Flake-shaped ferromagnetic particle composites for microwave absorption – CARPE DIEM

The objectives of the CARPE DIEM project are to elaborate, characterize and investigate by means of modeling new materials of sub-millimeter thickness allowing to absorb microwave radiations within the broadest frequency range including the spectral window 1-6 GHz.
The foreseen applications encompass shielding of electronic components for the civilian domain and stealth technology for the military domain.

The research activities will address composite materials consisting of a polymeric matrix loaded by ferromagnetic flake-shaped particles. These ones produced by ball milling have typically a lateral size ranging from 10 µm up to 100 µm and a thickness lower than 1 µm. The electromagnetic responses of these composite materials, characterized by their permittivity and permeability spectra, depend on the structural, magnetic, electrical and geometrical properties of flakes but also on their volume fraction and their dispersion features (orientation, relative spatial positions, potential aggregates) within the composite. Exploiting these degrees of freedom should enable us to reduce the permittivity level and to enhance the permeability one. This opens the way for designing a new generation of microwave absorbers in breakthrough with the state of-the art.

The CARPE DIEM project intends to investigate in detail various physical mechanisms governing the microwave behavior of such composite materials. Regarding the permeability spectra, these ones exhibit usually two resonance lines located around 100 MHz and above 1 GHz, respectively. The purpose will be to identify the parameters responsible for the amplitudes and spectral positions of these lines. In particular, the effect of the fabrication process of flakes through the induced magneto-elastic coupling on the permeability spectra will be studied. In addition, mixing magnetic particles with various compositions and/or shapes in the same composite and its impact on the high-frequency magnetic response of composites will be analyzed. Regarding the dielectric properties, the works will explore different ways to reduce the permittivity level either by controlling the dispersion of flakes within the composite or by structuring the composite materials at the millimeter scale.

This project splits into an experimental part including synthesis of materials and the associated characterizations within the microwave range, and a modeling counterpart based on electromagnetic and micromagnetic simulations. The double goal of these simulations is to get a deeper understanding of the involved physical phenomena and to design the samples to be manufactured.

To reach the global objective, the CARPE DIEM project gathers three partners (DASSAULT AVIATION, l’IPCMS and l’Onera) with complementary skills and having a strong experience on this topic coming from two PhD theses advised by the CARPE DIEM partners and defended in 2013.