Fiber optic evanescent wave fuel gauge and leak detector using eccentric core fibers
AssigneeHughes Aircraft Company
InventorsVictor Vali, David B. Chang, I-Fu Shih, Albert F. Lawrence
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Abstract
An optical fiber evanescent wave fuel sensor, employing a light source with a wavelength selected to be at the strong infrared absorption lines of the fuel, typically hydrocarbons. The amount of light leaking from the optical fiber is an exponential function of the length of the fiber in the liquid, and is independent of the relative indices of refraction of the fuel and fiber cladding material.
Claims13
A fiber optic evanescent wave sensor system for measuring the level of a particular liquid in a container, comprising:
- a light source for generating light at a wavelength band at which said liquid is highly absorptive;
- an optical fiber having a first end into which the light from said source is injected, said fiber further comprises a sensing length of fiber and a second end from which said injected light is reflected disposed in said liquid, said sensing length of fiber characterized in that it comprises an eccentric core clad by a cladding layer of a material said eccentric core cladding layer being of a thickness selected to provide significant evanescent wave loss of said light when immersed in said liquid;
- and
- means responsive to the intensity of the light injected into said fiber and to the intensity of said reflected light for determining the light loss from the sensing fiber due to evanescent wave loss and for processing said light loss to determine the level of said liquid in said container.
A method for measuring the level of a known liquid in a container, comprising the steps of:
- disposing an optical fiber having a reflective end into the liquid in the container;
- injecting light into said fiber at a wavelength at which said liquid is highly absorptive, said fiber characterized in that it comprises an eccentric core clad by a cladding layer of an eccentric core cladding material being of a thickness selected to provide significant evanescent wave loss of said light when immersed in said liquid;
- and
- providing an indication of the intensity of the injected light;
- providing an indication of the intensity of the injected light reflected at said reflective end and which has traversed the portion of said fiber immersed in said liquid;
- determining from said indication of said respective injected light intensity and said reflected light intensity the evanescent wave loss of light passing through said fiber and processing said loss to determine the level of said liquid in said container.
A fuel lever sensor for measuring the level of hydrocarbon fuel in a vehicle fuel tank, comprising:
- a light source for generating light at a wavelength band at which the fuel is highly absorptive, said band being dependent on the carbon-hydrogen bonds of the hydrocarbon fuel;
- an optical fiber having a first end into which the light from said source in injected, and a sensing length of fiber and a second end from which said injected light is reflected disposed in said fuel tank and into said fuel, said sensing length of fiber characterized in that it comprises eccentric core clad by a cladding layer of a material being of a thickness selected to provide significant evanescent wave loss of said light when immersed in said fuel;
- means for measuring the intensity of said injected light;
- means for measuring the intensity of said reflected light;
- and
- means responsive to the intensity of the light injected into said fiber and to the intensity of said reflected light for determining the light loss from the sensing fiber due to evanescent wave loss and processing said light loss to determine the level of said liquid in said container.
Dependencies are inferred from the claim text.