Home / Examples / Electromagnetic Analysis [Hertz] / Example 41: Frequency-Selective Reflector

Example 41: Frequency-Selective Reflector

General

Analyzed is a frequency-selective reflector that allows specific electromagnetic waves pass through.
Unless specified in the list below, the default conditions will be applied.

Results will vary depending on Femtet version and the PC environment.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	mm

Analysis Condition

Item	Settings
Solver	Electromagnetic Analysis [Hertz]
Analysis Type	Harmonic Analysis

Tab	Setting Item	Setting
Mesh	Frequency-Dependent Meshing	Reference Frequency: 77 [GHz] Select The conductor bodies thicker than the skin depth constitute the boundary condition
Harmonic Analysis	Sweep Type	Select [Linear Step by Division Number].
	Sweep Setting	Minimum Frequency: 40 [GHz] Maximum Frequency: 90 [GHz] Division: 200
	Frequency Sweep	Select Fast Sweep S-parameter Tolerance: 1x10-3

Model

The model consists of a frequency-selective reflector and the air.

The dielectrics (Sub) are placed on the conductive plate (Metal) and encircled by curved slits.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
5, 30, 31, 32, 33, 34, 35, 36, 37/Solid	Sub	006_Glass_epoxy *
38/Solid	Air	000_Air *
39, 40, 41, 42, 43, 44, 45, 46, 47, 48/Solid	Metal	008_Cu (*)

* Available from the material DB

Boundary Condition

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
Port_001/Face	Electric	Port	Select Reference Impedance: Use the characteristic impedance calculated from the port structure Integral Path Set Path1
Port_002/Face	Electric	Port	Reference Impedance: Select Use the characteristic impedance calculated from the port structure. Integral Path Set Path1
EW/Face	Electric	Electric Wall
Outer Boundary Condition	Electric	Magnetic Wall

Set up Mesher/Solver

Setting Item

Settings

Frequency-Dependent Meshing

Reference Frequency: 77 [GHz]

Select The conductor bodies thicker than the skin depth constitute the boundary condition

Results

S-parameters are shown below. The transmission characteristic is observed at around 77 GHz.

Shown below are the current densities at 40 GHz (transmission characteristic does not appear) and at 77 GHz (transmission characteristic appears) on the frequency-selective reflector.

At 40 GHz, the current is flowing throughout the entire area of the conductor whereas the current is concentrated near the slit at 77 GHz.

Its value is large.

The electromagnetic field that causes the concentrated current near the slit is the resonant mode of the frequency-selective reflector. The resonant mode generates the transmission characteristic at a specific frequency.

The figures below show the electric fields at 40 GHz and 77 GHz. At 40 GHz, the incident electromagnetic wave is blocked by the frequency-selective reflector and not transmitted.

At 77 GHz, the electromagnetic wave is transmitted through the frequency-selective reflector.

For a clear comparison, the scale factor for drawing vectors is set at 10 times, and the maximum value is set at 3k [V/m].