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Foundations of electromagnetism
Published in Riadh Habash, BioElectroMagnetics, 2020
Amplitude modulation (AM) broadcasting, for example, has a frequency of 1 MHz and a wavelength of about 300 m. Meanwhile, microwave ovens use a frequency of 2.45 GHz and a wavelength of only 12 cm. It is important to note that only the EM waves of certain wavelength within 0.4 µm and 0.76 µm are directly perceptible as light waves.
Toward New Reactor and Reaction Engineering
Published in Salmi Tapio, Mikkola Jyri-Pekka, Wärnå Johan, Chemical Reaction Engineering and Reactor Technology, 2019
Salmi Tapio, Mikkola Jyri-Pekka, Wärnå Johan
Microwaves have recently received attention as an alternative energy source for chemical processes. Microwave irradiation is a form of electromagnetic energy. Microwaves consist of an electric component as well as a magnetic one. The microwave region of the electromagnetic spectrum is situated between infrared radiation and radio frequencies. Microwave irradiation ranges from 30 GHz to 300 MHz, corresponding to wavelengths of 1 cm to 1 m. Microwave heaters use specific, fixed frequencies 2.45 GHz (wavelength 12.2 cm) or 0.9 GHz (wavelength 33.3 cm), in an effort to avoid interferences with RADAR (wavelength from 1 to 25 cm) and telecommunication applications. All domestic microwave ovens operate at the frequency of 2.45 GHz. In comparison with conventio nal heating, energy transfer does not primarily occur by convention and conduction but by dielectric loss in the case of microwave heating [21, 24].
Electromagnetic Emanations from Power Sources and Fixed Specialized Equipment
Published in William J. Rea, EMF Effects from Power Sources and Electrosmog, 2018
Today, microwave ovens are standard upscale devices in kitchens around the world. Microwave ovens basically work by subjecting water or other polarized materials in food to heat generated by electromagnetic waves of about 2.4 megahertz (MHz), moving water molecules around and cooking things from the inside out. One hertz is 1 cycle per second, about the rate of the resting human heart of a well-conditioned adult. A megahertz is a million cycles per second, faster than anyone could count and the speed at which the brains of computers (microprocessors) usually work. Gigahertz is 109 hertz cycles per second. Modern phones work as fast as computers, sending out between 800 million and 2.4 billion cycles per second, quite close to the power needed to cook an egg.
Novel drying techniques for controlling microbial contamination in fresh food: A review
Published in Drying Technology, 2023
Dayuan Wang, Min Zhang, Ronghua Ju, Arun S. Mujumdar, Dongxing Yu
Microwave is a widely used electromagnetic wave used for heating purposes in the food sector, involving applications including cooking, sterilization, and drying. The frequencies used in microwave ovens are 2450 MHz for domestic microwaves and 915 MHz and 2450 MHz for industrial microwaves, with a greater penetration depth of 915 MHz.[65,66] The principle of microwave heating is that the dipole molecules in the food absorb microwave energy and convert it into heat.[67] The heating characteristics depend on the dielectric properties of the food, which are determined by the temperature, moisture content and composition of the food.[68] Microwave-based dielectric heating whose heat is generated volumetrically has a higher heating efficiency than conventional drying systems, which will retain more original qualities of foods.[69–71] Although its volumetric heating is more uniform than many conventional heating methods, uneven temperature distribution is one of the main problems associated with microwave heating.
Microwave drying of fabrics
Published in Journal of Microwave Power and Electromagnetic Energy, 2019
Wenjie Fu, Jiewen Deng, Xiaoyun Li
Microwave energy, which uses electromagnetic power with frequencies between 300 MHz and 300 GHz, can be used successfully to heat dielectric materials. The main advantages of using microwaves for heating are rapid heat transfer, volumetric and selective heating, compactness of equipment, speed of switching on and off, and minimal environmental impacts, as there are no combustion products (Osepchuk 1984; Santos et al. 2003). Thus, microwave heating is usually applied at the most widely used frequencies, i.e. 2.45 GHz and 915 MHz, which allows for industrial, scientific, and medical applications (Rejasse et al. 2007; Walters et al. 2014; Adarsh and Devaraju, 2017; Patel and Mehta 2017; Raaholt et al. 2017; Poogungploy et al. 2018). For domestic applications, a well-known application is the microwave oven, which operates at 2.45 GHz.
The next-generation consumer microwave oven: a review
Published in Journal of Microwave Power and Electromagnetic Energy, 2022
The oscillating field inside a microwave oven heats the food by inducing dipole and ion movement in the target substrate. The dielectric properties of the substrate define how that material reacts to microwaves (Wäppling Raaholt 2020). The feedback antenna and the oven control adjust the output frequency in the RF oven in real time to provide the most efficient absorption for the target substrates. To take advantage of this feedback loop, the Solid-State RF system works better if the consumer can tell the oven what type of food (e.g. protein, starch, or vegetable) is placed inside the chamber, and control algorithms select the best input frequency based on the food's dielectric properties (RF Energy Alliance 2014; Drucker 2020).