Search

The FDTD (Finite Difference Time Domain) method has proven to be effective in modeling high-frequency electromagnetic problems in telecommunications industry. Recently it has been successfully applied in microwave power engineering. In order to accurately model scenarios typical in this field one has to deal with the movement of objects placed inside cavities. This paper describes a simple algorithm that makes it possible to take into account object rotation -- important in simulations of domestic microwave ovens. Results of example simulations are presented and an experimental verification of the simulation tool is performed. [ABSTRACT FROM AUTHOR]

Microwaves have become an essential part of the modern kitchen, but their potential as a reservoir for bacterial colonization and the microbial composition within them remain largely unexplored. In this study, we investigated the bacterial communities in microwave ovens and compared the microbial composition of domestic microwaves, microwaves used in shared large spaces, and laboratory microwaves, using next-generation sequencing and culturing techniques. The microwave oven bacterial population was dominated by Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes, similar to the bacterial composition of human skin. Comparison with other environments revealed that the bacterial composition of domestic microwaves was similar to that of kitchen surfaces, whereas laboratory microwaves had a higher abundance of taxa known for their ability to withstand microwave radiation, high temperatures and desiccation. These results suggest that different selective pressures, such as human contact, nutrient availability and radiation levels, may explain the differences observed between domestic and laboratory microwaves. Overall, this study provides valuable insights into microwave ovens bacterial communities and their potential biotechnological applications.

Microwaves have become an essential part of the modern kitchen, but their potential as a reservoir for bacterial colonization and the microbial composition within them remain largely unexplored. In this study, we investigated the bacterial communities in microwave ovens and compared the microbial composition of domestic microwaves, microwaves used in shared large spaces, and laboratory microwaves, using next-generation sequencing and culturing techniques. The microwave oven bacterial population was dominated by Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes, similar to the bacterial composition of human skin. Comparison with other environments revealed that the bacterial composition of domestic microwaves was similar to that of kitchen surfaces, whereas laboratory microwaves had a higher abundance of taxa known for their ability to withstand microwave radiation, high temperatures and desiccation. These results suggest that different selective pressures, such as human contact, nutrient availability and radiation levels, may explain the differences observed between domestic and laboratory microwaves. Overall, this study provides valuable insights into microwave ovens bacterial communities and their potential biotechnological applications. [ABSTRACT FROM AUTHOR]

This paper describes a method and device for effectively cooling a high voltage transformer inside a microwave oven, with the aim of swiftly removing heat generated during operation, hence improving both the microwave oven's and the transformer's performance and quality. The device incorporates corrugated tank surfaces, electrical connection-lines with protrusions, and epoxy to prevent cooling oil leakage. The transformer is inserted into a designated tank and sealed to separate the coil and core from the outside environment, allowing for better cooling and protection against electrical shock. Additionally, an oil is injected to absorb heat generated by the high temperature of the core and coil. The effectiveness of this method is validated through the finite element method and CFD techniques. Numerical analysis revealed a significant decrease in the maximum temperature rise of the transformer by around 44.2 °C. This finding suggests that transformer oil cooling is a more effective method for controlling temperature rise in microwave ovens compared to traditional cooling methods. [ABSTRACT FROM AUTHOR]

Domestic microwave ovens offer rapid cooking but face challenges such as non-uniform temperature distribution and hot spots. A novel solid-state heating system, which precisely controls microwave frequency and power, provides a promising alternative to traditional microwave ovens utilizing magnetron systems. This study compared the effects of solid-state microwave cooking on the quality of broccoli, red peppers, and carrots with those of traditional microwave and conventional cooking. The traditional microwave cooking used in this study operated at 2450 MHz, while the solid-state system functioned between 902 and 928 MHz. Weight loss was highest for conventional cooking, reaching a maximum of 34%, whereas microwave cooking resulted in a maximum of 11.65% and solid-state microwave cooking in 17.04%. The total phenolic content obtained through conventional cooking ranged between 61.58 and 116.51 mg GAE (gallic acid equivalents)/100 g dry basis, while microwave cooking resulted in a range of 88.04–110.92 mg, and solid-state microwave cooking achieved values between 76.14 and 122.91 mg. Furthermore, reductions in chlorophyll content were observed to be 68.2%, 25.6%, and 35.7% for conventional, microwave, and solid-state microwave cooking, respectively. Lycopene content after conventional cooking decreased to 224.73 mg/100 g dry basis, compared to 289.55 mg after microwave cooking and 242.94 mg after solid-state microwave cooking. β-carotene content showed a decrease of 14.5% in conventional cooking, while both microwave methods showed an increase of 14.7%. These results suggest that solid-state microwave cooking may have promising positive effects on food quality. [ABSTRACT FROM AUTHOR]

The oil amounts of raw and roasted mustard seeds were reported between 12.05 (control) and 16.30% (oven). Total phenolic and flavonoid amounts of untreated (control) and roasted mustard seeds were recorded to be between 473.90 (control) and 569.96 mgGAE/100 g (oven) to 345.48 (control) and 479.76 mg/100 g (microwave), respectively. Antioxidant capacity results of untreated and roasted mustard seeds were determined to be between 6.71 (oven) and 6.97 mmol/kg (control). Total phenolic and flavonoid amounts of oven-roasted seeds were higher than those of control and microwave-roasted seeds. L* values of mustard seeds varied between 35.04 and 65.52. Heat treatment caused a decrease in L* values. The lowest L* value was observed in the sample dried in conventional oven. The quantitative values of gallic and 3,4-dihydroxybenzoic acids of mustard seeds were recorded to be between 8.47 (control) and 117.31 mg/100 g (microwave) to 2.16 (control) and 11.79 mg/100 g (microwave), respectively. Erucic acid values of the oils extracted from raw and roasted mustard seeds were reported between 41.38 (control) and 42.81% (microwave). Oleic and linoleic acid amounts of mustard oils differed between 26.06 (microwave) and 26.90% (control) and between 13.08 (oven) and 13.98% (control), respectively. The oven roasting system had the most effect on the element and protein contents of the seeds, followed by the microwave in decreasing order. As with the bioactive components of the seeds, the amounts of phenolic constituents of roasted mustard seeds increased significantly compared to the control. [ABSTRACT FROM AUTHOR]

This paper proposes a probe to monitor the electromagnetic field inside the microwave oven. Although magnetrons are now small and efficient, and solid-state ovens can control the power delivered to the food, neither can “see” the electromagnetic field inside the microwave oven. Therefore, the proposed field detector probe, which is a rectenna (antenna and rectifier), converts the RF (2.45 GHz) signal, inside the cavity, to a dc voltage. The antenna is a simple planar monopole, which is not matched due to the high power levels inside the oven. Two types of rectifiers are proposed, the first one is based on diodes (SMP1302 or SMP1304) and the second one is based on an LDMOS power transistor—BLC2425M8LS300P, provided by Ampleon. By comparing the output dc voltage of the probe when connected to a signal generator (in the laboratory) with the voltage generated by the field detector probe (inside the microwave oven), the electromagnetic field can be mapped. Doing this allows microwave oven manufacturers to optimize and adjust the cooking appliance based on the electromagnetic field, which induces food heating. [ABSTRACT FROM AUTHOR]

Metallic stirrers are commonly used in mode-stirred reverberation chambers but are less common in microwave ovens, because the use of a metallic axis creates a coaxial port in the cavity wall where the axis is introduced, which may result in significant microwave leakage levels. However, due to electromagnetic, mechanical, temperature, or chemical requirements, metallic axes must be used in some cases. In this paper, we present a high power coaxial filter that enables the use of metallic stirrers in microwave applications. The filter employs two-port coaxial cavities that are analyzed to determine their design parameters. These cavities are coupled via coaxial lines to achieve proper attenuation levels. The cavities were designed using commercial electromagnetic (EM) software, and a filter prototype was validated using vector network analyzer (VNA) measurements. The simulated and measured results show that a three-stage configuration can achieve attenuations greater than 70 dB at the 2.45 GHz ISM band, allowing the use and external handling of the metallic axis inserted into microwave ovens with negligible microwave radiation leakage. [ABSTRACT FROM AUTHOR]

Microwave applications, such as microwave ovens and mobile phones, are ubiquitous and indispensable in modern society. As the utilization of microwave technology is becoming more widespread, the effects of microwaves on living organisms and physiological processes have received increased attention. This study aimed to investigate the effects of microwaves on calcium carbonate biomineralization as a model biochemical process. A magnetron oscillator was used to generate 2450 MHz microwaves because magnetrons are relatively inexpensive and widespread. We conducted transmission electron microscopy (TEM), atomic force microscopy (AFM), TEM-electron energy-loss spectroscopy (EELS), dynamic light scattering (DLS), and high-performance liquid chromatography (HPLC) measurements to analyze the calcium carbonate precipitates. Our findings showed the formation of string-like precipitates of calcium carbonate upon microwave irradiation from one direction, similar to those obtained using a semiconductor oscillator, as reported previously. This implied that the distribution of the frequency had little effect on the morphology. Furthermore, spherical precipitates were obtained upon microwave irradiation from two directions, indicating that the morphology could be controlled by varying the direction of microwave irradiation. Magnetrons are versatile and also used in large-scale production; thus, this method has potential in medical and industrial applications. [ABSTRACT FROM AUTHOR]