New technologies for the realization of 3D or flexible, ultra-thin and light electromagnetic absorbers – 3DRAM

The realization of composite materials is based on the mixing of a polymer with powders (metals, carbon, ferrites) in molten state. Three different techniques of mixing were used: propeller mixer, internal mixer and mini-extruder. These different techniques were compared through the rheological, microstructural and microwave properties of samples of composite materials.
Mixing laws allow us correlating the evolution of the microwave properties of composite materials as a function of load rates to their microstructural characteristics.
The conception of microwave absorbers coupling metasurfaces and composite materials were done through electromagnetic simulations. These metasurfaces consists in metallic periodic patterns (squares or crosses).
Moreover, 3D printing-compatible filaments made of composite materials were realized. At the moment, the printability of these composite materials is under study.

Preliminary works of the project were focused on the evaluation of commercial materials 3D printed by fused deposition modeling (FDM) for microwave absorption applications. An ABS polymer loaded with carbon particles was selected to design a microwave termination at X-band. This device showed similar performances than a precision commercial termination (VSWR < 1.025 between 8 and 12 GHz) for a cost 10 to 100 times lower. These resultst confirmed the interest to develop new materials for these applications.
Different types of composite materials were realized. Our study was, for the moment, focused on two polymers (polyethylene PE and polyvinyl chloride PVC) and two types of micron-scale loads (platelets of graphite and spheres of nickel-iron alloy).
Systematic characterizations (morphological, rheological, microwave) were performed as a function of the load rate (10 to 40% in volume).
The evolution of the microwave properties as a function of the load rate in the compsite was correlated to its microstructure, especially the presence of aggregates at low concentration.
An hybrid microwave absorbers, made of a PE/NiFe sheet, an epoxy substrate and multi-scale metallic paches was designed. Results of simulation showed that an absorption level of more than 10 dB can be obtained between 2 and 4 GHz for a low thickness (6 mm). A preliminary step consisted in realizing a demonstrator measured in a WR-284 waveguide. First measurements showed that a good agreement is observed between experimental results and simulated ones, thus validating the possibility to increase the bandwidth of absorption by coupling a metasurface and a composite absorbing material.
3D-printing-compatible filaments were realized with PE/NiFe et PE/C composites. The study of the printability is under progress.

The future prospects of the project will concern the development of materials and the modeling and realization of microwave absorbers.
New formulations of composites will be tested, especially in using ferrimagnetic powders (nickel ferrite family). Our studies concerning the 3D printing of composites will be followed with the final aim to realize 3D rpinted microwave devices (terminations).
The modeling of hybrid microwave absorbers will be pursued with the aim to take benefit of the coupling between metasurfaces and composite materials in order to increase the bandwidth of absorption. A free space measurement of an hybrid microwave absorber will be performed before the end of the project.

The results of the project led to 1 publication, 1 communication in an international conference and 5 communications in national conferences:
1. Y. Arbaoui, V. Laur, A. Maalouf, P. Queffelec, D. Passerieux, A. Delias, P. Blondy, “Full 3D printed microwave termination: a simple and low cost solution”, IEEE Trans. Micr. Th. & Tech., 64 (2015), p. 271-278
2. Y. Arbaoui, V. Laur, A. Maalouf, P. Queffelec, “3D printing for microwave: materials characterization and application in the field of absorbers”, IEEE International Microwave Symposium, Phoenix, session poster, mai 2015
3. Y. Arbaoui, A. Chevalier, V. Laur, A. Maalouf, J. Ville, P. Roquefort, P. Agaciak, T. Aubry, P. Queffelec, “Elaboration, caractérisation et modélisation de composites magnétiques : application aux métamatériaux absorbants Partie 1”, 14ème Journées de Caractérisation Microondes et Matériaux, Calais, Session poster, mars 2016
4. Y. Arbaoui, V. Laur, A. Maalouf, P. Queffelec, “L’impression 3D pour les hyperfréquences : caractérisation EM et application dans le domaine des absorbants”, 19èmes Journées Nationales Microondes, Bordeaux, Session orale, juin 2015
5. R. Niemiec, É. Lheurette, L. Burgnies, V. Sadaune et D. Lippens, “Élaboration, caractérisation et modélisation de composites magnétiques : application aux métamatériaux absorbants Partie 2”, 14ème Journées de Caractérisation Microondes et Matériaux, Calais, Session orale, mars 2016
6. N. Fernez, L. Burgnies, É. Lheurette, V. Sadaune et D. Lippens, “Ingénierie de la dispersion pour des absorbants électromagnétiques ultra-minces, large-bandes à base de métamatériaux”, 14ème Journées de Caractérisation Microondes et Matériaux, Calais, Session orale, mars 2016
7. R. Niemiec, É. Lheurette, L. Burgnies, D. Lippens, “Absorbants large bande à l’aide de composites ferromagnétiques pour la bande S”, assemblée générale du GDR ONDES : Interférence d’ondes, Lyon 19 – 21 octobre 2015

Potential applications of electromagnetic absorbers strongly increased over the past few years. Radar absorbing materials were mainly used for stealth applications in the past but are now also integrated in industrial processes (electromagnetic compatibility in RF systems, antennas…). Moreover, the strong development of wireless technologies has led to an increase in the human exposure to electromagnetic waves. This fact gives rise to new public health issues and house protection against electromagnetic radiations is thus a pretty hot topic. Potential applications of radar absorbers are nowadays numerous and new technologies have thus to be developed to answer to these growing needs.
This project has two main objectives: i) ultra-thin absorbers for low frequency applications (<4 GHz) and ii) 3D absorbers or Frequency Selective Surfaces (FSS).
The need in ultra-thin low-frequency absorbers concerns both military and civil engineering. Indeed, at these frequencies, the most efficient solutions consist in using ferrite ceramics (heavy and expensive) or loaded polymer foams (thick). Flexible magnetic composites can also be used but their absorption capacities are lower. This project proposes to design and fabricate ultra-thin absorbers thanks to the coupling of metasurfaces and composite materials. Considering the frequency band of interest (1-4 GHz), potential applications will concern not only stealthiness of military systems but also the house protection against radiations (GSM, Wifi, 3G, 4G) and a decrease of the electromagnetic interactions between civil radars and wind plants.
The second objective of the project is to develop technological means for the realization of 3D absorbers and FSS. These 3D objects will be applied to electronic war (protection against electromagnetic attacks) or to electromagnetic compatibility issues (absorbent packaging for microwave devices). 3D printing of composite materials and 3D selective metallization processes will be used to realize the demonstrators.