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| Environmental Technology Listing |
Title of Listing: | | SMART CABLE |
Category: | | Characterization Technologies |
Subcategory: | * | Water, Waste, Soil, All Listings |
Media: | | Water, LNAPL, Soil |
Contaminants: | | Petroleum Hydrocarbons, Soil Moisture, Water Table |
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Technology Description: | |
Noverflo, Inc. is developing a distributed fiber optic-based sensor system, SMART CABLE, for in situ continuous detection, identification, and location of: 1) chemical contaminants in fluids and soils and 2) liquid interfaces. SMART CABLE uses an optical fiber to transmit recognition signals to either a portable or a fixed instrument. The recognition signals are generated by sensors which use two different principles to divert the bound light in the fiber into the target fluid. Type I sensors perform this function irreversibly by cutting the fiber while Type II sensors divert the light in a reversible manner. In either case, a contact between the target fluid and the sensor changes the intensity of the signal at the end of the fiber which is being monitored. An Optical Time Domain Reflectometer (OTDR) connected to either end of the optical cable is commonly used as a light pulse along the fiber optic cable. Essentially, the system acts like a one-way radar, sending a light pulse along the fiber optic cable. A Light Emitted Diode (LED) at one end of the fiber and a photodetector at the other end, is commonly used with Type II sensors.
Type I sensors, mounted on the jacket of the fiber, rely on the swelling and dissolution of polymers to selectively generate a cutting force. Enzymes can be incorporated into the polymer to obtain very high molecular specificity. Type II sensors are based on modification of the fiber at selected intervals in a manner which changes the refraction of light at the clad/liquid interface. SMART CABLE can be viewed as an array of chemical switches which are turned on when a preset concentration threshold of the analyte has been reached.
Since the OTDR operates as a one-way radar a failure of one or several sensors doesn't disable the rest of the SMART CABLE system. When a sensor cuts the cable, the light pulse launched from the ODTR is reflected at the cut end. The response time of the pulse is a direct measurement of the contaminant location. Type II sensors are reversible when used to differentiate between liquids. They are irreversible when enzymes are used to detect specific chemicals.
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Performance Status/
Limitations: | |
Since SMART CABLE relies on the intimate contact between the target fluid and the surface of the sensor, the contamination plume must be intercepted to attain the recognition signal. Type I sensors are currently limited to the detection of hydrocarbon liquids, water, moisture and certain acids. If all the sensors in the bore hole have been activated (the fiber was cut at all sensor locations) part of the cable must be replaced to continue operation. If several bore holes are connected in series, cable splicing is required after all the sensors in a bore hole have been activated. The added attenuation due to splicing must be considered when cable lengths are initially selected. Type II sensors presently use fibers with high optical attenuation and therefore their range is limited to 100 feet. The range of Type I sensor is 50 miles.
In contrast to the detection of water and hydrocarbon liquids, the measurements of pH and concentrations of chemical compounds in the ppm range requires additional study before SMART CABLE can be used in the field. Data on the osmotic pressure of various polymer solutions as a function of pH and contaminant concentration are being generated for the construction of prototypes with high molecular selectivity. These sensors exploit the osmotic pressure to cut the fiber.
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Topics
Technologies, Characterization
Additional Topics/Tags/Keywords
Fiber Optic Sensor, Petroleum Hydrocarbons |
Organization: | | Noverflo, Inc. |
Address: | | 1724 Yale Place
| Phone: | Description | Number |
City: | | Rockville | | Primary | (301) 340-1625 |
State/Province/Territory: | | MD | 2. | | |
Zip/Postal Code: | | 20850 | 3. | | |
Country: | | United States | 4. | Fax: | (301) 762-3511 |
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