Magnetoacoustic properties of self-biased Terfenol-D 2-2 composites

Self-biased Terfenol-D 2-2 composites exhibit high frequency of actuation and good magnetomechanicalproperties; however, their potential usefulness is highly dependent on their magnetoacousticproperties, particularly for ultrasonic applications. The speed of sound,c , and its variation with an externally applied magnetic field have been measured for the above composites using a 10MHz longitudinal pulse. When the sound propagates parallel to the layers, the acoustic impedance was found to be independent of the external applied field, and lower than that for bulk Terfenol-D. The magnetomechanical coupling coefficient was found to be generally low (up to 0.35) and dependent on the volume ratio of materials, being higher for the specimens with greater content of Terfenol-D. The low attenuation, low acoustic impedance, and high frequency of actuation make this structure an interesting alternative for use in underwater∕sound navigation and ranging and other ultrasonic applications. When the pulse propagates orthogonal to the layers, c was found to vary by up to 3% with the application of an external field, but the acoustic attenuation was found to be very high due to the multiple reflections produced at the interfaces between the layers. This latter phenomenon has been calculated theoretically.