The National Academy of Sciences (Washington, DC) is bullish on fiberoptics technology. A recent report issued by the academy's National Materials Advisory Board says that laser and fiberoptic sensing have a bright future in undergirding new sensors for use in industry and research.
For example, optical technologies could provide new sensors for industrial applications such as monitoring the curing of thermosetting resins and controlling epitaxial processes in manufacturing semiconductors, according to the board. Fiberoptic systems also could play important roles in "smart" structures that can sense and compensate for changes in their shape and in new chemical sensors.
The report, Expanding the Vision of Sensor Materials*, was produced by the panel at the request of NASA and the Pentagon's Advanced Research Projects Agency as a guide for those agencies in how to spend their research dollars. On that question, the board's advice was loud and clear: the government should not focus on developing new materials for use in sensors. Rather, government-funded research and development should center on applying materials originally developed for uses other than sensors to sensor problems. That approach likely will produce new sensors more quickly and at lower cost.
That recommendation may not play well with many materials researchers, admits Robert Schafrik, staff director for the study at the academy. "Not everyone will perceive it as common sense," he says.
One problem, he says, is that there is a "kind of a mismatch" between researchers who study new materials for possible use in sensors and those who are actually designing sensors—the two camps often don't know what each is doing. Nevertheless, the board strongly recommended that the federal government continue to support university research in sensor-related fields, particularly in technologies with little chance of being used commercially within a decade. Industry cannot justify such projects, but they are essential for "a stable effort" nationally. (However, the panel doesn't recommend any specific funding levels.)
As evidence that researchers should focus on teaching old materials new tricks, the board cites the use of fiberoptic components in sensors. Fiberoptic components originally were developed by the communications industry, but subsequently these materials found use in many sensor instruments. "The sensor community very creatively took advantage of these materials without the need to support a major development of fibers," the board says.
The academy panel also argues that the government should consider sponsoring "focused programs in which sensors are treated as a separate field of endeavor," rather than just as a part of a larger project. System managers often regard sensors as almost an afterthought, Schafrik says.
Sensors monitor resins
As a case study, the report gives considerable attention to the development of new sensors for monitoring the curing of resins such as those used in aircraft parts or printed-circuit boards. Currently, manufacturers generally use thermocouples—devices that produce an electrical signal based on temperature differences—to measure the temperature of the resin as it cools. But the manufacturer can only estimate the quality of the resin from the temperature. And the fact that thermocouples have to be manually placed by an operator into the resin material is a roadblock to high-volume production of resins.
By contrast, a fiberoptic system could directly sense key characteristics of the resin and do it at high enough speed to allow large-scale manufacturing of high-quality resin parts, says the panel. Laser and fiberoptic technology also have "considerable potential" for use in so-called "intelligent processing" of resins, in which conditions such as temperature and pressure are adjusted automatically, based on how well the resin is curing.
The committee cites a photon-scattering intrinsic sensor as the approach that could replace thermocouples. In such a device, a laser beam scattered off the resin would be analyzed. Some research has shown that such an approach can measure characteristics of the resin such as the degree to which it has cured. But the committee says that much more data can be gleaned from the approach, such as viscosity and heat capacity.
"The advantages of fiberoptics technology include small size, ruggedness, survivability in hostile and inaccessible environments, simplicity of construction, ability to monitor multiple parts at one time in an autoclave, and low cost," the report says. With such a list of plusses, perhaps its no surprise that fiberoptics technology looms so large in the committee's vision for sensors.
*Copies of the report are available for $35 from National Academy Press, 2101 Constitution Avenue NW, Box 285, Washington, DC 20055; tel. (800) 624-6242.