by
Charles T. Troy
Laser/Fiber Sensor Solves Film-Thickness
Riddle
By exploiting the best attributes of laser and fiber optics,
Professor Lawrence W. Evers and graduate students at Michigan Technological
University have solved a seemingly intractable problem for the auto industry:
How to measure liquid-film thickness.
The University's new device provides the first actual measurement
of fuel films forming on an operating engine's intake port. The technique
is expected to pave the way for improvements in the fuel-injection process.
The sensor works by transmitting
a laser beam via fibers that surround the sensor's perimeter. A cone of
light formed by the film reflects to the sensor and continues, via fiber
again, through a filter and finally to a detector. Changes in the index
of refraction and the resultant voltage changes at the detector are correlated
into thickness values.
Experimental sensors have worked with oil, water, ice and a
variety of other fluids. In one significant experiment, the device provided
thickness readings of a lubricant film when mounted in a bearing.
The prospect of using the sensor to study bearing lubrication
was born at the 1995 Society of Automotive Engineers Congress and Exposition
at Cobo Hall in Detroit, where the device was first displayed. Attendees
looking at the laser-powered fiber-sensor suggested the bearing operation
poses an expensive threat to industrial equipment, and the fiber/laser was
suggested as a reliable early-warning technology.
The University is exploring commercial partnerships for this and other possible applications.