Nickel zinc ferrites (NZF) have been considered as one of the basic components in high frequency electromagnetic applications especially in the field of telecommunications. In the present study, the aim was to produce high quality nickel zinc ferrite ceramics at low soaking temperatures. For this purpose, conventional ceramic manufacturing method based on mixed oxide precursors was followed using calcium fluoride, CaF2, as sintering additive. During the sintering studies, it was noticed that both the microstructure and the electromagnetic properties of the NZF ceramics were modified to a great extent by CaF2. Therefore, material characterization studies involving microstructural, dielectric and magnetic properties were conducted with respect to CaF2 content of ceramics and soak duration. The results showed that due to the presence of CaF2 in ceramics, significant improvements were achieved not only in kinetics of sintering but also in the parameters / DC electrical resistivity, dielectric constant and dielectric loss factor. For example, 1.0 wt% CaF2 added NZF ceramic produced in this study had a DC electrical resistivity of 1011 &amp / #61527 / -cm which was 100,000 times bigger than the one attained in pure NZF ceramic. On the other hand, the dielectric constant exhibited a flat behavior up to 40 MHz with a value around 16. In addition, no resonance peak was observed in dielectric loss factor spectra, and the typical values of dielectric loss factor lied below 0.01. Besides the achievements mentioned, the magnetic properties such as relative magnetic loss factor and hysteresis parameters were also improved.

La miniaturisation des antennes s'accompagne d'une dégradation leurs performances (bande passante, gain, efficacité), surtout avec l'utilisation de substrats matériaux diélectriques. Pour relever le défi « intégration / performances », la conception de nouveaux matériaux tels que les ferrites magnétoélectriques constitue une alternative des plus prometteuses. Ce travail met en avant les principaux paramètres à l'élaboration de ferrite spinelle par coprécipitation. Un traitement thermique modéré a permis l'obtention de céramiques semi poreuses pour la montée en fréquence. En parallèle, l'anisotropie magnétocristalline, liée à la composition (rapport Nickel / Zinc, Cobalt, Fer 2+…) ; ainsi que l'anisotropie magnétoélastique lors de l'application d'une contrainte, étendent encore le domaine des faibles pertes des ferrites de Nickel-Zinc de 400 MHz à plus de 1 GHz. Ces matériaux ont ainsi pu équiper des antennes sur les fréquences du DVH-H (470 – 830 MHz) et répondent aux normes du DVB-H. De façon à profiter pleinement de la miniaturisation, nous avons proposé une antenne imprimée. Une bonne corrélation est trouvée entre les résultats de simulation et de mesure, ainsi que des relations adaptées aux antennes patch. Enfin dans le domaine émergent des communications On / Off bodies, nous avons développé des antennes flexibles sur un substrat de type PDMS. Pour assurer une bonne efficacité de l'antenne, celle-ci est encapsulée, ce qui évite une métallisation hasardeuse (fissures, manque d'adhérence). / Antenna miniaturization, especially with dielectric substrates, is accompanied by a radiation loss (bandwidth, gain, efficiency). To meet the challenge "integration / performance", the design of new materials such as magnetodielectrics ferrites is a promising alternative. To satisfy these requirements, this work highlights the main parameters of ferrite spinel development by coprecipitation. A moderate thermal treatment leads to semi porous ceramics. In parallel, the magnetocrystalline anisotropy, related to the composition (ratio Nickel / Zinc, Cobalt, Iron 2+ ...), and the magnetoelastic anisotropy with application of stress, extend the field of low-loss from 400 MHz to over 1 GHz, in the Nickel-Zinc ferrite. These materials were able to equip antennas on DVH-H frequencies (470-830 MHz). In order to take full advantage of miniaturization, we proposed a printed antenna. A good correlation between simulation results and measurement is obtained, together with relations adapted to patch antennas. Finally, in the emerging field of communications On / Off bodies, we have developed flexible antennas on PDMS substrate. To ensure good antenna efficiency, it is encapsulated, thereby avoiding a hazardous metallization (cracks, loss of adhesion).