OPTOMECHANICAL DEVICES
Incorporating news from O plus E magazine, Tokyo
NAGANO—A research group at the Industrial Research Laboratory of Nagano Prefecture has developed a so-called "optical heat magnetism motor" that can be driven by a laser, the sun, or other sources of near-infrared light. The group uses newly developed heat-sensitive magnetic materials for this motor. The compact device gains a driving force from extreme changes in the magnetic properties of the material near room temperature.
In the past, driving technologies based on magnetic transformation used boiling and chilled water. Because rare-earth elements were required in these heat-sensitive magnetic materials, commercialization seemed unlikely, as the materials were too expensive. Another possible solution was based on ferrite-type oxides or iron-rhodium alloys; however, the alloys proved too expensive or the manufacturing too difficult to achieve the temperature dependencies necessary to drive the motor.
In order to surmount these obstacles, the Nagano group uses a combination of nickel and aluminum. An alloy with good magnetic characteristics is created using both mechanical alloying and plasma discharge. In addition, by changing the ratio of the composition, the Curie temperature of the magnetic material can be varied continuously.
The motor has a flat construction consisting of many chips of heat-sensitive magnetic material placed on top of a nonmagnetic flat disk. Experiments have revealed that by controlling the irradiation pattern of the laser beam, either continuous rotation or a stepping motion can be induced. The rotation direction also can be easily changed. In one example, a speed of approximately 100 rpm at 1 W of optical power can be reached using an arrangement of 39 chips placed on top of a 20-mm-diameter disk.
Because neither electricity nor electrostatic forces are used in the rotating parts, the devices can be microscaled, with inexpensive semiconductor lasers used as the driving light source. By changing the composition of the material and changing the Curie temperature, the operation temperature range can be adjusted. The motors can be controlled remotely by combining light sources such as lasers with the outputs from optical fibers. Because these devices can operate using only a small lens and sunlight, they show promise as temperature sensors and as driving mechanisms in places where electricity is not available.
Courtesy O plus E magazine, Tokyo
