Microwire microelectrode arrays (MEAs) are implanted in the brain for recording neuron activities to study the brain function. Among various microwire materials, carbon fiber stands out due to its small diameter (5–10 μ m), relatively high Young's modulus, and low electrical resistance. Microwire tips in MEAs are often sharpened to reduce the insertion force and prevent the thin microwires from buckling. Currently, carbon fiber MEAs are sharpened by either torch burning, which limits the positions of wire tips to a water bath surface plane, or electrical discharge machining, which is difficult to implement to the nonelectrically conductive carbon fiber with parylene-C insulation. A laser-based carbon fiber sharpening method proposed in this study enables the fabrication of carbon fiber MEAs with sharp tips and custom lengths. Experiments were conducted to study effects of laser input voltage and transverse speed on carbon fiber tip geometry. Results of the tip sharpness and stripped length of the insulation as well as the electrochemical impedance spectroscopy measurement at 1 kHz were evaluated and analyzed. The laser input voltage and traverse speed have demonstrated to be critical for the sharp tip, short stripped length, and low electrical impedance of the carbon fiber electrode for brain recording MEAs. A carbon fiber MEA with custom electrode lengths was fabricated to validate the laser-based approach.

Electrochemical discharge machining (ECDM) is distinguished as a novel process that involves thermal heating and chemical dissolution for the micromachining of “difficult-to-machine” materials like ceramics and quartz. This paper comprehensively reviews the study on gas film, the effect of various input parameters on ECDM performance, such as electrical parameters, electrolyte parameters, and tool electrode parameters, are also likewise discussed. Moreover, a summarized report on thermal modeling, gas film, discrete input parameters, hybridization, and variants in the ECDM process is also provided in a lucid manner. Based on the review, it is concluded that the machining performance of the ECDM process especially in terms of material removal rate (MRR), roughness, tool wear (TW), and thermal cracks is strongly influenced by the input parameters. The formation of the gas film induces variable machining features that can be controlled by altering the machining conditions. Additionally, the paper highlights the future areas that may leads to improve the overall machining performance of the ECDM process.

Dielectrophoresis (DEP) is a force applied to microparticles in nonuniform electric field. This study discusses the fabrication of the glassy carbon interdigitated microelectrode arrays using lithography process based on lithographic patterning and subsequent pyrolysis of negative SU-8 photoresist. Resulting high-resistance electrodes would have the regions of high electric field at the ends of microarray as demonstrated by simulation. The study demonstrates that combining the alternating current (AC) applied bias with the direct current (DC) offset allows the user to separate subpopulations of microparticulates and control the propulsion of microparticles to the high field areas such as the ends of the electrode array. The direction of the movement of the particles can be switched by changing the offset. The demonstrated novel integrated DEP separation and propulsion can be applied to various fields including in vitro diagnostics as well as to microassembly technologies.

Microstructures determine flow properties of microfluidic chip. Micromold forming is an effective method to realize mass manufacturing of microfluidic chips. This requires to machine some kind of special microstructure of high surface quality on a metal/alloy workpiece. Micro V-shaped grooves are the typical microstructures of the chip micromolds used for controlling microfluid or weld packaging. In this research, a scanning micro-electrochemical machining (ECM) process of V-shaped grooves is proposed using a tool electrode fabricated by micro–electrical discharge machining (EDM) on-machine. Theoretical and experimental research was conducted for achieving the V-shaped grooves with a given angle on die steel. A long-distance V-shaped groove with the given angle of 67 deg and the depth of 125 μ m was successfully machined.

Electrical discharge machining (EDM) causes surface defects such as resolidified layer and microcracks, and a finishing process is usually needed to remove these defects. In this paper, a hybrid process was proposed where electrochemical machining (ECM) was performed as a finishing process after EDM using the same tool electrode on the same machine. By using two kinds of disk-type rotary electrodes, rectangular grooves and grooves with convex inner structures were fabricated. Surface topography were investigated by using scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDX), and laser-probe surface profilometer. The material removal mechanism of resolidified layers was clarified. The surface roughness of the rectangular groove was improved from 3.82 μ m Ra to 0.86 μ m Ra after ECM. Electrode rotation was effective for flushing electrolytic products when fabricating inner structures. As there is no need for exchanging tools and machines, tool alignment error can be prevented and productivity can be improved. Therefore, the proposed EDM/ECM hybrid process contributes to rapid fabrication of microscale products with high surface integrity.

This study compares fluid velocity magnitude and direction for three different glassy carbon (GC) electrode systems effecting alternating current (AC) electroosmotic pumping. The flow behavior is analyzed for electroosmotic pumping performed with asymmetric coplanar electrodes. Subsequently, effects of adding microposts array of two different heights (40 μ m and 80 μ m) are studied. Experimental results demonstrate that as peak-to-peak voltage is increased above 10 V peak-to-peak, the flow reversal is achieved for planar electrodes. Utilization of microposts-enhanced asymmetric electrodes blocks the flow reversal and alters the magnitude of the fluid velocity at the application of larger voltages (above 10 V peak-to-peak). Understanding of the consequences of three-dimensional geometry of asymmetric electrodes would allow designing the electrode system for AC electroosmotic pumping and mixing, as well as bidirectional fluid driving with equal forward and backward flow velocities.

Silver nanoparticles were electrodeposited from 0.3 M oxalic acid electrolyte on a pure aluminum working electrode under silver ion concentration-limited condition. A silver wire was held in a glass tube containing 1.0 M KCl solution as the counter electrode. Ion exchange between the glass tube and the main electrodeposition bath through a capillary was driven by the overpotentials as high as 10 V supplied by an electrochemical workstation. Due to the reaction between chlorine anion and silver cation to form AgCl solid at the Ag/AgCl electrode, the silver ion concentration-limited condition holds in the electrolyte. It is found that silver grows at the aluminum working electrode to form nanoparticles with an average size of about 52.4 ± 13.6 nm. With the increasing of the deposition time, the silver nanoparticles aggregate into clusters. The silver particle clusters are separated with approximately 112.6 ± 19.7 nm due to the hydrogen bubble-induced self-assembling, which is shown by the confined deposition of silver on a gold coating. The surface roughness of the aluminum substrate leads to the reduced uniformity of silver nanoparticle nucleation and growth.

In spite of its applications in macromanufacturing processes, water jet processing has not been extensively applied to the field of micromanufacturing owing to its poor tolerance and lack of effective control of the jet impingement position. This paper investigates the phenomenon of liquid dielectrophoresis (LDEP) using a localized nonuniform static electric field to deflect and control the jet's trajectory at the microscale for a water jet in air. A new analytical modeling approach has been attempted by representing the stable length of a water jet as a deformable solid dielectric beam to solve for the deflection of the jet under the action of the electric field. This method bypasses the complicated flow analysis of the water jet in air and focuses specially on the effect of the electric field on the trajectory of a laminar water jet within the working length. The numerical analysis of the phenomena for this electrode configuration was carried out using comsol . Preliminary proof-of-concept experiments were conducted on a 350 μ m diameter sized water jet flowing at 0.6 m/s using a pin plate electrode configuration where a deflection of around 10 deg was observed at 2000 V. The results from the simulation are in good agreement with the results obtained in the preliminary experiments. This novel approach of modeling the water jet as a deformable dielectric beam might be useful in numerous applications involving precise control of the water jet's trajectory particularly in microwater jet material processing.

A novel method of using atomized dielectric spray in micro-electric discharge machining (EDM) (spray-EDM) to reduce the consumption of dielectric is developed in this study. The atomized dielectric droplets form a moving dielectric film up on impinging the work surface that penetrates the interelectrode gap and acts as a single phase dielectric medium between the electrodes and also effectively removes the debris particles from the discharge zone. Single-discharge micro-EDM experiments are performed using three different dielectric supply methods, viz., conventional wet-EDM (electrodes submerged in dielectric medium), dry-EDM, and spray-EDM in order to compare the processes based on material removal, tool electrode wear, and flushing of debris from the interelectrode gap across a range of discharge energies. It is observed that spray-EDM produces higher material removal compared to the other two methods for all combinations of discharge parameters used in the study. The tool electrode wear using atomized dielectric is significantly better than dry-EDM and comparable to that observed in wet-EDM. The percentage of debris particles deposited within a distance of 100 μ m from the center of EDM crater is also significantly reduced using the spray-EDM technique.

Product miniaturization has become a trending technology in a broad range of industries and its development is being pushed by the requirements for complexity and resolution of micromanufactured products. However, there still exists a gap in the manufacturing spectrum for complex three-dimensional (3D) structure generation capabilities with micron and submicron resolution. This paper extends the near-field electrospinning (NFES) process and develops a direct-writing (DW) technology for microfiber deposition with micrometer resolution. The proposed method presented uses an auxiliary electrode to generate an electric field perpendicular to the fiber flight path. This tunable electric field grants the user real-time control of the fiber flight path, increasing the resolution of the deposited structure. The use of an auxiliary electrode ring for fiber manipulation is proposed to further improve control over the deposition process.

The objective of this research is to develop a novel, multimaterial additive manufacturing technique for fabricating laminated polymer nanocomposite structures that have characteristic length-scales in the tens of millimeters range. The three-dimensional (3D) printing technology presented in this paper combines the conventional inkjet-based printing of ultraviolet (UV) curable polymers with the deposition of either aligned or random nanoscale fiber mats, in between each printed layer. The fibers are first generated using an electrospinning process that produces the roll of fibers. These fibers are then transferred to the part being manufactured using a stamping operation. The process has been proven to manufacture multimaterial laminated nanocomposites having different 3D geometries. The dimensional accuracy of the parts is seen to be a function of the interaction between the different UV-curable polymer inks. In general, the addition of the nanofibers in the form of laminates is seen to improve the mechanical properties of the material, with the Young’s modulus and the ultimate breaking stress showing the most improvement. The pinning and deflection of microcracks by the nanoscale fiber mats has been identified to be the underlying mechanism responsible for these improved mechanical properties. The thermogravimetric analysis (TGA) reveals that these improvements in the mechanical properties are obtained without drastically altering the thermal degradation pattern of the base polymer.

Low energy-short pulsed electric discharge coupled with precise movement of circular electrode in micro-electrical discharge-milling (μ-EDM-milling) enables generation of three-dimensional (3D) cavities in the order of few tens of microns. Use of unshaped rotating electrode alters the spark discharge pattern that is primarily driven by the shape and size of the cavities being machined. In this paper, effects of five different cavities: circular, triangular, square, channel, and cross channel (square pillars) on the machining performance have been studied. These cavities having a nominal dimension of 1000 μm were machined on steel sample using 200 μm tungsten carbide electrode. The machining performance has been evaluated by analyzing dimensional accuracy, surface integrity, profile error, and formation of recast layers. The results highlight significant shape effect on machining performance in μ-EDM-milling. Circular holes machined by die sinking (tool advancement in Z-axis) are found to be more accurate, and square shaped pillars machined in two settings by generating cross channels at 90 deg have poor dimensional control. On the other hand, triangular cavities have the highest surface finish and profile uniformity compared to other shapes. The microscopic study in scanning electron microscopy (SEM) reveals significant variations in globule formation, recast layer deposition, flow of eroded molten metal, and final shape of cavities, which are found to be dependent of tool rotation.

In electrochemical micromachining (EMM) of microfeatures using straight cylindrical microtools, sidewalls of the structure tapers as depth increases. Disk microtool electrodes are used to minimize the taper formation during the machining of microfeatures. At present disk microtool electrodes are fabricated by wire electrical discharge grinding, reverse electro discharge machining (EDM), and microwire electro discharge machining method, which needs separate EDM machine as well as fabricated microtools suffer from thermal defects like microcracks on surface, residual stress, deformation, and needs careful handling. To overcome these limitations, new method is proposed to fabricate disk microtool electrode by EMM. Also the influences of EMM process parameters like applied voltage, pulse frequency, duty ratio, electrolyte concentration on shank diameter, material removal rate, and surface quality are investigated. Disk microtool electrode of disk height 70 μm, disk diameter 175 μm, shank diameter 93 μm, and shank height 815 μm have been fabricated from tungsten microrod of 300 μm diameter by proposed method and used to machine microfeatures like cylindrical hole with reduced taper angle, reverse taper hole, taper free microgroove, and 3D microstructure with plane surfaces on stainless steel by EMM. Effects of disk height on machining accuracy during generation of microhole, in the form of taper angle are also presented in the paper. Proposed method of developing disk electrode by EMM will be very useful for fabricating disk microtool electrodes with different disk diameters, disk heights, shank diameter, and shank height with desired surface quality by controlling various process parameters. Disk microtools with lower disk heights are more effective to generate microfeatures with minimum taper.

Microholes are widely used in industrial products, such as engine nozzles and filters for biomedical industry. Electrical discharge machining (EDM) is one of processes to drill microholes in alloy with high aspect ratio. However, the achievable aspect ratio of a microhole by micro-EDM is limited. To improve the aspect ratio of a microhole drilled by micro-EDM, the planetary movement of electrode is applied during machining. It was found that the machining efficiency of microhole drilling can be further improved by proper setting of planetary movement of electrode, such as the electrode feed rate and movement speed of electrode in XY plane. In this paper, a theoretical model is proposed to optimize parameters of the planetary movement of electrode. Microholes are drilled aided with planetary movement using different machining parameters to verify the model. Experimental results agree with theoretical values, which indicate the validity of the proposed model. This model provides certain theoretical basis for machining parameter selection when microholes are drilled aided with planetary movement.

Carbon nanotube (CNT)-based piezoresistive strain sensors have the potential to outperform traditional silicon-based piezoresistors in MEMS devices due to their high strain sensitivity. However, the resolution of CNT-based piezoresistive sensors is currently limited by excessive 1/f or flicker noise. In this paper, we will demonstrate several nanomanufacturing methods that can be used to decrease noise in the CNT-based sensor system without reducing the sensor's strain sensitivity. First, the CNTs were placed in a parallel resistor network to increase the total number of charge carriers in the sensor system. By carefully selecting the types of CNTs used in the sensor system and by correctly designing the system, it is possible to reduce the noise in the sensor system without reducing sensitivity. The CNTs were also coated with aluminum oxide to help protect the CNTs from environmental effects. Finally, the CNTs were annealed to improve contact resistance and to remove adsorbates from the CNT sidewall. The optimal annealing conditions were determined using a design-of-experiments (DOE). Overall, using these noise mitigation techniques it is possible to reduce the total noise in the sensor system by almost 3 orders of magnitude and increase the dynamic range of the sensors by 48 dB.