Showing papers on "Liquid dielectric published in 2019"

Concentration Measurement of Microliter-Volume Water–Glucose Solutions Using $Q$ Factor of Microwave Sensors

Abstract: A glucose concentration sensor for microliter-volume water–glucose solutions is presented. The proposed sensor is composed of an open-loop microstrip resonator with a dielectric liquid holder (5–25- $\mu \text{L}$ volume) glued onto the gap between the line ends. The resonator is coupled to two microstrip lines forming a two-port network whose S-parameter response provide information about the dielectric properties of the liquid under study. Three versions of the sensor at resonant frequencies between 2 and 7 GHz are presented. The sensors are assessed by measuring the complex permittivity of standard liquids reported in the scientific literature. Models of the sensors are presented, which properly match the experimental results. This paper presents an experimental study of the sensors as glucose concentration retrievers. The main novelty is the use of $Q$ factor and the maximum S21 of the resonance as sensing magnitudes. The dependence of these parameters on the glucose concentration of the solutions obeys almost linear relationships. Good sensitivities have been obtained for the proposed sensors, which are coherent with previous works by other authors.

A field-plated Ga2O3 MOSFET with near 2-kV breakdown voltage and 520 mΩ · cm2 on-resistance

Abstract: A composite field-plated Ga2O3 MOSFET with highly doped ohmic-capping layer is fabricated. An output current of 20 mA mm−1 and on-resistance of 520 mΩ cm2 shows big improvement upon the previous experiment on similar field plated devices. The breakdown voltage is measured to be 1975 V on an L gd = 25 μm device. At elevated temperatures, the breakdown voltage decreases to <1 kV at 130 °C, while the on-resistance and saturation current are almost unchanged. The breakdown may be limited by the dielectric liquid strength. The on-resistance is limited by high interface state density that is attributed to the thermal process during the field oxide deposition.

Open Complementary Split-Ring Resonator Sensor for Dropping-Based Liquid Dielectric Characterization

Abstract: A microwave sensor with a coplanar waveguide semilumped meander open complementary split-ring resonator (MOCSRR) is proposed to analyze the dielectric properties of liquid. The proposed method operates at subgigahertz frequencies and uses a small volume of liquid (>0.08 mL) on a substrate-integrated slot container. A resonance reflection coefficient notch frequency and its magnitude in decibels are observed for complex permittivity ( $\varepsilon'+j \varepsilon $ ”) characterization. A strong electric field distributed on the edge of the designed MOCSRR slot provides a sensitive compact area to detect small variations in the liquid sample or concentration. Operations need not be constrained to micropipette operations or microfluidic channel fabrication. A specific volume of the sample liquid must be dropped in the detection zone to analyze complex permittivity. To test the proposed methods, binary mixtures of ethanol and water were loaded, and a 58.7 MHz shift in resonant frequency and a variation of 6.77 dB were attributed to a complex permittivity perturbation phenomenon when ethanol concentration was varied from 0% to 100%. Different concentrations of ethanol and liquid were evaluated and analyzed. The proposed sensor exhibited repeatability and easy operation in detecting liquids with high relative permittivity, such as water and lossy liquids.

Flow structure and heat transfer of electro-thermo-convection in a dielectric liquid layer

Abstract: Electrothermohydrodynamic flow of dielectric liquid in a square cavity driven by the simultaneous action of Coulomb and buoyancy forces is studied numerically. A high resolution upwind scheme is applied to study the flow bifurcations and heat transfer. We focus on the strong injection case with the nondimensional injection parameter C fixed at C = 10. Two Prandtl numbers Pr = 1 and Pr = 10, two Rayleigh numbers Ra = 105 and Ra = 106, as well as two mobility numbers M = 10 and M = 20 are considered to evaluate the dependence of flow structure and heat transfer on these parameters. Multistates are found to coexist in a wide range of parameter regimes. Various flow patterns such as one-cell, two-cell, four-cell, and multicell flow are observed. The electric field is found to enhance heat transfer more efficiently for large Prandtl number fluid at low mobility parameter and relatively low Rayleigh number.

Passive Wireless UHF RFID Antenna Label for Sensing Dielectric Properties of Aqueous and Organic Liquids

Abstract: The in situ wireless sensing of dielectric properties for organic aqueous solutions with a wide range of relative permittivities is presented. The use of an ultra-high frequency passive label antenna design attached to either clear borosilicate glass bottle or Petri plate is proposed, which allows for the unobtrusive, safe monitoring of the liquid solutions. The meandered dipole antenna (with a parasitic loop matching component) frequency is highly reliant on the chosen container as well as on the liquid present within, and adjusts with shifting dielectric properties. Tested solutions of high-relative permittivity (such as water) along with low permittivity, lossy liquids (such as xylene) presented distinctive frequency characteristics with read distances of up to 7 m for each type of container tested. The sensor was also able to detect ‘unknown’ solutions and determine the dielectric properties by utilizing standard curve analysis with an accuracy of ±0.834 relative permittivity and $\pm 0.050\,\,\text {S}\cdot \text {m}^{-{1}}$ conductivity (compared to a standard dielectric measurement system available on the market). With the accuracy known, tuning the design to fit any necessary frequency is possible as a means to detect specific changes in any one liquid system. This sensor is a possible candidate for discreet real-time monitoring of liquid storage containers and an alternative for low-cost bulk liquid dielectric property identification, which could be implemented in areas requiring, constant, or remote monitoring as needed.

Significantly Enhanced Electrical Performances of Eco-Friendly Dielectric Liquids for Harsh Conditions with Fullerene.

Abstract: The eco-friendly vegetable liquid is increasingly used because of the growing demand for environmentally friendly dielectric liquid. A vegetable liquid/fullerene nanofluid was fabricated via ultrasonic processing with good dispersion of the fullerene nanoparticles. It was observed that a small amount of fullerene (~100 mg/L) can significantly improve the electrical properties of vegetable insulating liquid (dissipation factor decreased by 20.1%, volume resistivity increased by 23.3%, and Alternating Current (AC) dielectric breakdown strength increased by 8.6%). Meanwhile, the trace amount of fullerene is also able to improve the electrical performances (i.e., dissipation factor and electrical resistivity) of the vegetable nanofluid under harsh conditions of long-term thermal aging compared with the blank contrast. The reduced acid values (25%) and dissolved decomposition gases (58.2% for hydrogen) in the aged vegetable nanofluid indicate the inhibition of molecule decomposition of vegetable liquid with fullerene. The improved electrical performances and thermal resistance of the vegetable nanofluid contribute to the electron affinity of fullerene proved by calculation of electron density distribution on the surface. The thermogravimetric analysis of the nanofluid under different atmospheres interprets that the oxygen absorbed inevitably in the fullerene contributes to the performance deterioration of the nanofluids during the initial aging. This work provides a potential method towards eco-friendly dielectric liquid with great electrical performances for harsh environments.

Compact Ultra-Wideband Monopole Antennas Using Novel Liquid Loading Materials

Abstract: An ionic liquid (IL) is used to make antennas for the first time. Unlike water, the proposed material has a large liquid range (-69.8 °C-350 °C), a relative permittivity of 3, an extremely low dielectric loss, and very stable thermophysical material properties. It can be used for liquid dielectric resonator antennas (DRAs) or as a loading material for performance enhancement. Importantly, the proposed liquid loading scheme is relatively simple and of low cost, but it can markedly improve the antenna performance. As design examples, a liquid-loaded wideband linearly polarized (LP) monopole antenna with an omnidirectional radiation pattern is first presented. Then, the LP antenna is modified to a wideband circularly polarized (CP) antenna with boresight radiation. These antenna examples demonstrate a frequency coverage of 1.25-5 GHz, a wide CP bandwidth, a relatively high gain (>4 dBi), high radiation efficiency >85%, and an electrical size of 0.42 λ 0 x0.42λ 0 x0.17λ 0 . The experimental results show that the liquid loading works well under a wide range of temperatures. It effectively reduces the antenna electrical size by 40% and improves the impedance matching by 5 dB. Therefore, the proposed liquid loading scheme can be applied to a variety of antenna/RF designs.

Package-in-Dielectric Liquid Patch Antenna Based on Liquid Metal Alloy

Abstract: A fully dielectric packaged liquid patch antenna based on liquid metal alloy is presented. In this letter, there are two hollow cavities embedded in a dielectric box, including a rectangular cavity placed at the upper portion acting as the radiating element, and a nonplanar cavity with a central groove under the radiating element serving as the ground plane. The antenna is realized by a three-dimensional printing technique, alleviating assembly tolerance, and uncertainties from a printed-circuit-board approach, which would degrade an antenna performance. The radiating element and the ground plane are fully metallized by filling liquid metal alloy. Unlike traditional liquid antennas, the liquid packaging antenna is completely metallized by conductive liquids, which does not contain any solid metals. The proposed antenna is designed to operate at 5.2 GHz. Results show that the proposed liquid patch antenna produces a satisfactory impedance matching, and a good agreement between simulation and measurement in terms of radiation characteristics is achieved at the desired frequency.

Effect of finite conductivity on the nonlinear behaviour of an electrically charged viscoelastic liquid jet

Abstract: In this paper a one-dimensional numerical study on the nonlinear behaviour of an electrically charged jet of Oldroyd-B viscoelastic, Taylor–Melcher leaky dielectric liquid is carried out. The effect of surface charge level, axial wavenumber and finite conductivity on the nonlinear evolution of the jet is investigated. Different structures including beads-on-a-string with/without satellite droplets, quasi-spikes and spikes are detected, and their domains in the plane of the non-dimensional axial wavenumber and the electrical Bond number are illustrated. The underlying mechanisms in the formation of the structures are examined. It is found that tangential electrostatic force plays a key role in the formation of a quasi-spike structure. Decreasing liquid conductivity may lead to a decrease in the size of satellite droplets or even the complete removal of them from a beads-on-a-string structure, induce the transition from a beads-on-a-string to a quasi-spike structure or postpone the appearance of a spike. On the other hand, finite conductivity has little influence on filament thinning in a beads-on-a-string structure, owing to the fact that the electrostatic forces are of secondary importance compared with the capillary force. The difference between the finite conductivity, large conductivity and other cases is elucidated. An experiment is carried out to observe spike structures.

Numerical Study of Electroconvection in a Dielectric Layer Between Two Cofocal Elliptical Cylinders Subjected to Unipolar Injection

Abstract: The problem of electroconvection in an annular space between two elliptical concentric cylinders filled with a dielectric liquid and subjected to internal unipolar injection is considered. A finite volume method is used to solve the governing equations, including the Navier–Stokes ones and a simplified set of the Maxwell equations. For the first time the whole set of these coupled equations is solved, using the elliptical-cylindrical coordinates. We first validate numerical simulation in this field by comparing the results obtained with those available in the literature. The numerical solution of the electroconvection problem is then followed by a detailed analysis of the flow structure and electric charge distribution. It is shown that the multicellular convective pattern is observed. It is noticed that unipolar charge injection from the internal electrode significantly changes the topology of the fluid flow. Finally, the influence of various system parameters, such as the injection level and electric Rayleigh number, is also investigated.

Stability analysis of electroconvection with a solid-liquid interface via the lattice Boltzmann method

Abstract: Electroconvection in dielectric liquid is extended from single phase to solid-liquid interaction. Stability criteria and bifurcation are numerically predicted by the lattice Boltzmann method. Effects of interface position, permittivity and mobility ratios, and electric conductivity are considered.

Electrohydrodynamics in leaky dielectric fluids using lattice Boltzmann method

Abstract: The application of an electric field on a multi-component leaky dielectric fluid system leads to an electric stress at the fluid–fluid interface. To capture the effect of these electric stresses, we report a new method to couple the electrostatics and hydrodynamics of leaky dielectric fluids within the framework of the lattice Boltzmann method. The developed methodology relies on obtaining time invariant solution to the equation governing the divergence of current density in the flow domain using a time marching lattice Boltzmann equation or through a finite-difference formulation. The coupling between the low spurious velocity hydrodynamics model and the leaky dielectric counterpart is also illustrated through the use of three case studies involving interaction of single or multiple droplets suspended in an outer fluid under the action of an external electric field. The results obtained from the developed methodology are shown to be in excellent agreement with earlier published analytical and numerical results. Further, the numerical experiments demonstrate that the developed methodology is applicable for both steady- and time-dependent flows.

Application of CFD and vapor bubble dynamics for an efficient electro-thermal simulation of EDM: an integrated approach

Abstract: Micro-chip removal and heat dissipation are two important and essential utilities of dielectric medium along with its vital contribution in plasma channel formation, which has a significant influence in metal removal, tool wear, and surface integrity. The vapor bubbles, which are formed after every progressive spark, expand and collapse in the electric field and finally condensed inside the dielectric medium. As the localized heat and excess temperature of the eroded spot increases, the dynamic properties of the bubbles accelerate and develop a lower pressure region, which is responsible for dielectric flushing. In this paper, the integrated approach of vapor bubble dynamics and computational fluid dynamics is used to study the dynamic behavior and heat dissipation of dielectric fluid through the plasma channel. At the very beginning of machining, the excess temperature is comparatively low; so, the detached bubbles are condensed inside the fluid medium and are not able to move above the free surface. However, as the temperature of the machined zone rises, excess temperature also increases and bubbles are able to carry the heat up to the free surface of the dielectric medium and finally condense. This phenomenon is very much analogous to the boiling process. Earlier, many simulation processes are used by researchers to investigate heat flux and heat dissipation rate of the dielectric fluid, but, here, vapor bubble dynamics and periodic heating are introduced to consider heat absorption by vapor bubbles, which gives more accurate heat transfer analysis of electric discharge machining. It is observed that the adopted model has the accuracy level of more than 95% with 4.5–4.6% of average prediction error and 1.5–2% more efficient than the existing models.

Wettability Manipulation by Interface-Localized Liquid Dielectrophoresis: Fundamentals and Applications.

Abstract: Electric field-based smart wetting manipulation is one of the extensively used techniques in modern surface science and engineering, especially in microfluidics and optofluidics applications. Liquid dielectrophoresis (LDEP) is a technique involving the manipulation of dielectric liquid motion via the polarization effect using a non-homogeneous electric field. The LDEP technique was mainly dedicated to the actuation of dielectric and aqueous liquids in microfluidics systems. Recently, a new concept called dielectrowetting was demonstrated by which the wettability of a dielectric liquid droplet can be reversibly manipulated via a highly localized LDEP force at the three-phase contact line of the droplet. Although dielectrowetting is principally very different from electrowetting on dielectrics (EWOD), it has the capability to spread a dielectric droplet into a thin liquid film with the application of sufficiently high voltage, overcoming the contact-angle saturation encountered in EWOD. The strength of dielectrowetting depends on the ratio of the penetration depth of the electric field inside the dielectric liquid and the difference between the dielectric constants of the liquid and its ambient medium. Since the introduction of the dielectrowetting technique, significant progress in the field encompassing various real-life applications was demonstrated in recent decades. In this paper, we review and discuss the governing forces and basic principles of LDEP, the mechanism of interface localization of LDEP for dielectrowetting, related phenomenon, and their recent applications, with an outlook on the future research.

Bio-Inspired Soft Proboscis Actuator Driven by Dielectric Elastomer Fluid Transducers

Abstract: In recent years, dielectric elastomer actuators (DEAs) have attracted lots of attention for providing multiple degree-of-freedom motions, such as axial extensions, torsion, bending, and their combinations. The wide applications include soft robots, artificial muscles, and biomimetic animals. In general, DEAs are composed of stretchable elastomers sandwiched by two compliant electrodes and actuated by applying external electric stimuli. Since most DEAs are limited by the breakdown thresholds and low strain-to-volume ratios, dielectric fluid transducers (DFTs) have been developed by substituting dielectric elastomers with dielectric fluids for high breakdown threshold voltages. In addition, DFTs have large rate of lateral extensions, due to their fluid contents, and are beneficial for soft actuators and pumping applications. In this research, we exploited DFTs to develop a soft spiral proboscis actuator inspired by the proboscises of butterflies for achieving uncoiling and coiling motions under external voltages. The bio-inspired spiral proboscis actuator (BSPA) was composed of a coil-shaped tube, a DFT-based pouch, and a spiral spring for mimicking the tubular part, a mechanism to uncoil the tube, and a mechanism to coil the tube, respectively. When applying external voltages to the pouch, the high dielectric fluid was injected into the empty coiled tube for uncoiling where the tube elongated from a compact volume to a stiff and flexible shape. When removing the exciting voltages, the tube retracted to its original coiled shape via the elastic spring. A prototype was designed, fabricated, and examined with high stimulating voltages. It was demonstrated that the proboscis actuator could achieve uncoiling and coiling motions consistently for several cycles. Compared to convection DEA-based pumps with fixed shapes, the proposed actuator is soft and beneficial for portable applications and coiling/uncoiling motions.

Dielectrophoretic interaction of two particles in a uniform electric field

Abstract: The local electric field distorsion induced by a dielectric particle leads to particle–particle interactions and assembly which is very interesting for their useful applications on microfluidic devices. Particles behavior becomes more complicated if several particles interact at the same time. This paper presents a comprehensive numerical analysis of the assembly and particle–particle interactions for two similar and dissimilar dielectric particles immersed in a dielectric fluid using the immersed interface method based on two-dimensional direct-current dielectrophoresis. The immersed interface method is a finite-difference (or finite element) based numerical method which its key advantage is implementing internal electrostatic boundary conditions over particles surfaces using a uniform mesh. This helps to better study the effect of electromagnetic fields on particles. When a single particle exposed to a uniform electric field, electric stresses are induced over its surface symmetrically. So the particle experiences no resultant DEP force. But if two particles are close enough to each other in an electric field, the electric stress distribution over each particle surface is not symmetric anymore. So there will be a resultant DEP interaction force between particles which makes them attract or repulse each other, depending on dielectric properties of buffer fluid and particles and their orientation with respect to electric field lines, as well. The effect of a nearby particle on electric stress distribution over the other particle is investigated in the present study to better explain the physics of particles DEP interaction. Also it is shown that by decreasing the distance between particles, the electric field gradient on particles becomes more intense. Numerical results show that in a dielectric medium, regardless of their initial position and orientation, two similar and dissimilar particles tend to form a parallel and perpendicular chain with respect to the applied electric field lines, respectively. Interaction and assembly of multiple particle chains in experiment observation can be explained by this numerical study.

Standardized methods for the determination of breakdown voltages of liquid dielectrics

Abstract: IEC 60156 and IEC 60897 were standardized with the purpose of evaluating the breakdown voltage of liquid dielectrics both under AC and impulse voltages. AC breakdown voltage determination is a simple method but only able to provide information on the presence of contaminants. The limit of this test is the large scatter in the results and, for this reason, this IEC standard has been recently revised. Impulse breakdown voltage determination allows discrimination of different dielectric liquids, also in terms of their chemical composition. This test has only limited application because of the dimensions of the high voltage generator. The present paper shows a comparison among breakdown voltages of various mineral oils and natural esters under both AC and impulse voltages. The paper presents also an effort to describe how these two tests may reveal the electrical performance of the dielectric liquid under test.

Electromagnetic heating control via high-frequencyresonance of a triple-layer laminate

Abstract: Beamed energy transport requires the use of heat exchangers to collect the thermal energy produced from the absorption of electromagnetic radiation. To explore the high-frequency effects of wave–geometry interactions on this heat transfer, we consider a central dielectric layer, possessing a temperature-dependent loss factor, surrounded by two fluid channels filled with a lossless dielectric fluid. Considering an asymptotically thin domain, we derive a diffusion–reaction equation, assuming no flow in the fluid. We show that the high-frequency effects generate a new energy balance leading to a previously unknown steady-state solution. A characterization of the steady-state-dependent parameters is performed in an effort to determine a mechanism to control the nonlinear heating. Diffusive effects are shown to produce regions of the power response where steady-state solutions are replaced by traveling-wave solutions. These regions are also location to the greatest heating efficiency. Analytical approximations to the wave speed and location of these regions are found using boundary layer theory.

Capillary-gravity waves on a dielectric fluid of finite depth under normal electric field

Abstract: In this work we consider two-dimensional capillary–gravity waves propagating under the influence of a vertical electric field on a dielectric of finite depth bounded above by a perfectly conducting and hydrodynamically passive fluid. Both linear and weakly nonlinear theories are developed, and long-wave model equations are derived based on the analyticity of the Dirichlet–Neumann operator. Fully nonlinear computations are carried out by using a time-dependent conformal mapping method. Solitary waves are found, and their stability characteristics subject to longitudinal perturbations are studied numerically. The shedding of stable solitary waves is achieved by moving a Gaussian pressure on the free surface with the speed close to a phase speed minimum and removing the pressure after a period of time. The novel result shows that a depression bright solitary wave and an elevation generalized solitary wave co-exist in the solitary-wave excitation.

Dielectrophoretic buoyancy and heat transfer in a dielectric liquid contained in a cylindrical annular cavity

Abstract: The effect of a thermoelectric body force on the flow of a dielectric fluid with a radial temperature gradient and an alternating electric voltage in a cylindrical annular cavity has been studied by a direct numerical simulation. The radial temperature gradient induces a vertical ascending flow near the hot surface and descending flow near the cold surface. A radial dielectrophoretic force with the electric field acting induces a thermoelectric convection in the form of columnar vortices that can transfer heat from the hot surface to the cold one. The heat transfer coefficient in the dielectric fluid significantly increases with the applied electric voltage.The effect of a thermoelectric body force on the flow of a dielectric fluid with a radial temperature gradient and an alternating electric voltage in a cylindrical annular cavity has been studied by a direct numerical simulation. The radial temperature gradient induces a vertical ascending flow near the hot surface and descending flow near the cold surface. A radial dielectrophoretic force with the electric field acting induces a thermoelectric convection in the form of columnar vortices that can transfer heat from the hot surface to the cold one. The heat transfer coefficient in the dielectric fluid significantly increases with the applied electric voltage.