Soda-Straw-Like Fiber Optic Sensors

By Roland Piquepaille

At Sandia National Laboratories (SNL), researcher Jonathan Weiss, nicknamed the "light wizard," uses inexpensive soda-straw-like glass tubes for solving a variety of sensing problems. His twelve patents cover areas such as detecting if a car battery is about to die or if dangerous chemical materials are about to escape from a landfill into groundwater. He also developed a sensor which can tell the difference between two liquids in a container. This could be used by oil companies which need to safely determine when to stop pumping oil from the ground before water invades a tank. This market represents about $750 million per year and these sensors should be available in two years according to an interesting story from the Albuquerque Tribune, "Bright Idea: Random chat leads to sensor pact." Apparently, Weiss found an industrial partner for SNL on a flight between Albuquerque and New York. Read more...

Here is a picture from Jonathan Weiss holding soda-straw-like glass tubes (Credit: Randy Montoya). And here is a link to a larger version (655 KB).

Please read the SNL news release for details about the dead battery problem and the waste detection device through landfills. And let's focus here on Weiss's fiber optic sensor that uses light to tell the difference between two liquids in a container.

Imagine you're in the oil business and you've pumped oil and water (just the way it increasingly comes out of the ground) into a holding tank. You want to retrieve only the oil floating atop the water so you can transport the least possible weight from the oil field to a refinery. How do you know -- accurately, safely, and simply -- when to stop pumping?

Here is the description of Weiss's solution.

Take two five-foot-long optical fibers made of plastic. Mount them vertically in a tank that holds water with oil on top. Send light down one fiber, and then detect light carried back up by the second fiber. The strength of the detector's signal depends on the height of the oil/water interface. If the tank is all water, the signal is very strong, and the pumping machine is instructed to stop pumping fluid; there is no oil left.

The Albuquerque Tribune gives more details on why this sensor will be built by Custom Electronics, a New York state company.

When physicists Jonathan Weiss and Allen Anderson, [from Custom Electronics,] met on an airplane, a business opportunity popped out of the quantum mist.

The two didn't know each other before that flight a year ago, but now Weiss is a Sandia-employed consultant for Anderson's company, which is working with the lab to license Weiss' technology.

"My co-worker and I ended up getting separated, and I ended up sitting next to Jonathan and his wife. He told me he was a physicist and I said, hey, I'm a physicist, too," [said Anderson, the company's director of product development.]

The product could be ready in the next two years according to Anderson. He added that SNL found found a market potential between $250 million and $750 million for the device.

Weiss received a patent in February 2004 for this sensor. You can find technical details on this patent by visiting the United States Patent and Trademark Office and search for patent number 6,693,285.

Here is a direct link to this patent named "Fluorescent fluid interface position sensor." And here is the abstract.

A new fluid interface position sensor has been developed, which is capable of optically determining the location of an interface between an upper fluid and a lower fluid, the upper fluid having a larger refractive index than a lower fluid. The sensor functions by measurement, of fluorescence excited by an optical pump beam which is confined within a fluorescent waveguide where that waveguide is in optical contact with the lower fluid, but escapes from the fluorescent waveguide where that waveguide is in optical contact with the upper fluid.

Sources: Sandia National Laboratories news release, January 11, 2005; Sue Vorenberg, The Albuquerque Tribune, January 24, 2005; and various websites

Related stories can be found in the following categories.

• Energy
  
• Environment
  
• Optics
  
• Sensors