HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. ”Characterization in a Wide Frequency Range (40 MHz 67 GHz) of a KTa0.65Nb0.35O3 Thin Film for Tunable Applications” Grégory Houzet, Thierry Lacrevaz, Cédric Bermond, Bernard Flechet, Arnaud Le Febvrier, Stéphanie Deputier, Maryline Guilloux-Viry, Patrick Quéffélec

A Y-junction circulator based on empty substrate integrated coaxial line (ESICL) technology is proposed in this paper. As ESICL is a novel transmission line, many of the common waveguide devices have not yet been developed in this technology, i.e., only filters, a power divider, a 90° hybrid directional coupler or transition structures have been presented but no nonreciprocal devices. In this paper, a ferrite-based circulator has been designed and fabricated to operate at a central frequency of 12 GHz. Measurements performed with the help of an electromagnet confirms the stability of the circulator response under different DC biasing fields. Also, measurements with magnets have been done to integrate the circulator in communication systems. In addition, different temperature tests from 20° C to 90°C have been carried out with the aim of checking the scattering parameters variations. The experimental results confirm the results obtained by the full wave simulations: insertion loss better than -1 dB isolation and return loss below -10 dB from 10 to 14 GHz.

Tungsten substituted nickel-zinc ferrite nanoparticles with chemical composition of Ni0.5Zn0.5WxFe2-xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8 & 1.0) were successfully synthesized by a chemical co-precipitation method. The prepared ferrites were pre sintered at 850 degrees C and then annealed at 1000 degrees C in a muffle furnace for 3 h each. This sintered powder was inspected by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM) to study the structural, optical, and magnetic properties. XRD measurement revealed the phase purity of all the nanoferrite samples with cubic spinel structure. The estimated crystallite size by X-ray line broadening is found in the range of 49-62 nm. FTIR spectra of all the samples have observed two prominent absorption bands in the range 400-700 cm(-1) arising due to tetrahedral and octahedral stretching vibrations. Vibrating sample magnetometer experiments showed that the saturation magnetizations (Ms) decreased with an increase in non-magnetic tungsten ion doping. The electrical resistivity of tungsten doped Ni Zn nano ferrites were examined extensively as a function of temperature. With an increase in tungsten composition, resistivity was found to decrease from 2.2 x 10(5) Omega cm to 1.9 x 10(5) Omega cm which indicates the semiconducting behavior of the ferrite samples. The activation energy also decreased from 0.0264 to 0.0221 eV at x = 0.0 to x = 1.0. These low coercive field tungsten doped Ni-Zn ferrites are suitable for hyperthermia and sensor applications. These observations are explained in detail on the basis of various models and theories.

A ferromagnetic material involving nickel-iron particles embedded in a polyethylene matrix is synthesized and electrically characterized between 1 and 12 GHz. These measurements show the combination of electric and magnetic activity along with significant loss terms. We take benefit of these properties for the design of broadband electromagnetic absorbers. To this aim, we use a fractal structuring based on Moore curves. The advantage of etching patterns over metallic ones is clearly evidenced, and several pattern absorbers identified by their Moore's order iteration are designed and analyzed under oblique incidence.

This paper presents a theoretical tool, which combines a generalized permeability tensor model, a homemade 3D magneto-static solver, and a commercial electromagnetic simulation software Ansys HFSS™ for accurate modeling of ferrite-based devices regardless of their state of magnetization. A magneto-static analysis is carried out to find the internal biasing fields in the ferrite sample. Permeability tensor components are computed using a generalized permeability tensor model. Real and imaginary parts of permeability tensor components are then integrated into the commercial 3D electromagnetic simulation software HFSS retaining the spatial variations of internal biasing fields in the ferrite sample. Frequency domain simulations are done using HFSS. This theoretical modeling approach is validated by comparing the theoretical simulation results with experimental ones in the case of a coaxial line loaded by a magnetized ferrite. Proposed approach is then applied to the design of a microstrip Y-junction circulator. Finally, a demonstration prototype is manufactured in the Low Temperature Co-fired Ceramics technology.

This article presents the miniaturization of an UWB planar monopole antenna covering the VHF band through the use of low loss Magneto-Dielectric Materials (MDM). A new structure of the planar monopole antenna using slots have been proposed, which allows to reach high miniaturization rates by covering partially the antenna with MDM. This new monopole structure shows a miniaturization rate of 60% by covering about only 12 % of the antenna surface by the MDM.

Microwave load (or termination) is a one port device which makes it possible to convert efficiently microwave energy into heat. Important parameters of a load are its Voltage Standing Wave Ratio (VSWR) and its power handling capability. In a receiver, loads are placed at unconnected ports of hybrid couplers or power dividers to keep the VSWR of the signal path as low as possible. They are also commonly used to convert circulators in isolators by ensuring a good isolation between ports. Coaxial and rectangular waveguide loads are commonly fabricated by using absorbing materials. Materials are chosen depending on the desired power handling capability. Low and medium power rectangular waveguide loads usually consist of lossy composites that are molded or machined in the form of a tongue, multiple steps, tapered spears or a pyramid in order to minimize VSWR over a wide bandwidth. Molding or machining processes have a high impact on the cost of the termination. In this context, the use of 3D printing technologies appears to be a way to optimize these devices cost, especially during the prototyping step or for the production in small series. Our studies were focused on the use of Fused Deposition Modeling (FDM) which is the cheapest 3D printing method and for which a large number of composite materials that can exhibit interesting absorption properties (high loss tangent) are available. In this paper, we will at first describe the 3D printing process and materials that were used to fabricate microwave loads. Then, demonstrators in different frequency bands will be described.

A series of Co2+ substituted Li0.5CoxFe2.5−xO4 (x = 0.1, 0.3, 0.5) has been prepared by a citrate precursor method. The distribution of cations on A-site and B-site was studied by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Mössbauer Spectroscopy. XRD confirmed the formation of ordered α-phase with prominent peaks at (220), (311), (400), (422), (511), (440). SEM and TEM confirmed the homogeneous formation of cubic phase with an average crystallite size of 50 nm. From FTIR studies, the bands at 603.78, 606.14 and 610.08 cm−1 confirmed the formation of Fe3+–O2− bond at tetrahedral (A-site), whereas bands at 477.25, 474.84 and 471.69 cm−1 confirmed the formation of Fe3+–O2− bond at octahedral site (B-site); shifting in frequency was observed with an increased amount of cobalt doping. Further, Raman spectra revealed the distribution of cations at tetrahedral and octahedral site by means of modes A1g, T2g, Eg. Mössbauer spectra with two magnetic sextets confirmed two different environments of Fe3+ ions. With an increase in cobalt doping, the crystallite size was observed to increase and hence an increase in relative area B/A ratio confirming the occupancy of Co2+ at B-site. The temperature dependence of DC resistivity was found to decrease with an increase in temperature. With an increase in cobalt substitution, DC resistivity was observed to increase from 2.32 × 106 to 3.46 × 107 Ω cm. A decrease in activation energy is noticed in the present investigation and this observed semiconducting behavior makes these nanomaterials suitable in NTC (negative temperature coefficient) devices. These observations were explained on various models and theories.

Yttrium Iron Garnet based ferrites are used in nonreciprocal devices like microwave circulators and isolators. The low dielectric and magnetic losses of those materials provide the required properties. The main drawbacks of circulators are their size and cost, due to complex mechanical assembling of the different materials. Adapting the different materials to a common LTCC (Low Temperature Co-fired Ceramics) process should be a possible solution to simplify the complex manufacturing process. We showed that cationic substitutions (bismuth and copper) enable a considerable decrease of the sintering temperature, from about 1450°C to down to 950°C. Furthermore, due to bismuth cations, a high permittivity is achieved allowing the reduction of the circulator core size. Assemblies of ferrite and dielectric tapes metallized with silver or gold are studied. The first results of circulators in LTCC-technology with gold and silver screen printing are presented and the compatibility of the different elements is analyzed.

An efficient and inexpensive process is presented that produces highly oriented bulk compacts made of BaM particles. Barium hexaferrite particles (BaM, nominal composition BaFe11O19) were prepared by a chemical coprecipitation method, using different rates and types of precipitating agents (NaOH and Na2CO3). It was demonstrated that when a large excess of Na2CO3 is used, a noteworthy packing of hexagonal BaM platelets is obtained, after mechanical compaction and firing at moderate temperature (1140 degrees C), without including any more steps than those required for a conventional sintering process. The hysteresis loop displays a very competitive squareness of 0.88 (normalized remanent magnetization) and a coercivity of 215 kA/m, which make this BaM bulk ferrite suitable for self-biased applications. (C) 2017 Elsevier B.V. All rights reserved.

Cet article decrit une nouvelle methodologie pour la conception des dispositifs hyperfrequences a ferrite. Un modele general de tenseur de permeabilite, capable de decrire tout etat d’aimantation des materiaux magnetiques aimantes, est mis a profit en l’associant a une analyse magnetostatique multi-echelle. Un solveur magnetostatique 3D a ete developpe et l’evolution de l’aimantation au sein d’une cellule du maillage est decrite par un modele de cycle d’hysteresis. Cette approche permet ainsi de tenir compte de maniere precise du caractere inhomogene des proprietes d’un ferrite. Couplee a un solveur electromagnetique, elle autorise la simulation predictive des structures integrant des materiaux magnetiques.

The general field of the invention is that circulators and microwave isolators having three metal tracks (11, 12) arranged in Y and a central core (14) of ferrite. At least the central portion of the substrate is a barium hexaferrite and / or strontium which a part of barium ions and / or part of the strontium ion has been replaced by lanthanum ions and a portion of iron ions has been replaced by ions cobalt, the general chemical formula of said barium strontium hexaferrite being BaxSryLazFe12-wCowO19, the sum of the indices x, y and z being equal to 1, x being between 0 and 1, the index y being between 0 and 1, the index z is between 0 and 0.5 and the index w is between 0.05 and 0.4.

This study deals with the dielectric properties of recycled glass foams and their use as microwave absorbers. Glass wastes from Cathode Ray Tube have been used to produce foams by heating a mixture consisting of glass cullet and foaming agents (carbon or a combination of carbon, TiO2, MnO2 and AIN). As only part of the carbon introduced into the initial load oxidizes and contributes to the foaming process, the residual fraction acts as an electromagnetic absorber. The effect of the carbon load rate on the foams density and microwave properties was studied. These materials present a low permittivity and high dielectric losses in X-band. Foams density mainly controls the dielectric properties. Carbon-based glass foams show a great potential as microwave absorbers with a shielding effectiveness of 20 dB/cm at 12 GHz. Moreover, a tradeoff between the density and shielding efficiency can be achieved by controlling the load rate of carbon. (C) 2017 Elsevier Ltd. All rights reserved.

The use of 3D technology in the field of microwave electronics requires the development of new materials adapted to these applications. In this study, magnetic composites composed of polyethylene (PE) matrix filled with Nickel–Iron alloy (Ni 81 Fe 19 ) are prepared using two elaboration devices: first, a propeller mixer for small quantity of samples, and then, a twin screw extruder able to produce higher samples amounts. Microstructural and rheological characterizations are suggested in order to study the feasibility of shaping PE/NiFe composites with 3D printer using Fused Deposition Modeling technique. A shear-thinning behavior with the dispersion of NiFe micrometric particles allows the use of 3D printer to shape final composites. A microwave characterization is also performed. Electromagnetic properties are predicted by the adjustment of a model based on mixing laws taking into account demagnetization effect and interactions between NiFe particles. The production of composite filaments and first printing tests are also presented.

Nano crystalline Ni–Zn ferrites of composition Ni0.5Zn0.5Fe2O4have been prepared by a chemical co-precipitation method. The powdered samples were sintered at a temperature of 800°C and 900°C for three hours. X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Fourier Transform Infrared (FTIR) Spectroscopy were used to study their structural and morphological changes. The enhanced magnetic properties were investigated by using a Vibrating Sample Magnetometer (VSM). The saturation magnetization was found to increase from 73.88 to 89.50emu/g as a function of sintering temperature making this material useful for high frequency applications. Electromagnetic studies showed sustained values of permittivity up to 1GHz. These results have been explained on the basis of various models and theories.

This article describes a new set of tools developed to improve the conception and modeling of non-saturated ferrite-based devices such as twin toroid phase shifters. These new simulation tools benefit from a generalized permeability tensor model able to describe the permeability tensor of a ferrite sample whatever its magnetization state. This model is coupled to a homemade 3D multi-scale magnetostatic analysis program, which describes the evolution of the magnetization through the definition of a hysteresis loop in every mesh cell. These computed spectra are then integrated into 3D electromagnetic simulation software that retains the spatial variations of the ferrite properties by using freshly developed macro programming functions. This new approach allows the designers to accurately model complex ferrite devices such as twin toroid phase shifters. In particular, we demonstrated a good agreement between simulated and measured phase shifts as a function of applied current values with a predicted maximum phase shift of 0.96 times the measured value.

Cet article presente la premiere demonstra-tion experimentale d’un effet non-reciproque dans des dis-positifs realises en technologie Molded Interconnect Device (MID). Le substrat est constitue d’un polymere cyclo-olefine (COP) mis en forme par moulage dont les proprietes dielectriques ont ete etudiees dans la bande d’interet. La non-reciprocite est ici obtenue par l’utilisation d’un hexa-ferrite pre-oriente. En l’absence de champ applique, le cir-culateur presente des pertes d’insertion de 3,32 dB et une isolation proche de 14 dB a 30,7 GHz. Ces performances, bien que modestes, constituent un premier jalon dans la re-alisation de circulateurs a bas cout a grande echelle dans cette technologie