Pair Of Planar Electrodes Research Articles

A Self-Adaptive and Wide-Range Conductivity Measurement Method Based on Planar Interdigital Electrode Array

Conductivity is a crucial parameter in water quality detection, which can roughly represent overall concentration of various inorganic ions. However, traditional conductivity sensors can only afford high performance measurement in a relatively low range while the concentration may vary much more in realworld water environment. This paper proposes a high-precision and wide-range measurement method based on a novel planar interdigital electrode sensor array and a self-adaptive algorithm. The array is composed of 3 pairs of planar electrodes with various cell constants aiming at different subdivided conductivity sections. The follow-up circuit and the self-adaptive algorithm keep the optimal electrode pair dominates the output of the array. Numerical simulations were utilized to optimize sensor parameters before fabrication. PCB manufacturing technique was used which guaranteed a relatively low manufacturing cost and stable performance. Experiments were conducted to verify the sensing performance and results showed that the array can maintain precise measurement from 0.5μs/cm to 500ms/cm.

Simultaneous microfluidic pumping and mixing using an array of asymmetric 3D ring electrode pairs in a cylindrical microchannel by the AC electroosmosis effect

Abstract The present studies of AC electroosmosis (ACEO) micropumps for simultaneous pumping and mixing are mainly involved in the designs of the planar electrode pairs in a rectangular microchannel, such as the diagonal/herringbone shape of electrodes on top and bottom of the substrates. The two mixing samples usually flow into the left and right half of the inlet, respectively. However, the flow rate is limited because of the less electrodes on the walls, and the mixing is only appropriate for the channel of small diameters owing to the vortices appearing near the surface of electrodes. To solve the problem, we proposed an ACEO micropump with an array of asymmetric ring electrode pairs in a cylindrical microfluidic channel, and established a three-dimensional (3D) theoretical model by the standard Poisson–Boltzmann (PB) theory and convection–diffusion equation. In this paper, the two mixing samples flow into the inner and outer circular pipe of the inlet, respectively. Thus, the samples can be exchanged from the outer pipe area to the inner pipe area, so that it can strengthen the mixing by the vortices around the ring electrode surfaces in the microchannel. The microfluidic velocity field, vorticity field and concentration field are investigated in detail to explain the mechanism of pumping and mixing. To further improve the mixing performance, we designed and researched the combination sequences PnMm of ring electrode pairs based on the pumping mode of “forward driving of electrode pair” and the mixing mode of “reversal driving of electrode pair”. The simulation results show that the ring ACEO micropump with the inner and outer pipe inlet can rapidly pump the microflows and efficiently mix the samples simultaneously compared with the planar multifunctional ACEO micropumps. The numerical simulation of the ring ACEO micropump in this paper is of significant importance for the development of multifunctional microfluidic devices in biochemical field, and feasible fabrication techniques should be experimentally investigated in future studies.

A Performance-testing Platform for a Conduction Micropump with an FR-4 Copper-clad Electrode Plate.

Here, a conduction micropump with symmetric planar electrode pairs prepared on flame-retardant glass-reinforced epoxy (FR-4) copper-clad laminate (CCL) is fabricated. It is used to investigate the influence of chamber dimensions on the performance of a conduction micropump and to determine the reliability of the conduction pump when acetone is used as the working fluid. A testing platform is set up to evaluate conduction micropump performance under different conditions. When the chamber height is 0.2 mm, the pump pressure reaches its peak value.

Electrical discharge characteristics of a dielectric liquid under external flow in a microchannel with planar electrode configuration

The effect of fluid flow on discharge characteristics in a dielectric liquid was determined. Tests were performed for flow in a 100 micron high, 5 mm wide, 50 mm long microchannel at Reynolds numbers up to 13 and applied DC potentials up to 1.5 kV through 100 micro planar electrode pairs along the floor of the channel. The current within the conduction regime increased as the flow rate increased for the case where the flow was in the same direction as the applied electric field. In the injection regime, there was an optimum flow rate for maximum current.

Effect of doping ferrocene in the working fluid of electrohydrodynamic (EHD) micropumps

The effect of doping ferrocene in the working fluid of electrohydrodynamic micropumps was investigated under the application of DC electric fields. The micropump consisted of 100 planar electrode pairs that were embedded along the bottom wall of a 100-micron-high, 5-mm-wide and 26-mm-long microchannel. The width of the emitter and collector electrodes was 20 and 40 µm, respectively, with inter-electrode spacing of 30 µm. A redox dopant, ferrocene, was diffused homogeneously into the working fluid HFE-7100 at 0.05, 0.1 and 0.2 % concentration by weight. The static pressure head generation and flow rate at different back pressure conditions were measured under different applied DC voltages. The current and pressure generated with the doped working fluid were significantly higher than with pure HFE-7100 under an applied DC field. A maximum static pressure of 6.7 kPa and flow rate of 0.47 mL/min at no back pressure were achieved at 700 V.

Ion drag electrohydrodynamic (EHD) micro-pumps under a pulsed voltage

The use of pulsed voltages to improve the performance of an Electrohydrodynamic (EHD) micropump with HFE7100 as the working fluid was investigated. The micropump consisted of 100 planar electrode pairs that were embedded along the bottom wall of a 100 μm high microchannel. The pressure generation was measured at different operating pulse voltage parameters. An optimum pulse repetition rate and duty cycle for the pump geometry and fluid was found for maximum static pressure. The maximum pressure at the optimum pulse repetition rate was 75% greater than the average of the pressures generated at the two DC voltage levels.

Electrothermal effect on the immunoassay in a microchannel of a biosensor with asymmetrical interdigitated electrodes

In this paper, we study the AC electrothermal (ACET) effect on the binding reaction of immunoassays which a ligand (anti-C-reactive protein) immobilized on a microchannel wall specifically binds analyte (C-reactive protein (CRP)) flowing through a configuration of a microchannel with asymmetrical planar electrode pairs. The Navier–Stokes equations coupled with the Laplace and energy equations, the Fick’s second law in convection–diffusion coupled with the first order Langmuir adsorption model are used. The set of equations is solved in a two-dimensional configuration using the finite element method. Three cases of the thermal boundary conditions are investigated to study the effect of the temperature field on the binding reaction efficiency. The electrical conductivity of the buffer solution, the thermal conductivity of the base material and the surface reaction length are also discussed in this work. The simulation results show that the heterogeneous immunoassay is improved when the external surfaces of the cover and the substrate are kept at a constant temperature. For the best case studied in this work, the enhancement factors of the binding curve can be raised up to 3.46 and 2.84 for the association and dissociation phases, respectively, with 4Vrms applied voltage and operating frequency of 100kHz and electrical conductivity of 0.01S/m.

Electrohydrodynamic Injection Micropump With Composite Gold and Single-Walled Carbon Nanotube Electrodes

The presence of microfeatures/nanofeatures with sharp asperities on the emitter electrodes of ion drag electrohydrodynamic (EHD) micropumps is likely to enhance the local electric field and charge injection significantly, and thus the pressure generation and flow rates. The objective of this paper is to investigate the performance of EHD micropumps with single-walled carbon nanotubes (SWCNT) on the emitter electrodes. The micropumps had 100 pairs of planar electrodes where the width of the emitter and collector electrodes was 20 and 40 $\mu \text{m}$ , respectively, with a cross-sectional domain of $100~\mu \textrm {m} \times 5$ mm. Two micropumps with interelectrode spacing of 120 and 40 $\mu \text{m}$ were tested with a smooth emitter surface, and where SWCNT were electrophoretically deposited on the emitter electrodes using HFE7100 as the working fluid. The threshold voltage for charge injection lowered by a factor of 3 and 1.4 for the two pumps with SWCNT on the emitter electrodes compared with the smooth electrode case. The corresponding static pressure head increased by a factor 5, while the flow rate at no external back pressure increased by a factor 3 for the pump with interelectrode spacing of 120 $\mu \text{m}$ . For the pump with interelectrode spacing of 40 $\mu \text{m}$ , a maximum static pressure of 4.7 kPa was achieved at 900 V with SWCNT on the emitter electrode. [2014-0308]

Fabrication of continuous flow microfluidics device with 3D electrode structures for high throughput DEP applications using mechanical machining.

Microfluidics is the combination of micro/nano fabrication techniques with fluid flow at microscale to pursue powerful techniques in controlling and manipulating chemical and biological processes. Sorting and separation of bio-particles are highly considered in diagnostics and biological analyses. Dielectrophoresis (DEP) has offered unique advantages for microfluidic devices. In DEP devices, asymmetric pair of planar electrodes could be employed to generate non-uniform electric fields. In DEP applications, facing 3D sidewall electrodes is considered to be one of the key solutions to increase device throughput due to the generated homogeneous electric fields along the height of microchannels. Despite the advantages, fabrication of 3D vertical electrodes requires a considerable challenge. In this study, two alternative fabrication techniques have been proposed for the fabrication of a microfluidic device with 3D sidewall electrodes. In the first method, both the mold and the electrodes are fabricated using high precision machining. In the second method, the mold with tilted sidewalls is fabricated using high precision machining and the electrodes are deposited on the sidewall using sputtering together with a shadow mask fabricated by electric discharge machining. Both fabrication processes are assessed as highly repeatable and robust. Moreover, the two methods are found to be complementary with respect to the channel height. Only the manipulation of particles with negative-DEP is demonstrated in the experiments, and the throughput values up to 105 particles / min is reached in a continuous flow. The experimental results are compared with the simulation results and the limitations on the fabrication techniques are also discussed.

Ferroelectric photovoltaic properties in doubly substituted (Bi0.9La0.1)(Fe0.97Ta0.03)O3 thin films

Doubly substituted [Bi0.9La0.1][Fe0.97Ta0.03]O3 (BLFTO) films were fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition. The ferroelectric photovoltaic properties of ZnO:Al/BLFTO/Pt thin film capacitor structures were evaluated under white light illumination. The open circuit voltage and short circuit current density were observed to be ∼0.20 V and ∼1.35 mA/cm2, respectively. The band gap of the films was determined to be ∼2.66 eV, slightly less than that of pure BiFeO3 (2.67 eV). The PV properties of BLFTO thin films were also studied for various pairs of planar electrodes in different directions in polycrystalline thin films.

Fully enclosed bearing-structured self-powered rotation sensor based on electrification at rolling interfaces for multi-tasking motion measurement

A fully enclosed bearing-structured self-powered rotation sensor (SPRS) is developed for multi-tasking motion measurement. Due to contact electrification between fine-sized rolling beads and a pair of planar electrodes, the SPRS produce cycled electric signals when attached to a revolving axis. They are then analyzed to reveal the rotation rate of the axis and other corresponding derivable parameters, including speed, acceleration, and traveling distance. The device displays high precision, broad range, quick response, and excellent durability. It has novel dual roles as a rotation sensor and a structural ball bearing, making it easily applicable to a variety of circumstances. Integrated with a signal-processing interface, the compact-sized and light weighted SPRS was practically demonstrated in providing real-time motion monitoring for a vehicle wheel. It is promised to be used in a wide range of areas, including transportation, automation, consumer products, and industrial monitoring.

Alternating Current Electrohydrodynamics Induced Nanoshearing and Fluid Micromixing for Specific Capture of Cancer Cells

We report a new tuneable alternating current (ac) electrohydrodynamics (ac-EHD) force referred to as “nanoshearing” which involves fluid flow generated within a few nanometers of an electrode surface. This force can be externally tuned via manipulating the applied ac-EHD field strength. The ability to manipulate ac-EHD induced forces and concomitant fluid micromixing can enhance fluid transport within the capture domain of the channel (e.g., transport of analytes and hence increase target–sensor interactions). This also provides a new capability to preferentially select strongly bound analytes over nonspecifically bound cells and molecules. To demonstrate the utility and versatility of nanoshearing phenomenon to specifically capture cancer cells, we present proof-of-concept data in lysed blood using two microfluidic devices containing a long array of asymmetric planar electrode pairs. Under the optimal experimental conditions, we achieved high capture efficiency (e.g., approximately 90%; %RSD=2, n=3) with a 10-fold reduction in nonspecific adsorption of non-target cells for the detection of whole cells expressing Human Epidermal Growth Factor Receptor 2 (HER2). We believe that our ac-EHD devices and the use of tuneable nanoshearing phenomenon may find relevance in a wide variety of biological and medical applications.

AC electro-osmotic micromixer using a face-to-face, asymmetric pair of planar electrodes

This paper is the first to report the mixing performance of an AC electro-osmotic (AC-EO) micromixer based on the two sets of vortices generated by a face-to-face, asymmetric pair of planar electrodes. The larger top electrode of the asymmetric electrode pair was rectangular (30×60mm2) and the much smaller bottom electrode was also rectangular (500×700μm2) and featured two protrusions. Due to the highly three-dimensional flow pattern generated by the unique shape of the face-to-face electrode pair, the mixing enhancement factor (mixing time by diffusion/mixing time by the micromixer) exhibited by the reported micromixer ranged from 290 to 360 and the mixing performance values were uniform across the entire height of the fluid cavity. The usefulness of the mixer in hybridizing single-stranded deoxyribonucleic acids and mixing Escherichia coli with RNA stains was also demonstrated experimentally. A numerical investigation was conducted to study the three-dimensional AC-EO flow patterns induced by the face-to-face, asymmetric electrode pair. This analysis made it possible to identify a detailed flow pattern and the formation mechanism of the vortices. The confluence of inward AC-EO flows from the edges of the bottom-electrode protrusion locally induced a large inward-pumping force and was responsible for the formation of the four vortices at the four corners of the bottom electrode. The numerical and experimental results of this research provide information that will be useful in future applications and research in the area of microfluidic manipulation.

Label-free, high-throughput, electrical detection of cells in droplets

Today, droplet based microfluidics has become a standard platform for high-throughput single cell experimentation and analysis. However, until now no label-free, integrated single cell detection and discrimination method in droplets is available. We present here a microfluidic chip for fast (>100 Hz) and label-free electrical impedance based detection of cells in droplets. The microfluidic glass-PDMS device consists of two main components, the droplet generator and the impedance sensor. The planar electrode pair in the main channel allows the detection of only cells and cell containing droplets passing the electrodes using electrical impedance measurements. At a measurement frequency of 100 kHz non-viable cells, in low-conducting (LC) buffer, show an increase in impedance, due to the resistive effect of the membrane. The opposite effect, an impedance decrease, was observed when a viable cell passed the electrode pair, caused by the presence of the conducting cytoplasm. Moreover, we found that the presence of a viable cell in a droplet also decreased the measured electrical impedance. This impedance change was not visible when a droplet containing a non-viable cell or an empty droplet passed the electrode pair. A non-viable cell in a droplet and an empty droplet were equally classified. Hence, droplets containing (viable) cells can be discriminated from empty droplets. In conclusion, these results provide us with a valuable method to label-free detect and select viable cells in droplets. Furthermore, the proposed method provides the first step towards additional information regarding the encapsulated cells (e.g., size, number, morphology). Moreover, this all-electric approach allows for all-integrated Lab on a Chip (LOC) devices for cell applications using droplet-based platforms.

On the Modeling and Simulation of Ion Drag Electrohydrodynamic Micropumps

A numerical model for ion-drag electrohydrodynamic (EHD) micropumps has been developed. The Poisson and charge conservation equations are solved to determine the electric body force within the flow domain. The charge distribution at the electrodes is assumed to depend on the magnitude and the gradient of the electric field at the surface of the electrode. The flow field is then determined by solving the momentum equation with the inclusion of the electric body force. Simulations were performed for micropump configurations that consisted of a series of planar electrode pairs embedded along the bottom wall of a microchannel. A two-dimensional segment of the channel with a single electrode pair is simulated using periodic boundary conditions at the inlet and outlet for the charge and electric fields. An empirical model was developed to estimate the charge boundary condition for the simulations. The simulation results were in good agreement with existing experimental data. The model was then used to perform a parametric study of the effect of channel height on the pump performance.

A parametric study of AC electrothermal flow in microchannels with asymmetrical interdigitated electrodes

In this study, the AC electrothermal (ACET) flow in a microchannel with asymmetrical planar electrode pairs, in the same configuration as an AC electroosmosis (ACEO) pump, is studied numerically. The electrical, temperature and velocity fields in the microchannel are obtained by solving the coupled electrical, momentum and energy equations. The effects of electrode size, gap and length ratios, electrical conductivity of electrolyte solution, thermal conductivity of microchannel base material, as well as voltage and the frequency of AC on ACET flow are investigated in details. It is found that in the operating frequency range of the ACEO pump, i.e. 100 Hz–100 kHz, the velocity of the ACET flow is frequency-independent and moves in the same direction as the ACEO flow, and effects of electrode size, gap and length ratios on flow velocity have the same trend as the ACEO flow. Because the ACET flow velocity is proportional to electrical conductivities of electrolyte solution linearly and to the fourth power of the applied voltage, while the ACEO flow velocity decreases with the increase of electrical conductivity of the electrolyte solution and is only proportional to the square of applied voltage, therefore the ACET flow should not be neglected in an ACEO pump for the cases of high conductivity of electrolyte solution and relatively high AC voltage where ACEO and ACET effects are comparable.

Three-dimensional non-linear AC electro-osmotic flow induced by a face-to-face, asymmetric pair of planar electrodes

This paper demonstrates a three-dimensional, non-linear, AC electro-osmotic extensional flow induced by the capacitive charging of a face-to-face pair of planar electrodes. These two planar electrodes facing each other had different sizes and shapes. The extensional flow was attributed to the rectification of the stagnation-point flow in the center region by the three-dimensional vortices at the corners of the smaller electrode. The measured flow velocity near the edge of the electrode was on the order of millimeters per second. The shape of the electrode affected the distribution of the electric field and thereby modified the electro-osmotic flow. A change in the shape of the smaller electrode would significantly affect the flow fields and could cause a variation of a factor of 10 in the measured flow velocity. An equivalent electronic circuit of the experimental apparatus was developed. Based on the equivalent electronic circuit, the calculated critical frequency was in good agreement with the measured optimal velocity frequency. The quadratic dependence of the velocity on the voltage drop across the liquid, a characteristic of the capacitive charging process, was also reported in this paper.

On-chip determination of spermatozoa concentration using electrical impedance measurements

In this article we describe the development of a microfluidic chip to determine the concentration of spermatozoa in semen, which is a main quality parameter for the fertility of a man. A microfluidic glass-glass chip is used, consisting of a microchannel with a planar electrode pair that allows the detection of spermatozoa passing the electrodes using electrical impedance measurements. Cells other than spermatozoa in semen also cause a change in impedance when passing the electrodes, interfering with the spermatozoa count. We demonstrate that the change in electrical impedance is related to the size of cells passing the electrodes, allowing to distinguish between spermatozoa and HL-60 cells suspended in washing medium. In the same way we are able to distinguish between polystyrene beads and spermatozoa. Thus, by adding a known concentration of polystyrene beads to a boar semen sample, the spermatozoa concentrations of seven mixtures are measured and show a good correlation with the actual concentration (R(2)-value = 0.97). To our knowledge this is the first time that the concentration of spermatozoa has been determined on chip using electrical impedance measurements without a need to know the actual flow speed. The proposed method to determine the concentration can be easily applied to other cells. The described on-chip determination of the spermatozoa concentration is a first step towards a microfluidic system for a complete quality analysis of semen.

Biased AC electro-osmosis for on-chip bioparticle processing

Real-time detection of bioparticles is of great importance in deterring infectious diseases and bioterrorism. For bioparticle solutions with concentrations at an infectious level, culturing is typically used to increase the particle concentration to a detectable level, which is time consuming and often unfeasible under field conditions. Therefore, a real-time particle concentration technique is in demand to bridge the gap between the detectable level and infectious level of bacterial solutions. This paper describes a novel electrokinetic method that can potentially concentrate particles in real time. By studying surface flows on planar electrode pairs, two distinct ac electro-osmosis (ACEO) flows have been identified which are due, respectively, to capacitive and Faradaic charging of electrode double layers. Biased ACEO, combining dc bias with ac signals, breaks the symmetry of electrode charging, leading to asymmetric surface flows and a variety of directed surface flows that can concentrate, manipulate, and transport particles. Surface flows of opposite directions on planar electrodes produce stagnation lines that function as long-range particle traps and lead to net flows for micropumping. The device fabrication and operation are simple and compatible with integrated circuit technology

Measurement of Spatial Distributions of Electron Density and Electron Temperature in Direct Current Glow Discharge by Double Langmuir Probes

The spatial distributions of electron temperature and density in a dc glow discharge that is created by a pair of planar electrodes were obtained by using double Langmuir probes. The contribution of double Langmuir probes measurement is to provide a relatively quantitative tool to identify the electron distribution behavior. Electrons gain energy from the imposed electric field, and electron temperature (Te) rises very sharply from the cathode to the leading edge of the negative glow where Te reaches the maximum. In this region, the number of electrons (Ne) is relatively small and does not increase much. The accelerated electrons lose energy by ionizing gas atoms, and Te decreases rapidly from the trailing edge of the negative glow and extends to the anode. Ne was observed to increase from the cathode to the anode, which is due to the electron impact ionization and electron movement. The electron density was observed to increase with increasing discharge voltage while the electron temperature remained approximately. At 800 V and 50 mTorr argon glow discharge, Te ranged from 15 to 52 eV and Ne ranged from 6.3×106/cm3 to 3.1×108/cm3 in the DC glow discharge, and Te and Ne were dependent on the axial position.