magnetoacoustic

Magnetoacoustic refers to phenomena in which magnetic fields and acoustic (elastic) waves interact in a medium. The term covers both waves in magnetized plasmas and waves in magnetically active solids, where the coupling between magnetic, elastic, and sometimes electric properties leads to characteristic propagation and resonance behaviors.

In magnetized plasmas, the framework of magnetohydrodynamics describes magnetoacoustic waves as compressional modes modified by the magnetic field. There are fast and slow magnetoacoustic waves, with phase speeds between the Alfvén speed and the sound speed, depending on propagation direction relative to the field. These waves are important in solar and space physics and in laboratory fusion devices.

In solids, magnetoelastic coupling arises when strain or acoustic waves influence magnetic order and vice versa. This can produce magnetoelastic (magnetostriction) waves and phenomena like magnetoacoustic resonance. The effect is exploited in sensors and actuators and in nondestructive evaluation, using materials with strong magnetoelastic coupling such as Terfenol-D.

In biomedical imaging, magnetoacoustic tomography or magnetoacoustic imaging uses ultrasound signals generated by the Lorentz force when biological tissue conducts current in a magnetic field. Detected acoustic waves are used to reconstruct electrical conductivity or permittivity distributions, offering a complementary modality to traditional imaging.

Research on magnetoacoustic phenomena spans theory and experiment, encompassing plasma physics, condensed matter physics, and applied imaging. Key concepts include wave mode conversion, anisotropic propagation, and the role of material properties such as magnetization, elasticity, and conductivity.