Multi-gap interferometric sensors

Abstract

An apparatus for estimating a property includes a hollow core tube and an input light guide disposed at least partially within hollow core tube. The apparatus also includes a second gap disposed within the hollow core tube and separated from the input light guide by an air gap width. The second gap is formed of a first solid material and has a second gap width. The apparatus also includes a third gap disposed at least partially within the hollow core tube and being further from the input light guide than the second gap. The third gap is formed of a second solid material and has a third gap width.

What is claimed is: 
     
         1 . A computer based method for estimating a property, the method comprising:
 receiving at a computing device a series of data values based on an amplitude of reflected light from a sensor that includes an air gap, a second gap and a third gap;   providing an estimate of a width of the air gap, an estimate of a width of the second gap, and an estimate of a width of the third gap to a curve fitting algorithm on the computing device;   receiving intermediate gap widths for the second and third gaps;   verifying the intermediate gap width for the third gap to create a verified third gap width; and   providing a revised estimate of the width of the air gap to the curve fitting algorithm, the revised estimate being based on the verified third gap.   
     
     
         2 . The method of  claim 1 , wherein verifying includes:
 in the event that the intermediate gap width for the third gap is within a predefined range, setting the verified third gap equal to the intermediate gap width for the third gap;   otherwise, adding or subtracting a preset value to the intermediate gap width until the intermediate gap width is within the predefined range and then setting the verified third gap equal to the intermediate gap width for the third gap.   
     
     
         3 . The method of  claim 2 , wherein the predefined range is less than a fringe order of the light applied to sensor. 
     
     
         4 . The method of  claim 2 , wherein the preset value is less than half of the mean wave length of the light applied to the sensor. 
     
     
         5 . The method of  claim 1 , wherein the estimates of the second gap width and the third gap width is not based on a spectral analysis of the data values. 
     
     
         6 . The method  claim 1 , where the estimates of the second gap width and the third gap width are within a range of possible widths based on the materials forming the second gap and the third gap.