Narrowband Electromagnetic Wave Absorption Sheet
Narrowband Electromagnetic Wave Absorption Sheet (FJM Series) is an absorption material designed by combining resistive film and spacer structure for electromagnetic wave countermeasures at specific frequencies such as automotive millimeter-wave radar.
It is an applied configuration of the FJM Series aimed at "pinpoint absorption/attenuation of specific frequencies."
While general EMC countermeasure materials "evenly weaken a wide frequency range," narrowband types are designed with the concept of "strongly suppressing only the problematic frequency."
It contributes to improved reliability of radar and communication systems by suppressing only unnecessary reflections and interference while maintaining necessary signal quality.
Why is "Narrowband Absorption" Necessary?
Common Cases in Automotive Applications
- Want to use millimeter-wave radar
However,
- Reflections inside radar housing
- Reflected waves from surrounding components
- Multiple reflections in specific directions
cause range measurement errors and false detections
このとき In this case, using wideband absorption material may not achieve the necessary attenuation effect.
"Achieving high attenuation effect only at the frequency you want to affect"
This is the concept of narrowband absorption.
Mechanism of Narrowband Absorption Sheet
The narrowband type of FJM Series combines
- Resistive film (S250/S350, etc.)
- Spacer structure
- Layer configuration (laminated design)
to create a "structure that resonates at a specific wavelength and efficiently attenuates electromagnetic waves."
Basic Structure of FJM Narrowband Absorption Sheet
A typical configuration example is as follows.
"Surface layer: FJM resistive film (S250/S350)" is the main absorption component, and "spacer layer/adhesive layer (optional)" determines the resonance frequency.
Structural Features
- Surface resistive film: Consumes electromagnetic waves as heat
- Spacer: Thickness/dielectric properties
determine "which frequency to absorb."
An absorption material designed with material + structure, this is the essence of FJM narrowband type.
Absorption Characteristics
Free Space Method
How is the Absorption Frequency Determined?
The absorption peak is mainly determined by:
Spacer thickness
Thick → Lower frequency side
Thin → Higher frequency side
Resistive film grade
S250: Balanced type for polarization plane
S350: High attenuation effect for circular polarization
Layer configuration
Single layer
Multi-layer (multiple spacers)
With these combinations,
- 24GHz
- 60GHz
- 76-78GHz
- Specific frequency
etc., it is possible to match the absorption peak.
Usage in Automotive Millimeter-Wave Radar [Specific Examples]
Narrowband absorption is very effective in situations where metal shielding would "reflect everything."
| Usage Purpose | Want to increase gain without reducing radar sensitivity |
|---|---|
| Installation Example |
|
| Effect |
|
Difference from Wideband Absorption Sheet
| Item | Narrowband absorption | Wideband absorption |
|---|---|---|
| Target | Specific frequency | Wide frequency range |
| Design | Custom design | General- purpose design |
| Radar Impact | Minimal | May have impact |
| Main Use | Radar | General electronics |
| Adjustment Freedom | High | Lower |
- "Millimeter-wave Radar" = Narrowband
- "Multiple Frequencies" = Wideband
This is the basic distinction.
Benefits of Narrowband Absorption Sheet
Design Aspect
- Does not attenuate radar waves
- Optimization possible for each frequency
- Achieves both EMC countermeasures and performance assurance
Implementation Aspect
- Thin and lightweight
- Post-application possible in film form
- Compatible with curved surfaces and limited spaces
Evaluation Aspect
- Easy to measure and verify effects
- Easy condition setting → fine adjustment