Investigation of Microwave Absorption Mechanisms in Microcellular Foamed Conductive Composites
Abstract
:1. Introduction
2. Materials and Methods
2.1. Synthesis of Conductive Foams
2.2. Electromagnetic Modelling Technique
3. Results and Discussion
3.1. Electromagnetic Model of the Foam
3.2. Experimental Validation of the Model
3.3. Absorption Mechanism in Foamed Composite
3.3.1. Interaction with Walls
3.3.2. Influence of Air
3.4. Parametric Study
3.4.1. Influence of Thickness of Wall and Size of Cell
3.4.2. Influence of Electromagnetic Parameters of Polymer
3.4.3. Influence of Frequency and Size of Cell
3.4.4. Influence of Global Thickness of Composite
3.5. Guidelines for the Design of Foamed Composites for Microwave Absorption
- The reflection factor at input of the foamed composite has to be minimised in order to favour absorption. For this:
- The fraction of air inside the foam has to be maximised; in other words, the ratio d/t has to be maximised, see Section 3.3.2 and Section 3.4.1, Figure 5.
- The dielectric constant of the composite material has to be as low as possible, in order to minimise the reflection R by virtue of (15), see Section 3.4.2, Figure 6.
- The absorption can be directly favoured by increasing the global thickness D of the composite (Section 3.4.4 and Figure 9); for some applications, however, compactness is a key issue so that a trade-off between thickness and absorption must be found.
- The absorption is also favoured by the conductivity of the composite material forming the foam (see Section 3.4.2 and Figure 6). However, a prohibitive conductivity can induce a prohibitive reflection R that reduces the penetration of the microwave signal in the foamed composite. Again, a trade-off between absorption and reflection has to be found.
3.6. Towards an Optimised Design
4. Conclusions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Appendix A
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Sample Composite | Case n°1 | Case n°2 | Case n°3 |
---|---|---|---|
Cell size d (μm) | 15 | 80 | 46.3 |
Frequency range (GHz) | 15–17 | 26–40 | 28–38 |
Wall thickness t (μm) | 2 | 7 | 5 |
Overall thickness D (mm) | 20 | 20 | 8 |
A (%) | 75/75 | − | 70/76 |
R (dB) | − | 8.2/8.7 | 7/7 |
EMI (dB) | − | 72/75 | 50/54 |
Sample Composite | Case n°1 | Case n°2 | Case n°3 |
---|---|---|---|
Dielectric constant εr of solid composite | 6 | 30 | 18.7 |
Dielectric constant εr of foamed composite | 1.35 | 4 | 3.18 |
Zp/Zair = 1/ for solid composite | 0.408 | 0.182 | 0.2351 |
Zp/Zair = 1/ for foamed composite | 0.8607 | 0.5 | 0.5608 |
Γ for solid composite | 0.421 | 0.692 | 0.693 |
Γ for foamed composite | 0.075 | 0.333 | 0.2814 |
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Huynen, I. Investigation of Microwave Absorption Mechanisms in Microcellular Foamed Conductive Composites. Micro 2021, 1, 86-101. https://doi.org/10.3390/micro1010007
Huynen I. Investigation of Microwave Absorption Mechanisms in Microcellular Foamed Conductive Composites. Micro. 2021; 1(1):86-101. https://doi.org/10.3390/micro1010007
Chicago/Turabian StyleHuynen, Isabelle. 2021. "Investigation of Microwave Absorption Mechanisms in Microcellular Foamed Conductive Composites" Micro 1, no. 1: 86-101. https://doi.org/10.3390/micro1010007