Parallel Plate Electrodes Research Articles

Strongly nonlinear dynamics of electrolytes in large ac voltages

We study the response of a model microelectrochemical cell to a large ac voltage of frequency comparable to the inverse cell relaxation time. To bring out the basic physics, we consider the simplest possible model of a symmetric binary electrolyte confined between parallel-plate blocking electrodes, ignoring any transverse instability or fluid flow. We analyze the resulting one-dimensional problem by matched asymptotic expansions in the limit of thin double layers and extend previous work into the strongly nonlinear regime, which is characterized by two features--significant salt depletion in the electrolyte near the electrodes and, at very large voltage, the breakdown of the quasiequilibrium structure of the double layers. The former leads to the prediction of "ac capacitive desalination" since there is a time-averaged transfer of salt from the bulk to the double layers, via oscillating diffusion layers. The latter is associated with transient diffusion limitation, which drives the formation and collapse of space-charge layers, even in the absence of any net Faradaic current through the cell. We also predict that steric effects of finite ion sizes (going beyond dilute-solution theory) act to suppress the strongly nonlinear regime in the limit of concentrated electrolytes, ionic liquids, and molten salts. Beyond the model problem, our reduced equations for thin double layers, based on uniformly valid matched asymptotic expansions, provide a useful mathematical framework to describe additional nonlinear responses to large ac voltages, such as Faradaic reactions, electro-osmotic instabilities, and induced-charge electrokinetic phenomena.

Generation of Dielectric Barrier Discharge Plasma in Supercritical Argon for Material Synthesis

Plasma discharge was generated by high-frequency (HF) power in supercritical argon (critical pressure: 4.86 MPa, critical temperature: 150.7 K). Dielectric barrier discharge (DBD) enabled us to continue to generate a stable plasma even in high-pressure argon in more than 1 h by using parallel plate electrodes. Furthermore, a discharge plasma at a high pressure was generated in a wide area (150 mm2) between these electrodes for material synthesis. From optical emission spectra of argon at atmospheric pressure to critical pressure, it was observed that the plasma at a high pressure generated the same active species as the plasma at a low pressure. A weak broadening of plasma emission spectra was observed when pressure increased. Moreover, a carbon thin film was synthesized from n-pentane by using the novel reaction field of DBD. The carbon thin film was analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Raman spectroscopy.

Surface Treatment of Polyethylene Terephthalate Films Using a Microsecond Pulse Homogeneous Dielectric Barrier Discharges in Atmospheric Air

Drived by a μs pulse high-voltage power supply, a homogeneous DBD in atmospheric air is generated between two plane-parallel electrodes, with PTFE plates as dielectric barriers. The discharge generated shows homogeneous discharge characteristics. The light emission is radially homogeneous and covers the entire surface of the electrodes, and a single current pulse with duration of about 1 s and amplitude of less than 1 A appears in each voltage pulse. The homogeneous DBD is used to treat the polyethylene terephthalate (PET) films to improve their surface hydrophilicity, and as the main operating parameters, the effects of discharge power density of the homogeneous DBD on the surface treatment are also studied. The surface properties of PET films before and after treatments are studied using the following: 1) contact angle and surface energy measurement; 2) attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR); 3) X-ray photoelectron spectroscopy (XPS); and 4) scanning electron microscopy (SEM). The results of contact angle and surface energy measurements reveal that the homogeneous DBD treatment can improve the surface hydrophilicity of PET films, as it can induce a remarkable decrease in water contact and a remarkable increase in surface energy. The results of SEM, XPS, and FTIR shows that improvement of the hydrophilicity due to both the introduction of oxygen-containing polar groups onto the surface and the etching of the surface. It is found that increasing discharge power density of homogeneous DBD can induce more effective treatment of PET films, and less treatment time is needed to achieve the same level of surface treatment by increasing the discharge power density.

Nondestructive Measurement of Moisture Content Using a Parallel-Plate Capacitance Sensor for Grain and Nuts

A simple, low-cost instrument that measures impedance and phase angle was used along with a parallel-plate capacitance system to estimate the moisture content (MC) of in-shell peanuts and yellow-dent field corn. Moisture content of the field crops is important and is measured at various stages of their processing and storage. A sample of about 150 g of in-shell peanuts or corn was placed separately between a set of parallel plate electrodes and the impedance and phase angle of the system were measured at frequencies 1 and 5 MHz. A semi-empirical equation was developed for peanuts and corn separately using the measured impedance and phase angle values, and the computed capacitance and the MC values obtained by standard air-oven method. The multilinear regression (MLR) method was used for the empirical equation development using an Unscrambler 9.7 data analyzer. In this paper, a low-cost impedance analyzer designed and assembled in our laboratory was used to measure the impedance and phase angles. MC values of corn samples in the moisture range of 7% to 18% and in-shell peanuts in the moisture range of 9% to 20%, not used in the calibration, were predicted by the equations and compared with their standard air-oven values. For over 96% of the samples tested from both crops, the predicted MC values were within 1% of the air-oven values. This method, being nondestructive and rapid, will have considerable application in the drying and storage processes for peanuts, corn, and similar field crops.

Electrothermally actuated resonant rate gyroscope fabricated using the MetalMUMPs

This paper presents an electrothermally actuated resonant microgyroscope fabricated using commercially available standard MEMS process, MetalMUMPs. A Chevron-shaped thermal actuator has been used to drive the proof mass, whereas parallel plate electrodes have been used for sensing the rotation induced Coriolis force. The proposed model consists of three coupled proof masses that are driven together using a frame. To achieve larger bandwidth and increased sensitivity, the microgyroscope is operated with a slight mismatch in the resonant frequencies of the drive and sense-mode. Modal analysis in IntelliSuite predicted the drive and sense-mode resonant frequency at 5.37 and 5.2kHz, respectively. A brief theoretical description of the resonant microgyroscope and mechanical design considerations of the proposed model are also discussed. Prototype fabrication using MetalMUMPs has also been investigated in this study. Microsystem Analyzer MSA-400 has been used to test the prototype at atmospheric pressure. The resonant frequency of the fabricated device is measured to be 5.98kHz for the sense-mode. A drive displacement of 4.2μm peak-to-peak is achieved by the proof mass when the device is operated at 1.3Vac applied at 2.99kHz consuming a power of 0.36W. The proposed device has a size of 1.8×2.0mm2. The large voltage–stroke ratio and low damping of chevron-shaped thermal actuator compared to traditional comb drive may result in a high quality factor microgyroscope operating at atmospheric pressure.

A new spectroscopic method for resolving the electronic symmetry properties of the highly excited molecules produced in photoexcitation

A novel method of spectroscopy for highly excited states of molecules in the valence excitation range has been established through the detection of metastable hydrogen atoms in the 2s state formed by photoexcitation. The detector for the metastable hydrogen atom is composed of a stack of parallel plate electrodes that creates a localized electric field and triggers the emission of the Lyman-alpha photon from the atom and a chevron pair of microchannel plates that detects the photon. For linear molecules, the angle-resolved detection of the metastable hydrogen atom enables us to measure cross sections in which electronic symmetries of highly excited molecular states are resolved. Such symmetry-resolved cross section measurements were carried out for doubly excited states of H(2).

A novel micropit device integrates automated cell positioning by dielectrophoresis and nuclear transfer by electrofusion

Nuclear transfer (NT) cloning involves manual positioning of individual donor-recipient cell couplets for electrofusion. This is time-consuming and introduces operator-dependent variation as a confounding parameter in cloning trials. In order to automate the NT procedure, we developed a micro-fluidic device that integrates automated cell positioning and electrofusion of isolated cell couplets. A simple two layer micro-fluidic device was fabricated. Thin film interdigitated titanium electrodes (300 nm thick, 250 microm wide and 250 microm apart) were deposited on a solid borosilicate glass substrate. They were coated with a film of electrically insulating photosensitive epoxy polymer (SU-8) of either 4 or 22 microm thickness. Circular holes ("micropits") measuring 10, 20, 30, 40 or 80 microm in diameter were fabricated above the electrodes. The device was immersed in hypo-osmolar fusion buffer and manually loaded with somatic donor cells and recipient oocytes. Dielectrophoresis (DEP) was used to attract cells towards the micropit and form couplets on the same side of the insulating film. Fusion pulses between 80 V and 120 V were applied to each couplet and fusion scored under a stereomicroscope. Automated couplet formation between oocytes and somatic cells was achieved using DEP. Bovine oocyte-oocyte, oocyte-follicular cells and oocyte-fibroblast couplets fused with up to 69% (n = 13), 50% (n = 30) and 78% (n = 9) efficiency, respectively. Fusion rates were comparable to parallel plate or film electrodes that are conventionally used for bovine NT. This demonstrates proof-of-principle that a micropit device is capable of both rapid cell positioning and fusion.

Embedded Microstructures by Electric-Field-Induced Pattern Formation in Interacting Thin Layers

Electric-field-induced interfacial instabilities and pattern formation in a pair of interacting thin films are analyzed on the basis of linear stability analysis and long-wave nonlinear simulations. The films are coated onto two parallel plate electrodes and separated by an air gap between them. A linear stability analysis (LSA) is carried out for viscoelastic films to show that the ratios of material properties to films thickness control the length scale and timescale significantly and the presence of the second layer increases the overall capacitance and thus can lead to a smaller length scale as compared to the instability in a single film. Long-wave nonlinear analysis for interacting viscous layers indicates that the instabilities are always initiated by the antiphase squeezing rather than the in-phase bending mode of deformation at the interfaces. Nonlinear simulations on patterned electrodes show that this novel geometry for electric field patterning can be employed to generate intricate, embedded 3-D periodic patterns and to miniaturize patterns. Simulations are presented for e-molding of a number of periodic self-organized patterns such as pincushion structures, straight/corrugated embedded microchannels, and microbubbles. A few interesting examples are also shown where (1) the pathway of evolution changes without altering the equilibrium morphology when kinetic parameters such as viscous forces are changed and (2) the self-organized equilibrium morphology does not reproduce the underlying patterns on the electrodes.

Separation of Ions from Volatile Organic Compounds Using High-Field Asymmetric Waveform Ion Mobility Spectrometry-Mass Spectrometer

A combination of high-field asymmetric waveform ion mobility spectrometry (FAIMS) with mass spectrometer (MS) was analyzed. FAIMS separates ions from the volatile organic compounds in the gas-phase as an ion-filter for MS. The sample ions were created at ambient pressure by ion source, which was equipped with a 10.6 eV UV discharge lamp (Å = 116.5 nm). The drift tube of FAIMS is composed of two parallel planar electrodes and the dimension is 10 mm × 8 mm × 0.5 mm. FAIMS was investigated when driven by the high-filed rectangular asymmetric waveform with the peak-to-peak voltage of 1.36 kV at the frequency of 1 MHz and the duty cycle of 30%. The acetone, the butanone, and their mixture were adopted to characterize the FAIMS-MS. The mass spectra obtained from MS illustrate that there are ion-molecular reactions between the ions and the sample neutral molecular. And the proton transfer behavior in the mixture of the acetone and the butanone is also observed. With the compensation voltage tuned from −30 V to 10 V with a step size of 0.1 V, the ion pre-separation before MS is realized.

Characterization of the mechanical behavior of human skin by means of impedance spectroscopy

There is increased interest for the use of impedance spectroscopy to measure skin dielectric properties in vivo. The aim of such measurements can be either to evaluate the hydration state of the skin, to detect diseased states such as skin cancer, to follow the progress of transdermal drug delivery, or simply to gather data on skin tissue impedance to be used in theoretical studies. However, obtaining reliable data can be difficult. Namely, skin is a highly nonhomogeneous multi-layered structure whose composition and dimensions differ depending on the location on the body and interindividual variations. Also, impedance measurements on skin are accompanied by a number of artefacts. We performed a series of impedance measurements using an Agilent/HP 4284A precision LCR meter with parallel plate electrodes pressed on the skin, at different locations on the body. We observed substantial impedance changes over the course of the measurement. These changes can be mainly attributed to skin deformation caused by the electrodes pressing against skin. The analysis showed that skin mechanical properties and layer thicknesses can be inferred from these temporal changes. Such data on mechanical properties of skin tissue give valuable extra information, crucial for successful estimation of the impedance of different skin layers.

Optically Modulated Electrokinetic Manipulation and Concentration of Colloidal Particles near an Electrode Surface

We study a recently demonstrated AC electrokinetic technique for manipulation and concentration of colloidal particles on an electrode surface. The technique uses indium tin oxide (ITO)-based parallel-plate electrodes on which highly localized infrared (1064 nm) laser illumination is shone. We show that the highly localized laser illumination leads to a highly nonuniform heating of the electrode substrate, which in turn drives an electrothermal microvortex resulting in a rapid transport of particles toward the illuminated site. Hundreds of polystyrene particles, with diameters ranging from 2.0 to 0.1 microm, suspended in a low conductivity solution (2.0 mS/m) could be aggregated at selected locations on the electrode by activating the laser illumination at suitable AC frequencies. Subsequent deactivation of the laser illumination causes the particles to scatter, and we explore this dynamical behavior for 1.0 microm particles using Delaunay tessellations and high-speed videography. We establish that drag from the electrothermal microvortex acts against a repulsive force, which decreases with increasing AC frequency, to create stable particle clusters. Moreover, experimentally we show that this particle capturing technique can be characterized by a critical frequency: a frequency at which the captured colloidal particle cluster becomes unstable and particles are carried away into the bulk by the electrothermal microvortex. This critical frequency increases with decreasing particle diameter for similar particles. For 0.1 microm particles, comparison of aggregation at different AC frequencies is achieved by the comparison of fluorescent intensity profiles of the aggregations.

Structural and electronic properties of dual plasma codeposited mixed-phase amorphous/nanocrystalline thin films

A dual-plasma codeposition system capable of synthesizing thin films of mixed-phase materials consisting of nanoparticles of one type of material embedded within a thin film semiconductor or insulator matrix is described. This codeposition process is illustrated by the growth of hydrogenated amorphous silicon (a-Si:H) films containing silicon nanocrystalline inclusions (a/nc-Si:H). A capacitively coupled flow-through plasma reactor is used to generate silicon nanocrystallites of diameter 5 nm, which are entrained by a carrier gas and introduced into a capacitively coupled plasma enhanced chemical vapor deposition reactor with parallel plate electrodes, in which a-Si:H is synthesized. The structural and electronic properties of these mixed-phase a/nc-Si:H films are investigated as a function of the silicon nanocrystal concentration. At a moderate concentration (crystalline fraction 0.02–0.04) of silicon nanocrystallites, the dark conductivity is enhanced by up to several orders of magnitude compared to mixed-phase films with either lower or higher densities of nanoparticle inclusions. These results are interpreted in terms of a model whereby in films with a low nanocrystal concentration, conduction is influenced by charges donated into the a-Si:H film by the inclusions, while at high nanocrystal densities electronic transport is affected by increased disorder introduced by the nanoparticles.

Effect of electrode temperature on the evolution of photoplasma under electric field

A photoplasma is produced by two-step resonant photoionization scheme by shining pulsed lasers on an atomic beam of barium (Ba). There is an interest in ion collection from photoplasma by electrostatic field when ion collection assembly is maintained at high temperature. A double furnace system consisting of two resistively heated furnaces has been developed. One furnace is placed on the top of the other in high vacuum chamber. The lower furnace is used to generate a wedge shaped barium atomic beam while the upper one heats the ion collection assembly. The photoplasma evolves in an external electric field produced by two parallel plate electrodes. The motion of electrons and ions in electric field generates currents that are recorded across series resistors connected to the electrodes. It is observed that a large dc current flows in the circuit when electrodes are kept at high temperature (~800 K). The large current is probably due to thermionic emission from Ba coated electrodes, electron impact ionization of vapor between electrodes, thermal ionization of vapor and leakage through insulator that holds the electrodes etc. When electrodes are at room temperature, the photoplasma is embedded in the atomic beam, where as it is produced in a vapor cell when electrodes are at high temperature. The photo-ion pulse is superimposed on the dc background current and its amplitude as well as time duration increase compared to that when electrodes are at room temperature.

2-D assembly of colloidal particles on a planar electrode

Electrical voltage externally applied between parallel-plate electrodes can cause colloidal particles located near one of the electrodes to aggregate; thus monodisperse particles can be driven to form hexagonally close-packed arrays which can be useful in the fabrication of photonic materials. The mechanism for lateral motion of particles on the electrode surface is electroosmotic flow driven by the action of the applied electric field acting either on the equilibrium charges in the diffuse layer of the particles (ECEO) or on charge induced by the electric field on the surface of the electrode (ICEO). For steady currents, ECEO dominates whereas ICEO dominates for high-frequency alternating current. For intermediate frequencies (10 Hz to 1 kHz) both mechanisms are active. This critical review attempts to integrate concepts from electrochemistry and colloid chemistry to understand this electrokinetic phenomenon.

Verification of a Charging Potential Measurement Method using a Parallel Plate Electrostatic Analyzer

The analysis and evaluation of spacecraft charging are important tasks related to spacecraft design. Plasma parameters and charging potential data are needed for charging and discharging predictions. A new type of electrostatic analyzer using two-stage parallel electrodes has been developed to measure the charging potential of a spacecraft over a wide range, from one volt to tens of kilovolts. The spacecraft charging potential is determined by analyzing the energy spectrum shift. A proof-of-concept model of the new electrostatic analyzer was tested in a vacuum chamber filled with Xe plasma. The experimental results agreed very well with the theoretical predictions. The device, made of two parallel plate electrodes, can measure the charging potential by scanning the electrode voltage over only one-tenth of the actual charging potential. The simple structure and low-voltage operation make the device suitable for operation on a small satellite.

11806 電界内における異物の挙動解析(OS5 運動と制御(1),オーガナイズドセッション)

In the relay, the contact trouble occurs because of a foreign body that exists on the electrodes. This paper presents the results of experimental and analytical studies of the motion of a charged particle under uniform electric field. The experimental apparatus consists of parallel plate electrodes vibrated with a shaker. The particle was charged in the rotating cylinders which are made of ABS or PTFE. The motion of the charged particle has been carefully investigated with a high speed camera. It was found that the motion of the charged particle depends on parameters such as electric field strength, amplitude and frequency.

Flow Behavior and Microstructure Developed between Parallel Plate Electrodes for Electro-Rheological Nano-Suspensions under No External Electric Fields

The flow behavior of nano-suspensions with particle volume fractions of φ = 2.4 and 4.4 vol% was investigated under no electric fields using a rotational rheometer with fixtures of parallel plates (or electrodes), the gap distances of which were narrower than several hundred micrometers. For the sample of φ = 4.4 vol%, the apparent yield stress was observed with gap distances of 50μm and 300μm. On the other hand, the flow behavior was strongly dependent on the gap distance for the sample of 2.4 vol%. These results were discussed in terms of the size of the microstructure and the gap distance between the parallel plates of the rheometer.

A Study on Electrostatic Tuning of Resonant Frequency for SOI-MEMS Resonators

Electrostatic tuning characteristics of the electrostatic resonators fabricated using SOI-MEMS technology with various configurations and voltage bias conditions were systematically studied using the FEM simulator. The basic structures of the resonators consist of a 1mm×1mm proof mass and four 200μm-long, 3μm-wide beams, whose thicknesses are 10μm, resulting in the resonant frequencies of the fundamental resonant mode without applied voltages which were about 5kHz. The resonant frequencies of the resonators with parallel-plate electrodes decreased quadratically with the applied voltage, while those of the resonators with comb electrodes gave no significant change. When the influence of the substrate was taken into consideration, the resonant frequency change by the applied voltage was reduced by several percents.

Capacitively Coupled Capillary Plasma Sources

Capacitively coupled capillary Ar and He plasmas have been generated in a quartz tube with the inner/outer diameters of 1.0/3.0 mm at the RF (13.56 MHz) powers of 3-7 W using the externally attached parallel-plate electrodes. Plasma expansion along a tube axis was a maximum at a gas pressure of 10-20 kPa, in which Vpp was a minimum and so Paschen's minimum condition was satisfied. The capillary plasma was magnetized by a strong magnetic field of 0.4 T to sustain the plasma at a low pressure, since the plasma did not ignite at the gas pressure below 2-4 kPa. The optical emission spectrum analysis revealed that atomic excitation temperature increased with decreasing gas pressure. Furthermore, it was found that the metastable atoms play an important role in the plasma sustenance at a high gas pressure.

Excitation of large-amplitude parametric resonance by the mechanical stiffness modulation of a microstructure

In this work we report on an approach allowing efficient parametric excitation of large-amplitude stable oscillations of a microstructure operated by a parallel-plate electrode, and present results of a theoretical and experimental investigation of the device. The frame-type structure, fabricated from a silicon on insulator (SOI) substrate using deep reactive ion etching (DRIE), consists a pair of cantilever-type suspensions connected at their ends by a link. The time-varying electrostatic force applied to the link by a parallel-plate electrode is transformed into a periodic tension of the beams, resulting in the modulation of their flexural stiffness and consequently the mechanical parametric excitation of the structure. The lateral compliance of the beams allows for large-amplitude in-plane oscillations in the direction parallel to the electrode while high axial stiffness prevents undesirable instabilities. The lumped model of the device, considered as an assembly of geometrically nonlinear massless flexures and a rigid massive link and built using the Rayleigh–Ritz method, predicted the feasibility of the excitation approach. The fabricated devices were operated in ambient air conditions by a combination of a steady (dc) and time-dependent (ac) components of voltage and the large-amplitude responses, up to 75 µm, in the vicinity of the principal parametric and primary resonances were registered by means of video acquisition and image processing. The shapes of the experimental resonant curves were consistent with those predicted by the model. The location and size of the instability regions on the frequency–voltage plane (parametric tongues) were quantitatively in good agrement with the model results. Theoretical and experimental results indicate that the suggested approach can be efficiently used for excitation of various types of microdevices where stable resonant operation combined with robustness and large vibrational amplitudes are desirable.