Electrostatic Traveling Wave Research Articles

Dry particle size separation using electrostatic traveling wave methods

Electrostatic traveling wave (ETW) methods have grown in popularity as a method to manipulate and separate fine particles. This is of interest to mineral processing and In-situ Space Resource Utilization. Here, we demonstrate that ETW can be used to separate particles by size. First, our numerical calculation and simulation results show the competing effect of DEP and Coulomb force on particle motion direction, which depends on the frequency, particle size and charge. Then we define the “crossover frequency” allowing prediction of operating parameters to separate particles. At the “crossover frequency” – a particle is equally likely to move forward or backward. The crossover frequency decreases as particle size increases, and the proportion of particles moving backward increases as frequency increases. Four size groups of ballotini particles (glass) were transported and collected at different wave field frequencies. Finally, we have demonstrated experimentally the separation of particles between 30–50 µm and 75–110 µm. Simulation and experiment results revealed the effects of frequency, particle size and charge on particle motions. And the model can be used to guide the design of separation systems.

Numerical Solution of the Electric Field and Dielectrophoresis Force of Electrostatic Traveling Wave System.

Electrostatic traveling wave (ETW) methods have shown promising performance in dust mitigation of solar panels, particle transport and separation in in situ space resource utilization, cell manipulation, and separation in biology. The ETW field distribution is required to analyze the forces applied to particles and to evaluate ETW design parameters. This study presents the numerical results of the ETW field distribution generated by a parallel electrode array using both the charge simulation method (CSM) and the boundary element method (BEM). A low accumulated error of the CSM is achieved by properly arranging the positions and numbers of contour points and fictitious charges. The BEM can avoid the inconvenience of the charge position required in the CSM. The numerical results show extremely close agreement between the CSM and BEM. For simplification, the method of images is introduced in the implementation of the CSM and BEM. Moreover, analytical formulas are obtained for the integral of Green's function along boundary elements. For further validation, the results are cross-checked using the finite element method (FEM). It is found that discrepancies occur at the ends of the electrode array. Finally, analyses are provided of the electric field and dielectrophoretic (DEP) components. Emphasis is given to the regions close to the electrode surfaces. These results provide guidance for the fabrication of ETW systems for various applications.

Reduction of Dust on Solar Panels through Unipolar Electrostatic Traveling Wave

In this study, a novel electrostatic cleaning scheme has been applied to a new designed and developed electrode having high cleaning efficiency. In this method, a high voltage, four-channel, 1 Hz square wave signal is applied to a specially designed electrode array. Models of the electric field distribution of the proposed electrode array were developed and analyzed using Ansys Maxwell simulation software and printed circuits boards (PCBs) were produced. The performance of dust removal using the electrodes was evaluated. A 1 MW solar power plant was taken as a case study, and performance and cost were compared with the classical panel cleaning method (wet cleaning system). Our study has shown that the electrostatic cleaning method can be carried out with lower cost and higher efficiency than existing methods.

Numerical modeling of particle motion in traveling wave solar panels cleaning device

One of the promising solutions of dust accumulation on solar panels consists of using electric potential waves to prevent dust adhesion and to remove the dust layer. This study aims to understand the particle motion mechanisms on an electrostatic traveling wave conveyor. Understanding the effect of the operating parameters on particle trajectories and displacement distance is an essential step to improve the efficiency of this device and to understand the factors that can limit its performance. A numerical model that takes into account Coulomb force, dielectrophoretic, and image forces, but also gravity, drag force, and van der Waals adhesion force is carried out. The effect of rotating electric field, frequency, and electric potential harmonics on the particle trajectories and their characteristics are analyzed and discussed. The results reveal that the particles move according to four main movement modes. The frequency is a key parameter to control particle velocity and displacement. A hyper-synchronous movement during which the particles reach velocities much higher than the propagation velocity of the traveling wave has been obtained under certain conditions.

Practical performance of an electrostatic cleaning system for removal of lunar dust from optical elements utilizing electrostatic traveling wave

The removal of lunar dust deposited on solar panels, heat radiators, and optical elements (e.g., lens and mirrors) is one of the critical issues for a long-term lunar exploration. We have developed a cleaning system to remove the deposited lunar dust using an electrostatic traveling wave. When a four-phase rectangular voltage is applied to a transparent plate consisting of circular vortical ITO (indium tin oxide) electrodes printed on a glass substrate to move the electrostatic field toward the outer direction, the lunar dust on the plate is removed outwards following the movement of the electrostatic traveling wave. In this study, the effects of pressure and temperature that simulate the lunar environment were investigated, and it was demonstrated that high performance was maintained in a harsh lunar environment. It was confirmed that the low-frequency mechanical vibration generated by the movement of a rover improves the cleaning efficiency. The actual energy consumption of this system was evaluated, and it was demonstrated to be negligible with a simple high voltage source.

Application of Electrostatic Force on Moon, Mars and Asteroids

Because mitigation, sampling, and utilization technologies of regolith are critically important for lunar, Mars, and asteroid explorations, we are conducting the following research and development; (1) electrostatic cleaning of dust on optical elements, (2) electrostatic and magnetic cleaners for dust adhering to spacesuits, (3) electrostatic shield for dust entering into mechanical seals of equipment, (4) transport of regolith based on electrostatic traveling-wave and me-chanical vibration, (5) electrostatic particle-size classification, (6) electrostatic and magnetic sampling of regolith, (7) electrostatic precipitation in the Martian environment, and (8) electrostatic manipulation of a small particle.

Particle-size sorting system of lunar regolith using electrostatic traveling wave

A particle-size sorting system of lunar regolith using an electrostatic traveling wave is developed for In-Situ Resource Utilization on the Moon to extract indispensable resources from the regolith and realize long-term exploration. The regolith is sorted by utilizing a balance between the electrostatic and gravitational forces, which are determined depending on particle size, in vacuum conditions where the particles are not subjected to air drag. In this study, the effect of particle charge on the particle motion is confirmed by conducting model experiments and numerical calculations based on the distinct element method. In addition, it was experimentally demonstrated that particles less than approximately 20 μm in diameter were efficiently separated from the bulk of a lunar regolith simulant FJS-1 in a vacuum condition (∼1.5 × 10−2 Pa), and the performance of the size sorting system on the Moon was predicted by the numerical calculations. The system utilizes only the electrostatic force, and it does not require any gas, liquid, or mechanical moving parts.

A new design of Electrostatic Traveling Wave (ETW) micropump and the effect of parameters on the flow rate

In this study, a novel Electrostatic Traveling Wave (ETW) micropump is designed and fabricated, in which the fluid is driven by a three-phase Electrostatic Traveling Wave. The experiments show that the micropump is able to generate a flow rate of 135μl/s. The effect of the key variables (voltage, frequency and height of fluid) on the flow rate is investigated using the Response Surface Methodology (RSM). The correlation of the involved parameters was examined by employing the Central Composite Design (CCD) method through designating set up experiments that will determine the interaction of the variables. Furthermore, optimization was performed; the roles of parameters and their interactions were analyzed. The Analysis of Variance (ANOVA) shows that all parameters have a significant influence on the flow rate. The highest interaction of variables belongs to the frequency and height of fluid with the optimized condition of 25Hz and 2.0606mm, respectively. Under the optimized condition, results show good agreement between the measured flow rate and the fitted one.

Technology for Electrostatic Separation of Charged Toner Particles with Different Sign by Utilizing Electrostatic Traveling Wave

The author has studied toner transport utilizing electrostatic traveling wave with high-speed photography, measurements of toner charge distributions, and numerical simulations. In this study, the author has concentrated on the toner cloud above the main transport stream. The mechanism of the toner cloud formation has been identified, and a method to separate the correct sign toner from the wrong sign toner particles utilizing the mechanism has been developed. For the fewer toner particles and a lower speed toner transport, we used high-speed photography to observe an arch-shaped toner cloud above the transport. Using a simplified model, we have found that such an arch-shaped toner cloud is formed by the effect of air-drag. On the other hand, in the development system conditions such as a higher toner concentration and a faster speed toner transport, the arch-like cloud becomes dense because of the effect of the electrostatic attraction force. The author has proposed that the cloud comprises the same number of toner particles of both signs, and has designed toner separation and re-charging system using vertical toner transporting.

Sampling of Small Regolith Particles from Asteroids Utilizing an Alternative Electrostatic Field and Electrostatic Traveling Wave

To realize reliable and autonomous regolith sampling from asteroids in space, the author has developed a new sampling system that uses electrostatic force. This system uses a combination of electrostatic capture and transport of particles. High voltage is applied between parallel screen electrodes of the sampling device. As a result of the electrostatic force, particles are captured by the screen electrodes. The captured particles are then transported by an electrostatic traveling wave and transferred to a collection capsule. It has been demonstrated that lunar soil simulant, iron particles, and crushed ice can be sampled if the end of the screen electrode is in contact with the regolith for a short period of time (within 1 s). Because gravity is extremely low on small asteroids, the process of sampling particles on asteroids will be easier than that on the Earth.

543 静電力を利用した小惑星からのサンプリング技術

To realize reliable regolith sampling for autonomous operation in space, the authors have developed a new sampling system that employs electrostatic force. This system employs a combination of electrostatic capture and transport of particles. High voltage is applied between parallel screen electrodes of the sampling device. Owing to electrostatic force, particles are captured at the screen electrode of the device. The captured particles are then transported by an electrostatic traveling wave and transferred to a collection capsule. It has been demonstrated that lunar soil simulant can be sampled if the end of the screen electrode is in touch with the regolith for short period, within one second. Because gravity is extremely low on small asteroids, the process of sampling particles on asteroids will be easier than that on the Earth.

Electrostatic Cleaning Device for Removing Lunar Dust Adhered to Spacesuits

AbstractThe removal of lunar dust adhered to an astronaut’s spacesuit is critical for long-term lunar exploration. The author is developing a cleaning device that utilizes electrostatic force; this system employs a combination of electrostatic capture and electrostatic transport of dust. High voltage is applied between a screen electrode and an aluminum film deposited on a Mylar sheet positioned under the surface fabric of the spacesuit. By means of electrostatic force, dust adhered to the fabric is captured at the screen electrode of the device. The captured dust is then transported by an electrostatic traveling wave and transferred to a collection bag. The capture rate increased with the amount of dust adhered to the fabric and reached a value of 82%. Although small particles trapped between fabric fibers were difficult to remove, this system should be used in preliminary cleaning of spacesuits, saving valuable time for astronauts on the Moon.

Some techniques on electrostatic separation of particle size utilizing electrostatic traveling-wave field

The author has developed five kinds of techniques on electrostatic separation of particle size utilizing the balance of the electrostatic and gravitational force. The first is an inclined plate conveyer system. A plate conveyer consisted of parallel electrodes was constructed and four-phase electrostatic traveling wave was applied to the electrodes to transport particles on the conveyer. Particles were separated with size under the voltage application of appropriate frequency based on the feature that small particles were transported upward against the gravity but large particles were apt to fall down. The second technique is an inclined tube system. The principle is common with that of the inclined plate system. The third technique utilizes a circular electrostatic conveyer similar with the mass spectroscopy but utilizes the feature that small particles fly high altitude compared to that of the large particle. The forth technique, a vortex system, also utilizes the difference of flying locus of small and large particles. The last technique is the combination of the linear conveyer and an electrostatic separation roller located at the end of the conveyer. Small particles were attached onto the roller charged by a charger roller. Although the yield was reduced to realize the high separation performance with the former four techniques, relatively high yield was realized without reducing the separation performance with the roller system. This technique is expected to be utilized to the separation of toner and carrier particles used in electrophotography.

Computer Simulation of a Traveling-Wave Direct Energy Convertor.

Beam-circuit code is presented to simulate a Traveling-Wave Direct Energy Converter (TWDEC), which recovers the energy of fusion protons escaping from a FRC/D3He fusion reactor. A transmission line loop for propagation of the electrostatic traveling wave is designed using lumped constant elements L.C.R. Electrostatic coupling between proton beam and circuits is treated by directly solving Poisson’s equation. Circuit equations are transformed to temporal finite-difference equations, which are solved following the leap-flog scheme. Simulation results display desirable performance characteristics. Traveling wave with a fixed frequency is excited spontaneously without any external power supply. The wave is kept its equilibrium state under loading, and the wave is stable to variation of the load.

Theory of Current Generation by Electrostatic Traveling Waves in Collisionless Magnetized Plasmas

The general formula which gives the current density generated by an electrostatic traveling wave in a collisionless magnetized plasma is derived within the framework of quasilinear theory. This formula shows that the ion response is indispensable to generating the current via wave-particle interaction. The current which is obtained by use of this formula in the case of lower hybrid waves is in agreement with the experimental values.

Two-dimensional electrostatic E×B trapping

The nonlinear motion of a charged particle in a uniformly magnetized, two-dimensional plasma is analyzed in the presence of finite amplitude electrostatic waves traveling in the plane perpendicular to the magnetic field. In a strongly magnetized plasma, no particle trapping occurs in a single electrostatic traveling wave of arbitrary amplitude, since the induced E×B motion is orthogonal to the direction of wave propagation. However, particle orbits can be trapped when there are at least two mutually orthogonal components of the electrostatic field with finite wave amplitude cE⊥/B⩾ω/k⊥ such that a particle drifts one wavelength in a waveperiod. Exact integrability of the two-wave system implies that there is no stochastic particle behavior. Perturbation of this nonlinear equilibrium by additional waves with incommensurate phase velocities will destroy the coherent island structure and lead to stochastic diffusion. The threshold amplitude for strong nonlinear behavior in the coherent wave case helps to explain the many-wave turbulence criterion for the onset of particle diffusion in a two-dimensional plasma.