Dielectric Loss Heating Research Articles

Analysis of Temperature Field in the Dielectrophoresis-Based Microfluidic Cell Separation Device

Cell separation techniques based on dielectrophoresis are of high interest as an effective method of performing cell separation non-invasively on cells. However, dielectrophoresis devices have the problem that cells in the device are exposed to a high-temperature environment due to the generation of Joule heat caused by high-voltage application and dielectric-loss heat when the applied voltage is AC voltage. There is concern that the heat generated in the device may affect cell viability, cell cycle and apoptosis induction. In this study, the temperature field inside the dielectrophoretic cell separation device was experimentally and numerically investigated. The temperature rise at the bottom of the flow channel in the device was measured using the LIF method, and the thermofluidal behavior of the device was numerically simulated by adopting a heat generation model that takes the Joule and dielectric-loss heating into account in the energy equation. The temperature rise in the device was evaluated and the effect of the heat generation on cells in the device is discussed.

Electrochemical attack and corrosion of platinum electrodes in dielectrophoretic diagnostic devices.

Though the advances in microelectronic device fabrication have realized new capabilities in integrated analytical and diagnostic platforms, there are still notable limitations in point-of-care sample preparation. AC electrokinetic devices, especially those leveraging dielectrophoresis (DEP), have shown potential to solve these limitations and allow for sample-to-answer in a single point-of-care device. However, when working directly with whole blood or other high conductance (~ 1S/m) biological fluids, the aggressive electrochemical conditions created by the electrode can fundamentally limit the device operation. In this study, platinum wire-based electrode devices spanning circular polytetrafluorethylene (PTFE) wells and a planar microarray device with sputtered platinum electrodes were tested in plasma and PBS buffers of differing concentration across a wide range of frequencies and electric field intensities (AC voltages) to determine their respective safe regions of operation and to gain an understanding about the failure mechanisms of this class of device. At frequencies of 10kHz and below, the upper bound of operation is the degradation of electrodes due to electrochemical attack by chlorine overcoming the native platinum oxide passivation. At higher frequencies, 100kHz and above, the dielectric loss and subsequent heating of the buffer will boil before the electrodes suffer observable damage, due to the slow irreversible reaction kinetics. Effective dielectrophoretic capture of small biological particles at these frequencies is limited, and heat/oxidative denaturation of target material are a major concern. A new class of smaller devices, ones capable of high throughput at voltages low enough to maintain the integrity of the platinum passivation layer, is needed to mitigate these fundamental limitations.

Device‐level thermodynamic model for an electrocaloric cooler

An electrocaloric (EC) cooling device model is proposed to study the influence of material properties, operating conditions, and device design on the coefficient of performance (COP). Because the EC temperature change cannot be predicted by ferroelectric material models, a Gaussian-fit model is proposed that achieves accurate predictions for a range of materials. The COP is calculated by considering the heat transfer and work in a thermodynamic cycle that is integrated with the material model. The device model is based on the experiments of Ma et al (Science. 2017;357:1130) and includes contact and convective thermal resistances, the work to apply the electric fields, and dielectric loss heating. A copolymer and a terpolymer are analyzed. The predicted heat flux is in good agreement with the experimental data while the predicted COP is lower. This difference is attributed to an over-prediction of the work because experimental hysteresis loop data are not available. Parametric analysis reveals that: (a) the terpolymer performance is stable over a wide range of operating temperatures, while good performance of the copolymer is limited to near its Curie temperature, and (b) small contact thermal resistances allow for high-frequency operation and a large heat flux.

Localized Dielectric Loss Heating in Dielectrophoresis Devices

Temperature increases during dielectrophoresis (DEP) can affect the response of biological entities, and ignoring the effect can result in misleading analysis. The heating mechanism of a DEP device is typically considered to be the result of Joule heating and is overlooked without an appropriate analysis. Our experiment and analysis indicate that the heating mechanism is due to the dielectric loss (Debye relaxation). A temperature increase between interdigitated electrodes (IDEs) has been measured with an integrated micro temperature sensor between IDEs to be as high as 70 °C at 1.5 MHz with a 30 Vpp applied voltage to our ultra-low thermal mass DEP device. Analytical and numerical analysis of the power dissipation due to the dielectric loss are in good agreement with the experiment data.

Influence of Externally Imposed and Internally Generated Electrical Fields on Grain Growth, Diffusional Creep, Sintering and Related Phenomena in Ceramics

Microwaves and spark plasma sintering (SPS) enhance sinterability. Simple electrical fields, applied by means of a pair of electrodes to bare specimens, have been shown to accelerate the rate of superplastic deformation, reduce the time and temperature for sintering, and to retard the rate of grain growth. By inference, the influence of electrical and electromagnetic fields on grain boundary energetics and kinetics is unmistakable. Often, in ceramics, grain boundaries are themselves endowed with space charge that can couple with externally applied fields. The frequency dependence of this coupling ranging from zero frequency to microwave frequencies is discussed. The classical approach for modeling grain growth, creep, and sintering, considers chemical diffusion (self‐diffusion) under a thermodynamic driving force, underpinned by a physical mechanism that visualizes the flow of mass transport in a way that reproduces the phenomenological observations. In all instances, the final analytical result can be separated into a product of three functions: one of the grain size, the second related to the thermodynamic driving force, and the third to the kinetics of mass transport. The influence of an electrical field on each of these functions is addressed.The fundamental mechanisms of these electrical interactions are discussed in the following ways: (i) dielectric loss and Joule heating in the crystal and at the grain boundary, (ii) the coupling between mechanical stress and the electrochemical potential of charged species, (iii) the interaction between applied electrical fields and the intrinsic fields that exist within the space charge layers, (iv) and the possibility of nucleating defect avalanches under electrical fields. We limit ourselves to ceramics that have at least some degree of ionic character. In these experiments the electrical fields range from several volts to several hundred volts per centimeter, and the power dissipation from Joule heating is of the order of several watts per cubic centimeter of the specimen. Metals, where very high current densities are obtained at relatively low applied electric fields, leading to phenomenon such as electromigration, are not considered.

Influence of Humidity and of the Electric and Magnetic Microwave Radiation Fields on the Remediation of TCE-contaminated Natural Sandy Soils

The influence of moisture content (15% w/w) on the remediation (vaporization) of trichloroethylene (TCE) present in natural sands, chosen as a TCE-polluted model system for soils, was investigated with regard to applied microwave power levels, the depth of the sand sample, and the dielectric factors. The heating process occurring in the sand samples arises through the microwave conduction loss heating and dielectric loss heating mechanisms. The characteristic relevance of the electric and magnetic microwave radiation fields to the heating mechanisms was also examined. Heating by the magnetic microwave radiation field was considerable when magnetite was added to the dry and wet sand samples as the microwave absorber. Optimal microwave conditions are reported for a single-mode microwave applicator. Near-quantitative elimination of the TCE contaminant was achieved for sandy soils within a very short time.

Engineering design of an RF vacuum window for the ITER ICRH antenna

The RF vacuum window design proposed for ITER is similar to the one in operation on JET. It uses titanium alloys for the outer and inner conductors and double conical ceramic insulators. However, unlike the JET window, beryllia is the dielectric material. The design is complicated considerably by the need for continuous RF operation, which necessitates active cooling. Residual stress after manufacture has been optimised with particular attention given to subcritical crack growth in the ceramic. In addition, finite element methods were used to model the steady state temperature gradient from the combined effects of volumetric heating of neutron irradiation, RF surface heating and dielectric loss heating. A scoping study is included in the modelling methodology of bonded joints and on the hydraulic requirements of the window cooling system.

Microwaves thermal conditioning of preforms

Free blowing of PET preform has been performed successfully and quickly in a rotating system which has been designed for dielectric loss heating. Investigations of the thermomechanical behaviour of PET and biaxial-stretch blow moulding have shown that an inverted temperature profile is needed prior to its stretching. A temperature profile modelling was carried out using the permittivity at different temperatures of the amorphous PET. It was necessary to solve the Maxwell's and heat equations to determine the best profile and power tuning. Transient external surface wall predicted temperature was found to agree well with IR result. This work needs further investigation for a complete heating of the preform and better energy efficiency. Industrial application involves the integration of the moulding step and the design of the overall process. So far it has been found that the microwave assisted process is at least five times faster than IR heating.

Rapid Synthesis of a Pt1Ru1/Carbon Nanocomposite Using Microwave Irradiation: A DMFC Anode Catalyst of High Relative Performance

Thermal treatment of (η-C2H4)(Cl)Pt(μ-Cl)2Ru(Cl)(η3:η3-2,7-dimethyloctadienediyl) (1)/Vulcan carbon composites under appropriate oxidizing and reducing conditions using microwave dielectric loss heating affords PtRu/Vulcan carbon nanocomposites consisting of PtRu alloy nanoparticles highly dispersed on a powdered carbon support. Two such nanocomposites containing 16 or 50 wt % total metal and alloy nanoclusters of 3.4- or 5.4-nm average diameter are formed within only 100 or 300 s of total microwave heating. XRD and on-particle EDS analyses reveal that complex 1 serves as a reliable single-source molecular precursor for the formation of PtRu nanoparticles having a nearly 1:1 metal alloy stoichiometry. Preliminary measurements of the catalytic activity of these nanocomposites as supported direct methanol fuel cell (DMFC) anode catalysts indicate that the 50 wt % nanocomposite has a performance superior to that of a 60 wt % commercial catalyst and a normalized performance equivalent to that of a proprietary unsupported Pt1Ru1 catalyst.

Improved microwave oven synthesis of amides and imides promoted by imidazole; convenient transport agent preparation

Microwave dielectric loss heating without solvent or support yields amides and imides from aromatic and sterically hindered acids in the presence of imidazole in good to excellent yields under mild irradiation conditions.

Microwave induced time-resolved infrared radiometry for subsurface defect detection and characterization

The use of microwaves as a heating source in time-resolved infrared radiometry provides the ability to heat surface and subsurface microwave-absorbing regions of a specimen directly. This can improve the contrast and spatial resolution of such regions and enhance their detectability when compared with conventional laser or flash lamp sources. Applications such as subsurface water detection or the detection of carbon fiber contaminates in epoxy composites are investigated experimentally and analytically. Due to recent technical developments in the speed, detector array size, and sensitivity of infrared cameras, time resolved infrared radiometry has become an important NDE tool which allows fast area inspection at high spatial resolution. While much prior work has focused on the detection of structural defects or disbonds in a variety of materials, the increasing importance of composite materials requires new approaches to inspection which allow characterization of local material properties. Defects in such materials may have little thermal contrast compared to the matrix material and may be invisible using conventional TRIR methods. However, where the embedding material is a weak microwave absorber, localized microwave absorbing regions can be detected easily. There are three different classes of absorption processes: (1) dielectric loss (e.g. water), (2) magnetic loss, and (3) Joule heating (e.g. electromagnetic radiation interaction with conducting fibers). Examples of Processes 1 and 3 are presented in this paper. All experiments use an HP 6890B Oscillator (5-10 GHz) to produce microwaves at a frequency of 9 GHz. This signal is amplified to a maximum power of 2.3 W by a Hughes 1277 X-band traveling wave tube amplifier and fed into a single flare horn antenna through rectangular wave guide. The antenna has a beam width of about 50 deg. and is placed about 15 cm from the sample. Both the angle of incidence and the polarization of the microwave field relative to the sample are controlled. A 128x128 InSb focal plane array (Santa Barbara Focalplane) operating in the 3-5 pm band is used for detection of the IR radiation. The camera has a temperature resolution of about 3 mK and a frame rate as fast as 305 Hz or 3.3 ms per frame. The frame synchronization pulse of the infrared camera triggers the microwave oscillator and the sample temperature is monitored as a function of time during the microwave pulse. This allows longer observation times with low power input and hence small temperature rises, as in time resolved infrared radiometry with optical heating [1,2]. The fist example focuses on dielectric heating of regions of subsurface water. Water-based defects include blisters in fiberglass or composite structures, or under coatings and paints as a source of corrosion. One example which is shown in Fig. la is a disbonded epoxy coating on a steel pipe. Infrared radiometry with optical heating is not very successful with these kinds of defects since the thermal effusivity of water is well matched to the steel and hence shows little thermal contrast in a surface temperature image. In the microwave regime, water has a broad strong absorption band associated with a maximum in the dielectric relaxation near 18 GHz and there is strong absorption at 9 GHz. Fig. lb shows an infrared image of the epoxy-coated steel pipe heated with a 15 s microwave pulse when the disbond is filled with water. The image outlines the disbonded region with no heating of bonded regions showing high contrast at the water defect as compared to optical (surface) heating where the whole sample would be heated. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:19947132 C7-564 JOURNAL DE PHYSIQUE IV Figure la (left): Disbonded epoxy coating on a steel pipe. Figure lb (right): Infrared image of the water filled disbond after a 15 s microwave pulse. The time-dependence of the surface temperature can provide information about the subsurface region. A second sample shown in the insert in Fig. 2 is made from Plexiglass with voids filled with water placed at different depths below the surface using Teflon spacers. The time dependence of the relative surface temperature of points is plotted in Fig. 2 for each thickness . For a 3-layer system with thermal diffusivities a i , thermal conductivities q and layer thicknesses d and L and with an absorption coefficient p in the second layer, the surface temperature vs. time during and after a microwave pulse of duration to (one-dimensional heating) is: with G(h,x,t) = H o h ~ e + h a a o l e r f c { ~ ~ ] d ~ . (2)

Application of microwave dielectric loss heating effects for the rapid and convenient synthesis of ruthenium(II) polypyridine complexes

The complexes [Ru(LL)3](PF6)2 [LL=2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) and 4,4′-di-terbutyl-2,2′-bipyridine (bipy*)] and [Ru(terpy)2] (PF6)2 (terpy=2,2′,2″-terpyridine) have been rapidly and conveniently synthesised using microwave dielectric loss heating effects. The compounds were prepared in good yields (60–94%) in a Teflon autoclave, which can sustain temperatures up to 250°C and pressures of 80 atm, using MeOH as a solvent. Two 20s exposures to microwaves (2450 MHz and 650 W) were sufficient to achieve these yields.

Design and application of a reflux modification for the synthesis of organometallic compounds using microwave dielectric loss heating effects

A commercially available microwave oven has been modified so that syntheses involving the refluxing of organic solvents can be safely and conveniently undertaken. The applications of this technique for accelerating the rates of reactions leading to the synthesis of some commonly used organometallic and coordination compounds are described.

Application of microwave dielectric loss heating effects for the rapid and convenient synthesis of coordination compounds

A wide range of coordination compounds of substitutionally-inert transition metal ions have been rapidly and conveniently synthesized using microwave dielectric loss heating effects. The compounds were synthesized in good yields in a Teflon autoclave, which can sustain temperatures up to 250°C and pressures up to 80 atm. With microwave techniques, reactions requiring 24 h take place in approximately 1 min.

ChemInform Abstract: Application of Microwave Dielectric Loss Heating Effects for the Rapid and Convenient Synthesis of Organometallic Compounds.

ChemInform Abstract: Application of Microwave Dielectric Loss Heating Effects for the Rapid and Convenient Synthesis of Organometallic Compounds.

Application of microwave dielectric loss heating effects for the rapid and convenient synthesis of organometallic compounds

Diolefin-rhodium(I) and -iridium(I) complexes have been synthesised in a sealed Teflon container by use of microwave heating. The products are obtained in excellent yields and in less than 1 minute compared with many hours by conventional reflux techniques. Furthermore, the sandwich cation [Rh(η-C 5H 5) 2] + can be obtained directly from RhCl 3·χH 2O and C 5H 6 by this new technique.

Application of microwave dielectric loss heating effects for the rapid and convenient synthesis of intercalation compounds

Intercalation compounds of α-VO(PO4)·2H2O with pyridine, 4-methylpyridine, and 4-phenylpyridine have been synthesised two orders of magnitude more quickly using microwave dielectric loss heating effects than with conventional thermal methods; the samples retain a high degree of crystallinity and are therefore readily characterised by powder X-ray crystallographic techniques.

Light Beam Deflection in Polymer Films by Dielectric Loss Heating

Light beam deflection caused by local refractive index change in polymer optical waveguide films was investigated experimentally and theoretically. The local refractive index change was induced by dielectric loss heating with an RF electric voltage applied to the electrodes deposited on the optical waveguide films. The incident light was deflected by the induced refractive index gradient in the film plane. The deflection angle depends on the guide thickness and the film thermal conductivity. The angle was approximately 5 degrees for a 190 µm thick polymethylmethacrylate film. Deflection speed was 150–200 msec. An application to a new 1×3 switch was also proposed and demonstrated.

EPRI ߞManufacturers 500/550 kv cable research project cable C ߞSummary of field test performance at Waltz mill

General performance of the 550 kV prototype cable system during long-term accelerated field tests at Waltz Mill is summarized, based primarily on the record of periodic power factor measurements of system components through a range of overload temperatures. Hazards to system stability imposed by extreme overload service are discussed in relation to thermo-mechanical strains and dielectric loss heating effects. Stable field performance is substantiated by results of Laboratory examination and tests of returned cable and accessories.

Some possibilities of heating by centimetric power

A study of the basic principles, range of applications, and methods of utilization of dielectric loss heating by electro-magnetic energy at radio-frequencies above 500 Mc/s.New problems arise because linear dimensions of the system and load are now large compared with the operating wavelength. In particular, the mode of formation of stationary wave patterns in the load, methods of preventing consequent non-uniform heating, and methods of avoiding or automatically correcting mismatch due to reflected waves reaching the generator are dealt with in detail.Methods of localizing the dissipation of high frequency power in the load are analysed and three basic systems—resonator, beam and transmission line—are distinguished, and are illustrated by application to the performance of suitable heating operations.