluid flow behaviour at higher conductivities as reported in a pioneering literature. These results can provide valuable insights into induction pumping of lab-on-chip microfluidic samples.

Fabrication of high-aspect-ratio microstructures using dielectrophoresis-electrocapillary force-driven UV-imprinting

We propose a novel method for fabricating high-aspect-ratio micro-/nano-structures by dielectrophoresis-electrocapillary force (DEP-ECF)-driven UV-imprinting. The force of DEP-ECF, acting on an air–liquid interface and an air–liquid–solid three-phase contact line, is generated by applying voltage between an electrically conductive mold and a substrate, and tends to pull the dielectric liquid (a UV-curable pre-polymer) into the mold micro-cavities. The existence of DEP-ECF is explained theoretically and demonstrated experimentally by the electrically induced reduction of the contact angle. Furthermore, DEP-ECF is proven to play a critical role in forcing the polymer to fill into the mold cavities by the real-time observation of the dynamic filling process. Using the DEP-ECF-driven UV-imprinting process, high-aspect-ratio polymer micro-/nano-structures (more than 10:1) are fabricated with high consistency. This patterning method can overcome the drawbacks of the mechanically induced mold deformation and position shift in conventional imprinting lithography and maximize the pattern uniformity which is usually poor in capillary force lithography.

Feasibility investigations on compound process: a novel fabrication method for finishing with grinding wheel as restraint

This article describes the validity of a compound precision finishing process that combines grinding with abrasive jet finishing for micro-removal machining. Experiments were carried out with a M7120 plane grinder and a workpiece material of 40Cr steel, which was ground to a surface roughness with a mean value of Ra = 0.6 μm. The machined surface morphology was studied using a scanning electron microscope (SEM), and a metallography microscope. Microcosmic geometry parameters were measured with a TALYSURF5 instrument. The experimental results show that this novel processing method can effectively diminish longitudinal geometry parameter values of the ground surface, moreover attain an isotropic surface and uniform veins in the parallel and perpendicular machining directions. Furthermore, the finished surface has little comparability compared with a grinding machining surface. The effectiveness of the process was verified.