Abstract
Acoustic structures with active control capabilities are crucial in practical noise reduction. In this work, magnetic tunable sound absorption channels were developed to achieve magnetic acoustic control. The magnetic switch made of hard magnetic composites were inserted in the channel and their magnetic anisotropy was utilized to shift the frequency of peak sound absorption. The sound absorption channels were composed of several lateral Helmholtz units with different lengths, which possessed tunable sound absorption peaks by varying the volume of the channels. The peak sound absorption frequency was inversely proportional to the length of the Helmholtz units and multiple units with similar lengths could produce continuous sound absorption peaks in one sound absorption channel. Owing to the magnetic anisotropy, the magnetic switches performed different force and movement statuses under magnetic fields with different directions. The surface treated magnetic switches could slide in the channels smoothly by magnetic fields with different directions, which could turn the sound absorption channels in the whole testing frequency range. Therefore, the magnetic sound absorption channels exhibit excellent tunability under applying the external magnetic fields and promise a great potential in complex magnetic control.
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