Vincent Laur

Magnetodielectric effect in trilayered Co65Fe35B20/PVDF/Co65Fe35B20 composite materials. Prediction and measurement for tunable microwave applications

The variation in the permeability of a multilayered polyvinylidene fluoride/CoFeB (piezoelectric/magnetostrictive) composite material under the action of a dc voltage is demonstrated. The driven-voltage permeability is first predicted using a finite element method-based multiphysics calculation. The simulation allows us to determine a magnetic anisotropy field of 45 Oe induced in the ferromagnetic layers by the mechanical coupling between magnetostrictive and piezoelectric layers due to the applied dc voltage. A variation of 30% for the permeability of the ferromagnetic layers is then measured using a radiofrequency permeameter and under the application of a dc voltage of 15 V applied on the ferromagnetic layers, which also act as electrodes for the bias of the polyvinylidene fluoride (PVDF). An additional measurement of the trilayered structure under the application of a dc magnetic field is finally performed to evaluate the magnetic field needed to get a 30% variation in the magnetic layers permeability...

KTa/sub 0.6/Nb/sub 0.4/O/sub 3/ ferroelectric thin film behavior at microwave frequencies for tunable applications

In this study about the relationships between structural and microwave electrical properties of KTa1-xNbxO3 (KTN) ferroelectric materials, a KTN thin film was deposited on different substrates to investigate how KTN growth affects the microwave behavior. Interdigital capacitors and stubs were made on these films through a simple engraving process. Microwave measurements under a static electric field showed the importance of the substrate on the circuit behavior and, notably, on the tuning factor

Full 3-D Printed Microwave Termination: A Simple and Low-Cost Solution

This paper describes the realization and characterization of microwave 3-D printed loads in rectangular waveguide technology. Several commercial materials were characterized at X-band (8-12 GHz). Their dielectric properties were extracted through the use of a cavity-perturbation method and a transmission/reflection rectangular waveguide method. A lossy carbon-loaded Acrylonitrile Butadiene Styrene (ABS) polymer was selected to realize a matched load between 8 and 12 GHz. Two different types of terminations were realized by fused deposition modeling: a hybrid 3-D printed termination (metallic waveguide + pyramidal polymer absorber + metallic short circuit) and a full 3-D printed termination (self-consistent matched load). Voltage standing wave ratio of less than 1.075 and 1.025 were measured over X-band for the hybrid and full 3-D printed terminations, respectively. Power behavior of the full 3-D printed termination was investigated. A very linear evolution of reflected power as a function of incident power amplitude was observed at 10 GHz up to 11.5 W. These 3-D printed devices appear as a very low cost solution for the realization of microwave matched loads in rectangular waveguide technology.

Intercomparison of Permittivity Measurement Techniques for Ferroelectric Thin Layers

The dielectric properties of a KTa0.65Nb0.35O3 (KTN) ferroelectric composition for a submicronic thin layer were measured in the microwave domain using different electromagnetic characterization methods. Complementary experimental techniques (broadband methods versus resonant techniques, waveguide versus transmission line) and complementary data processing procedures (quasi-static theoretical approaches versus full-wave analysis) were selected to investigate the best way to characterize ferroelectric thin films. The measured data obtained from the cylindrical resonant cavity method, the experimental method that showed the least sources of uncertainty, were taken as reference values for comparisons with results obtained using broadband techniques. The error analysis on the methods used is discussed with regard to the respective domains of validity for each method; this enabled us to identify the best experimental approach for obtaining an accurate determination of the microwave dielectric properties of ferroelectric thin layers.

KTN Dielectric Properties at Microwave Frequencies: Substrate Influence

To determine the dielectric properties of ferroelectric thin-films over a wide range of frequencies we developed a simple and efficient method based on the measurement of coplanar waveguide realized on ferroelectric/dielectric heterostructures by using a Spectral Domain Approach. We applied this method to KTa 1−x Nb x O 3 (KTN) thin-films deposited on different substrates. The strong differences observed in the dielectric behavior of KTNs according to the growth substrate suggest that it is affected not only via the resulting microstructure, but also by the induced strains. Accuracy of the method was estimated to 15 and 10% on permittivity and loss tangent, respectively.

Microwave study of tunable planar capacitors using mn-doped ba 0.6 sr 0.4 tio 3 ceramics

This paper deals with the microwave study of coplanar tunable capacitors using Mn-doped Ba0.6Sr0.4TiO3 ceramics. These ceramics are developed to improve performance at microwave frequencies (i.e., compromise between tuning capabilities and insertion losses). Interdigitated capacitors were first fabricated on thick Mn-doped BST ceramics. The capacitors showed reduced tuning factor because of a parasitic capacitance between the contact pads. The use of Mn-doped BST/ SiO2 bilayers led to a significant enhancement of the capacitor performance (57% of agility under 200 V at 1 GHz).

Modeling and characterization of self-biased circulators in the mm-wave range

The development of future telecommunication systems requires the miniaturization of circulators. Apart from using planar technologies, removing magnets appears as one of the main solutions to improve the integration of circulators. This technological step requires the use of oriented hexaferrites in their remanent state. Thus, the unusual properties of these materials were used to design and realize a millimeter-wave self-biased circulator in rectangular waveguide. Without magnets, insertion losses of 1.79 dB and an isolation level of 28.1 dB were measured at 41.4 GHz. These results demonstrate the strong potential of these materials for the design of self-biased circulators.

Ferrite-based phase shifters design: The modeling problem of non-saturated anisotropic ferrites

Modeling the microwave behavior of ferrite in a non-saturated state is a burning issue for ferrite phase shifter designers. In this paper, a WR-90 waveguide loaded by a ferrite slab is studied. Classical simulations, using the Polder tensor, are not consistent with the measurements even in the case of a totally saturated state. An improvement was observed by using a generalized permeability tensor model, enhanced by taking into account an extra dynamic demagnetizing field.

3D printed ferromagnetic composites for microwave applications

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 (Ni81Fe19) 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.

Self-Biased Y-Junction Circulators Using Lanthanum- and Cobalt-Substituted Strontium Hexaferrites

In this paper, we propose the application of polycrystalline lanthanum- and cobalt-substituted strontium hexaferrites in the realization of self-biased circulators. These materials present a high anisotropy field, dependent on the substitution rate, which makes it possible to reach operating frequencies in the millimeter-wave range. A first demonstrator was successfully designed and realized using a 20% rate of substitution (Sr0.8La0.2Fe11.8Co0.2O19). This circulator showed insertion losses of 1.79 dB and an isolation level of 28.1 dB at 41.4 GHz without magnets. Performances can be significantly improved by applying a low magnetic field (Happ=2100 Oe). According to the literature, increasing the substitution rate makes it possible to increase the anisotropy field, and thus, the internal field. Consequently, a 30% substituted strontium hexaferrite was tested. It appears that the anisotropy field was not higher in this case. However, magnetic losses are much lower and enabled us to halve insertion losses of the self-biased circulator (0.87 dB at 41 GHz).