Home / Examples / Coupled Analysis / Electromagnetic-Thermal Analysis [Hertz/Watt] / Example 2: Microwave Oven Transient Analysis

Example 2: Microwave Oven Transient Analysis

General

The heating of a piece of meat on the bone placed in a microwave oven is simulated.
It is solved by coupling the electromagnetic harmonic analysis and the thermal transient analysis.
The temperature-dependent relative permittivity and dielectric tangent are taken into account.
Unless specified in the list below, the default conditions are applied.

This example is calculated using Femtet ver.2023.0.0.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	mm

Analysis Conditions

Item

Settings

Solver

Electromagnetic Analysis [Hertz]

Thermal Analysis [Watt]

Analysis Type

Electromagnetic Analysis: Harmonics Analysis

Thermal Analysis: Transient Analysis

The harmonic analysis and the transient analysis are set as follows.

Tab

Setting Item

Settings

Mesh

General Mesh Size:

Element Type

2nd-order Element

Adaptive Mesh

Off (to shorten the calculation time)

Frequency-Dependent Meshing

Reference Frequency: 2.45x109 [Hz]

Electromagnetic-Thermal Analysis

Electromagnetic Analysis Type

Harmonic Analysis

Thermal Analysis Type

Transient Analysis

Weight Function

Select

Weight Function

No.	Time	Weight
1	0	1
2	40	1
3	40.1	0
4	60	0

Harmonic Analysis

Frequency

Minimum: 2.45x109 [Hz]

Maximum: 2.45x109 [Hz]

Input

500 [W]

Transient Analysis

Table

No.	Calculation Steps	Output Interval	Timestep [s]
1	6	1	10

Initial Temperature

20 [deg]

Model

The model is the same as that in the example 1.

On the top of a cavity box, is placed a waveguide, into which electromagnetic waves enter. A port (PORT1) is set at the end of the waveguide.

A piece of meat on the bone is placed on a plate.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name	Mesh Size
0/Solid	CAVITY	000_Air(*)
5/Solid	WAVEGUIDE	000_Air(*)
6/Sheet	Imprinting body
13/Solid	PLATE	PLATE	10
75/Solid	BONE	BONE	10
96/Solid	MEAT	WATER	10

* Available from the material DB

Material Name

Tab

Value

PLATE

Permittivity

Relative Permittivity: 7.0

tanδ: 0.0

Thermal Conductivity

1.5 [W/m/deg]

BONE

Permittivity

Relative Permittivity: 7.0

tanδ: 0.1

Thermal Conductivity

1.5 [W/m/deg]

WATER

Permittivity & tanD

No.	Temperature	Relative Permittivity	tanδ
1	0	88.15	10.5
2	10	84.14	8.5
3	20	80.36	7.0
4	30	76.78	5.8
5	40	73.39	4.7
6	50	70.15	3.8
7	60	67.03	3.0
8	70	64.01	2.5
9	80	61.06	2.2
10	90	58.15	2.0

Thermal Conductivity

1.5 [W/m/deg]

Boundary Conditions

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
PORT1/Face	Electric	Port	Reference Impedance: Select [Use the characteristic impedance calculated from the port structure].
EW/Face	Electric	Electric Wall
Outer Boundary Condition	Electric	Electric Wall

The default setting is [Magnetic Wall] for the electric boundary, and [Adiabatic] for the thermal boundary.

Results

The temperature inside the meat can be observed to rise and fall according to the weight function of the input power of electromagnetic waves.

The contours of temperature after 40 sec represent the temperature distribution inside the meat.