Dielectrophoretic Force Research Articles

Particle-Induced Electrostatic Repulsion within an Electric Curtain Operating below the Paschen Limit.

The electric curtain is a platform developed to lift and transport charged particles in air. Its premise is the manipulation of charged particles; however, fewer investigations isolate dielectric forces that are observed at lower voltages (i.e., less than the Paschen limit). This work focuses on observations of simultaneous dielectrophoretic and electrostatic forces. The electric curtain was a printed circuit board with interdigitated electrodes (0.020 inch width and spacing) coated with a layer of polypropylene, where a standing wave or travelling wave AC signal was applied (50 Hz) to produce an electric field below the Paschen limit. Soda lime glass beads (180–212 µm) demonstrated oscillatory rolling via dielectrophoretic forces. In addition, several particles simultaneously experienced rapid projectile repulsion, a behavior consistent with electrostatic phenomena. This second result is discussed as a particle-induced local increase in the electric field, with simulations demonstrating that a particle in close proximity to the curtain’s surface produces a local field enhancement of over 2.5 times. The significance of this is that individual particles themselves can trigger electrostatic repulsion in an otherwise dielectric system. These results could be used for advanced applications where particles themselves provided triggered responses, perhaps for selective sorting of micrometer particles in air.

Bubbles in Transformer Oil: Dynamic Behavior, Internal Discharge, and Triggered Liquid Breakdown

It is generally accepted that the presence of bubbles severely degrades the electric strength of liquid dielectrics, but the influencing factors and mechanisms have yet to be elucidated. Dynamic behavior, partial discharges (PDs) inside bubbles, and their effects on the breakdown of transformer oil are investigated experimentally and theoretically in this study. The results show that, under a nonuniform electric field, the presence of bubbles does not significantly affect the PD inception voltage (PDIV) and breakdown voltage (BV) of the liquid, as bubbles migrate to the region with lower field strength under dielectrophoretic force. In a uniform electric field, conversely, bubbles greatly reduce PDIV and BV; an increase in the number of bubbles or a slower voltage rise rate appears to exacerbate this effect. The PDIV observed in the experiment is much higher than the theoretical value calculated by the Townsend theory or streamer criterion, which may be due to the lack of free electrons inside the bubble, thus resulting in scarce internal discharge. The addition of X-rays enhances the radiation ionization and then eliminates the inconsistency between the theoretical and measured values of PDIV, which supports our hypothesis. The bubble-triggered breakdown of liquid dielectrics, namely, once a discharge occurs inside the bubble, likely triggering the breakdown of the liquid gap, is observed. The electric field enhancement caused by surface charges and the instability of the gas–liquid interface may account for this.

Front Cover: High‐throughput sorting of nanoliter droplets enabled by a sequentially addressable dielectrophoretic array

DOI: 10.1002/elps.202100057 The cover picture shows sorting of microdroplets using the sequentially addressable dielectrophoretic array (SADA). The SADA is an array of electrodes (as shown in gold in the cover picture) that generates localized electric field synchronized to the position and speed of flowing target droplets (as indicated by the blue curves in the cover picture). The resulting dielectrophoretic force displaces only the target droplets from the default flow, enabling the separation of target and non-target nanoliter droplets in a high-throughput manner.

Effect of the thickness of polyethylene insulation on flame spread over electrical wire with Cu-core under AC electric fields

Effect of the thickness of polyethylene (PE) insulator on flame spread over electrical wire with high thermal conductivity of Cu-core is experimentally investigated by varying the applied AC voltage (VAC) and frequency (fAC) in the ranges of 0 – 5 kV and 0 – 1000 Hz, respectively. Three outer wire diameters (Dout= 0.8, 1.1, and 1.5 mm) with the same core diameter (Dc= 0.5 mm) are used. For the baseline cases without applying electric field, the flame spread rate (FSR) decreases with an increase in the outer wire diameter. When AC electric fields are applied to the wires, flame shapes and FSRs are appreciably influenced. The FSR behaviors with AC electric fields are classified into four sub-regimes as the frequency increases: a decreasing FSR (Regime I) having a leaning flame toward the burnt wire side, an increasing FSR (Regime II) showing a splitting phenomenon from a single-peak flame to a double-peak one due to a dielectrophoresis phenomenon, a decreasing FSR again (Regime III) generating a globular molten PE near the flame front and forming a liquid film of molten PE via continuously migrating a part of molten PE toward the burnt wire side, and an increasing FSR again (Regime IV) showing vortex flames at the front and rear flame edges along with an electrospray of molten PE. These emphasize diverse effects of the dynamic behaviors of molten PE. The onset condition for the formation of the vortex structure is identified as fAC,cr∼VAC−2Dout, supporting that such phenomenon is generated by induced magnetic field. An intermittent rotation of secondary (main) molten PE around the wire is a new observation. The mechanism is suggested by a dielectrophoretic force. Excluding the cases experiencing an intermittent leaning flame toward the burnt wire side and an irregularly splitting flame, FSR under the influence of such complex dynamic-behaviors of molten PE could reasonably be characterized with the gradient of electric field intensity taken at the outer surface of PE insulator, the area ratio between insulator and core, and AC frequency in all the regimes.

Application of the Taguchi method to explore a robust condition of tumor-treating field treatment.

Tumor-treating fields have potential as minimally invasive cancer treatment. This study aimed to explore the optimum tumor-treating field conditions that minimize unpredicted variations in therapeutic outcomes resulting from differences in cell size and electrical properties. The electric field concentration that induces a dielectrophoretic force near the division plane of a mitotic cell was calculated by finite element analysis for 144 cases, based on different combinations of six noise factors associated with cells and four controllable factors including frequency, as determined by the Taguchi method. Changing the frequency from 200 to 400 kHz strongly increased robustness in producing a dielectrophoretic force, irrespective of noise factors. However, this frequency change reduced the force magnitude, which can be increased by simply applying a higher voltage. Based on additional simulations that considered this trade-off effect, a frequency of 300 kHz is recommended for a robust TTF treatment with allowable variations. The dielectrophoretic force was almost independent of the angle of applied electric field deviated from the most effective direction by ±20 degrees. Furthermore, increased robustness was observed for extracellular fluid with higher conductivity and permittivity. The Taguchi method was useful for identifying robust tumor-treating field therapy conditions from a considerably small number of replicated simulations.

Numerical Study of Airborne Particle Dynamics in Vortices Subject to Electric Field

Capture, selective collection and flight manipulation of airborne particulate are three important functional requirements in various actively growing aerosol technology applications. Aerodynamic drag, particle inertia and dielectrophoretic (DEP) force due to externally applied electrostatic forces influence the behavior of micron sized particles significantly, in such situations. In this work, we numerically study how a combination of these forces uniquely influences the behavior of uncharged or mildly charged airborne particles, distinct from that with their individual influences. Uncharged particle movements in a numerically fabricated well structured steady vortical flow between two curved electrode surfaces are analyzed. Vortical air circulation towards and away from the electrode tip enhances and deteriorates electrostatic particulate capture on the electrodes, termed as co and counter directions with respect to the electrostatic force on particles respectively. Particles in counter vortices under an electric field reveals a rich variety of unique behaviors due to the interplay of drag, inertia and DEP forces. Distortion of the vortex structure due to convexity of electrode surfaces results in an inverse inertial limit cycle trajectory trapping of particles; with the airborne particles spatially segregated, trapping larger particles further inside the vortex than the smaller particles.Value of a dimensionless number $\xi_v$, the ratio of DEP force and particle inertia, represents the combination of the operating flow and electric field strengths. Inertial cut-off of particle capture in this configuration abruptly shift to DEP capture at a critical value of $\xi_v\approx 0.2$, as its value increases. Selective deposition of particles within a closed range of size and density, emerges due to the interplay of vortex trapping, inertial expulsion and electrostatic capture.

C-Mems Platform for the 3d Positioning of Microparticles Using an Array of Individually Addressable Microelectrodes and Dielectrophoretic Forces

C-Mems Platform for the 3d Positioning of Microparticles Using an Array of Individually Addressable Microelectrodes and Dielectrophoretic Forces

Numerical Design Study of Continuous Separation of Blood Cells in a Microfluidic Device using Combined Dielectrophoretic and Hydrodynamic Forces

Numerical Design Study of Continuous Separation of Blood Cells in a Microfluidic Device using Combined Dielectrophoretic and Hydrodynamic Forces

Particle Sorting Technique Using Microfluidic Devices with Integrated Dielectrophoresis Electrodes

Micro-order particle sorting technology is essential for research applications in the chemical, environmental, and biomedical fields, as well as in various industrial sectors. Many microfluidic devices have been proposed to sort and collect microparticles in the liquid phase. On the other hand, there are not many microfluidic devices for sorting and collecting particles in the gas phase, such as PM2.5 and other dust particles. In our previous study, we successfully developed an electrostatic precipitation technique that uses dielectrophoretic forces to retain microbeads in the gas phase. In this study, we will integrate the dielectrophoresis electrodes into a microfluidic device and apply them as a particulate sorting and selection.

Deep-Learning Based Estimation of Dielectrophoretic Force.

The ability to accurately quantify dielectrophoretic (DEP) force is critical in the development of high-efficiency microfluidic systems. This is the first reported work that combines a textile electrode-based DEP sensing system with deep learning in order to estimate the DEP forces invoked on microparticles. We demonstrate how our deep learning model can process micrographs of pearl chains of polystyrene (PS) microbeads to estimate the DEP forces experienced. Numerous images obtained from our experiments at varying input voltages were preprocessed and used to train three deep convolutional neural networks, namely AlexNet, MobileNetV2, and VGG19. The performances of all the models was tested for their validation accuracies. Models were also tested with adversarial images to evaluate performance in terms of classification accuracy and resilience as a result of noise, image blur, and contrast changes. The results indicated that our method is robust under unfavorable real-world settings, demonstrating that it can be used for the direct estimation of dielectrophoretic force in point-of-care settings.

Window with Electrostatic Protection against Dust, Smoke, and Viruses

The article analyzes the effect of dangerous aerosols on the human body. In order to purify the air from aerosols, the effect of an electric field on them is considered. The electric and dielectrophoretic forces acting on submicron particles in an inhomogeneous electric field of two parallel wires are calculated. It is shown that part of this field is identical to the field between the wire and the grounded plate electrode located in the middle between the wires. This allows using a known formula for the electric field of a two-wire line to calculate the field gradient and the effect of dielectrophoresis on neutral particles. Smoke and dust particles already carry a negative charge, and a more or less uniform electric field is enough to move them. To filter neutral water droplets infected with the virus, you need either a field with a large gradient or a corona discharge. The paper shows that the polarization of particles in an electric field causes the particles to stick together, and larger particles settle faster on the electrodes of the filter. The design of a transparent electrostatic precipitator is proposed, which can be used to protect indoor air from external smoke, dust, or viruses.

Nanoparticle-based multiplex biosensor utilising dual dielectrophoretic forces for clinical diagnosis of Alzheimer’s disease

The significant correlation between amyloid-beta (Aβ) and tau accumulated in the brain and the levels observed in plasma means that the quantification of plasma Aβ and tau is gaining attention as an alternative to conventional Alzheimer’s disease (AD) diagnostic methods, such as neuroimaging and psychological memory evaluation. However, there remain limitations, such as low accuracy and reproducibility of AD diagnosis using plasma Aβ and tau quantification in clinical samples. Here, we propose an interdigitated microelectrode (IMEs)-based impedimetric biosensor that uses polystyrene beads (PS) and dielectrophoretic (DEP) force and demonstrate its clinical applicability in AD diagnosis. In the quantification of Aβ and tau present in 1% standard plasma as well as in phosphate-buffered saline (PBS), the biosensor showed almost more than 2-fold higher sensitivity compared to the reference without PS and DEP force. Furthermore, by quantifying the levels of Aβ and tau in the clinical plasma samples, we successfully distinguished between clinically diagnosed AD patients and normal controls with high accuracy (p < 0.0001). These results suggest that our biosensor has high applicability and excellent potential for the clinical diagnosis of AD.

Individual Microparticle Manipulation Using Combined Electroosmosis and Dielectrophoresis through a Si3N4 Film with a Single Micropore.

Porous dielectric membranes that perform insulator-based dielectrophoresis or electroosmotic pumping are commonly used in microchip technologies. However, there are few fundamental studies on the electrokinetic flow patterns of single microparticles around a single micropore in a thin dielectric film. Such a study would provide fundamental insights into the electrokinetic phenomena around a micropore, with practical applications regarding the manipulation of single cells and microparticles by focused electric fields. We have fabricated a device around a silicon nitride film with a single micropore (2–4 µm in diameter) which has the ability to locally focus electric fields on the micropore. Single microscale polystyrene beads were used to study the electrokinetic flow patterns. A mathematical model was developed to support the experimental study and evaluate the electric field distribution, fluid motion, and bead trajectories. Good agreement was found between the mathematic model and the experimental data. We show that the combination of electroosmotic flow and dielectrophoretic force induced by direct current through a single micropore can be used to trap, agglomerate, and repel microparticles around a single micropore without an external pump. The scale of our system is practically relevant for the manipulation of single mammalian cells, and we anticipate that our single-micropore approach will be directly employable in applications ranging from fundamental single cell analyses to high-precision single cell electroporation or cell fusion.

Finite ion size and ion permittivity effects on gel electrophoresis of a soft particle

Electrophoresis of a soft particle embedded in a hydrogel medium is studied by considering the hydrated ions as charged dielectric spheres of finite radius. The Nernst-Planck equation for the transport of ions is modified to take into account the ion steric repulsion and the ion-solvent dielectric interactions (MNP-model). The effective polarizability of the hydrated ions lowers the dielectric permittivity of the ionic solution and consequently, the permittivity of the medium varies with local ionic concentration. This spatial variation of the permittivity creates a Born energy difference in ions leading to a Born force experienced by the ions. In addition, ions experience a dielectrophoretic force due to the polarization under the imposed external electric field. The ion steric repulsion are modeled by the Carnahan-Starling equation of state. The convection of ions are governed by the Brinkman extended Navier-Stokes equations. The modified Nernst-Planck equation coupled with the Brinkman Navier-Stokes equations and the equation for electric field are solved numerically through a control volume approach. The ion steric interactions and ion-solvent interactions create a saturation of mobile ions in the polyelectrolyte layer (PEL) of the soft particle, which leads to an attenuation of the counterion condensation of the PEL. This short range steric repulsion and ion-solvent interactions have significance for higher bulk ionic concentration as well as higher range of charge density of the soft particle. These interactions are elucidated by comparing with the mobility obtained by the standard model (PNP-model). The Dukhin number and the effective charge density of the PEL are determined to illustrate the mobile ion saturation. The discrepancy between the present modified model from the standard model magnifies for the case of salts of multivalent counterions.

A dielectrophoresis-based microfluidic chip for trapping circulating tumor cells using a porous membrane

Circulating tumor cells (CTCs) have been widely considered as novel biomarkers for the clinical diagnosis of cancer. CTCs are the cells detached from the parent tumors and shed into the blood stream to initiate tumor metastasis. Although CTCs are rare, their detection in one’s blood sample is essential for cancer early diagnosis and for starting the treatment procedure. Here, we introduce a novel method for trapping CTCs using dielectrophores, which effectively employs pores of a replaceable porous membrane as CTC traps. The applied dielectrophoretic force efficiently traps and holds CTCs in a stable position and further enables us to perform various on-chip analysis with them. First, using finite element method, the performance of the system was simulated for different physical conditions. Then, the chip was fabricated and its trapping performance was experimentally validated. Cells were entered into the microchannel and trapped in the pores of a polydimethylsiloxane membrane. The proposed microfluidic chip is capable of detecting rare cells in a large cell population.

RBIO-06. MECHANISM OF ACTION AND ASSOCIATED EFFECTS OF TUMOR TREATING FIELDS (TTFIELDS) ON LIVING CELLS USING SIMULATIONS

Abstract Following FDA approval, TTFields treatment has become a commonly used modality for treating patients with Glioblastoma (GBM) and Mesothelioma. From the early 2000’s, extensive research has been performed in in-vitro systems for studying the effects of TTFields on living cells. These studies have shown that multiple cellular functions are affected by TTFields. However, the physical mechanism by which the fields exert effects on cells are not well understood. We propose an analytical model for predicting the geometric and electrical parameters enabling amplification of the electric field in the living cells. This amplification favors the emergence of local heating, dielectrophoretic (DEP) force, or electrostatic pressure at TTFields frequencies. This model is supported by simulations of cells in different configurations. Computational studies were performed with Comsol Multiphysics software. Cell models were constituted of cytoplasm, membrane and extracellular matrix. A field of 1V/cm was generated at different frequencies between 10kHz and 1GHz. Maximal field amplification of X20 of the applied field (@200 kHz) was observed in a model of confluent cells with 5nm intercellular distance. Such field amplification could create electrostatic pressure on the membrane potentially leading to its deformation and to stress on the cytoskeleton. Analytical calculations show the field gradient could result in DEP forces of ~10pN on the membrane. Such force could potentially disrupt the membrane or junctions. Results show that a 10nm pore in membrane would lead to a 450 times amplification in the pore’s vicinity, potentially resulting in forces of between 0.1pN and 100pN on intracellular structures. Those forces are sufficient for disrupting microtubules. Specific Absorption Rates of up to 106 W/kg were observed in the vicinity of the pore, suggesting that strong thermal effects may also explain the effect of TTFields on cells. Our generic analytical model predicts the conditions for field amplification at TTFields frequencies.

Electroprewetting near a flat charged surface.

We look at the wetting of a pure fluid in contact with a charged flat surface. In the bulk, the fluid is a classical van der Waals fluid containing dissociated ions. The presence of wall and ions leads to strong dielectrophoretic and electrophoretic forces that increase the fluid's density at the wall. We calculate the fluid's profiles analytically and numerically and obtain the energy integrals. The critical surface potential for prewetting is obtained. In the phase diagrams, the line of first-order transition meets a second-order transition line at a critical point whose temperature can be higher or lower than the bulk critical temperature. The results are relevant to droplet nucleation around charged particles in the atmosphere and could possibly explain deviations from expected nucleation rates.

Concentration-Polarization Electroosmosis near Insulating Constrictions within Microfluidic Channels.

Electric fields are commonly used to trap and separate micro- and nanoparticles near channel constrictions in microfluidic devices. The trapping mechanism is attributed to the electrical forces arising from the nonhomogeneous electric field caused by the constrictions, and the phenomenon is known as insulator-based-dielectrophoresis (iDEP). In this paper, we describe stationary electroosmotic flows of electrolytes around insulating constrictions induced by low frequency AC electric fields (below 10 kHz). Experimental characterization of the flows is described for two different channel heights (50 and 10 μm), together with numerical simulations based on an electrokinetic model that considers the modification of the local ionic concentration due to surface conductance on charged insulating walls. We term this phenomenon concentration–polarization electroosmosis (CPEO). The observed flow characteristics are in qualitative agreement with the predictions of this model. However, for shallow channels (10 μm), trapping of the particles on both sides of the constrictions is also observed. This particle and fluid behavior could play a major role in iDEP and could be easily misinterpreted as a dielectrophoretic force.

Modeling Brownian Microparticle Trajectories in Lab-on-a-Chip Devices with Time Varying Dielectrophoretic or Optical Forces.

Lab-on-a-chip (LOC) devices capable of manipulating micro/nano-sized samples have spurred advances in biotechnology and chemistry. Designing and analyzing new and more advanced LOCs require accurate modeling and simulation of sample/particle dynamics inside such devices. In this work, we present a generalized computational physics model to simulate particle/sample trajectories under the influence of dielectrophoretic or optical forces inside LOC devices. The model takes into account time varying applied forces, Brownian motion, fluid flow, collision mechanics, and hindered diffusion caused by hydrodynamic interactions. We develop a numerical solver incorporating the aforementioned physics and use it to simulate two example cases: first, an optical trapping experiment, and second, a dielectrophoretic cell sorter device. In both cases, the numerical results are found to be consistent with experimental observations, thus proving the generality of the model. The numerical solver can simulate time evolution of the positions and velocities of an arbitrarily large number of particles simultaneously. This allows us to characterize and optimize a wide range of LOCs. The developed numerical solver is made freely available through a GitHub repository so that researchers can use it to develop and simulate new designs.

An improved numerical method for lunar dust transport during electric curtain-traveling wave removal in the lunar environment

The law of dust removal by electric curtain in the lunar environment is considerably different from that in Earth's environment. This paper proposes an improved calculation method, which successfully simulates the kinematics of lunar dust transport during removal by electric curtain-traveling waves in the lunar environment. The numerical formula of the dielectrophoretic force component is derived based on a six-node triangular (T6) finite element method (FEM) in electromagnetics. A discrete element method (DEM) based on the Johnson–Kendall–Roberts soft-sphere model is chosen to simulate lunar dust particle transport under the action of the electric curtain dust removal system in the lunar environment. The validity, accuracy, and reliability of the present DEM algorithm are verified by comparing the experimental and numerical results. The final dust removal rate is positively correlated with frequency when the surface energy between the particles and insulating film is γf≥0.0075 J/m2. The final dust removal rate is negatively related to the surface energy between the particles and the film but positively related to the applied voltage and the charge of the particles. This research is of great significance to the mitigation of the lunar dust pollution problem that the crewed lunar exploration project will face in the future.