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Peptide Synthesis and Characterization Stages
Published in Mesut Karahan, Synthetic Peptide Vaccine Models, 2021
In the 1940s microwave irradiation was first used in radars during World War II, and in subsequent years was used in ovens for heating. Dr Percy Lebaron Spencer found microwaves’ heating capacity by chance during laboratory tests. He noticed that the candy in his pocket warmed up as a result of exposure to microwave energy. After that invention, home-type microwave ovens were developed. Later, microwave devices for research purposes were constructed. The main reasons for the slow development of microwave technology were the lack of understanding of the principles of dielectric heating, safety, and influence on health. One of the important properties of microwaves is the fact that they do not contain enough energy to chemically change substances through ionization; thus, being an example of non-ionizing radiation (Tang 2015).
Radiofrequency Fields
Published in Bertil R. R. Persson, Freddy Ståhlberg, Health and Safety of Clinical NMR Examinations, 2019
Bertil R. R. Persson, Freddy Ståhlberg
This analysis clearly emphasizes the difference between “inductive” and “dielectric” heating. The rise in temperature caused by an Rf pulse of a given power: Is inversely proportional to the duration of that pulseIncreases as the square of the frequency under conditions corresponding to the inductive or to the dielectric limitIncreases more rapidly than the frequency squared for conditions between these limits
Electromagnetic Field Exposure Assessment in Workers and the General Public: Measurement Techniques and Experimental Dosimetry
Published in Gaetano Licitra, Giovanni d'Amore, Mauro Magnoni, Physical Agents in the Environment and Workplace, 2018
Radiofrequency dielectric heating (also known as capacitive or radio frequency heating) is a process used in industry to heat non-metallic objects. Dielectric heating is used for drying materials such as ceramics, leather, tobacco and paper and for gluing and drying wood. The same process is used for plastic sealing, where RF heating is used in the plastics manufacturing and processing industry. These devices generally operate within the frequency range of 10 to 100 MHz with output power between 0.2 and 1000 kW. Typical operating frequencies are 13.56 MHz, 27.12 MHz and 40.68 MHz. Electric field strengths at the operator's position can typically range from 10 to 1000 V m−1, and magnetic field strengths from 0.1 to 20 A m−1 (Chen et al. 1991, ILO 1998, Wilen et al. 2004) (Table 9.6).
Strong correlation between specific heat capacity and water content in human tissues suggests preferred heat deposition in malignant tumors upon electromagnetic irradiation
Published in International Journal of Hyperthermia, 2022
Mechanisms of dielectric heating of aqueous solutions, biological media and of tissues using VHF and HF are the same as described above for microwaves. Heating results from oscillations of ions interlinked with water dipoles and of free electrons caused by applied RFs [6,48]. Due to inertia of the hydration spheres, the phase difference between the alternating electric field and oscillations increases with frequency. This results in a dielectric loss and in the generation of frictional heat. As depicted in Figure 3, dielectric loss in different tissues and in NaCl solutions (salinity between 0.5% and 0.9% w/v) increases to a similar extent with decreasing frequency [60,64]. In addition, data in Figure 4 show that dielectric loss caused by microwaves and by RFs also increases with (increasing) water content of tissues [61,65].
Heating technology for malignant tumors: a review
Published in International Journal of Hyperthermia, 2020
H. Petra Kok, Erik N. K. Cressman, Wim Ceelen, Christopher L. Brace, Robert Ivkov, Holger Grüll, Gail ter Haar, Peter Wust, Johannes Crezee
Electromagnetic heating techniques apply a high frequency alternating sinusoidal electromagnetic (EM) field generated using one or more antennas. These EM fields cause dielectric heating by molecular dipole rotation/polarization/vibration in the MHz range and ionic conduction in the kHz range. Polar molecules (e.g., water) have an electric dipole moment and therefore these molecules align continuously with the alternating field. Electric forces cause rotating molecules to push, pull, and collide with other molecules, thereby distributing the energy to adjacent molecules and atoms, causing dielectric heating. In conduction, ions in tissue oscillate due to the forces exerted by the electric current. This current faces internal resistance because of the collisions of charged particles with neighboring molecules or atoms, causing dielectric heating. Tissue heating is dominated by ionic conduction in the extracellular fluid for lower frequencies (<1 MHz) with the cell membranes acting as isolators, and by dipole polarization at higher frequencies (>1 MHz). For frequencies >1 MHz the cell membranes become permeable to the E-fields and the microscopic structure of tissues can be neglected [23].
Antiangiogenic evaluation of ZnWO4 nanoparticles synthesised through microwave-assisted hydrothermal method
Published in Journal of Drug Targeting, 2018
Carla Júnia Santos, Daniel Crístian Ferreira Soares, Carolina de Aguiar Ferreira, André Luís Branco de Barros, Armando da Silva Cunha Junior, Francisco Moura Filho
The higher reaction speed of hydrothermal systems coupled to microwave radiation can be explained by two main effects, so-called thermal and non-thermal or specific [23,24] effects. The thermal effect, also called dielectric heating, is the result of the dipolar polarisation from the dipole–dipole interactions of the material and the electromagnetic field, which depends exclusively on the dielectric properties of the material [23,25–29]. The non-thermal effect, on the other hand, is characterised by the ability of the microwave radiation to alter the thermodynamic properties of the reaction system, either by an enthalpic effect as a result of the free energy storage of microwave or vibrational energy of a molecule or functional group or an entropic effect due to the alignment of the molecules caused by the energy of microwave radiation. Altogether, these effects create a new reaction pathway with lower activation energy [30–32]. Besides these increase in reaction speed, MAHS methodology also allows the possibility of obtaining particles in the nanoscale, with high purity and crystallinity [33–36] and was the method of choice for our synthesis step.