Temperature insensitive fiber-optic torque and strain sensor

A method of measuring strain in a workpiece that is insensitive to ambient temperature fluctuations, comprising the steps of:

• illuminating a strain-sensitive material with a beam of selectively polarized light, the beam of selectively polarized light being substantially perpendicular to the surface of the workpiece, the strain-sensitive material being in physical contact with the surface of the workpiece;
• measuring a first intensity of a first polarization component and a second intensity of a second polarization component of the beam of selectively polarized light making at least one pass through the strain-sensitive material, the first and second polarization components being orthogonal to each other and tilted with respect to strain-induced fast and slow orthogonal axes in the strain-sensitive material parallel to the surface of the workpiece so that each of said first and second polarization components has a projection along both strain-induced fast and slow orthogonal axes;
• and
• calculating from the first and second intensities a difference between strains along the strain-induced fast and slow orthogonal axes in the strain-sensitive material, the difference being substantially independent of ambient temperature fluctuations.

A temperature insensitive strain sensor that is insensitive to ambient temperature fluctuations, comprising:

• a strain-sensitive material adapted to be physically contacted to a surface of a workpiece;
• light source means and light beam polarization means for illuminating said strain-sensitive material with a beam of selectively polarized light, said beam of selectively polarized light being substantially perpendicular to the surface of the workpiece;
• and
• detection means for measuring an intensity of at least one of a first polarization component and a second polarization component in the beam of selectively polarized light making at least one pass through said strain-sensitive material, the at least one of a first and second polarization components being tilted with respect to strain-induced fast and slow orthogonal axes in the strain-sensitive material parallel to the surface of the workpiece so that at least one of the at least first and second polarization components has a projection along both strain-induced fast and slow orthogonal axes;
• and
• processing means connected to said detection means for calculating from the intensity of the at least one of a first polarization component and a second polarization component a difference between strains along the strain-induced fast and slow orthogonal axes in said strain-sensitive material, the difference between strains being substantially independent of ambient temperature fluctuations.

A temperature insensitive strain sensor that is insensitive to ambient temperature fluctuations, comprising:

• a strain-sensitive material adapted to be physically contacted to a surface of a workpiece;
• light source means and light beam polarization means for illuminating said strain-sensitive material with a beam of selectively polarized light, said beam of selectively polarized light being substantially perpendicular to the surface of the workpiece;
• and
• detection means for measuring an intensity of a first polarization component and a second polarization component in the beam of selectively polarized light making at least one pass through said strain-sensitive material, each of the first and second polarization components being tilted with respect to strain-induced fast and slow orthogonal axes in the strain-sensitive material parallel to the surface of the workpiece so that each of the first and second polarization components have a projection along both strain-induced fast and slow orthogonal axes;
• and
• processing means connected to said detection means for calculating from the intensities of the first and second polarization components a difference between strains along the strain-induced fast and slow orthogonal axes in said strain-sensitive material, the difference between strains being substantially independent of ambient temperature fluctuations.