Controllable acoustic media having anisotropic mass density and tunable speed of sound

摘要

We present an experimental demonstration of a reconfigurable acoustic metafluid having anisotropic, actively controllable speed of sound for ultrasonic waves. The acoustic metamaterial is based upon suspensions of subwavelength discoid particles whose orientation and interparticle interactions are manipulated by external magnetic fields. Measured sound speeds are direction- and frequency-dependent, changing in a nonlinear fashion with particle concentration when an external magnetic field is applied. The observed changes in sound speed are significantly greater than that expected for suspensions of oriented but non-interacting oblate-spheroidal particles, suggesting that interactions between particles are important even for particle volume fractions below 0.5%.