Radio-frequency Dielectric Heating Research Articles

Modeling and Operation of Series-Parallel Resonant Load in Industrial RF Dielectric Heating Application

Radio Frequency (RF) based heating application is used in multiple industries like drying cross-laminated woods, food and packaging, melting silicon etc. These industrial RF heating plants operate at frequencies of 6.78 MHz, 13.56 MHz, or 27.12 MHz (ISM band). Historically, the high frequency requirement has forced the industry to rely on vacuum tube based RF generator, which are only 60% efficient. Modern semiconductors like wide bandgap (WBG) devices have achieved the high frequency operation that is required to replace the inefficient vacuum tubes. However, a comprehensive study of load network for an industrial RF heating plant has not been undertaken such that an existing plant can be retrofitted with semiconductor based turn-key solution. In this paper the authors present design equations for an industrial RF dielectric heating load structure and suggest necessary modifications required to replace vacuum tube RF generator with voltage source converter (VSC). A new figure of merit (FOM) is defined that impacts the load structure efficiency. Finally, a small-scale prototype load is manufactured as a case study. The prototype demonstrated an output power of 750 W at 6.76 MHz with an overall efficiency of 90% from DC input to RF load which can not be achieved with a vacuum tube technology.

A 3D LTCC-Based Ceramic Microfluidic System with RF Dielectric Heating of Liquids.

The design, fabrication and functional evaluation of the radio-frequency dielectric heating of liquids in an LTCC-based ceramic microfluidic system are described and discussed. The device, which relies on the dielectric heating of liquids, was fabricated using a low temperature co-fired ceramic (LTCC) technology. A multilayered ceramic structure with integrated electrodes, buried channels and cavities in micro and millimetre scales was fabricated. The structure with the dimensions of 35 mm × 22 mm × 2.4 mm includes a buried cavity with a diameter of 17.3 mm and a volume of 0.3 mL. The top and bottom faces of the cavity consist of silver/palladium electrodes protected with 100 μm thick layers of LTCC. The power, used to heat a polar liquid (water) in the cavity with the volume of 0.3 mL, ranges from 5 to 40 W. This novel application of RF dielectric heating could enable the miniaturization of microfluidic systems in many applications. The working principle of such a device and its efficiency are demonstrated using water as the heated medium.

Application of a dry heat treatment to enhance the functionality of low-heat nonfat dry milk

Nonfat dry milk is a valuable food and ingredient because it contains proteins, fat, carbohydrates, minerals, and vitamins. When manufactured, this product is classified into high heat (HH) or low heat (LH) depending on the pre-heat treatment used in pasteurization. Radio frequency dielectric heating, if used alone or as part of a dry heat technology, may induce component interactions in milk powders, which could alter or improve functionality. To pursue this objective, LH was subjected to radio frequency dielectric heating to 80, 85, and 90°C with a subsequent hold period of 60 or 90 min in an oven, set at the designated temperature, 80, 85, or 90°C, assessed for functionality in liquid and gel systems, cooled, and subsequently compared with LH and HH. The functionality assessment included heat stability and foaming, emulsion, and gelling properties. For foaming, LH presented a statistically lower overrun and foam stability compared with all dry-heated LH. The LH dry-heated at ≥85°C exhibited significantly greater foaming capacity than did the LH. Emulsification properties were not significantly different as a function of dry heating compared with LH. As gels, water-holding capacity was greater and syneresis was significantly less for all gels made with the dry-heated LH at <85°C. Gel firmness and cohesiveness were not affected by dry heating. The heat coagulation time at native pH was significantly greater for LH that were dry-heated for 90 min compared with LH. At adjusted pH (6.4 to 7.2), the heat stability was improved if the LH was dry-heated. The dry-heated LH had significantly less foaming properties, but greater emulsion activity compared with the HH. Overall, the dry heat treatment conditions of this study did not result in acid-induced gels with equivalent properties as gels made with HH. Syneresis was similar for all gels except for those made from the dry-heated LH to 90°C and held for 60 min, as this gel had significantly more syneresis than did the gels made from HH. However, the heat stability of dry-heated LH at native, 6.8, 7.0, and 7.2 pH was greater compared with the heat stability of HH. The application of a dry heat treatment enhanced the functional properties of LH, opening the opportunity to develop food products that can use this modified nonfat dry milk such as ice cream, bakery, and meat products.

Eradication of Glioblastoma Multiforme stem-cells with Immunotargeted-molecular-robotic-NANOSURGERY (ITMRN)

GBM stem cells are resistant to conventional treatment forming recurrent-tumors via angiogenesis.Thus,they are considered primary targets for novel therapeutic strategies for GBM. We obtain relapsed chemo-radioresistant GBM stem cells overexpressing CD133 from which we develop a GBM model that we treat with immunotargeted pegylated silver nanobots(PEG-AgNPs) which are covalently conjugated to anti-CD133 MAbs for targeting Brain-Cancer-Stem-Cells(BCSCs) after receptor-mediated-endocytosis.Then,we treat them with radiofrequency-dielectric-heating(RFDH) as a novel postsurgical-adjuvant-treatment. Post-treatment,the silver nanobots AgNPs release Ag+ ions which disrupt mitochondrial-respiratory-chain(MRC) blocking ATP-synthesis by production of ROS which damage the DNA of CSCs leading to cell-cycle arrest at G2/M phase and type-1 PCD of stage-D2 or apoptosis.The capacitive nonionizing radiofrequency-dielectric-heating of 13.56MHz exerts hyperthermic cytotoxicity increasing the intracellular-Temperature of BCSCs up to 50 degrees Celcius leading to the necrosis of Brain-Cancer-Stem-Cells(BCSCs). This immunotargeted molecular robotic nanosurgical approach may be used as an adjuvant treatment against GBM which is resistant to conventional chemo/radiation therapy by eradicating its cancer-stem-cells.

Effect of Reduction Agent on ZnO Reduction by Radio-frequency Dielectric Heating

Effect of Reduction Agent on ZnO Reduction by Radio-frequency Dielectric Heating

Investigation of the Effect of Dielectric Properties of the Biscuit on RF Power Uniformity using a Finite Element Computer Model

Background: Biscuit baking process is a major energy consuming and quality deciding process. In conventional biscuit baking process which rely on conduction, convection, radiation mode of heat transfer a condition called checking arises. Checking arises due to the build-up of stresses in the product being heated. The cause for the stresses is the differential moisture content between the outer surface and the centre bone of the biscuit and causes cracking of biscuit. Radio Frequency (RF) Post Baking is a proven solution to this problem. But the wide scale industrial use of RF post baking of biscuits is limited by energy efficiency and cost of the RF heating system. Energy efficiency can be improved by having better RF power uniformity/heating uniformity in the sample (biscuit) being RF heated. The uniformity of radio frequency power distribution defined by a metric called Power Uniformity Index (PUI) is used to evaluate the efficiency of the radio frequency heating. Methods: A finite element computer model of the RF heating system for post baking biscuits with staggered electrode configuration was developed using comsol multiphysics software. The dielectric properties of biscuit were varied from a scale of 0 till 80 and its effect on the RF power distribution and hence the heating uniformity in radio frequency post baking of was observed. Findings: The simulation results obtained indicate that the dielectric properties of the sample (biscuit) do have significant effect on RF power distribution and hence the heating uniformity when the values of dielectric constant and loss factor are lower than 10. Application: The results obtained give an insight into the effect of dielectric properties of biscuit on the RF power distribution in RF dielectric heating of biscuits.

TR-17 * IMMUNOTARGETED-MOLECULAR-ROBOTIC-NANOSURGERY (ITMRN) ERADICATES GBM STEM-CELLS WITH RADIOFREQUENCY DIELECTRIC HEATING (RFDH) MEDIATED VIA SILVER-IMMUNONANOBOTS LINKED WITH anti-CD133 MAbs

INTRODUCTION: GBM stem cells are resistant to conventional treatment forming recurrent-tumors via angiogenesis. Thus, they are considered primary targets for novel therapeutic strategies for GBM. METHODS: We obtain relapsed chemo-radioresistant GBM stem cells overexpressing CD133 from which we develop a GBM model that we treat with immunotargeted pegylated silver nanobots(PEG-AgNPs) which are covalently conjugated to anti-CD133 MAbs for targeting Brain-Cancer-Stem-Cells (BCSCs) after receptor-mediated-endocytosis. Then, we treat them with radiofrequency-dielectric-heating (RFDH) as a novel postsurgical-adjuvant-treatment. RESULTS: Post-treatment, the silver nanobots AgNPs release Ag+ ions which disrupt mitochondrial-respiratory-chain(MRC) blocking ATP-synthesis by production of ROS which damage the DNA of CSCs leading to cell-cycle arrest at G2/M phase and type-1 PCD of stage-D2 or apoptosis. The capacitive nonionizing radiofrequency-dielectric-heating of 13.56MHz exerts hyperthermic cytotoxicity increasing the intracellular-Temperature of BCSCs up to 50 degrees Celcius leading to the necrosis of Brain-Cancer-Stem-Cells(BCSCs). CONCLUSION: This immunotargeted molecular robotic nanosurgical approach may be used as an adjuvant treatment against GBM which is resistant to conventional chemo/radiation therapy by eradicating its cancer-stem-cells.

Validation of radio-frequency dielectric heating system for destruction of Cronobacter sakazakii and Salmonella species in nonfat dry milk

Cronobacter sakazakii and Salmonella species have been associated with human illnesses from consumption of contaminated nonfat dry milk (NDM), a key ingredient in powdered infant formula and many other foods. Cronobacter sakazakii and Salmonella spp. can survive the spray-drying process if milk is contaminated after pasteurization, and the dried product can be contaminated from environmental sources. Compared with conventional heating, radio-frequency dielectric heating (RFDH) is a faster and more uniform process for heating low-moisture foods. The objective of this study was to design an RFDH process to achieve target destruction (log reductions) of C. sakazakii and Salmonella spp. The thermal destruction (decimal reduction time; D-value) of C. sakazakii and Salmonella spp. in NDM (high-heat, HH; and low-heat, LH) was determined at 75, 80, 85, or 90°C using a thermal-death-time (TDT) disk method, and the z-values (the temperature increase required to obtain a decimal reduction of the D-value) were calculated. Time and temperature requirements to achieve specific destruction of the pathogens were calculated from the thermal destruction parameters, and the efficacy of the RFDH process was validated by heating NDM using RFDH to achieve the target temperatures and holding the product in a convection oven for the required period. Linear regression was used to determine the D-values and z-values. The D-values of C. sakazakii in HH- and LH-NDM were 24.86 and 23.0min at 75°C, 13.75 and 7.52min at 80°C, 8.0 and 6.03min at 85°C, and 5.57 and 5.37min at 90°C, respectively. The D-values of Salmonella spp. in HH- and LH-NDM were 23.02 and 24.94min at 75°C, 10.45 and 12.54min at 80°C, 8.63 and 8.68min at 85°C, and 5.82 and 4.55min at 90°C, respectively. The predicted and observed destruction of C. sakazakii and Salmonella spp. were in agreement, indicating that the behavior of the organisms was similar regardless of the heating system (conventional vs. RFDH). Radio-frequency dielectric heating can be used as a faster and more uniform heating method for NDM to achieve target temperatures for a postprocess lethality treatment of NDM before packaging.

高周波誘電加熱による急速解凍装置

高周波誘電加熱による急速解凍装置

A unique electrical thermal stimulation system comparable to moxibustion of subcutaneous tissue.

Moxibustion strengthens immunity and it is an effective treatment modality, but, depending on the material quantity, shape, and composition, the thermal strength and intensity can be difficult to control, which may cause pain or epidermal burns. To overcome these limitations, a heat stimulating system which is able to control the thermal intensity was developed. The temperature distributions on epidermis, at 5 mm and 10 mm of depth, in rabbit femoral tissue were compared between moxibustion and the electric thermal stimulation system. The stimulation system consists of a high radio frequency dielectric heating equipment (2 MHz frequency, maximum power 200 W), isolation probe, isolation plate, negative pressure generator, and a temperature assessment system. The temperature was modulated by controlling the stimulation pulse duty ratio, repetition number, and output. There were 95% and 91% temperature distribution correlations between moxibustion and the thermal stimulus at 5 mm and 10 mm of depth in tissue, respectively. Moreover, the epidermal temperature in thermal stimulation was lower than that in moxibustion. These results showed that heat loss by the electric thermal stimulation system is less than that by the traditional moxibustion method. Furthermore, the proposed electric thermal stimulation did not cause adverse effects, such as suppuration or blisters, and also provided subcutaneous stimulation comparable to moxibustion.

Short communication: Radio frequency dielectric heating of nonfat dry milk affects solubility and whey protein nitrogen index

The US infant formula market is estimated at over $3.5 billion, of which 75% are dairy-based formulas. Dried dairy powders pose a significant food safety risk, with Cronobacter sakazakii and Salmonella spp. being pathogens of particular concern. Radio frequency dielectric heating (RFDH) can provide rapid, uniform heat treatment of dry powders; thus, it potentially may be used as a postprocess lethality treatment for nonfat dry milk (NDM) or powdered infant formula. Because RFDH is a heat treatment, the functionality of the NDM may be altered and should be evaluated. High heat- and low heat-NDM were RFDH processed at temperatures ranging from 75 to 90°C for 5 to 125min. Products were then assessed for whey protein nitrogen index (WPNI), solubility, and color. In low heat-NDM, RFDH decreased WPNI and solubility if the process was done at ≥80°C; however, in high heat-NDM, RFDH had a greater effect on solubility than WPNI and some color properties were altered. Further investigation of RFDH is merited to validate its application as a pathogen control process for NDM across processing parameters that result in acceptable functional properties for infant formula and other food products containing NDM.

Silicon wafer bonding through RF dielectric heating

This paper presents a new silicon wafer bonding process based on radio-frequency (RF) heating of an intermediate dielectric layer. The method uses a capacitive RF field to heat a dielectric interlayer up to its glass transition temperature and permanently join two wafers. A 500 W 14 MHz source was used to deliver RF power to the substrates. A 5 cm diameter 300 μm thick silicon wafers with 2–20 μm thick polyimide intermediate layers were successfully bonded (>95% bond area) in less than 7 min. The results of the pull tests indicate a bond strength of >1.5 MPa for cured polymers, which is greater than the strength of other low-temperature adhesive bonds, e.g. bonds with a photoresist layer used as an adhesive. Steady-state heat transfer equations were solved to estimate the dielectric junction temperature ( T 0 ∼300 °C comparable to the glass transition temperature of polyimide).

THERMAL PROPERTIES OF RADISH AND ALFALFA SEEDS

ABSTRACTThermal conductivity, specific heat, and density were measured in a temperature range of 30C to 80C, and moisture content of 4.6% to 6.5% for radish seeds, 5.0% to 7.3% for alfalfa seeds typically encountered in the radio frequency dielectric heating for seeds. Thermal conductivity and specific heat were determined using a linear heat source probe and a modified calorimeter method, respectively. Thermal conductivity of radish and alfalfa seeds ranged from 0.050 to 0.091 W/mC (SD: 0.011) and 0.075 to 0.120 W/mC (SD: 0.012), respectively. Specific heat was in the range of 0.290 to 0.479 kJ/kgC (SD: 0.051) for radish seeds and 0.333 to 0.593 kJ/kgC (SD: 0.076) for alfalfa seeds. Density of radish and alfalfa seeds ranged from 684 to 675 kg/m3 (SD: 5.592) and 819 to 804 kg/m3 (SD: 8.921), respectively. Thermal diffusivity of the seeds was also determined, and the values varied from 25.13 × 10−8 to 34.47 × 10−8 m2/s for radish seeds and 27.14 × 10−8 to 29.73 × 10−8 m2/s for alfalfa seeds. Regression models were fitted to the experimental data for each thermal property, and showed second order polynomial relationships with temperature and moisture content.

Enhancement of electron temperature in a laser-induced plasma using a radio-frequency electric field

An experimental study of the enhancement of the electron temperature of a laser-induced plasma by use of radio-frequency dielectric heating has been carried out. A radio-frequency electric field of 140 MHz is used to heat the plasma produced by multistep resonant photoinization. It is clearly observed that the electron temperature increases from 0.3 to 1.0 eV when a radio-frequency input power of 1.0 W is applied. Also, applying heating induces a plasma oscillation. This is due to the generation of ion waves in the plasma, and therefore, means that the enhanced electron temperature is higher than the ion temperature. It is expected that this method will improve the efficiency for extracting ions rapidly from a laser-induced plasma in atomic vapor laser isotope separation.

Application of the 50 Ω Radio Frequency Technology in the Automotive Industry: Fast Bonding of Composite Materials: Rear Doors of the Citroen Zx and Citroen Xantia Cars

AbstractIn the field of plastic and composite materials the radio frequency dielectric heating is more and more used. Compared to traditional techniques such as conduction and convection heating, the radio frequency technology is interesting, because it allows fast heating of thick materials and heat insulation materials.As bonding techniques are more and more integrated in production lines, the polymerization of glues must be realized in a very short time. The 50 use of the Ω radio frequency technology makes this heating process possible.The authors describe the industrial application of this technology to the CITROEN ZX and CITROEN XANTIA cars. Steps involved in implementing this industrial process (laboratory - pilot -industrial equipment) are presented and analysis the technical and economic results of this application.

Bonding adhesive joints with radio-frequency dielectric heating

Abstract The feasibility of using radio-frequency (RF) dielectric heating to cure thermoset adhesives has been evaluated. Thermoset and thermoplastic polymer panels have been bonded to steel using conventional one-and two-part epoxy and two-part urethane adhesives. Process cycle times for adhesive cure using RF heating were about 20 to 60 seconds, compared with about 20 to 30 minutes for the same materials using conventional oven-cure methods. Thermoset substrates bonded included glass fibre-reinforced composite panels based on sheet moulding compound (SMC) and resin transfer moulding styrene-vinylester (RTM). Thermoplastics such as polycarbonate, polyarylate, Noryl, ABS and polymethylmethacrylate were also successfully bonded. RF bonding experiments were performed by preparing and testing lap-shear joints as well as by joining a large test structure with a 25 mm x 1.25 m bondline. Bonding of painted steel to SMC composite, SMC to SMC and steel to RTM composite were also accomplished using the RF dielectric heating process.

AN INTEGRAL MODEL FOR DRYING OF HYGROSCOPIC AND NONHYGROSCOPIC MATERIALS WITH DIELECTRIC HEATING

ABSTRACT Heat and mass transport phenomena in drying assisted by microwave or radio-frequency dielectric heating are analyzed. When drying at temperatures near boiling point or with high temperature gradients, the effect of the gas phase pressure gradient on moisture transfer within the solid can be important. The governing heat and mass transfer equations, including consideration of internal heat generation and the effect of the gas phase pressure gradient, are derived and solved in a one-dimensional system using an integral method. The integral model has been used to simulate dielectrically-enhanced convective drying of beds of polymer pellets, glass beads and alumina spheres with flow over the bed surface. Model predictions of drying rates and temperatures agree well with experimental data for these cases. The model provides a relatively fast and efficient way to simulate drying behavior with dielectric heating, and may be useful in design and optimization of dielectrically-enhanced convective drying p...

Use of Microwave and Lower Frequency RF Energy for Improving Alfalfa Seed Germination

ABSTRACTThe use of radiofrequency (RF) electric energy for increasing the germination of alfalfa (lucerne) seed through exposures that lower the percentage of hard seeds (seed coats impermeable to water) is discussed. The influence of various biological and physical factors is considered, and results of experimental findings are reviewed briefly. RF treatments of alfalfa seed at frequencies of 5, 10, 39, and 2,450 MHz effectively reduced hard-seed percentages and provided increases in normal seedling germination when proper exposures were used. Treatments were generally more effective at lower seed moisture contents. Optimum germination response to RF dielectric heating depends mainly upon elevation of seed temperature to proper levels (about 75° C for alfalfa seed of 6% to 7% moisture). Some aspects of practical application of RF methods to seed treatment are discussed.

Laboratory drying of herbage by radio-frequency dielectric heating

Losses of dry matter from herbage during hot-air drying have been reported,(1) and seem to be due to continued respiration of the herbage during the early stages of drying. These losses are reduced by more rapid drying. Preliminary tests showed that herbage can be rapidly dried by radio-frequency heating on the laboratory scale. The paper describes modifications made to a commercial radio-frequency oven to make it suitable for drying material of high moisture content. The oven will dry 300 g of herbage from 80% to 10-25% moisture content in 15 min. Comparative tests showed the radio-frequency oven to give an average dry matter yield ½% higher than that obtained by drying herbage in an efficient hot-air oven.

The Use of Radio Frequencies to Obtain High-Power Concentrations for Industrial-Heating Applications

By the use of radio-frequency power it is possible to obtain controlled power concentrations which far exceed those obtainable by other means. For example, in the induction heating of steel or other metals, the application of 100 kilowatts to a square inch of area on the work is not difficult. At a frequency of 1 megacycle, 99 per cent of the resulting heat generation is confined to a layer approximately 1/16 inch thick. If very high power concentrations are used for short heating times, the resulting high temperatures may be localized in the regions of heat generation. This technique results in more uniform case-hardening, less distortion, and high heating efficiency, as well as high production rates. The effect of frequency upon power concentration is discussed. It is shown that the optimum frequency varies with the size and shape of the work to be heated. Induction-heating technique is contrasted, and compared, with radio-frequency dielectric heating. In the latter class of work, the heat generation is equally distributed throughout the body of the work. With the use of radio-frequency dielectric heating, power concentrations in the order of 1 kilowatt per cubic inch can be obtained in thick wood sections, as for gluing operations. This is to be contrasted with the application of heat by heated press platens where power concentrations of only about 0.05 watt per cubic inch can be attained. Again, the optimum frequency is determined by the size and shape of the work.