Electro-conjugate Fluid Micropump Research Articles

High power density of microhydraulic source by MEMS technology and its application

This paper intrdouces an electro-conjugate fluid (ECF) micropump whose pumping sources are fabricated by MEMS technology and mounted on the inside of fluidic channels. ECF is a kind of functional and dielectric fluid. A strong and active jet flow of ECF is generated between electrodes surrounded by ECF, when high DC voltage is applied to the electrodes. Our ECF micropump consists of triangular prism and slit electrode pairs (TPSEs), which can be fabricated by the MEMS technology based on the micromolding of a thick photoresist followed by the electroforming. The experimental results prove that the MEMS-fabricated ECF micropump can be a good candidate as a microhydraulic pressure source for various microactuator systems. The paper also introduces the integration of TPSEs for higher output power. Thanks to the modular design of a TPSE, the output pressure and flow rate of the ECF micropumps are increased by only integrating TPSEs in series and parallel, respectively. In addition to this 2D integration of TPSEs, this paper describes the multilayer fabrication, which is the 3D integration of TPSEs to realize high-aspect-ratio TPSEs. These proposed MEMS-fabricated ECF micropumps as microhydraulic power sources have been applied for various applications, such as soft robots, focus-tunable microlens, droplet-based lab-on-a-chip devices, and so on.

Active microvalve driven by electro-conjugate fluid jet flow with a hydraulic power source on a chip

Powered microvalves are necessary for a variety of microfluidic applications such as on-demand droplet generators and droplet capture systems. Currently, a central challenge for these microvalve systems is the miniaturization of bulky power sources and control components, for example, air compressors, hydraulic pumps, solenoid valves, and regulators. In this paper, we propose a polydimethylsiloxane (PDMS)-based microvalve integrated with an on-chip power source, an electro-conjugate fluid (ECF) micropump. The assembled PDMS membrane of the device deforms and then blockades the port in the microchannel via fluidic pressure generated by the ECF micropump with the application of high DC voltage. Following finite element method simulations, we utilized 15 electrode pairs for the on-chip ECF micropump. By combining a MEMS process and the bonding process, we successfully realized the designed device and proceeded to evaluation of its performance characteristics. First, we evaluated the performance of the ECF micropump, which showed a maximum output pressure and a flow rate of 49.7 kPa, 87.3 mm3 s−1, respectively, at an applied voltage of 2.0 kV. Second, we found that the minimum sealing pressure of the microvalve was 10 kPa without any load condition. Third, we investigated the cracking pressures, which were 20 kPa and 50 kPa at the applied voltages of 1.5 kV and 2.0 kV to the ECF micropump, respectively. This study experimentally demonstrated the feasibility of the proposed microvalve device and its potential to be integrated into other microfluidic devices for precision control of liquid volumes.

Multilayer Fabrication of Micromolding and Electroforming with the Planarization of Grinding for High-Aspect-Ratio Microelectrodes in Electro-conjugate Fluid (ECF) Micropumps

Previously, we described a single layer fabrication combining thick photoresist (KMPR) micromolding and electroforming to fabricate ECF micropumps with triangular prism and slit electrode pairs (TPSEs). However, the fabricated TPSEs have a height limitation due to the limitation of KMPR’s aspect ratio caused by serious swelling and deformation of KMPR micromolds. To solve this problem and realize high-aspect-ratio TPSEs, we propose to utilize the multilayer fabrication instead of the single layer one. After each prior micromolding layer fabrication, the precision surface grinding technique is introduced to achieve the excellent planarization of the KMPR micromolds and electroplated TPSEs between the first layer and the second one. We apply this method to successfully fabricate the 3D-integration ECF micropump (3D-EMP) with TPSEs of 880 µm in height. Also, we validate this method by experimentally investigating and comparing the output performance of ECF micropumps composed of double layer TPSEs and previous single layer ones. The novel MEMS fabrication method combining multilayer micromolding and electroforming with the planarization is promising and applicable to a broad range of high-aspect-ratio metallic microstructures.

Configurations of triangular prism and slit electrode pairs to enhance the performance of electro-conjugate fluid micropumps

Previously, electro-conjugate fluid (ECF) micropumps with triangular prism and slit electrode pairs (TPSEs) have been developed and utilized for various mechanical, optical, chemical, and biomedical applications. However, the structural parameters of TPSEs have been determined by trial-and-error rather than systematical analysis. To this end, we select four structural parameters (i.e. hole width of a slit electrode: w, hole depth of a slit electrode: t, tip angle of a triangular prism electrode: , and gap between the triangular prism electrode and slit one: d) and implement the optimization to investigate their effects on the characteristic performance of ECF micropumps mainly depending on the combination of MEMS fabrication and experimental validation. Firstly, as a supplementary means, the simulation analysis is conducted with just consideration of the electric field intensity generated by TPSEs. After MEMS fabrication, the characteristic performance is experimentally characterized by comprehensively considering the generated electric field intensity, the flow dynamics, and the defect of microfabrication. The results show that the designed ECF micropump can attain the maximal output power under an applied DC voltage of 2 kV at the conditions of the slit hole width w = 200 µm, the slit hole depth t = 200 µm, the triangular tip angle = 60°, and the electrode gap d =200 µm. This optimization of TPSEs offers the helpful design guidance of ECF micropumps with higher output performance and promotes their further widespread use.

Micro ECF (electro-conjugate fluid) hydraulic power sources based on the modular design of TPSEs (triangular prism and slit electrode pairs)

The paper presents a novel micro hydraulic power source by using the electro-conjugate fluid (ECF) jetting based on the modular design of a triangular prism and slit electrode pair (TPSE). ECF jetting is a phenomenon of electrohydrodynamics (EHD) related to the direct conversion of electrical energy into kinetic energy in the fluid. ECF is a functional fluid that can generate a strong and active jet flow between an anode and cathode in ECF, when a high DC voltage is applied. A micropump utilizing ECF jetting can work as a micro hydraulic power source for micro actuation, cooling, and propulsion in various fields. Since each field requires a different output pressure and flow rate, it is difficult to realize a general-purpose micropump to meet all objectives. Assuming that one anode and cathode pair in ECF generates the same output pressure and flow rate, an electrode pair was set as a module that is a TPSE in this paper, and a new approach to the modular design is proposed that satisfies the necessary output pressure and flow rate in each application by simply allocating TPSEs in series and parallel. Four different kinds of ECF micropumps, namely (a) ten TPSEs in series and no TPSE in parallel, (b) ten TPSEs in series and three TPSEs in parallel, (c) ten TPSEs in series and five TPSEs in parallel, and (d) ten TPSEs in series and three TPSEs in parallel separated by walls, were designed and fabricated by MEMS fabrication. The experimental results showed that output pressure was affected only by serialized TPSEs not parallelized ones, and the output flow rate was raised by using increasing numbers of TPSEs in parallel, verifying the versatility and effectiveness of the proposed modular design for realizing multi-purpose ECF hydraulic power sources.

A droplet-generator-on-a-chip actuated by ECF (electro-conjugate fluid) micropumps

The traditional power sources for generating droplets are bulky devices such as syringe pumps, constant pressure systems and so on, resulting in difficult integration with other microfluidic components. To overcome this limitation, we propose and develop a droplet generator with its power sources on a chip (22 × 21 × ~ 1 mm). The compact droplet generator consists of two ECF (electro-conjugate fluid) micropumps, a T-junction channel geometry made of SU-8, a water chamber and three I/O ports. In our methodology, the two ECF micropumps are used to pump the continuous phase fluid (oil) directly and the dispersed phase fluid (water) indirectly on a chip. ECF is a kind of functional and dielectric oil, which can generate a strong and active ECF jet when its corresponding electrodes are applied to high DC voltages. Our ECF micropump is composed of triangular prism and silt electrode pairs (TPSEs) and is able to control flow rates precisely on a chip. In our device, the water in oil droplet is formed by the T-junction geometry. Using MEMS technology, we successfully fabricate the droplet-generator-on-a-chip. Span 80 and dibutyl decanedioate (DBD, Tokyo Chemical Industry Co., Ltd) are used as the surfactant and one type of ECF, respectively. Prior to the characteristic experiments of the T-junction generator, we investigate viscosity, electrical conductivity and relative permittivity of the mixtures of DBD and Span 80 at different concentrations (0 wt%, 1 wt%, 3 wt% and 5 wt%). We also research the impact of the mixtures on the performance of ECF micropumps and the wettability of SU-8 fluidic channels. After that, we confirm the flow pattern diagrams of two-phase fluids, the generated droplet diameter and the droplet production rate for our droplet-generator. Therefore, our droplet generator powered by ECF micropumps can realize the droplet generation on a chip.

Active sorting of droplets by using an ECF (Electro-conjugate Fluid) micropump

This paper proposes an on-demand method to sort water-in-oil (W/O) droplets by using an ECF (Electro-Conjugate Fluid) micropump on a chip. ECF is a kind of functional and dielectric oil, which can generate a strong and active flow (called ECF jet) when a high DC voltage is applied to its corresponding anode & cathode in ECF. Targeting at on-demand droplets sorting, we design a new sorter including several parts: a T-junction droplet generator made of SU-8, a sorting area, an ECF micropump, and I/O ports. The ECF combined with a suitable concentration of a surfactant (Span 80) and DI (deionized) water are utilized as the continuous and the dispersed fluids, respectively. The mixture of ECF and Span 80 can also be pumped by our ECF micropump and then forms the ECF jet. The fabrication of the sorter is based on the photolithographic patterning of thick resists (KMPR and SU-8) and the electroforming. We model the ECF micropump and also analyze the sorting performance of our sorter based on the FEM analysis. To validate the sorter, we investigate the influence of two vital parameters of the strength of ECF jets and the droplet sizes on the sorter. Then, we also research the working zones (areas), throughput and sorting efficiency in terms of flow rate ratios and the applied voltages of our device.

Development of MEMS-fabricated bidirectional ECF (electro-conjugate fluid) micropumps

The previously reported unidirectional ECF micropumps are not applicable to some soft actuators, which need inflating and deflating processes. To overcome this limitation, we propose, design, fabricate and characterize an ECF (Electro-Conjugate Fluid) bidirectional micropump. The simply designed bidirectional ECF micropump has five sets of electrodes. One set of electrodes are composed of two triangular electrodes with a face-to-face distribution and a shared and separated slit electrode. By applying DC voltage to one of the triangular electrodes and grounding the slit electrode, the device can generate an ECF jet along the triangular direction in the microchannel. Therefore, an ECF jet can be achieved in each direction by simply switching the applied DC voltage to one of the two triangular electrodes. This bidirectional ECF micropump without any mechanical moving parts is successfully fabricated by a MEMS-based process. We demonstrate the static and dynamic performance of our bidirectional ECF micropump. In the static evaluation, we primarily focus on the maximum pressure and flow rate generated by the bidirectional ECF micropump. In the dynamic evaluation, we test the responsiveness, model the relationship between switching frequency and output pressure, and compare the theoretical values with the experimental results. Therefore, this study indicates that bidirectional ECF micropumps can be a good candidate for a driving source to realize reciprocating motions.

Comprehending electro-conjugate fluid (ECF) jets by using the Onsager effect

An electro-conjugate fluid (ECF) is a kind of functional fluid that produces active flow (ECF jet) when high DC voltage is applied to the electrode pairs. Thanks to the simple structure to generate ECF jet, its micropumps are suitable as a hydraulic pressure source in various microactuators. However, the working principle of ECF jet has not been clarified perfectly so that the best way to evaluate the ECF micropump is to investigate its output pressure and flow rate by characteristic experiments. To predict the output performance of ECF micropumps without the characteristic experiments, this paper proposes a mathematical model of the ECF jet based on the Onsager effect. The Onsager effect is a phenomenon in which conductivity linearly increases with respect to the electric field intensity. The spatial conductivity gradient in the nonuniform electric field of electrode pairs induces the electrical charge distribution in ECF. We assume that the Coulomb force by the Onsager effect generates ECF jet. We design and successfully fabricate the ECF micropumps in which 20 pairs of TPSEs (triangular prism and slit electrode pairs) are circularly arranged in a fluidic channel. The simulation based on the Onsager Effect is carried out by a commercially-available software (Comsol Multiphysics). To verify the simulation results, the flow velocity of ECF is measured by visualization experiments. The comparison of experimental results and simulation results proves that modeling ECF jet by the Onsager effect can be an excellent candidate to predict the output performance of the ECF micropumps.

A Novel Hybrid Removal Technology for High-Aspect-Ratio SU-8 Micromolds in ECF (Electro-Conjugate Fluid) Micropumps Fabrication by UV-LIGA

Previously, we have developed ECF micropumps with triangular prism and slit electrode pairs (TPSEs) fabricated by the UV-LIGA. However, the previous KMPR molds have a limit to attain higher-aspect-ratio TPSEs. As a promising substitute, the ultrathick SU-8 molds are preferable for the TPSEs due to higher-aspect-ratio ability, but their difficult removal remains an annoying problem. To solve this problem, we first propose a novel hybrid removal method combining $\text{C}O_{2}$ laser engraving with $O_{2}$ /CF4 plasma to achieve the fast, non-swelling, and complete removal of ultrathick SU-8 micromolds for higher-aspect-ratio TPSEs. The $\text{C}O_{2}$ laser engraving is utilized as the main process to remove most SU-8, while the $O_{2}$ /CF4 plasma is adopted as the post-treatment to remove the remaining SU-8. To gather the proper fabrication conditions, we quantitatively analyze the effects of laser power, laser scan speed, and laser-pass numbers on the SU-8 ablation thickness. We successfully fabricated TPSEs of $590~\mu \text{m}$ and $970~\mu \text{m}$ in height by selectively removing SU-8 micromolds of 620 and $1100~\mu \text{m}$ in thickness. This achievement confirmed that our hybrid removal technology could remove the crosslinked SU-8 effectively and efficiently. We further experimentally proved the fascinating potential of our hybrid removal in improving the output performance of ECF micropumps. This promising hybrid removal opens the door to the easier fabrication of ultrathick metallic microstructures by UV-LIGA. [2017-0320]

UV-LIGA technique for ECF micropumps using back UV exposure and self-alignment

This paper proposes and develops a novel UV-LIGA technique using back UV exposure and self-alignment to realize high aspect ratio micromachining (HARM) in high power density electro-conjugate fluid (ECF) micropumps. ECF is a functional fluid designed to be able to generate strong and active jet flow (ECF jetting) between anode and cathode in ECF when high DC voltage is applied. We have developed high power density ECF micropumps consisting of triangular prism and slit electrode pairs (TPSEs) fabricated by HARM. The traditional UV-LIGA technique for HARM is mainly divided into two approaches: (a) single thick layer and (b) multiple thin layers. Both methods have limitations—deformed molds in the former and misalignment between layers in the latter. Using the finite element method software COMSOL Multiphysics, we demonstrate that the deformed micro-molds critically impair the performance of ECF micropumps. In addition, we experimentally prove that the misalignment would easily trigger electric discharge in the ECF micropumps. To overcome these limitations, we conceive a new concept utilizing the seed electrode layer for electroforming as the UV shield and pattern photoresist (KMPR) by back UV exposure. The seed electrode layer should be composed of a non-transparent conductor (Au/Ti) for patterning and a transparent conductor (ITO) for wiring. Instead of ITO, we propose the concept of transparency-like electrodes comprised of thin metal line patterns. To verify this concept, KMPR layers with thicknesses of 70, 220, and 500 µm are experimentally investigated. In the case of 500 µm KMPR thickness, the concept of transparency-like electrode was partially proved. As a result, TPSEs with a height of 440 µm were successfully fabricated. Characteristic experiments demonstrated that ECF micropumps (367 mW cm−3) fabricated by back UV achieved almost the same output power density as ECF micropumps (391 mW cm−3) fabricated by front UV. This paper proves that the proposed UV-LIGA technique, using back UV exposure and self-alignment, can effectively fabricate TPSEs for ECF micropumps with high output power density.

A bio-inspired 3D-printed hybrid finger with integrated ECF (electro-conjugate fluid) micropumps

The paper proposes a novel 3D-printed hybrid finger embedding ECF (electro-conjugate fluid) micropumps inspired from the hydraulic mechanism of spider legs. Two integrated ECF micropumps control two bellows-like joints respectively through fluidic channels built in the finger to realize the compliant motion with 2 DOFs (degree-of-freedom). Instead of the traditional CNC machining, molding and multiple manual assembly, the 3D printing technology of hybrid-material (hard and soft material) is utilized to fabricate our hybrid finger, which consists of (a) one monolithic body with the combination of a finger body base covered with rubber sheets and two bellows-like joints, (b) three finger body covers combined with rubber sheets, solving the annoying problems related to the complicated machining, the elaborate molding, and the delicate assembly and interfacing of soft and hard components. The ECF micropump with TPSEs (triangular prism & slit electrode pairs) was designed and fabricated by the MEMS process based on the micro-molding with thick photoresist and nickel electroplating. Characteristics experiments including output pressure and output flow rate measurement demonstrated that the fabricated ECF micropump had high output power density. The hybrid finger with ECF micropumps was successfully realized and its driving experiments validated the feasibility of our concept.

Triangular Prism and Slit Electrode Pair for ECF Jetting Fabricated by Thick Micromold and Electroforming as Micro Hydraulic Pressure Source for Soft Microrobots

In this paper, we propose a triangular prism and slit electrode pair (TPSE) and its micromechanical systems (MEMS) fabrication process for a novel micropump using electro-conjugate fluid (ECF), which is based on a thick photoresist (KMPR) micromold (≥ 500 μm) and nickel electroforming. ECF is a kind of functional and dielectric fluid. The strong and active jet flow of an ECF is generated between two electrodes surrounded by the ECF when a high direct-current voltage is applied to the electrode pair. The micropumps generated by the ECF jetting can be used as micro hydraulic pressure sources for soft microrobots. By substituting these ECF micropumps for bulky air compressors or hydraulic pumps utilized in soft robots, we can realize advanced soft microrobots in which the driving sources are embedded. An MEMS-based TPSE for an ECF micropump was successfully fabricated by using the proposed MEMS fabrication process. The maximum output pressure without a flow and the flow rate without a load were 24.6 kPa and 27.5 mm3/s, respectively, at an applied voltage of 2 kV. The experimental results show that the MEMS-fabricated TPSE is a good candidate for electrode-type ECF micropumps utilized in various applications of soft microrobots whose pressure sources are embedded inside.

ECF micropump fabricated by electroforming with novel self-aligned micro-molding technology

This paper proposes and presents a novel ECF (electro-conjugate fluid) micropump with TPSEs (triangular prism and slit electrode pair) fabricated by electroforming process using newly developed self-aligned micro molds. ECF is a kind of functional and dielectric fluid. ECF micropump is based on the principle of ECF jet, which is a powerful and active jet flow generated between electrodes immerged in ECF, when high DC voltage is applied to the electrodes. Our previous research experimentally demontrated that the ECF micropump had high power density thanks to the 2D-integraton (serialized integration and paralleled integration) of our proposed MEMS fabrication method by using micro-molding and electroplating. Moreover, it was also proved that higher aspect ratio of TPSEs by the multilayer fabrication process resulted in higher flow rate of the ECF micropump. However, the multilayer fabrication has demerit to require precise alignment that is time-consuming and extremely difficult to be met. In order to improve alignment accuracy and alleviate fabrication difficulty, this paper proposes a novel self-aligned MEMS fabrication process for high aspect ratio TPSEs. The ECF micropump by this newly-proposed MEMS process was successfully fabricated and the feasibility was proved by experimentally investigating output performance of the ECF micropump.

电共轭流体微型泵的实验研究

电共轭流体微型泵的实验研究

Concept of a Focus-Tunable ECF Microlens and Fabrication of a Large Model Prototype

This paper proposes a novel elastomer-based tunable liquid-filled microlens by using an Electro-Conjugate Fluid (ECF) jet and MEMS technology. The common approach for tuning an elastomer-based microlens is to change the geometry of the boundary determined by the control pressure of the chamber by using an external pump. However, this paper proposes placing the ECF micropump inside the tunable microlens. The ECF is a dielectric fluid that works as a smart fluid, generating a powerful jet flow (ECF jet) when subjected to a high DC voltage. Since the ECF jet is generated only with a pair of tiny electrodes, the pumping mechanism can be easily inside the device. We fabricated the large model prototype of an ECF focus-tunable microlens by partially utilizing MEMS technology. The experimental results showed us the feasibility of the ECF microlens.

2208 三角柱-スリット形電極対の三次元集積化によるECFマイクロポンプ(マイクロデバイス,一般講演)

This paper proposes and presents an electro-conjugate fluid (ECF) micropump whose pumping sources are integrated inside flow channels three-dimensionally. ECF is a kind of functional and dielectric fluid. A strong and active jet flow of ECF is generated between electrodes surrounded by ECF, when high DC voltage is applied to the electrodes. To combine easy fabrication and high performance, we developed a novel ECF pumping source that consists of a triangular prism electrode and a slit electrode fabricated by MEMS technology. Thanks to the advantages of MEMS technology it is easy to integrate plenty of triangular prism and slit electrode pairs in a plane. The plane integration of these electrode pair results in the realization of ECF micropumps for high output power density. In order to obtain higher output power density, we make an attempt to integrate the triangular prism and slit electrode pair three-dimensionally in addition to the plane integration. To figure out the effectiveness of three-dimensional integration of ECF pumping sources, we develop the prototype and investigate the characteristics experimentally by using the prototype. The experimental results show that the ECF micropump by 3D integration can be a good candidate as a higher output power hydraulic power source.

2A2-K15 三角柱-スリット型電極の直列・並列化によるECFマイクロポンプの性能評価(アクチュエータの機構と制御)

Electro-Conjugate Fluid (ECF) is a kind of functional and dielectric fluid. When a high DC voltage is applied to a pair of electrodes immersed in the ECF, a strong and active jet flow of ECF (ECF-jet) is generated between these two electrodes. A high power tube-type ECF micropump that consists of triangular prism and slit electrode pairs was proposed and fabricated by MEMS technology including photolithography with thick photoresist and nickel electroplating in the previous report. In this paper, we present advanced ECF micropumps in which the electrode pairs were serialized and parallelized for high performance in demand. The experiment results of the ECF micropumps show that parallelizing the electrode pairs does not affect output pressure significantly and also prove that the flow rate is proportionally dependent on the number of parallelized electrodes.

1209 MEMS技術を用いた高出力管路形ECFマイクロポンプ(アクチュエータのためのマイクロナノプロセス,一般講演)

This paper proposes and presents an electro-conjugate fluid (ECF) micropump whose pumping sources are mounted on the inside of flow channels and are serially located through the flow channels. ECF is a kind of functional and dielectric fluid. A strong and active jet flow of ECF is generated between electrodes surrounded by ECF, when high DC voltage is applied to the electrodes. To combine easy fabrication and high performance, we propose a novel ECF-jet generator that consists of a triangular prism electrode and a slit electrode for the tube-type ECF micropump. In order to determine the main parameters of MEMS-based ECF micropump, this research performs the experimental optimization of the prototype fabricated by mechanical machining, by changing the following parameters: slit width; electrode gap ; and tip angle. Experimental results by the prototype show that the optimal values are 200μm in slit width, 200μm in electrode gap, and 19° in tip angle. Based on these values, MEMS-based tube-type ECF micropump is successfully fabricated. The maximum output pressure obtained is 19 kPa at 2 kV of the applied voltage. The result shows that the tube-type ECF micropump can be a good candidate as a driving source for forced liquid cooling systems, new microactuators and so on.