Coupling effects between elastic and electromagnetic fields from the perspective of conservation of energy

Coupling effects among different physical fields reflect the conversion of energies from one field into another substantially. For simple physical processes, their governing or constitutive equations all satisfy the law of conservation of energy (LCE). Then, an analysis is extended to the coupling effects. First, for the linear direct and converse piezoelectric and piezomagnetic effects, their constitutive equations guarantee that the total energy is conserved during the process of energy conversion between the elastic and electromagnetic fields. However, the energies are converted via the work terms, (βijkEi),kvj and (γijkHi),kvj, rather than via the energy terms, βijkEiejk and γijkHiejk. Second, for the generalized Villari effects, the electromagnetic energy can be treated as an extra contribution to the generalized elastic energy. Third, for electrostriction and magnetostriction, both effects are induced by the Maxwell stress. Moreover, their energies are purely electromagnetic and thus both have no converse effects. During these processes, the energies can be converted in three different ways, i.e., via the non-potential forces, via the cross-dependence of the energy terms, and directly via the electromagnetic interactions of ions and electrons. In the end, the general coupling processes which involve elastic, electromagnetic fields and diffusion are also analyzed. The advantages of using this energy formulation are that it facilitates discussion of the conversion of energies and provides better physical insights into the mechanisms of these coupling effects.

Modelling Propagating Bloch Waves in Magnetoelectroelastic Phononic Structures with Kagomé Lattice Using the Improved Plane Wave Expansion

We studied the dispersion diagram of a 2D magnetoelectroelastic phononic crystal (MPnC) with Kagomé lattice. The MPnC is composed of BaTiO3–CoFe2O4 circular scatterers embedded in a polymeric matrix. The improved plane wave expansion (IPWE) approach was used to calculate the dispersion diagram (only propagating modes) of the MPnC considering the classical elasticity theory, solid with transverse isotropy and wave propagation in the xy plane. Complete Bragg-type forbidden bands were observed for XY and Z modes. The piezoelectric and the piezomagnetic effects significantly influenced the forbidden band widths and localizations. This investigation can be valuable for elastic wave manipulation using smart phononic crystals with piezoelectric and piezomagnetic effects.

Harmonic Responses of Blades with Piezoelectric or Piezomagnetic Coatings

A successful prediction that whether a compressor blade is able to overcome the resonance fatigue and fatigue life of forced vibration is based on its harmonic response analysis.Hard coatings with metal or ceramic substrate are effective to change the natural characteristics and vibration amplitude of a compressor blade so that to improve the anti-vibration fatigue capability. In this paper, modal analysis and harmonic response analysis based on the finite element method are achieved to investigate the contributions of the two different hard coatings on the natural characteristics and vibration amplitude of a compressor blade. The two kinds of hard coatings are modeled by both anisotropic materials and involving their piezoelectric or piezomagnetic effects. The blade is modeled as an isotropic one. The natural frequencies and vibration amplitude of blade with different coating thickness are numerically calculated and compared. Results show that the hard coatings with different thickness play an important role in the natural characteristics and harmonic response analysis of the blade.

The Piezoelectric and Piezomagnetic Effects on the Surface Wave Speed

the piezoelectric and piezomagnetic effects and the influence of short and open circuit on the surface wave speed are investigated in this paper. First, the elastic, piezoelectric and piezomagnetic coefficients in the considered ordinate system are obtained by Bonde transformation from that in the crystal axes ordinate system. Then, the equation which surface wave speed satisfies is derived from the free traction condition on the surface of piezoelectric and piezomagnetic half space with consideration of short and open circuit case. Some numerical examples are given and the piezoelectric and piezomagnetic effects and the influence of short and open circuit on the surface wave speed are shown graphically.

NONRECIPROCAL MULTIFERROIC SUPERLATTICES WITH BROKEN PARITY SYMMETRY

Multiferroic materials are characterized by the coexistence of ferroelectric and ferromagnetic (or antiferromagnetic) orders, the coupling to lattice vibration can be invoked either through piezoelectric or piezomagnetic effects. In this paper, the polaritonic band structures of multiferroic superlattices composed of oppositely polarized domains are investigated using the generalized transfer matrix method. For the primitive cell with broken parity symmetry, the polaritonic band structure is asymmetrical with respect to the forward and backward propagation directions (nonreciprocality). In particular, the band extreme points move away from the Brillouin zone center. This asymmetry in band-gap positions and widths can be used to design compact one-way optical isolators, while the extremely slow light velocities near the asymmetrical upper edges of lower bands includes the essential ingredients for designing slow light devices.

Piezomagnetic effects induced by artificial sources at Mt. Vesuvius (Italy): preliminary results of an experimental survey

In order to put new constrains on magnetic effects associated with mechanical stresses, high frequency monitoring of the geomagnetic field was carried out during a seismic tomography experiment (TOMOVES'96 project) at Mt. Vesuvius. Eight proton precession and one Cesium magnetometers were installed along a profile on the SW flank of the volcano to observe possible magnetic changes induced by explosions. Measurements were performed at different sampling frequencies (10 Hz, 0.5 Hz and 0.1 Hz). A remarkable change in the intensity of the magnetic field was observed in only one case. The magnetic transient lasted 12-13 min, reaching the maximum amplitude of slightly less than 15 nT.

Magnetic-Coupling Properties in Polycrystals

Quantitative Texture Analysis procedures for characterisation of polycrystal pyromagnetic, magnetoelectric and piezomagnetic effects are proposed. The considered phenomena link the thermic, electric and elastic subsystems of a given body with its magnetic subsystem. Brief resumes of required thermodynamic, tensor and texture methods are given. Peculiar behaviour of magnetic (axial-tensor) quantities under colour symmetry operations is described. The use of Neumann's Principle in the investigation of the considered effects is discussed. Surface representation of magnetic-coupling properties is analysed in detail. Colour symmetry, combined with the axial nature of the related tensors, determines the shapes of properties' surfaces. Bunge's spherical harmonics treatment of surface representations is adapted to axial-tensor cases. Computer-generated cases of pyromagnetic, magnetoelectrie and piezomagnetic textures are solved.