A sensor using a small ring of the cobalt-ferrite composite would be strategically placed on the steering column. As a driver turned the wheel, the magnetization of the cobalt-ferrite ring would change in proportion to the amount of force applied by the driver. The change would be detected by a nearby field sensor that would interpret how much force should be applied to turn the wheels and then relay the information to an electrical power-assist motor. Unlike the hydraulic system, the electrical system would consume minimal energy when the steering wheel was not being turned. What makes the cobalt-ferrite composite ideal for this application is a property known as magnetostriction, Jiles said.
Magnetostrictive materials undergo slight length changes when magnetized.
Jiles and McCallum take advantage of that property, but in reverse. In their approach, the turn of the steering wheel would apply stress to the cobalt-ferrite ring, producing a change in the magnetic field it emits. Jiles said that's necessary because automakers don't agree on the best location on the steering column for the torque sensor. Some want it in the passenger compartment while others want it in the engine compartment, where it would be subjected to engine heat as well as winter conditions. McCallum added that cobalt ferrite also meets the strength and corrosion-resistance requirements for the sensor material.