RF MODULE

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Microwave Oven Introduction This is a model of the heating process in a microwave oven. The distributed heat source is computed in a stationary, frequency domain electromagnetic analysis followed by a transient heat transfer simulation showing how the heat redistributes in the food. Model Definition The microwave oven is a metallic box connected to a 1 kW, 2.45 GHz microwave source via a rectangular waveguide operating in the TE 10 mode. Near the bottom of the oven there is a cylindrical glass plate with a spherical potato placed on top of it. A part of the potato is cut away for mechanical stability which also facilitates the creation of a finite element mesh in the region where it is in contact with the plate. Symmetry is utilized by simulating only half of the problem. The symmetry cut is applied vertically through the oven, waveguide, potato, and plate. The reduced geometry is shown in Figure 3-27. Figure 3-27: Geometry of microwave oven, potato, and waveguide feed. 156 | CHAPTER 3: <strong>RF</strong> AND MICROWAVE MODELS
The walls of the oven and the waveguide are good conductors. The model approximates these walls as perfect conductors, represented by the boundary condition n × E = 0. The symmetry cut has mirror symmetry for the electric field and is represented by the boundary condition n × H = 0. The rectangular port is excited by a transverse electric (TE) wave, which is a wave that has no electric field component in the direction of propagation. At an excitation frequency of 2.45 GHz, the TE 10 mode is the only propagating mode through the rectangular waveguide. The cutoff frequencies for the different modes are given analytically from the relation where m and n are the mode numbers and c denotes the speed of light. For the TE 10 mode, m = 1 and n = 0. With the dimensions of the rectangular cross section (a = 7.8 cm and b = 1.8 cm), the TE 10 mode is the only propagating mode for frequencies between 1.92 GHz and 3.84 GHz. With the stipulated excitation at the rectangular port, the following equation is solved for the electric field vector E inside the waveguide and oven: where µ r denotes the relative permeability, j the imaginary unit, σ the conductivity, ω the angular frequency, ε r the relative permittivity, and ε 0 the permittivity of free space. The model uses material parameters for air: σ = 0 and µ r = ε r = 1. In the potato the same parameters are used except for the permittivity which is set to ε r = 65 − 20j where the imaginary part accounts for dielectric losses. The glass plate has σ = 0, µ r = 1 and ε r = 2.55. Results ( νc) mn = -- c 2 m ⎛---- ⎞ ⎝ a ⎠ 2 ⎛n -- ⎞ ⎝b⎠ 2 + – 1 2 jσ ∇× ( µ r ∇× E) – k ⎛ 0 εr – --------- ⎞ ⎝ ωε ⎠ E = 0 0 The first figure below shows the distributed microwave heat source as a slice plot through the center of the potato. From the rather complicated oscillating pattern that has a strong peak in the center, it is obvious that the potato acts as a resonant cavity for the microwave field. The voltage reflection coefficient at the waveguide port, S 11 , evaluates to about −4 dB, meaning that the potato absorbs about 60% of the input microwave power. The second figure shows the temperature in the center of the potato as a function of time for the first 5 seconds. Due to the low thermal conductivity of the MICROWAVE OVEN | 157
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COMSOL Multiphysics RF MODULE V ERS
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CONTENTS Chapter 1: Introduction Mo
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Results and Discussion. . . . . . .
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Chapter 4: Optics and Photonics Mod
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1 Introduction The RF Module Model
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highlights. The categories here inc
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TABLE 1-1: RF MODULE MODEL LIBRARY
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2 Tutorial Models This chapter cont
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Results and Discussion Figure 2-1 s
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4 Draw a square with corners at (
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COMPUTING THE SOLUTION Click the So
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Results and Discussion The dipole a
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PHYSICS SETTINGS Variables 1 Choose
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5 Click OK to close the dialog box
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Model Library path: RF_Module/Tutor
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4 From the Solve menu, open the Sol
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them from the eigenvalues. The appl
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5 On the Port page, set the values
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5 On the Port page, enter 36.4 in t
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Waveguide Optimization Introduction
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Results and Discussion Figure 2-3 s
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Modeling Using the Graphical User I
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3 Select Boundary 7 and set the Con
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POSTPROCESSING AND VISUALIZATION Fo
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The solution takes a few minutes to
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Night side Earth surface Ionosphere
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Results and Discussion The model pr
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4 Select both spheres and click the
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RF and Microwave Models In this cha
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measure of the transmittance and re
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y 1 cm is at about 7.5 GHz. At the
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By feeding the circulator at a diff
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Importing the Geometry from a Binar
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MESH GENERATION This model uses the
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It is more instructive to look at t
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Note: When displaying S-Parameter v
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Monoconical RF Antenna Introduction
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50 Ω, to obtain maximum transmiss
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Figure 3-7 shows the antenna radiat
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2 Select the RF Module>Electromagne
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13 Zoom in around (0, 0) using the
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4 In the Contour levels area, click
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2 Clear the Keep current plot check
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6 Click the Solve button on the Mai
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Results and Discussion The figure b
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PHYSICS SETTINGS Point Settings Def
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2 In the x-axis area, select the Ex
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Because the impedance is inversely
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4 From the Space dimension list, se
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2 Select Boundaries 1, 2, 4, and 6.
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4 On the Pointwise Constraints page
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12 Click the Solve button on the Ma
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Module. The electromagnetic cavity
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EIGENFREQUENCY VS. TEMPERATURE By r
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GEOMETRY MODELING 1 Go to the Draw
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3 Set dx, dy, and dz to u, v, and w
Page 113 and 114: 20 Select the Solve using solver se
Page 115 and 116: Computing the Solution Using a Para
Page 117 and 118: 8 Click Solve. 9 When the parametri
Page 119 and 120: H-Bend Waveguide with S-parameters
Page 121 and 122: Model Library path: RF_Module/RF_an
Page 123 and 124: 1 From the Postprocessing menu, cho
Page 125 and 126: The rectangular port is excited by
Page 127 and 128: Figure 3-16 shows a single-mode wav
Page 129 and 130: Figure 3-18: The S 21 parameter (in
Page 131 and 132: PHYSICS SETTINGS First set up the b
Page 133 and 134: FREEZING THE BOUNDARY MODE ANALYSIS
Page 135 and 136: 12 Click the Solve button on the Ma
Page 137 and 138: Microwave Cancer Therapy Introducti
Page 139 and 140: The model takes advantage of the pr
Page 141 and 142: DOMAIN AND BOUNDARY EQUATIONS—HEA
Page 143 and 144: Figure 3-23: The computed microwave
Page 145 and 146: solutions for both the electromagne
Page 147 and 148: 4 Select Subdomain 1, then enter th
Page 149 and 150: 1 Click the Plot Parameters button
Page 151 and 152: sar_in_human_head_interp.txt. That
Page 153 and 154: The bioheat equation produces a sim
Page 155 and 156: 3 Click OK. 4 From the Options menu
Page 157 and 158: 17 In the Work-Plane Settings dialo
Page 159 and 160: SETTINGS SUBDOMAIN 19 epsilonr_brai
Page 161 and 162: 4 Click the Init tab and type 0 in
Page 163: POSTPROCESSING AND VISUALIZATION 1
Page 167 and 168: Figure 3-29: Temperature in the cen
Page 169 and 170: 3 Click the block symbol again and
Page 171 and 172: 2 At the waveguide end, Boundary 23
Page 173 and 174: 4 Click OK to generate the plot bel
Page 175 and 176: 3 Click OK to generate the plot bel
Page 177 and 178: Because the filter cutoff should be
Page 179 and 180: the force is applied. Figure 3-32 d
Page 181 and 182: 6 Then the ECAD Import Options dial
Page 183 and 184: PHYSICS SETTINGS Subdomain Settings
Page 185 and 186: solver takes more steps than it sto
Page 187 and 188: 3 Select Subdomain 1 and clear the
Page 189 and 190: 13 Click the Solve button on the Ma
Page 191 and 192: Balanced Patch Antenna for 6 GHz In
Page 193 and 194: k0 = ω ε0 µ 0 All metallic objec
Page 195 and 196: divided by the input power. In Figu
Page 197 and 198: Reference 1. E. Recht and S. Shiran
Page 199 and 200: 10 Select the objects SQ2, CO1, and
Page 201 and 202: 43 Specify two spheres with the fol
Page 203 and 204: inputs are feeding the antenna, lik
Page 205 and 206: the width of the PML is equal to λ
Page 207 and 208: a toggle button that shifts between
Page 209 and 210: 5 Select Coarse solver from the tre
Page 211 and 212: maxE = max(EdB); minE = min(EdB); E
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13 Choose Extrude from the Draw men
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2 Click the Settings button. 3 In t
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Sea Bed Logging Introduction The Se
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Figure 3-39: Electric field magnitu
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PHYSICS SETTINGS Scalar Variables 1
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4 Click OK to generate the plot bel
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5 Click the General tab. From the P
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Optics and Photonics Models In this
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Model Definition The model is built
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Model Library path: RF_Module/Optic
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PHYSICS SETTINGS Scalar Variables S
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POSTPROCESSING AND VISUALIZATION By
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Model Definition The geometry is a
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2 In the list of application modes,
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Because the refractive index of GaA
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5 Click OK twice to see the followi
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Bandgap Analysis of a Photonic Crys
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a 2 a 3 × b1 = 2π----------------
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The five lowest bands for the (1, 1
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Modeling Using the Graphical User I
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Subdomain Settings 1 Open the Subdo
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3 Click the Parametric tab. Select
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3 Click OK to see the following plo
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fem.appl{1}.prop.analysis = 'harmon
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Model Definition The mode analysis
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2 Select the RF Module>Perpendicula
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4 On the Contour page, give Magneti
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includes only two independent param
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OPTIONS AND SETTINGS 1 Open the Con
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The problem becomes well-posed by a
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POSTPROCESSING AND VISUALIZATION Th
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7 Click OK. 8 From the Postprocessi
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the computed propagation constants
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3 The default eigenmode is the one
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Compare these ideal values of the p
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Stress-Optical Effects with General
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The PDE solved is Navier’s equati
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and εx ∂u = ∂x εy ∂v = ∂y
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Model Library path: RF_Module/Optic
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NAME EXPRESSION DESCRIPTION B2 0.65
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2 In the Subdomain Expressions dial
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4 Initialize the mesh in this geome
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Note: This model includes an extens
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3 Enter 1.46 in the text field Sear
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In these expressions, w 0 is the mi
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After 90 fs the pulse has reached t
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4 Select the RF Module>In-Plane Wav
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Boundary Conditions 1 From the Phys
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6 Click the Remesh button; when the
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2 On the General page, make sure th
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Propagation of a 3D Gaussian Beam L
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Figure 4-15: After 20 fs the pulse
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7 Click the Delete Interior Boundar
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Boundary Conditions 1 From the Phys
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5 From the Options menu, select Sup
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INDEX 3D electromagnetic waves mode
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efractive index 222, 254 resistance
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RF MODULE

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