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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]

In this study, we investigated the heat dissipation characteristics of gallium nitride (GaN) high-electron mobility transistors (HEMTs) fabricated on a freestanding GaN substrate (GaN-on-GaN HEMTs) by simulation. Although the GaN substrate has a lower thermal conductivity than the conventional silicon carbide (SiC) substrate, it was demonstrated that the GaN-on-GaN HEMT has a thermal resistance comparable to the conventional GaN-on-SiC HEMT in a simulated structure composed of a 100-μm-thick substrate and a 2-μm-thick GaN epitaxial layer. This is because GaN-on-GaN has a higher thermal conductivity of the GaN epitaxial layer and a lower thermal boundary resistance than GaN-on-SiC. Next, the thermal design of a 400-W/eight-channel selective heating microwave oven, which consists of eight pairs of patch antennas and power amplifier (PA) modules, involving a 50-W-class GaN-on-GaN HEMT PA, a driving amplifier, an oscillator, and several circuits, was carried out. The fan and fin specifications and enclosure configuration have been optimized to keep the temperature of the metal base on which the PA modules are mounted below 40 °C during full operation. Excellent agreement between the oven thermal simulation and the prototype thermocouple measurements was confirmed for the temperature difference between the metal base and the ambient. Finally, device dimensions for reliable operation were determined by simulating the channel temperature of the GaN-on-GaN HEMT PA during microwave heating. To keep the maximum channel temperature below 200 °C, the simulated device layout with a unit gate width (Wgu) of 100–300 μm and a gate-to-gate spacing (Lgg) of 30–70 μm was acceptable at a drain efficiency (ηD) of 75%. However, appropriate Wgu and Lgg were found to be required with a ηD of 65%. [ABSTRACT FROM AUTHOR]

A typical microwave oven generates an electromagnetic wave in an ISM band of 2.45 GHz. To prevent this unwanted microwave leakage through its front door, a circular perforated metal sheet is typically used with low shielding effectiveness (< 27 dB) and with poor visibility (< 50%) which is usually difficult to check the progress of cooking. In this paper, we investigate sheet resistance (RS) and optical transparency (OT) for electrical and optical performance of two transparent electrodes (TEs) including metal mesh film (MMF) and indium tin oxide (ITO) and compare those to the currently used perforated copper sheet (PCS) in commercial microwave oven. The measured RS and average OT in visible spectrum of MMF is 0.11 Ω/sq and 68.4%, and its figure of merit (FoM) is 203.8 which is the highest among them. The measured shielding effectiveness of MMF, ITO, and PCS at 2.45 GHz are 31.4, 21.0, and 25.5 dB, respectively. The results indicate that MMF has highest FoM and the best EMC performance among the TEs and PCS, which makes it the most suitable candidate for microwave ovens. [ABSTRACT FROM AUTHOR]

Theoretical and experimental investigations are carried out on the degradation in the performance of DS-SS wireless LAN systems (WLANs) (IEEE802.11b) systems caused by electromagnetic noise radiating from microwave ovens in the 2.4-GHz frequency band. Based on the time-domain oven-noise model, theoretical expressions for short-duration bit-error rates (BERs) and packet-error rate (PERs) are derived. Measurements were done using commercially available microwave ovens and a noise simulator that consisted of a function generator and an RF synthesizer. The PERs measured with actual oven noise were found to correlate well with those derived by simulated noise, and they were in reasonable agreement with the theoretical estimates given by the derived approximate formulae. It is concluded that the noise simulator and the derived approximate expressions were very useful in evaluating the BER and PER of WLAN systems that have incurred interference from microwave ovens. [ABSTRACT FROM AUTHOR]

Particle-in-cell (PIC) simulations of a microwave oven free-running 2.45 GHz “cooker” ten-vane magnetron operating with a “cold” explosive-emission cathode in a uniform axial magnetic field are performed with two computer codes, improved concurrent electromagnetic PIC (ICEPIC), and CST Particle Studio (CST-PS). PIC simulations are done to compare results obtained by these two codes to each other and, in such a way, identify all possible advantages and disadvantages of each code performance as a reliable tool allowing to predict all important characteristics of the magnetron operation. Results of the PIC simulations show that the range of applied voltages within which the magnetron is able to operate in the $\pi $ -mode at an external uniform axial magnetic field 0.19 T is much broader as it is predicted by the CST-PS code, from 4.00 to 4.70 kV, than as it predicted by the ICEPIC code, from 3.90 to 4.10 kV. It is also shown that while the magnetron startup time gradually decreases, as it is predicted by the ICEPIC code, from about 700 ns (3.90 kV) to about 100 ns (4.20 kV) with the applied voltage increase, it initially chaotically varies, as it is predicted by the CST-PS code, between about 1000 ns (4.03 kV) and about 300 ns (4.01 kV) and only then gradually decreases down to 10–20 ns (4.40–4.60 kV) with the applied voltage increase. Additional PIC simulation with MAGIC or VORPAL codes would be interesting to perform as well to compare the obtained with these codes simulation results with results described in this article. [ABSTRACT FROM AUTHOR]

Dramatic shortages of filtering facepiece respirator supplies generally occur following the outbreak of a pandemic such as COVID-19. Here, the decontamination and reuse of respirators are considered. Among decontamination methods, microwave irradiation has great potential because of easy access of microwave ovens. However, can a respirator be heated in a microwave oven for a certain time and then be reused? Herein, we demonstrate that dry microwave irradiation cannot heat infectious aerosols or droplets up to their deactivation temperature. The microwave absorption performance of a single aerosol or droplet was analyzed theoretically. The multiphysics simulation results indicate that a single aerosol or droplet can be barely heated under dry microwave irradiation. Experiments were carried out using a traveling wave system to verify the simulation. Following this, we simulated multiple aerosols and droplets on a respirator material, with the results indicating that the aerosols and droplets were at the same temperature as that of the respirator. Experimental measurements using a microwave oven demonstrated that the temperature increase of an N95 respirator under dry heating is less than 10 °C, which is far less than the temperature required to deactivate the COVID-19 virus. Although dry microwave heating cannot be used to heat the aerosols or droplets, microwave-generated steam has proved effective in deactivating infectious biological organisms. Therefore, to successfully decontaminate a used respirator in a microwave oven, a reservoir with a small amount of water beneath the respirator (or a steam bag to accommodate it) is essential to the decontamination process. [ABSTRACT FROM AUTHOR]

Standard operation of a conventional microwave oven 2.45-GHz “cooker” magnetron with 4.0–4.3 kV of pulsed applied voltages at 0.17–0.19-T magnetic fields results in generation of pulsed microwave power 1.8–2.8 kW, which is recalculated to an average microwave power 0.9–1.9 kW when the “cooker” magnetron operates with 50% duty cycle while driven by a “rectified” ac voltage from the wall-plug. It has been shown in many experimental studies of “cold-start” operation of a standard ten-vane 2.45-GHz “cooker” magnetron that it readily sustains, when properly conditioned, up to ~10-kV dc and up to ~14 kV of peak-to-peak ac applied voltage with just a few microamphere cold (field emission) leakage (anode) current. The latter suggests that a standard 2.45-GHz “cooker” magnetron may successfully operate in the desired, lowest $\pi $ -mode with much more output microwave power at even higher magnetic fields when driven by up to ~10 kV of dc or quasi-dc appropriate, synchronous applied voltage. Results of improved concurrent electromagnetic particle-in-cell (ICEPIC) simulations of magnetron operation at different magnetic fields with synchronous applied voltages show that, for example, with 8.0-kV applied voltage at 0.35-T magnetic field, the 2.45-GHz “cooker” magnetron is able to generate up to 6.0 kW of pulsed microwave power with an anode current of ~0.9 A. [ABSTRACT FROM AUTHOR]

Microwave selective/localized heating has been widely used in special areas, e.g., medical treatment and food processing, but the control of selective/localized heating in restricted space, e.g., microwave ovens, is difficult to accomplish. In this article, a Giuseppe Peano fractal phased-array antenna is designed, and the phase of each radiator is derived to achieve the arbitrary spatial division of the electromagnetic field in a cavity based on the superposition principle of waves. Then, a multiphysics model of microwave heating is established by coupling the electromagnetic field and heat transfer to simulate the directional control of microwave heating in a cavity. An experimental system is built, and the heating results are measured using an infrared thermal imager to verify the temperature distribution in different spatial regions. Finally, the feasibility of the model for different heating targets is discussed. [ABSTRACT FROM AUTHOR]

In this study, a reverberation chamber is used to perform measurements of shielding effectiveness (SE) and average total radiated power (ATRP) related to a domestic microwave oven for human exposure purposes. The ATRP is measured according to Annex E in the standard IEC 61000-4-21 procedure, and a new nondestructive procedure is proposed to measure SE that relies on the internal source of the microwave oven and on the reverberation chamber. Under mild hypothesis, the nondestructive procedure is both theoretically and experimentally equivalent to the IEEE 299.1 one. In addition, the measured ATRP values are within the limits defined in EN 62233. [ABSTRACT FROM AUTHOR]

Sample preparation is one of the most time-consuming steps in diagnostic assays, particularly those involving biological samples. In this paper we report the results of finite-difference time-domain (FDTD) simulations and thermographic imaging experiments carried out with the intent of designing a microplate for rapid, high-throughput sample preparation to aid diagnostic assays. This work is based on devices known as microwave lysing triangles (MLTs) that have been proven capable of rapid sample preparation when irradiated in a standard microwave cavity. FDTD software was used to model a microplate platform as a polystyrene substrate with an array of various passive scattering elements (PSEs) of different sizes, shapes, and interelement spacings in a 2.45 GHz field identical to that of a common microwave oven. Based on the FDTD modeling, several PSE arrays were fabricated by cutting PSEs out of aluminum foil and adhering them to the bottom of regular polystyrene microplates to make prototypes. Each prototype microplate was then irradiated in a microwave cavity for a range of different times, powers, and source angles and the heating effects were observed via a forward looking infrared (FLIR) camera. Based on the results, two prototype microplate platforms have been shown to demonstrate electromagnetic and thermal enhancements similar to those seen with MLTs as well as tunable thermal responses to radio frequency (RF) irradiation.

This article is the second in a continuing series of general interest papers on the applications of microwaves in areas of science and technology that might not be appreciated by the traditional engineer. What more appropriate application could there be than the first wide-spread commercial use of microwaves for food preparation. The development, use, and evolution (or lack of) of the microwave oven is the subject of this month's “Microwaves Are Everywhere.”

There is increasing research interest in the development of solid-state devices to provide intelligent uniform heating, spot heating, and so on. However, the use of the solid-state devices to realize the same 1-kW output power as a conventional microwave oven requires configuration complexity that, for the moment, prevents its wider adoption. Although there is a demand for microwave generators with average output power of several tens to several hundreds of watts, existing solid-state solutions cannot produce this level of power. These problems prompted us to investigate, both by analysis and prototyping, small injection-locked oscillators that use high-efficiency microwave generators to provide several hundred watts of output power. Using an imbalanced coupling resonator in the feedback circuit, we were able to achieve an output power of 210 W and an efficiency of 51% at 2.45 GHz, when injecting a reference signal at a level of less than 1/10 000 of the output power. The high-power and high-efficiency solid-state injection-locked oscillators described in this paper have the advantages of long life, tunable frequency and phase, and low-voltage operation. These characteristics are potentially useful for realizing precise temperature control in chemical reactions, as well as spot and uniform heating by microwave ovens. [ABSTRACT FROM AUTHOR]

This article presents experimental results of concrete cutting by a localized microwave-heating (LMH) applicator, fed by a ~0.25-kW solid-state microwave generator. The LMH applicator is a modified microwave-drill, operating in a stepwise pecking mode. Compared to the previously-presented, magnetron-based microwave-drill for concrete, the new device operates at a lower power; it is more compact, and it enables arbitrary cutting contours. In each pecking step in this mode, a small amount of concrete is softened by LMH, and mechanically removed. These sequential pecks are accumulated to form a long deep groove along the desired cutting contour. The lower microwave power applied in the pecking mode enables a narrower LMH applicator, which reduces the total amount of concrete removed in the cutting process (the kerf), and hence improves the overall efficiency. The solid-state LMH pecking module can be remotely controlled, and it is applicable to other masonry as well. Its silent and clean operation (with no vibration or dust effusion) classifies it as an environmental-friendly technology. The article introduces the LMH pecking concept for concrete cutting, and presents its experimental results. Concrete removal rates of ~0.35 cm3/min in ~0.5-cm pecking steps (accumulated to ~6-cm-long, ~6-cm-deep grooves) were obtained by applying a ~0.25-kW microwave power, in agreement with the LMH theory. The feasibility of a faster concrete cutting in practice by advanced LMH-based devices, also in array schemes, is discussed. [ABSTRACT FROM AUTHOR]

This article describes a set of simple experiments conducted at the University of Colorado (CU) Boulder and Technische Universit?t (TU) Wien, for teaching electromagnetic (EM) waves in the third year of undergraduate studies [electrical and computer engineering (ECEN) 3400 and ECEN 3410 at CU Boulder and wave propagation at TU Wien]. The experiments require simple household items and basic undergraduate circuit test equipment found in any electrical engineering department, namely, a function generator and oscilloscope. A subset of the experiments are packaged as take-home kits at TU Wien named Wave Propagation Season's Holiday Experiments and are gifted to the students in the last lecture before the winter holidays. The items are obtainable at a reasonable price in large quantities, such that the kits can be given away for free. At CU Boulder, the microwave oven leak detector experiment is held as a competition in which students win awards for the longest-detected range, lowest cost, and best quantitative readout. The experiments are designed to balance theory in EM waves and provide students with an appreciation of various types of waves across the EM spectrum as well as their similarities and unified mathematical description. [ABSTRACT FROM AUTHOR]

For long-term sustainable agriculture, it is critical that we recycle nutrition to the soil that it came from. One important source is sewage sludge, but it must be sanitized from undesired pathogens before it may be spread on arable land. One common method today is deposition in about six months or more. Not only is such a long deposition-time costly due to the required storage-space, in the future usage of the method is likely to be more restricted from a regulatory perspective. To heat up sewage-sludge is a known method to speed up the sanitation process. However, achieving an even guaranteed temperature is not easy with porous sewage sludge. This is mainly due to the limited heat conductivity of the sludge. Microwaves at a frequency of 2.45 GHz have a penetration depth of a few centimeters and therefore has an advantage compared to other heating methods which only heats the surface. In the proposed system, the sewage sludge is continuously processed through a series of microwave cavities. The pathogen removal effectiveness was studied for different exposure settings, e.g., conveyor speed and applied microwave power in each cavity.

We demonstrate the use of a novel efficient metallic susceptor for generating controllable and rapid localized heating for low-cost substrate bonding using commercial microwave ovens. A microwave oven is modeled and enhanced microwave susceptors are designed. Theoretical analysis and simulations confirm our proposed concept and match with our measured data. It is demonstrated that by the use of proposed susceptors, a polymethyl methacrylate substrate can be heated up to 160 °C in less than 8 s. We have also demonstrated that the heat generation is localized and selective, making this technique promising for microfluidic or substrate bonding applications. [ABSTRACT FROM AUTHOR]

An open-ended microwave oven system is presented and characterized for the rapid encapsulation of microelectronic components. In situ real-time measurement of the temperature of the curing materials is carried out by an infrared pyrometer integrated in the microwave head of the oven. An automatic computer-controlled closed feedback loop has been used to measure the temperature in the curing material and modulate the system operating power to obtain predefined curing temperature cycles for efficient curing. Uniform curing of the encapsulant material is achieved with typical cure time of \sim300∼s with a ramp rate of 1.66^\circC/s and a hold period of \sim100∼s. Differential scanning calorimeter based measurement for the curing of the polymer dielectric indicates a near 100% degree of cure. [ABSTRACT FROM AUTHOR]

With both Bluetooth and microwave ovens operating in the same frequency band, fears have arisen about the effects of microwave oven interference on Bluetooth networks. While Bluetooth devices use frequency hopping spread spectrum (FHSS), the high power output of microwave ovens may still pose a threat to Bluetooth networks. We therefore endeavored to characterize microwave oven behavior and understand its effect upon Bluetooth networks. Our experimental results show that Bluetooth devices will tolerate a high level of interference. With two Bluetooth devices forming a piconet placed within 1 m of an oven, the Bluetooth throughput was significantly greater than half of the maximum throughput rate. Moving to a distance around 10 m from the oven showed very little degradation to the throughput due to interference. The effects of microwave oven interference, while noticeable, are by no means fatal. The results also showed no gain from the forward error correction (FEC) used on some Bluetooth packets. [ABSTRACT FROM AUTHOR]

A touch panel microwave oven which is turned off does not mean that it is not consuming electric power. Although it is turned off, it still consumes 1 to 3 W when it is plugged into an ac socket. In this design the touch panel microwave oven consumes 3 mW when it is turned off and yet plugged in. A more effective circuit design for a touch panel microwave oven is proposed to reduce the standby power consumption, which is also easy to apply to future products. This power consumption in the standby state is lower than that of others and not only simple to set up but also inexpensive1. [ABSTRACT FROM PUBLISHER]

Back in the Mid-1960s rotary-dial telephones were the norm, music cassette tapes were brand new, and microwave ovens hadn’t made it into houses yet. That’s also when newly minted electrical engineer Thomas Furness joined a U.S. Air Force Lab and began developing what would become the first virtual reality (VR) systems, including the fighter-jet Super Cockpit that gives pilots 3D representations of avionics data, along with the ability to use voice commands, hand gestures, and even eye movements to control the aircraft. [ABSTRACT FROM AUTHOR]

In this study, the temperature distribution of a material (frozen tuna) that was heated in a commercial microwave oven is calculated by a coupled method using the finite-difference time-domain method, the semi-implicit method for pressure linked equations, the Monte Carlo method, and the radiative energy absorption distribution method. This method takes into consideration the melting heat during the phase change and the change in real and imaginary parts of the complex relative permittivity and heat conductivity during defrosting. Meanwhile, the temperature distribution of a sample of the frozen tuna is measured using an identical microwave oven and a thermograph. Then, the computed and monitored temperature distributions are compared. The calculated temperature distribution is found to agree well with the measured one, and the validity of the coupled method is confirmed. Additionally, the temperature distribution of a frozen heated material is verified both experimentally and theoretically. [ABSTRACT FROM AUTHOR]

Focuses on the application of microwave power. Connection of microwave technology to people's everyday life through microwave oven; Benefits of the system to the food industry; Use of the system in plasma discharge devices for ultraviolet curing and lighting.