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PDMS (Polydimethylsiloxane) chips are increasingly important for the application of fluorescence measurements due to their auto-fluorescence free, excellent transparency, and biocompatibility. However, the design of PDMS microfluidic chips requires to fabricate plenty of molds for structure optimization, resulting in high cost. In the present, PDMS chips with nafion membrane were fabricated by simple and low-cost method for bull serum albumin (BSA) enrichment. To optimize the laser cutting and bonding parameters, simulation models were established using Bilinear Kinematic and Mooney-Rivlin models, respectively. The influence of laser power and cutting speed on the width and depth of the micro-channels was investigated. And the effect of bonding pressure on the deformation of PDMS micro-channel and stress distribution near the micro-channels was also analyzed. The leakage test and BSA enrichment demonstrated the practicability and feasibility of the present fabrication method in this work.

The conventional fabrication methods for enrichment microfluidic devices require cleanroom, which are costly and time-consuming. Developing a facile and low-cost method to fabricate microfluidic chips could stimulate the progress of the applications of those chips. Here, we present an easy method for fabrication of a complete PDMS (Polydimethylsiloxane) microfluidic chip used for ion and protein enrichment. The method consists of three main fabrication steps: PDMS microchannels ablation by co2 laser, nation membrane deposition, and oxygen plasma assist bonding under pressure. To fabricate a desired microchannel, the laser ablation parameters, containing laser power and ablation speed, were analyzed. The parameters for oxygen plasma assist bonding were also investigated to improve the bonding quality of the chips (low dimension loss and high bonding strength). The following Rhodamine B enrichment tests demonstrate that the presented method allows fabrication of microfluidic chips with precise dimensions and leakage free.

Electrohydrodynamic (EHD) jet printing enables rapid prototyping high-resolution and low-cost lines with width of micrometer or even nanometer. However, EHD printing always suffers from nozzle clogging when the nozzle inner-diameter decrease to micro-scale. Thus fabrication of low cost nozzles becomes significantly important. In this work, 50 μm wide and 12.5 μm deep PMMA (Polymethyl Methacrylate) nozzles were fabricated without using traditional expensive glass capillary pulling approach. To replicate PMMA nozzle with high precision, the embossing condition was optimized according to replication precision, the deformation rate, and maximum stress. To nearly fully bond PMMA nozzle with intact PMMA microchannel, the bonding condition was optimized according the bonding rate and dimension loss of PMMA microchannel. The availability of the fabricated PMMA nozzle was finally verified by EHD printing experiments.

Microfluidic chips made by traditional materials (glass and silicon) are still important for fluorescence tests, biocompatible experiments, and high temperature applications. However, the majority of the present bonding methods suffer from ultra-clean requirement, complicated fabrication process, and low production efficiency. In the present work, an Electrohydrodynamic printing assist bonding method was proposed. By this method, the ultraviolet-cured-glue dots were printed onto the silicon substrate, and then the patterned glass and silicon substrate can be bonded together at room temperature. The influence of printing condition (nozzle inner-diameter, applied voltage, printing height, and flow rate) on the diameter of printed dot was analyzed by experiments. By the optimized printing condition, the glass-silicon microfluidic chip can be well bonded. The bonding strength and leakage test demonstrated the high bonding quality of the microfluidic chip (bonding strength of 28 MPa and leakage pressure of 3.5 MPa).

Carbon quantum dots (CQDs), having outstanding biocompatibility, attractive catalytic performance, excellent optical properties, and valuable environment friendliness, are emerging as a new paradigm to design luminescent devices and show great potential in application fields such as biomedical sensors, optical and photonic devices. Furthermore, CQDs are known as one of the most promising carbon-based nanomaterials in the 21st century. Therefore, they have attracted a lot of attention since they were first discovered in 2004. In this review, we explain the accepted photoluminescence mechanism of CQDs, including fluorescence and phosphorescence. There are two main types of synthesis strategies: top-down approach and bottom-up approach. At the same time, the main application fields, including ion detection, anti-counterfeiting, biological imaging, food safety, sensors, lubrication additives, are reviewed. Finally, the existing bottlenecks, pending problems and prospects for the future of CQDs are discussed.

EHD (Electrohydrodynamic) printing is a promising technique for alternative fabrication of highresolution micro- and nanostructures without employment of any molds or photo-masks However, the printing precision can be easily influenced by the printing conditions, such as applied voltage, printing distance (the distance between the nozzle tip and the substrate), and flow rate. Unfortunately, up to now there was no work which analyzed those influencing factors in-depth and systematically by theory and numerical simulation. In this paper, the theory of EHD printing was presented and the effect of applied voltage, printing distance, and flow rate on the width of printed line was analyzed by numerical simulation. The simulation results showed that the width of printed lines is proportional to printing distance, nozzle size, and flow rate. However, it is inversely proportional to the applied voltage.

Electrohydrodynamic (EHD) printing can rapidly fabricate micro- or nano-scale lines without employment of any mask, which is suitable for small volume production in industrial applications. However, it is required that the nozzles should be disposable since they can easily be blocked by the un-cleaned ink. CO2 laser is an excellent tool for fabrication of micro-trenches in most of polymers with low-cost and high-speed. This paper presented a low-cost PMMA (Polymethyl methacrylate) nozzle fabrication method based on laser cutting and PDMS (Polydimethylsiloxane) curing bonding. The influence of thickness on the maximum stress and deformation rate of PMMA substrate was investigated to decrease the deformation of PMMA nozzle after laser cutting. To avoid stress concentration in PMMA nozzle after thermal bonding, PDMS curing bonding method was proposed. The effect of spin-coating speed on PDMS thickness was studied. The O2 plasma conditions were optimized based on contact angle to improve the bonding strength of PMMA nozzle. The EHD printing experiments demonstrated the practicability of proposed nozzle fabrication method.

Electrohydrodynamic (EHD) jet printing is a promising direct writing method to produce micro- and nano-scale dots due to its easy manipulation, high resolution, and low cost. The effect of printing conditions on the diameter of printed dots was widely studied by both experiments and simulations. However, positional precision is also important for EHD printing. There is no published work on numerical simulation for the trajectory analysis of the ejected droplet. In the present work, a finite element model was established to investigate the droplet trajectory. The influencing factors, such as nozzle size, nozzle angle, applied voltage, ink density, and charge number in one droplet, were considered during numerical simulation. The influence of influencing factors on the electric intensity, droplet speed, and deposition direction was analyzed. The proposed simulation model provides a useful tool to analyze the droplet formation process and optimize the printing parameters to improve the positional precision of EHD printing.

EHD (Electrohydrodynamic) printing is a photomask-free and direct writing technique for alternative fabrication of high resolution micro- and nano-structures with low cost and simple equipment. It is critical to understand the motion trajectory of the ejected droplet under electric filed so as to precisely control the printing process. However, there is no work which analyzed this issue previously. Thus in this paper, a finite element model was established to study the electric field distribution near the nozzle and analyze the motion trajectory of the ejected droplet during EHD printing. By using established finite element method, the electric field distribution in the nozzle and near the nozzle tip was investigated. The influence of printing distance and applied potential on the maximum electric field intensity was analyzed. Based on the electric field distribution study, the droplet trajectory analysis was carried out to confirm the motion velocity and direction of the ejected droplets.

Nanochannels are key elements in building nano-systems for many applications, such as ion transportation, single molecule manipulation, and protein analysis. Commercially manufacturing of nanosystems lies in the development of a low-cost and concise method for nanochannels fabrication. In the present work, a novel PDMS nanochannels fabrication method was proposed based on PDMS spin-coating on a structure-induced wafer. All the influencing parameters which can affect the shape and size of PDMS nanochannels were optimized by proposed simulation method. The comparison between experiments and simulation showed good agreement and confirmed the developed simulation method. By the optimized conditions, 64 nm wide and 37 nm deep PDMS nanochannels can be fabricated.

Micro–nanofluidic chips have been widely applied in biological and medical fields. In this paper, a simple and low-cost fabrication method for micro–nano fluidic chips is proposed. The nano-channels are fabricated by thermal nano-imprinting on an SU-8 photoresist layer followed by thermal bonding with a second SU-8 photoresist layer. The micro-channels are produced on the second layer by UV exposure and then thermal bonded by a third layer of SU-8 photoresist. The final micro–nano fluidic chip consists of micro-channels (width of 200.0 ± 0.1 μm and, depth of 8.0 ± 0.1 μm) connected by nano-channels (width of 533 ± 6 nm and, depth of 372 ± 6 nm), which has great potential in molecular filtering and detection.

The coupled resonance mechanism of interface stratification of thin coating structures excited by horizontal shear waves is investigated by the forced vibration solution derived from the global matrix method, the integral transformation method, and the plane wave perturbation method. The interface shear stress reaches the peak at coupling resonance frequencies which are an inherent property of the structure, and decreases with the increase of coating thickness or the increase of shear wave velocity difference between the substrate and coating. At the coupling resonance frequency, the thin coating structure is more easily stratified at the interface. The result could provide a theoretical basis for the popularization and application of ultrasonic deicing/defrosting/de-accretion technology.

Electrohydrodynamic (EHD) jet printing can fabricate high resolution micro- and nano-scale lines with low cost and simple procedure. However, less attention has been paid to the fabrication of integrated nozzles with low cost and volume production capacity. In this work, three-layer SU-8 nozzles with slot dimension ranging from 10 to 50 μm were fabricated by ultraviolet photolithography and thermal bonding methods. The influence of the thicknesses (bottom and top layers) on the deformation of SU-8 nozzle was studied by numerical simulation. The results show that the suitable thicknesses should be 60 and 10 μm for bottom and top layer, to ensure the fabrication quality of SU-8 nozzles. Based on the established EHD printing platform, PEO (Polyethylene Oxide) lines with line-width from 750 nm to 8.2 μm can be printed by using the fabricated SU-8 nozzles, indicating the indicating the practicality of developed nozzle fabrication method.

In this paper, we propose a novel max-weight secure link selection (MWSLS) scheme to enhance physical layer security of decode-and-forward (DF) buffer-aided relay networks. The MWSLS scheme can select the link with the largest weight among all secure and available source-to-relay and relayto-destination links. By modeling the dynamic buffer state transitions as a Markov chain, we derive the closed-form expressions of the secrecy outage probability, the secrecy diversity gain, the average secrecy throughput and the end to end delay, which provide a comprehensive and effective way to evaluate the impacts of different parameters on the secrecy performance. The results of this paper reveal that: 1) For the case with small buffer sizes, a significant enhancement on the secrecy outage performance can be observed compared with the popular max-link secure link selection (MLSLS) scheme. 2) When L ≥ 3, the secrecy diversity gain of the system can achieve 2M, while the MLSLS scheme achieves the same secrecy diversity gain only when L → ∞ (where M denotes the number of relays and L is the buffer size). 3) The MWSLS scheme outperforms the MLSLS scheme in terms of the average secrecy throughput and the end to end delay in the low signal-to-noise ratio (SNR) regime, and obtain the same performance as the latter in the high SNR regime.

Efforts to directly printing nanoscale patterns by electrohydrodynamic jet for demanding device applications in electronics, medicine, and biotechnology have grown rapidly in recent years. However, printing of nano-patterns significantly depends on the fabrication of nanoscale nozzles. Here, we describe a low-cost and concise method for fabrication of SU-8 nano-nozzles only based on traditional UV photolithography. By this method, thermal and volume-shrinkage induced nanoscale crack can be automatically formed due to stress release after developing step. The influence of material, SU-8 layer thickness, and exposing duration on the stress in the SU-8 layer was analyzed to fabricate straight and long nano-crack. The result shows that the suitable material, SU-8 layer thickness, and exposing duration are silicon, 70 µm, and 46 s, respectively. Under the optimized condition, 60 µm long nano-crack with width of 250 nm and depth of 20 nm can be fabricated. The fluorescence image demonstrates the absence of blocking and leakage over the entire nano-crack.

The solution to the commercialisation of polymer microfluidic chips lies in the chosen of a low-cost and concise method. CO2 laser is an excellent tool for ablating arbitrary-shaped microchannels in most of thermoplastics. However, upheaval area is usually generates along the microchannel due to high temperature during laser ablation process which leads to the difficulty in fully bonding polymer microchannels. In this work, a new bonding method for fully bonding uneven substrates with homogenous surface property was developed based on water-soaking treatment. To prevent edge separating, an extra laser welding on the lateral of the chip was conducted. The influence of laser current on the width and depth of poly(ethylene terephthalate) (PET) microchannel was investigated. The mechanism of water-soaking bonding was explained and the parameters of this method were optimised. The experiments showed that PET chip can be fully bonded without any block or leakage and the bonding strength of PET chip can be as high as 3.4 MPa.

The solution to the commercialization of polymer microfluidic chips lies in the development of a low-cost and concise method. We present in this paper a gap-control method for obtaining low cost microfluidic chips on PMMA (polymethyl methacrylate) sheets based on traditional 3D printing technique—fused deposition modeling. The influence of 3D printing parameters such as printing temperature, printing speed, wire flow rate and initial layer thickness on printing quality is studied by experiments. The effect of O2 plasma parameters such as chamber power and treatment time on the adhesion strength between printed PLA (polylactic acid) structures and PMMA substrate is investigated. The dye filling tests demonstrate that there is no blocking or leakage over the entire microchannels. With this newly developed technology, low-cost and large scale microfluidic chips can be fabricated, which allows commercial manufacturing of microchannels over large areas.

High aspect ratio capability leads to a successful use of SU-8 photo-resist in a diversity of micro-scale polymer devices as a construction material. However, SU-8 structures fabricated by conventional photolithography technique suffer from high residual stress which results in the collapse of the fabricated structures. In the present work, a water assist ultrasonic method was proposed to decrease the residual stress in SU-8 structures. The mechanism of this method and ultrasonic parameters (power, temperature, and duration) on the remaining rate of SU-8 structures was studied. The experiments showed that only ultrasonic duration was conducive to the reduction of residual stress and a lower residual stress was associated with a longer ultrasonic duration. The proposed method is a potential candidate for fabricating of high aspect ratio SU-8 structures without any damage.

Lanthanum (La)-modified lead zirconate titanate (PLZT) thin films with doping concentration from 0 to 5 at.-% have been fabricated by sol-gel methods to investigate the effects of La doping on crystalline orientation, microstructure and dielectric properties of the modified films. The characterization of PLZT thin films were performed by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and precision impedance analysis. XRD analysis showed that PLZT films with La doping concentration below 4 at.-% exhibited (100) preferred orientation. SEM results indicated that PLZT films presented dense and columnar microstructures when La doping concentration was less than 3 at.-%, while the others showed columnar microstructures only at the bottom of the cross section. The maximum dielectric constant (1502.59 at 100 Hz) was obtained in a 2 at.-% La-doped film, which increased by 53.9 % compared with undoped film. Without introducing a seed layer, (100) oriented PLZT thin films were prepared by using conventional heat treatment process and adjusting La doping concentration.

A novel conical nozzle fabrication method for piezoelectric inkjet printhead is proposed based on the microelectromechanical system technology. By optimizing the exposure gap, exposure dose, postex...

Gadolinium (Gd)-doped lead zirconium titanate (PGZT) thin films have been prepared by Sol-Gel methods to investigate the effects of Gd doping on crystalline orientation, structural and elec...

This paper studies the outage performance of wireless powered relay networks using the Markov chain theory. By adopting the discrete-level model to the finite-capacity energy storage, the energy arrival and departure of the wireless powered relay is characterized, based on which the state transitions among all the energy states are formulated. The theoretical expressions of three kinds of outage probabilities, namely the connection outage probability (COP), the energy outage probability (EOP) and the overall outage probability (OOP) of the proposed network are derived. It has been found that the EOP would be significantly decreased by increasing the transmit power of source, the energy conversion efficiency, a ndbyr educing the distance of source-relay link, while the COP would decline severely by reducing the transmission rate and the distance of relay-destination link. The results also demonstrate that the OOP would be dominated by COP with short distance of source-relay link and long distance of relay-destination link. By contrast, when the distances of source-relay and relay-destination links get longer and shorter, respectively, the EOP would become dominant to the OOP. Numerical simulations have illustrated the validity of the theoretical analysis.

Limited battery capacity is one of the critical issues affecting the network lifetime of unmanned aerial vehicles(UAVs) because of its battery power supply. In this paper, an energy-efficient transmission scheme for buffer-aided UAV relaying networks is proposed. The relays are mounted on UAVs, which use buffers to store the received information and forward it to the destination when the channel quality is good. In particular, we consider adaptive link selection and adaptive power control for the considered network based on the channel state information(CSI), the buffer state and the remaining energy of UAVs. The transmit power is determined according to the amount of information in the buffer, and a threshold value of the transmit power is set to avoid the exponential growth of the transmission power caused by too much information in the buffer. Simulation results show that compared to conventional relaying protocols, the proposed scheme can improve the energy efficiency of buffer-aided UAV relaying networks and make a good trade off between the network lifetime and the average throughput.

Nano-imprint technology is a method of nano-pattern reproduction, has the characteristics of high resolution, high throughput, and low-cost. It can reduce the complexity and cost of the equipment while improving the resolution, which considered a promising industrial production technology. The key to nanoimprinting lies in the mold, and the quality of the mold directly determines the quality of the imprinted graphics. Here, a method for fabricating sub-100 nm concave 2D silicon nano-mold by side etch lift-off is proposed. The effects of different wet etching time and the metal deposition angle on the width of nanochannels were studied. The measurement result of dry etching shows that on the entire 4 inch silicon wafer, the width of the nanochannel varies by 4% and the depth by 2%. The width of the nanochannel between chips varies by 0.7%, and the depth variation is 1%. With this new method, high-precision and large-scale silicon nano-mold can be produced, which has great potential for realizing high-precision and low-cost manufacturing of nano devices.

In order to increase the Dots Per Inch (DPI) of the piezoelectric inkjet print-head, the width and length of the pressure chamber have become much smaller. This makes some previous waveform design methods no longer suitable for the design of high DPI piezoelectric inkjet print-head. In this paper, a new waveform design method based on numerical simulation for high DPI print-head is proposed. Different parameters of the unipolar trapezoidal waveform were optimized using the multi-physics simulation software COMSOL to acquire the optimal waveform for good quality jetting. And meniscus motion at the nozzle exit was measured to predict the jetting behavior of print-head and verify the simulation results. When the high DPI print-head was actuated by the optimized waveform with the rising time tr = 3 µs, dwelling time td = 16 µs, and falling time tf = 3 µs, the high DPI piezoelectric inkjet print-head was continuous injection.

SU-8 is becoming increasingly important for fabrication of mechanical, biological and chemical mini-devices. However, SU-8 suffers from high shrinkage during curing and postbake process. It is crucial to analyze the shrinkage behavior of the SU-8. In this article, the shrinkage behavior of different SU-8 patterns was studied by a developed finite element method. A variety of concave and convex patterns (grooves, lines, pillars and holes) is simulated for 1/8 and 8 aspect ratios. The shrinkage of the patterns with different shapes and the shrinkage of the patterns with different aspect ratio were compared. The numerical simulation results show that to fabricate SU-8 structures with low shrinkage, the following patterns should be firstly considered. (1) Convex pattern, (2) high aspect ratio pattern (aspect ratio of larger than 2), and (3) circular pattern. It is expected that the proposed simulation method has a high potential for the analysis of the shrinkage process for SU-8 patterns.

PDMS (polydimethylsiloxane) collapse method is a simple and low cost approach for micronanochannel fabrication. However, the bonding pressure which influences the size of the final PDMS micro/nanochannels has not yet been studied. In this study, the effect of the bonding pressure on the size and maximum local stress of the PDMS micronanochannels was investigated by both experimental and numerical simulation method. The results show that when the bonding pressure is lower than 0.15 MPa the experiment results can agree well with the simulation results. The fluorescent images demonstrate that there is no blocking or leakage over the entire micro/nanochannels.

Photo sensitive polymer SU-8, owing to its excellent mechanical properties and dielectric properties on polymerization, is widely used in MEMS device fabrications. However, the removing, stripping or re-patterning of the cross-linked SU-8 is a difficult issue. In this paper, CF4/O2 gas mixture provided by a plasma asher equipment was used for the patterning of cross-linked SU-8 material. The RF power, the temperature of the substrate holder, chamber pressure and gas concentration were optimized for the cross-linked SU-8 etching process. When the CF4/O2 mixture contains about 5%CF4 by volume, the etching rate can be reached at 5.2 μm/min.

Plastic nanofluidic devices are becoming increasingly important for biological and chemical applications. However, they suffer from high auto‐fluorescence when used for on‐chip optical detection. In this study, the auto‐fluorescence problem of plastic nanofluidic devices was remedied by newly developed fabrication methods that minimise their auto‐fluorescence: one by depositing a gold (Au) layer on them, the other by making them ultra‐thin. In the first method, the Au layer [minimum thickness is 40 nm on 150 μm SU‐8, 50 nm on 1 mm polyethylene terephthalate (PET), and 40 on 2 nm polymethyl methacrylate (PMMA)] blocks the auto‐fluorescence of the polymer; in the second method, auto‐fluorescence is minimised by making the chips ultra‐thin, selected operating thickness of SU‐8 is 20 μm, for PET it is 150 μm, and for PMMA it is 0.8 mm.

In this work, a thermal bonding method based on O2 plasma and water treatment was proposed to address the high dimension loss and low bonding strength issue during plastic planar nanofluidic device fabrication process. By this method, the PET (polyethylene terephthalate) planar nanofluidic device could be bonded at low temperature of 60 °C, force of 100 N and time of 15 min. To decrease the dimension loss and increase the bonding strength, thermal bonding parameters were optimized. The tensile test showed that the bonding strength of the PET planar nanofluidic device could be as high as 288.1 N. The fluorescence dye filling test indicated that there was no leakage and block in the PET planar nanofluidic device.

Polymethyl Methacrylate (PMMA) nanochannels are becoming increasingly important for biological, optical and electronic applications. To form a complete PMMA nanochannel/device, the open nanotrench will always be thermal bonded. However, the bonding process which influences the final fabrication precision of PMMA devices has not yet been studied systematically by numerical simulation. In this work, an elastic–plastic model was used for PMMA nanochannel bonding. The influence of temperature, pressure, aspect ratio, and friction coefficient on the dimension loss and max stress was studied systematically. By numerical simulation, all the main influence factors were optimized. It is expected that the proposed simulation method has a high potential for the polymer bonding process analysis.

Solutions to the typical problems of elastoplasticity, including planar problems in elastic mechanics, stress function, examples of plane problems in Cartesian coordinates and polar coordinates, etc., are presented first; then, elastoplastic analysis and plastic limit analysis of thick-walled cylinders, elastoplastic bending of beams, and stress analysis of tube under uneven external load, etc., are presented.

The physical relationships in elastic mechanics, i.e., generalized Hooke’s law, incremental equation and plastic yielding criteria in plasticity are presented first; then, ductile damage model corresponding to the dissipation of ductility of metal is briefly described in this chapter.

The general description of fatigue problems is given first, and then the uniform fatigue life equation for both low-cycle fatigue and high-cycle fatigue conditions and its improvement are presented, which include the mean stress effect.

In this chapter, the stress distribution around the notch root of a structure in plastic status is employed to represent the transfer and mitigation of stress concentration in the structure consisting of high ductile material; the elastic–plastic solution for a notched component and the slip-line field approach formulated in plastic mechanics are combined to perform the study.

In this chapter, the analysis of hydro-forming process of bimetallic composite tube and the corresponding expressions for predicting hydro-forming pressure and residual stress in the relevant process are briefly presented; the cone-head size effect on the interfacial bonding strength of bimetallic composite tube produced by drawing method is displayed as well. Plane strain assumption and elastic–perfectly plastic material model are employed in the derivation.