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Contactless Mode-Selective Resonance Ultrasound Spectroscopy: Electromagnetic Acoustic Resonance

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We describe a novel method for measuring elastic constants and internal friction in electrically conductive solids electromagnetic acoustic resonance EMAR. Contactless coupling based on the Lorentz-force mechanism is achieved by permanent magnets to supply the static magnetic field and a solenoidal coil surrounding a rectangular-parallelepiped specimen. Because the direction and symmetry of the Lorentz forces can be easily changed by changing the geometrical configuration of the static field and the coil, we can select a single vibration group of interest, filtering out the other vibration groups. In principle, seven vibration groups can be independently excited among eight possible vibration groups of a rectangular-parallelepiped specimen. This provides a big advantage in mode identification. The EMAR method is much less sensitive than the RUS method to the initial guessed Cij for the inverse calculation. For a copper monocrystal, we reached the same Cij with 100-varied guessed values. For silicon-carbide-fiber-reinforced titanium-alloy composites, we could vary the guessed values up to 20. We used a free-decay method to measure internal friction Qijexp -1. The contactless EMAR method enables one to measure intrinsic internal friction, free from energy loss into transducers and grips.

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  • Acoustics
  • Electricity and Magnetism

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