Micro-systèmes et contrôle d'écoulements

Les micro-systèmes magnéto-mécaniques présentent des possibilités intéressantes en matière de contrôle d'écoulements. Ils permettent de remplir les cahiers des charges des constructeurs aéronautiques ou automobiles. Ils sont également plus facilement intégrables sur les prototypes que les MEMS issus de microtechnologies entièrement intégrées. On présentera quelques tests en soufflerie. Les effets sur les écoulements seront discutés et les perspectives tracées

Multilayer modeling of thermoacoustic sound generation for thermophone analysis and design

International audienc

E -tunable magnetic susceptibility and reversible magnetization switching in YIG/Pt/PMN-PZT/Pt heterostructure by low electric and magnetic fields

International audienc

A millimeter-wave inflatable frequency-agile elastomeric antenna

This letter reports a millimeter-wave frequency agile microstrip antenna printed on an ultrasoft elastomeric PDMS substrate. The microstrip patch antenna is supported by a PDMS membrane suspended over an air cavity. The distance H between the patch and the ground plane, and thus the resonant frequency of the antenna, are tuned using pneumatic actuation, taking advantage of the extreme softness of the PDMS membrane. A continuous frequency shift varying from 55.35 to 51 GHz ( ≈8%) has been obtained for a tuning range of H between 200µm and 575µm. In all configurations, the antenna remains matched and its radiation characteristics are very satisfactory

A millimeter-wave microstrip antenna array on ultra-flexible micromachined polydimethylsiloxane (PDMS) polymer

The use of Polydimethylsiloxane (PDMS), an ultra flexible polymer, as a substrate for the realization of reconfigurable microwave devices in the 60-GHz band is presented. As bulk PDMS is demonstrated to be lossy at millimeter waves, membrane-supported devices are considered. A new reliable and robust technological process has been developped to micromachine membrane-supported transmission lines and microstrip antenna arrays. It is shown that transmission lines printed on 20-µm thick membranes exhibit similar performances as bulk substrates commonly used at millimeter-wave frequencies. A microstrip antenna array has been also designed and fabricated to demonstrate the feasibility of directive antennas supported by large membranes. Promising applications for mechanical beam-steering, beam forming and frequency tunable antennas are expected

The equilibrium distribution of magnetization and the processes of magnetization reversal in magnetoelastic nanostructures

International audienc

Explosive instabilities of acoustic waves propagating in antiferromagnet under magnetic and elastic pumping

We report results of our study for an explosive behavior of nonlinear ultrasound occurring when acoustic nonlinearity is efficiently modulated by another physical process. In the considered example, a Lamb wave propagates in an antiferromagnetic plate in the presence of a harmonically oscillating magnetic field and a shear resonance. In this situation, the magnetic pumping induces a backward phase conjugate Lamb wave. Thus the system supports three phonons: two of the Lamb waves and one of the shear resonant mode. The appropriate classical Hamiltonian contains a term describing the interaction of three waves with complex conjugate amplitudes. Correspondingly, the quantum counterpart of the Hamiltonian includes the product of three phonon creation operators. Therefore, it can be expected that the Lamb waves together with the shear resonant mode will be amplified with a huge factor. The amplification occurs in a two-phonon system as well i.e. when the modulation affects not the nonlinear parameter but the linear modulus. However, the amplitudes growth in the two-phonon system is exponential in time as it should be for a classical parametric amplification process, whereas the reported three-phonon system experiences an explosive instability. The explosive behavior means that in the beginning of the process the amplitudes grow exponentially and, soon after that, the positive feedback from the shear resonance induces a mathematical singularity in the time dependency of amplitudes. In other words, if the magnetic pumping is fixed and can not be depleted, the amplitudes become theoretically infinite at some finite moment of time after switching on the pumping. The corresponding synchronism condition is required which equates the magnetic pump modulation frequency to the sum of the double frequency of the Lamb wave and the shear resonance frequency. It is of interest to note that the effect of the additional resonance pumping is analogous to the action of the Feshbach resonance observed in ultra-cold gazes. In this study, we write out the equations of motions for the considered exemplar system using the Hamiltonian formalism which is most suitable for the demonstration of the quantum analogy and of the Feshbach-type resonance effect. Then we theoretically analyze the stationary solution and formulate the conditions for the instability that occurs when the stationary solution is not possible. Finally, we numerically solve the equations of motion and illustrate the explosive dynamics with a number of examples. It is shown that the explosive scenario can occur with a very low signal level i.e. Lamb waves amplitudes comparable to the spontaneous noise in the system. From the practical point, we propose an extremely effective channel for converting magnetic energy into mechanical energy. The considered nonlinearity modulation mechanism is possible to extend onto systems of different physical nature and to apply in acousto-electronics, electro- and hydrodynamics and in microsystems designing