BACKGROUND:   Particulate-based composite materials have heretofore been infused with particulates of random orientation. That is, the particulate does not form an organized pattern or structure. Lord and Sandlund (US patent 5,792,284) have produced particulate-based magnetorestrictive composites, wherein the particulates are aligned according to the magnetic field during processing. However, the particulates are not crystallographically oriented. Other processes produce materials by sintering thereby producing solid materials, as opposed to composite materials.

INNOVATION:  The present invention operates on a fundamentally different principle: shape anisotropy. Any arbitrary particle in a field exhibits an orientation which minimizes the energy condition for the particle/field system. One example of such a system is a magnetic particle of arbitrary dimension immersed on a non-magnetic medium. If a magnetic field is applied to this system, a torque will be exerted on the particle such that its motion will minimize the demagnetization energy of the particle. For example, an ellipsoid shaped particle will tend to rotate such that the major axis is aligned with the magnetic field. For magnetic particles, a second force exists that may also orient the particle. This second force is due to the magnetocrystalline anisotropy of the material. If the material either has a large magnetocrystalline anisotropy or has very little shape anisotropy, as a perfect sphere, the magnetocrystalline anisotropy can be used to orient the particle along the axis of easy magnetization.

Crystallographic alignment produces magneto-mechanical coupled materials with superior physical properties such as increased magnetostriction and increased permeability. This invention is of interest to engineering problems that require a high power density actuation material capable of operating in the frequency range of 0-100 KHz. Current commercially available laminated Terfenol-D is limited to a frequency range of 5-10 KHz. Applications include SONAR transducers, vibration reduction of machining equipment and ultrasonic vibrators.

DEVELOPMENT TO DATE:  The invention has been demonstrated using particles of the highly magnetorestrictive compound, Terfenol-D. The magnetorestriction of Terfenol-D is highly anisotropic. A composite with [112] orientation has been fabricated using shape anisotropy. Testing results indicate that this composite provides a larger saturation strain that non-oriented composites and decreased operating fields. The increase in saturation magnetorestriction over similar non-oriented composites is 35-40%. This has improved the properties of the composite to near that of the commercially available form while decreasing the electrical resistance by 2-4 orders of magnitude.

Reference: UCLA Case No. 2002-265

PCT Publication Number: WO/03/075290 A1