Microchannel Depth Research Articles

Influence of pulsed Nd3+ : YAG laser beam profile and wavelength on microscribing of copper and aluminum thin films

Evenly spaced conductive grids of copper and aluminum thin films on polyimide substrate are used for parabolic reflector antennas aboard telecommunications satellites. Laser microscribing of thin films using a flat-top and Gaussian laser beam profile is analyzed with 95% overlapping of the diameter of the laser spot. Laser scribing is performed using the Q-switched Nd3+: YAG (355, 532 nm) laser. The influence of laser irradiation and beam shape on the scribed microchannel width, depth, and surface characteristics is experimentally analyzed using a noncontact optical profilometer and scanning electron microscope (SEM). Laser scribing using a flat-top profile produced near rectangular microchannels in copper thin films. Using the Gaussian profile, the probability of melting is greater than vaporization as observed using SEM images; this melt pool plays a prominent role in resolidification at the edges. The depth of the scribe channel is observed to be 20% higher for the 532-nm wavelength compared to the 355-nm wavelength. The effect of different environments such as air, water, and vacuum on the channel depth and quality is reported. The response of aluminum and copper thin films for high fluences is also studied. Thermal modeling of the laser-material interaction has been attempted by assuming the plasma electron temperature as the laser ablation temperature for modeling the recession rate and depth for a single laser pulse. Model results agree with experimental data showing greater depth for 532 nm compared to 355 nm.

Two step silicon microfluidics for capillary valve applications

In this publication, we report on a robust and scalable process flow for fabrication of valves, compatible with other microfluidic components using silicon microfabrication techniques. The valves require an abrupt change in both the depth and width of a rectangular microchannel for proper functioning. We report on the process that allow for a very sharp interface between the two areas of the channel. A non-sharp interface will results in leaky valves. We show the variation in silicon etch depth as function of feature size. For small features (3–10)μm there is roughly a 50 percent increase in etch depth compared to 40μm features, while features above 40 μm show minimal differences in depth. For the formation of valves, this provides important design rules allowing one to make structures with precise dimensions. Initial characterization, demonstrating the functionality of the fabricated valves is also be presented.

Solid Microneedles for Transdermal Delivery of Amantadine Hydrochloride and Pramipexole Dihydrochloride.

The aim of this project was to study the influence of microneedles on transdermal delivery of amantadine hydrochloride and pramipexole dihydrochloride across porcine ear skin in vitro. Microchannel visualization studies were carried out and characterization of the microchannel depth was performed using confocal laser scanning microscopy (CLSM) to demonstrate microchannel formation following microneedle roller application. We also report, for the first time, the use of TA.XT Plus Texture Analyzer to characterize burst force in pig skin for transdermal drug delivery experiments. This is the force required to rupture pig skin. The mean passive flux of amantadine hydrochloride, determined using a developed LC–MS/MS technique, was 22.38 ± 4.73 µg/cm2/h, while the mean flux following the use of a stainless steel microneedle roller was 49.04 ± 19.77 µg/cm2/h. The mean passive flux of pramipexole dihydrochloride was 134.83 ± 13.66 µg/cm2/h, while the flux following the use of a stainless steel microneedle roller was 134.04 ± 0.98 µg/cm2/h. For both drugs, the difference in flux values following the use of solid stainless steel microneedle roller was not statistically significantly (p > 0.05). Statistical analysis was carried out using the Mann–Whitney Rank sum test.

Multi-beam laser-induced hydrodynamic shock waves used for delivery of microparticles and liquids in skin.

Laser radiation is often used to provide micro and nanoparticle delivery into the skin for medical and cosmetic purposes. This technique inherently has limited speed and effective penetration. We proposed and investigated a new method of rapid delivery of solid microparticles, nanoparticles and liquids into tissue through multiple microchannels created by a fractional laser microablation (FLMA) using Er:YAG-laser. The dependence of microchannel depth on laser pulse temporal structure and number of pulses and dermal coloration changes are studied in this paper. Microchannels created in the porcine skin in vitro by a fractional Er:YAG-laser were used to deliver Zirconium oxide (ZrO2) microparticles or hydrocortisone solution. Each laser pulse consisted of subpulses. Number of laser pulses (Np) and subpulses (Nsp) can be adjusted. The enhancement of delivery is expected due to hydrodynamic impact of laser pulse on the layer of the aqueous suspension of the particles or hydrocortisone solution placed on the skin surface. For color investigation, we used standard CIE Lab parameter analysis. The relationship between microchannel depth in the skin and number of laser pulses and subpulses was established. We found that free filling of microchannels with ZrO2-particle suspension has a low speed of ∼4 × 10(-5) mm/s. Particle delivery into microchannels induced by the hydrodynamic shock waves generated by Er:YAG-laser pulses is carried out with a high speed of 28.5 mm/s. We also found that skin color at ZrO2 -particle delivery differs from color of the intact skin, namely: the parameter L, which characterizes the "lightness" increased by 9 ± 1%; parameter a, which characterizes the "redness" decreased by 38 ± 4%; and parameter b, which characterizes the "yellowness" decreased by 21 ± 2%. The effective delivery of hydrocortisone was demonstrated using fluorescence method technique. Multi-beam laser-induced hydrodynamic shock waves generated by Er:YAG-laser pulses on the layer of the aqueous suspension of the particles or solution of a high molecular weight drug placed on the skin can be used for their rapid delivery into the skin.

Growth behavior of CVD diamond in microchannels of Cu template

Deposition of diamond inside the trenches or microchannels by chemical vapor deposition (CVD) is limited by the diffusion efficiency of important radical species for diamond growth (H, CH3·) and the pore depth of the substrate template. By ultrasonic seeding with nanodiamond suspension, three-dimensional (3D) penetration structure diamond was successfully deposited in cylindrical microchannels of Cu template by hot-filament chemical vapor deposition. Micro-Raman spectroscopy and scanning electron microscopy (SEM) were used to characterize diamond film and the effects of microchannel depth on the morphology, grain size and growth rate of diamond film were comprehensively investigated. The results show that diamond quality and growth rate sharply decrease with the increase of the depth of cylindrical microchannel. Individual diamond grain develops gradually from faceted crystals into micrometer cluster, and finally to ballas-type nanocrystalline one. In order to modify the rapid decrease of diamond quality and growth rate, a new hot filament apparatus with a forced gas flow through Cu microchannels was designed. Furthermore, the growth of diamond film by new apparatus was compared with that without a forced gas flow, and the enhancement mechanism was discussed.

Profile and depth prediction in single-pass and two-pass CO2 laser microchanneling processes

Polymer based microfluidic channels are used in many chemical and biological devices. Polymethylmethacrylate (PMMA) has emerged as a key material for such devices owing to its high optical transparency and mechanical strength. The use of CO2 laser processing for fabricating microchannels on PMMA has been proved as an efficient and cost effective method. In this work, theoretical models for predicting microchannel profile and depth have been proposed. A model for single-pass laser processing has been proposed based on energy balance. A two-pass laser process for microchannel fabrication produces smoother microchannels with better surface topography and reduced bulging around the microchannel edges. An energy balance based model has also been proposed for two-pass processing. The experimental verification of the proposed models was conducted. Spectroscopic tests were carried out to determine the absorptivity, and simultaneous thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) tests were performed to determine the thermo-physical properties of the PMMA used in the proposed model. The results predicted using the model were found to be in close agreement with the actual values.

Effect of Fluence and Pulse Overlapping on Fabrication of Microchannels in PMMA/PDMS Via UV Laser Micromachining: Modeling and Experimentation

This article presents modeling and experimental investigations on the effects of process parameters and the viability of directly fabricating microchannels in polymethyl methacrylate (PMMA) and polydimethylsiloxane (PDMS) polymers which are suitable for the fabrication of microfluidic devices due to their biocompatibility and transparent properties. Experimental work was conducted using a solid-state Nd:YAG laser with 355 nm ultraviolet (UV) wavelength and 5 ns pulse duration at various energy densities and pulse overlapping (PO). The study was focused on understanding the effects of two main process parameters: fluence and PO. This study closely investigates the effect of varying process parameters on the ablation depth and profile achieved and the resultant microchannel dimensional quality. It presents findings indicating that both process parameters have strong effects on the profile shape and variability of the microchannel width and depth. For PMMA polymer, the lowest dimensional variability for the microchannel profile is obtained with low fluence values and highest PO factor, whereas for PDMS polymer, it was observed that microchannel width and depth decreased linearly with increasing fluence and increased nonlinearly with increasing scanning rate. Further, process modeling is utilized for predicting microchannel profile and ablation depth, and these predictions were validated with experimental results obtained with pulsed laser micromachining at UV wavelength.

Study of micro electromagnetic bulging on a stainless steel foil

Electromagnetic micro-forming is a novel technology of micro-fabrication with high-energy rate which shows superiority in fabricating shallow and concave parts. In the research reported in this paper, micro electromagnetic bulging process was carried out with stainless steel foil, and the effects of discharge parameters and foil thickness on the deformation quality were analyzed. The results show that the surface quality and the forming depth of micro channels could be improved by increasing discharge energy and frequency. The discharge frequency has more effect on the micro electromagnetic forming quality. With the increase of the discharge frequency, the depth of micro channel reaches maximum value firstly and then decreases. The surface quality and depth of micro channel decreases with increase of the foil thickness. Optimum parameters arrays of micro channel with good surface quality and dimensional accuracy were obtained in the electromagnetic micro-forming of a stainless steel foil.

3D Finite Element Analysis of Cutting Forces in the Process of Machining Rectangular Microchannels

In the process of machining rectangular microchannels, severe friction occurs between the chip and the side face of the machined microchannel. The cutting forces have great effect on the miniature cutting tool. Thus, 3D FEM is adopted to study the cutting forces. The influences of the depth of the machined microchannel t, the cutting depth ac, the cutting width aw , the rake angle ○o and the cutting speed ν on the cutting forces are investigated. Results show that the main cutting force Fz and the thrust force Fy increase with the increase of t, ac and aw and have no obvious change with ν. Moreover, Fz decreases and Fy increases as γ○ increases.

Fabrication and Characterization of Cross-Connected Microchannel Porous Mesh Plates (CCMPMPs) by Multi-Cutter Milling

A new method for fabricating CCMPMPs, namely multi-cutter milling, is proposed and the fabrication principle is discussed. Then, a study of three microchannel parameters, the microchannel depth Hc, width Wc, and interval Ws, and two CCMPMP parameters, the porosity P and the total surface area per unit volume SV, is presented. Furthermore, 3D FEM has been adopted to study the effective stress distribution, the metal flow velocity distribution, and the cutting forces. The results show that CCMPMPs can be successfully machined. Hc, Wc, and Ws can be controlled by the radial depth of cut ae, the slotting cutter thickness Et, and the gasket thickness Eg, while P and SV can be changed by adjusting Hc, Wc, and Ws. Moreover, as ae increases, the average resultant force increases, and the friction between chip and the side face of the machined microchannel, and between chip and the rake face, plays an increasingly important role in it.

Investigation of the roughness effect on flow behavior and heat transfer characteristics in microchannels

Experiments were conducted to investigate the flow behavior and heat transfer characteristics in microchannels with various surface roughnesses. In the experiments, six test pieces with various roughnesses were fabricated in the stainless steel panel and divided into three groups. Each panel includes 30 microchannels in parallel with uniform geometrical parameters. Both width and depth of microchannels are 0.4mm. The relative roughness of surface in the microchannel is from 0.58% to 1.26%. All tests were performed with air. The experiments were completed with the Reynolds number in the ranges of 200–2100. The friction factor, heat transfer coefficient, Nusselt number and thermal performance were analyzed based on the experimental results. Results of experiments showed that the surface roughness in microchannel has a remarkable effect on the performance of flow behavior and heat transfer. Based on the experimental data, the friction factor and the Nusselt number increase with the increasing of the surface relative roughness. At the same time, the effect of roughness in the thermal performances is small within the range of experimental parameters. The results also indicate that the heat flux rarely affects the Nusselt number. In this paper, the corresponding empiric equations for flow resistance and heat transfer characteristics in microchannels were developed.

Suspension flow past a cylinder: particle interactions with recirculating wakes

AbstractExperimental observations of the flow of a suspension of solid fraction ${\it\phi}\approx 0.084$ over a circular cylindrical post in a shallow microchannel (depth smaller than the cylinder radius) find that the recirculating wake behind the obstacle at moderate Reynolds numbers is depleted or devoid of particles. Particles injected into the wake exit to regain the depleted state. By numerical simulation of the discrete particle motion, the basis for the depletion behind the cylinder is studied; rather than a shallow channel, the numerical simulations consider a periodic domain, mimicking the flow past an infinite cylinder. The Reynolds number is defined, using the average axial velocity ${\bar{U}}$, diameter of the obstacle $D$ and the kinematic viscosity of the suspension ${\it\nu}$, as $Re={\bar{U}}D/{\it\nu}$, and is studied for $Re<30$ in the simulation – conditions for which the pure fluid exhibits an extended steady closed-streamline (recirculating) wake behind the cylinder; unsteadiness is found to be suppressed by the channel walls in the experiments, allowing steady flow at a larger $Re$ than expected for an infinite cylinder (up to at least $Re=300$). The simulations use the lattice-Boltzmann method to determine the motion of the fluid and neutrally buoyant particles. The trajectory of a single particle (small relative to the cylinder) shows migration to a limit cycle inside the wake. With an increase of the number of particles in the wake alone (no particles in the free stream), particles can escape the wake due to velocity fluctuations. Simulation of the flow of suspensions of ${\it\phi}=0.04,0.06$ and 0.08 demonstrates that there is particle exchange between the wake and the free stream; the net flux of particles out of the wake leads to a particle-depleted wake, qualitatively very similar to the experimental observation.

Study on dimensional and corrosion properties of thixoformed A356 and AA7075 aluminum bipolar plates for proton exchange membrane fuel cells

Metallic bipolar plates for polymer exchange membrane (PEM) fuel cells are currently manufactured by stamping of thin sheets. However, there are dimensional and shape errors of microchannels because of forming limitation such as spring back of thin sheets after stamping. On the other hand, stamping process is limited to commercially available sheet alloys, which restricts the development of a high corrosion resistant substrate aluminum alloy. Here, thixoforming (a commercial semisolid route) that is applicable to a wide range of aluminum alloys is proposed for net-shape micromanufacturing of aluminum bipolar plates with high dimensional stability. High corrosion resistance cast A356 (Cu-free) and wrought AA7075 (∼2% Cu) aluminum billets are used for this study. Initial billets are heated at different semisolid temperatures. Subsequently, the semisolid slurries are injected into the die cavity. A356 and AA7075 aluminum bipolar plates are successfully fabricated by thixoforming with very small deviation of 0.7% and 1.5% from the nominal value of 0.300 mm in the microchannel depth, respectively. A multilayer coating of TiN/CrN is deposited on the surface of thixoformed bipolar plates through a commercially available magnetron sputtering technique. Electrochemical corrosion tests show that coated-thixoformed A356 (Cu-free) bipolar plates have significantly lower corrosion current densities than coated-thixoformed AA7075 (∼2% Cu) bipolar plates. This seems to be due to the deleterious effect of Cu alloying element on the corrosion resistance of aluminum alloys that clearly confirms the importance of substrate material development for corrosive PEM fuel cell environment. It is suggested that specific high corrosion resistance aluminum alloy for PEM fuel cell application can be simply designed and then thixoforming can be efficiently and cost effectively employed to fabricate net-shape aluminum bipolar plates.

Research on the Micro Sheet Stamping Process Using Plasticine as Soft Punch.

Plasticine is widely used in the analysis of metal forming processes, due to its excellent material flow ability. In this study, plasticine is used as the soft punch to fabricate array micro-channels on metal sheet in the micro sheet stamping process. This is because plasticine can produce a large material flow after being subjected to force and through the material flow, the plasticine can cause the sheet to fill into the micro-channels of the rigid die, leading to the generation of micro-channels in the sheet. The distribution of array micro-channels was investigated as well as the influence of load forces on the sheet deformations. It was found that the depth of micro-channels increases as the load force increases. When the load force reaches a certain level, a crack can be observed. The micro sheet stamping process was also investigated by the method of numerical simulation. The obtained experimental and numerical results for the stamping process showed that they were in good agreement. Additionally, from the simulation results, it can be seen that the corner region of the micro-channel-shape work piece has a risk to crack due to the existence of maximum von Mises stress and significant thinning.

Microfluidic-based metal enhanced fluorescence for capillary electrophoresis by Ag nanorod arrays

As metal nanorods show much higher metal enhanced fluorescence (MEF) than metal nanospheres, microfluidic-based MEF is first explored with Ag nanorod (ND) arrays made by oblique angle deposition. By measuring the fluorescein isothiocyanate (FITC) solution sandwiched between the Ag NDs and a piece of cover slip, the enhancement factors (EFs) are found as 3.7 ± 0.64 and 6.74 ± 2.04, for a solution thickness at 20.8 μm and 10 μm, respectively. Because of the strong plasmonic coupling between the adjacent Ag NDs, only the emission of the fluorophores present in the three-dimensional NDs array gets enhanced. Thus, the corresponding effective enhancement factors (EEFs) are revealed to be relatively close, 259 ± 92 and 340 ± 102, respectively. To demonstrate the application of MEF in microfluidic systems, a multilayer of SiO2 NDs/Ag NDs is integrated with a capillary electrophoresis device. At a microchannel depth of 10 μm, an enhancement of 6.5 fold is obtained for amino acids separation detection. These results are very encouraging and open the possibility of MEF applications for the Ag ND arrays decorated microchannels. With the miniaturization of microfluidic devices, microfluidic-based MEF by Ag ND arrays will likely find more applications with further enhancement.

A study of the micro-machining process on quartz crystals using an abrasive slurry jet

An investigation of the micro-channelling process on a quartz crystal using an abrasive slurry jet is presented. An experimental study is conducted first to understand the material removal process, surface quality as well as the effect of process parameters on the channelling performance, namely the material removal rate, channel depth, top channel width and channel wall inclination angle. It is found that a good micro-channel top edge appearance and bottom surface finish can be produced on quartz crystal by employing smaller particles with a relatively small jet impact angle, but at the sacrifice of material removal rate. Predictive models for material removal rate and micro-channel depth are then developed using a combination of the dimensional analysis method and the particle impact erosion theories, where the squeeze film effect on the impact erosion is considered. The models are verified experimentally and it is found that the model predictions are in good agreement with the corresponding experimental data.

Fabrication of Microchannels in Ceramics (Quartz) Using Electrochemical Spark Micromachining (ECSMM)

Electrochemical Machining (ECM) and Electric Discharge Machining (EDM) processes have high potential when applied in micro regimes for good accuracy and shape reproduction. But they have a limitation that only electrically conducting materials can be machined by them. To overcome this limitation, a combination of ECM and EDM processes has been conceived, and it is known as "electrochemical spark machining" (ECSM). ECSM is slowly gaining popularity in machining of non-conductive materials. Here, an attempt is made to perform machining at micro-level on quartz. It is piezoelectric in nature, and made up of a lattice of silica ( SiO 2) tetrahedral. For micromachining of quartz, the optimal value of voltage and work piece feed are found out. The depth of microchannel is increased to increase the aspect ratio of the microchannels to make them more useful to make the component such as a micromixer. Microchannels of different shapes are also generated. Finally, the microchannels of minimum width of 144 μm are obtained.

Laser micro-milling of microchannel on copper sheet as catalyst support used in microreactor for hydrogen production

Microchannel structure as catalyst support has been widely used to construct numerous microreactors for hydrogen production. In this work, the laser micro-milling technique was introduced into the fabrication process of microchannels with different geometry and dimensions. The effects of varying scanning speed, laser output power and number of scans on the surface morphology and geometrical dimension of microchannels have been investigated based on SEM observations. It is found that the change of scanning speed and laser output power significantly affected the surface morphology of microchannel. Moreover, the depth of microchannel was increased when the laser output power and number of scans were increased. Subsequently, the microchannels on copper sheet fabricated by the laser micro-milling technique were used as catalyst support to conduct the methanol steam reforming reaction. The better reaction performance of methanol steam reforming in microchannels indicates that laser micro-milling process is probably suitable to fabricate the microchannel reactor for the commercial application.

Laser micromilling of convex microfluidic channels onto glassy carbon for glass molding dies

This study reports the fabrication of convex microfluidic channels on glassy carbon using an ultraviolet laser processing system to produce glass molding dies. The laser processing parameters, including various laser fluences and scanning speeds of galvanometers, were adjusted to mill a convex microchannel on a glassy carbon substrate to identify the effects of material removal. The machined glassy carbon substrate was then applied as a glass molding die to fabricate a glass-based microfluidic biochip. The surface morphology, milled width and depth, and surface roughness of the microchannel die after laser micromilling were examined using a three-dimensional confocal laser scanning microscope. This study also investigates the transcription rate of microchannels after the glass molding process. To produce a 180μm high microchannel on the GC substrate, the optimal number of milled cycles, laser fluence, and scanning speed were 25, 4.9J/cm2, and 200mm/s, respectively. The width, height, and surface roughness of milled convex microchannels were 119.6±0.217μm, 180.26±0.01μm, and 0.672±0.08μm, respectively. These measured values were close to the predicted values and suitable for a glass molding die. After the glass molding process, a typical glass-based microchannel chip was formed at a molding temperature of 660°C and the molding force of 0.45kN. The transcription rates of the microchannel width and depth were 100% and 99.6%, respectively. Thus, the proposed approach is suitable for performing in chemical, biochemical, or medical reactions.

Stripping of acetone from water with microfabricated and membrane gas–liquid contactors

Stripping of acetone from water utilizing nitrogen as a sweeping gas in co-current flow was conducted in a microfabricated glass/silicon gas-liquid contactor. The chip consisted of a microchannel divided into a gas and a liquid chamber by 10 μm diameter micropillars located next to one of the channel walls. The channel length was 35 mm, the channel width was 220 μm and the microchannel depth 100 μm. The micropillars were wetted by the water/acetone solution and formed a 15 μm liquid film between them and the nearest channel wall, leaving a 195 μm gap for gas flow. In addition, acetone stripping was performed in a microchannel membrane contactor, utilizing a hydrophobic PTFE membrane placed between two microstructured acrylic plates. Microchannels for gas and liquid flows were machined in the plates and had a depth of 850 μm and 200 μm respectively. In both contactors the gas/liquid interface was stabilized: in the glass/silicon contactor by the hydrophilic micropillars, while in the PTFE/acrylic one by the hydrophobic membrane. For both contactors separation efficiency was found to increase by increasing the gas/liquid flow rate ratio, but was not affected when increasing the inlet acetone concentration. Separation was more efficient in the microfabricated contactor due to the very thin liquid layer employed.