# Smart Nanocomposites for Nanosecond Signal Control: The Nano4 waves Approach
## 1 Introduction  
As stated in ref. [1], artificial or composite materials dedicated to the control of wireless propagation of signals (popularized over the last decade under the term \"metamaterials\" in the scientific community) are multi-functional materials tailored to display electromagnetic (EM) properties not found in nature, through a nonconventional modification of their macroscopic effective permittivity and/or permeability, sometimes reaching negative values [2]. Superlensing beyond the diffraction limit [3], invisible cloaking of objects [4, 5], left-handed propagation reducing the size of devices to one tenth of their operating wavelength [6], frequency selective surface (FSS) [7, 8] or electromagnetic bandgap (EBG) structures [9, 10, 11, 12] are some of the outstanding developments in progress over various frequency ranges, going from GHz to optics.  
The NANO4 WAVES project has made a strong contribution in this area by demonstrating the potential of a clever hierarchical organization of nanoscale inclusions in composite materialsfor controlling nanosecond signals, with a dramatic impact on the electromagnetic propagation at wavelengths ranging from millimeters up to tenths of centimeters.  
The project has combined two major ideas:  
First, we have taken advantage of synergies at the nanoscale between carbonaceous and magnetic metal (oxides) nanoparticles, in order to generate unusual combinations of effective material properties (resonant or not), in particular tuned permittivity \(\varepsilon\), conductivity \(\sigma\) and magnetic permeability \(\upmu\), thanks to the interaction between waves and particles with size lower than the skin depth.  
Second, this synergy has been magnified through a clever hierarchical organization, from the nano to the millimeter scale, of these nano-inclusions in a polymer hosting matrix or printable ink providing extensive possibilities of structuration, conforming and molding.  
Experimentally, we have developed cutting-edge chemical functionalization of nanoparticles. The performance of these systems has been assessed from nano- to macro levels by advanced EM measurement techniques. Their composition and organization have been analyzed by state-of-the-art molecular, structural (Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM)) and 3D Time-of-Flight-Secondary Ion Mass Spectroscopy characterization techniques.  
As a result, the broadband tailoring of permittivity and permeability values has been demonstrated at the macro (or millimeter) scale, with particular control on losses and on anisotropy and periodicity, through specific strategies of conforming and the dispersion of high-aspect ratio inclusions. While classical composite metamaterials for EM signal processing usually consider losses as a drawback and try to minimize them, a major originality of the project has been to exploit absorption as an opportunity (concept of \"metamaterial absorbers\") for the design of antireflective thin coatings. This is paving the road towards simple and compact implementations of surface and volume EM metamaterials suited for a wide variety of stealth or cloaking applications based on multifunctional materials and surfaces.  
The project was split into five steps, strongly interconnected:  
1. Synthesis of carbonaceous and metal (oxide) nano-inclusions
2. Nano-objects characterization
3. Electromagnetic properties: from nanoscale to millimeter scale
4. Control of hierarchical organization
5. Design of EM control functionalities  
These steps are illustrated in the present contribution by a variety of original results obtained within the framework of this project.