 |
|
Theses
Parametric magnetoacoustic effects in magnetic dielectrics and composites materials
Parametric magnetoacoustic effects in magnetic dielectrics and composites materials
Abstract : Parametric interaction in active magnetoacoustic materials of various composition and structures is studied experimentally.
Influence of composition of nickel-based polycrystalline ferrite on sensitivity of sound velocities to DC and RF magnetic field is considered. Maximum magnetoelastic coupling 59% and magnetic sensitivity of shear wave velocity 100%/kOe were found for composition Fe2,026Ni0,95Co0,024О4. In the testing as an active medium for parametric wave phase conjugation this composition demonstrated extraordinary gain increment 4.5 μs-1.
Original amplitude-phase pulse (APP) method was elaborated and applied for studies of parametric sensitivity of perspective active materials with low (≈9 MRa) acoustic impedance: Terfenol-D based composite and porous nickel ferrite. Sensitivity of sound velocity to AC magnetic field is found as 4.39%/kOe and 3.39%/kOe in the composite and porous ferrite respectively.
The new parametric acoustic phenomenon of three-phonon bound excitation is observed in “easy plane” antiferromagnetic crystal α-Fe2O3 under transversal AC magnetic pumping. Sub-threshold and supercritical modes of the three-phonon excitations were studied by the APP method and described theoretically. The specific feature of the supercritical mode is forming of singularity in a finite pumping duration. Singularity is stabilized by intrinsic nonlinearity in the phonon system
Influence of composition of nickel-based polycrystalline ferrite on sensitivity of sound velocities to DC and RF magnetic field is considered. Maximum magnetoelastic coupling 59% and magnetic sensitivity of shear wave velocity 100%/kOe were found for composition Fe2,026Ni0,95Co0,024О4. In the testing as an active medium for parametric wave phase conjugation this composition demonstrated extraordinary gain increment 4.5 μs-1.
Original amplitude-phase pulse (APP) method was elaborated and applied for studies of parametric sensitivity of perspective active materials with low (≈9 MRa) acoustic impedance: Terfenol-D based composite and porous nickel ferrite. Sensitivity of sound velocity to AC magnetic field is found as 4.39%/kOe and 3.39%/kOe in the composite and porous ferrite respectively.
The new parametric acoustic phenomenon of three-phonon bound excitation is observed in “easy plane” antiferromagnetic crystal α-Fe2O3 under transversal AC magnetic pumping. Sub-threshold and supercritical modes of the three-phonon excitations were studied by the APP method and described theoretically. The specific feature of the supercritical mode is forming of singularity in a finite pumping duration. Singularity is stabilized by intrinsic nonlinearity in the phonon system
Cited literature [10 references]
https://tel.archives-ouvertes.fr/tel-00291549
Contributor : Régine Duplouich <>
Submitted on : Friday, June 27, 2008 - 12:46:58 PM
Last modification on : Tuesday, December 8, 2020 - 3:31:59 AM
Long-term archiving on: : Friday, May 28, 2010 - 9:04:28 PM
Contributor : Régine Duplouich <>
Submitted on : Friday, June 27, 2008 - 12:46:58 PM
Last modification on : Tuesday, December 8, 2020 - 3:31:59 AM
Long-term archiving on: : Friday, May 28, 2010 - 9:04:28 PM