SEISMIC SHAKING

In search of more powerful sonar, the U.S. Department of Energy originally developed terfenol-d for the Navy. Sonar power can be increased by either physically enlarging an older technology or by packing more power into the same size device. Terfenol-d packs the most power into a given size without degrading. Recognition of potential civilian uses quickly followed emergence from the lab.

Civilian applications requiring ruggedness include, for illustration, seismic uses where terfenol-d is the source for signaling or pulse-echo imaging. Combined with proper packaging, many of its inherent, natural properties aid terfenol-d in not only surviving but thriving in harsh environments. Even with proper packaging other materials would not be as capable of signaling while surviving near a drill string bit.

Proper packaging of terfenol-d into an actuator requires 1) end caps bonded on with a compliant substance, 2) a gap between the rod outside surface and coil inside surface, 3) a means of compressive preload, and 4) a means of applying that compressive preload without applying any twist to the terfenol-d.

In operation, one needs to consider that the failure modes to avoid are shock impact to the terfenol-d, avoided by sufficient preload, and overheating the coil. Coils are known to heat rapidly. This happens because of a tendency to observe how much mechanical output becomes possible with this technology but without considering that the amount of electrical input must be slightly greater than the amount of mechanical output. The electrical input can cause significant ohmic heating of the coil. This requires either active cooling, passing a fluid such as air between the rod and the coil, or duty cycling the actuator.