Understanding Microwave Heating Cavities (Artech House Microwave Library)


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The ray tracing method combined with uniform theory of diffraction UTD [ 54 ] is most frequently applied to radio coverage prediction [ 55 — 58 ].

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Editorial Reviews. About the Author. Tse Voon Chow Ting Chan is a postdoctoral fellow in the Understanding Microwave Heating Cavities (Artech House Microwave Library) - Kindle edition by Tse V. Chow Ting Chan, Howard C. Reader. Artech House, - Technology & Engineering - pages It aims to enhance the reader's understanding of the different classes of microwave heating cavities and their properties, the field distribution Artech House microwave library.

The ray tracing models potentially represent the most accurate and versatile methods for urban and indoor, multipath propagation characterization or prediction. In this study, the dosimetric analysis of the propagation channel due to microwave oven leakage has been performed with the aid of a 3D ray launching algorithm, which has been implemented in-house based on Matlab programming environment. The presented simulation method has been widely validated in different kind of complex indoor scenarios [ 59 — 63 ]. The principle of the ray launching method is to launch a bundle of rays from the transmitter at an elevation angle and with an azimuth angle as defined in the usual coordinate system.

The number of rays considered and the distance from the transmitter to the receiver location determine the available spatial resolution and, hence, the accuracy of the model.

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A finite sample of the possible directions of the propagation from the transmitter is chosen and a ray is launched for each such direction. When the launched ray interacts with an obstacle, reflection, transmission, and diffraction will occur, depending on the electric properties and the geometry of the impacted object, as is depicted in Figure 1. Principle of operation of the 3D ray launching method implemented in-house to perform indoor coverage analysis. Antenna patterns are incorporated to include the effects of antenna type.

Parameters such as frequency of operation, number of multipath reflections, cuboid dimensions, or separation angle between rays are specified. The material properties for all the elements within the scenario are also taken into account, given the dielectric constant and permittivity at the frequency range of operation.

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All these parameter possibilities make the presented simulation method a high accurate tool for obtaining radiated power estimations within complex indoor scenarios in an acceptable computational time. In this work a common domestic microwave oven has been used, with In order to simulate the behavior of the leaked microwave oven power in its surroundings, full wave electromagnetic results have been obtained with the aid of CST Microwave Studio.

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Would you like to report this content as inappropriate? Exposure Level Analysis Studies on the impact of electromagnetic wave exposure on humans and different kinds of animals have led to the specification of different standards, which have been designed to set a nonionizing radiation exposure level compatible with human health. IEEE standard for safety levels with respect to human exposure to radio frequency electromagnetic fields, 3 kHz to GHz. The whole simulation procedure of the estimation of the oven leakage has been described in detail previously [ 64 ]. This can be clearly seen in Figure 7 , where the left spectrogram has been taken with the oven operating at its highest power mode Watts and the right spectrogram represents the same situation but without the microwave oven.

The simulation model created for that purpose can be seen in Figure 2. The real dimensions of the oven as well as the real material characteristics have been taken into account to create an accurate simulation model.

Using these previous simulation results, an equivalent modeling of the oven has been done to be applied in the 3D ray launching simulation software described in Figure 1. The aim of this simulation is to fully estimate the interference created by the leaked power in a complete volume of an indoor scenario. The whole simulation procedure of the estimation of the oven leakage has been described in detail previously [ 64 ]. The microwave oven used for the measurements a and the schematic view of the created simulation model b.

Note that a porcelain bowl, filled with water, is placed in the center of the cavity for both the measurements and simulation. As can be also seen in the previously mentioned work [ 64 ], the spectrum of the leaked power exhibits a wideband nonuniform power distribution, so the radiated electric field value will be different depending on the frequency.

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Because of this, several simulation values have been calculated at different frequencies. As the goal of this work is to analyze the dosimetry and the level of the radiated electric field caused by a microwave oven in terms of human exposure, the simulation results shown in this paper correspond to the frequency which has the maximum power level 2. So the worst case is analyzed, or what is the same, the case of the highest dose is calculated. In Figure 3 an upper cut taken from the 3D full wave simulation is shown, where the distribution of the electric field inside the oven cavity can be seen.

The electric field which leaked through the front door can be seen. Screen capture of the upper cut taken from the CST simulation of the microwave oven. Note the leakage through the door downside of the picture. As previously stated, once the leakage around the oven has been obtained, equivalent sources have been calculated for the ray launching simulations performed afterwards. Thus, the behavior of the leaked electromagnetic power propagation can be analyzed, which will enable the estimation of the interference effect within the complete indoor scenario.

It is worth noting that, in principle, the surface current distribution on the microwave oven structure exhibits a uniform distribution in terms of time dependence. Therefore, in order to gain insight on potential modifications of the microwave oven model, the main contribution is provided by considering the maximum output power available. Figure 4 shows the results obtained in the simulation of the complete scenario, for 4 different maximum power levels.

The microwave oven is located at coordinates 0,0 , with the door orientated facing the positive values of the Y -axis. As expected, the highest electric field values can be found in the nearest zone of the oven, particularly in front of the door, as the radiated power is mainly due to the leakage through the door. It is worth noticing that, although in lesser extent, the leaked power also affects the zone behind the oven. The radiated electric field can easily reach more than 3 meters, which is a significant distance considering indoor scenarios as home environments. In order to provide insight in relation to the power levels expected as a function of maximum output power, Figure 5 depicts the region, as a function of distance in which emission levels will be present, in the case in which maximum power is applied for the oven of least maximum power i.

Linear E -field distribution in front of the oven as a function of maximum output power depending on the selected model of microwave oven. In order to validate the leakage estimations for the complete scenario, measurement results have been made.

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The scenario in which the measurements have been taken and the simulations have been run is placed in the ground floor of the Research and Development building of the Public University of Navarre. In Figure 6 the composition of the test bed and its schematic representation for the 3D ray launching algorithm is shown, where the microwave oven has been positioned on a wooden table at height 0.

The scenario has the inherent complexity of indoor scenarios due to the different elements within it, as interior columns, metallic elements, and walls made of different materials glass, wood, concrete, and bricks. The scenario where the measurements have been taken a and its schematic representation for the simulation by means of 3D ray launching software b.

In the first place, spectral measurements have been taken with the aid of an Agilent Field Fox NA spectrum analyzer. Specifically, two spectrograms have been obtained, the first one with the oven in operation mode and the second one without the oven. The spectrograms have been obtained for an interval of 5 minutes once the oven starts heating.

The aim of these measurements is to show how the leaked power from microwave oven is very strong and how it covers almost the whole ISM band of 2. This can be clearly seen in Figure 7 , where the left spectrogram has been taken with the oven operating at its highest power mode Watts and the right spectrogram represents the same situation but without the microwave oven.

Measured spectrograms within the scenario a with the influence of an operating microwave oven and b without the oven. Once the influence of an operating microwave oven has been shown, specific measurements have been taken in order to quantify the power level of the leaked electromagnetic field throughout the scenario.

These measurements have been taken with the same spectrum analyzer. To carry it out, an array of measurement-points has been set. The array consists in a total of measurement points taken every 0. The height has been set at 0.

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The received leakage has been measured for each position and for 30 seconds, while the microwave oven was in operation. As the spectrum analyzer gives received power level in dBm, a conversion to electric field values has been required. On the other hand, the same measurements have been performed, but with an EME Spy personal dosimeter see Figure 8.

Although most regulations require gathering data at a rate of one sample per second for a measurement time of six minutes, the shortest sample rate available for the EME Spy dosimeter device is one sample per 4 seconds, which has been the sample rate used for the measurements in this study. The overall measurement time for each measurement point has been set to 3 minutes instead of 6 minutes due to the big quantity of measurement points proposed for this study.

Besides, the purpose of these measurements is to validate the measurement data obtained by the spectrum analyzer as well as the simulation results, proving that the presented 3D ray launching algorithm can be also used for dosimetric assessment. As can be seen in Figure 7 a , the maximum value of the microwave oven's leaked power is obtained quite early, which has been the value compared with spectrum analyzer and simulation results.

Therefore, the 3 minutes set as measurement time are enough for the purpose of this part of the study. The EME Spy dosimeter used to obtain electric field values of the leakage of the microwave oven. The obtained measured values are shown in Figure 9. In this case, the shown data are the corresponding values obtained with the aid of the spectrum analyzer, once they have been converted to electric field values. Although the error between the simulation Figure 4 and the measurements Figure 9 at first glance appears to be quite high, it is due to the low field levels and the color scale that has been needed to be used.

Figure 10 a represents the radiated oven leakage versus linear distance for a central line, which corresponds to a straight line just in front of the microwave oven, as can be seen in Figure 9. Figures 10 b and 10 c represent the comparison for left and right lines. Received electric field distribution versus distance for 3 different radials a front, b right, and c left.

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Simulation as well as measurement results from spectrum analyzer and EME Spy personal dosimeter are represented, with good agreement among them. As can be seen in Figure 10 , the electric field values obtained with the spectrum analyzer and dosimeter are heavily similar, as expected. If measurements are compared to simulation results, a high accuracy is observed. Taking into account the points distributed within the scenario where the measurements have been taken, a total error mean of 0. Those values and the values obtained by means of the dosimeter are also close, as shown in Figure Specifically, the mean error between simulation results and dosimeter values is 0.

It is worth noting how important it is to use a well-developed and detailed microwave oven for simulations in order to obtain accurate dosimetric values throughout a scenario: The main reason for that phenomenon is that the power leaked through the oven's door is not uniformly distributed on the oven's surface, and, consequently, the radiation pattern of the whole oven is not symmetric. Besides, the scenario itself is not symmetric see Figure 6 , making the propagated multipath components different for both sides of the oven. Studies on the impact of electromagnetic wave exposure on humans and different kinds of animals have led to the specification of different standards, which have been designed to set a nonionizing radiation exposure level compatible with human health.

The most authoritative guidelines at international level have been developed by the ICNIRP, which has been previously commented on in this work. The ICNIRP criteria and guidelines specify limit values for occupational exposure as well as for general public exposure. At the frequency of operation of the current work around 2. The specific level for the working frequency of 2. IEEE thresholds of E -field for controlled environments. IEEE thresholds of E -field for uncontrolled environments.

In order to get the specific absorption rate SAR for human body, an in-house developed human body model has been used and situated in three places of the scenario doing three simulations. This human body model has been tested in several works [ 61 , 62 ], giving a good accuracy in the simulation results. This SAR calculation method has been extracted from [ 66 ] and is implemented in some papers [ 67 , 68 ]. The human body model parameters used in this study, as the age 35—39 years old , the height 1.

In Figure 15 the power distribution for this scenario is depicted. For this picture the scenario has been simplified because the interesting zone is in front of the microwave oven where the human body is located. The influence of the presence of the human body model in the overall radiated power distribution within the complete scenario can be seen, as lower power levels appear in the regions behind the human body model, depicted in Figure Power distribution for the part of the scenario where human body is placed when it is at 1.

In Figure 16 SAR results in body for three different simulations are depicted. Feedback If you need help or have a question for Customer Service, contact us. Would you like to report poor quality or formatting in this book? Click here Would you like to report this content as inappropriate? Click here Do you believe that this item violates a copyright? Your recently viewed items and featured recommendations. View or edit your browsing history. Get to Know Us. Not Enabled Word Wise: Not Enabled Enhanced Typesetting: Not Enabled Average Customer Review: Be the first to review this item Would you like to tell us about a lower price?

Chow Ting Chan , Howard C. Providing practical information along with experimental evidence, analysis of existing data, and simulations you can run yourself, this is a manual on microwave heating for engineers and non-engineers alike. It aims to enhance the reader's understanding of the different classes of microwave heating cavities and their properties, the field distribution patterns in loaded and unloaded cavities, cross-coupling between feeds in a multiple feed loaded multimode cavity, and empty, coaxially and eccentrically loaded single-mode cavities.