Interferometric load sensor and strain gage

Claim 1

An interferometric sensor comprising: (a) a rigid support fixture secured to an underlying structure; (b) a load sensitive fixture connected to said rigid support fixture by a beam to flexing and secured to the underlying structure; (c) a first right angle prism affixed to said rigid support, said first prism having a partially reflective exterior surface, a totally reflective interior surface and a substantially non-reflective exterior surface; (d) a second right angle prism affixed to said load sensitive fixture, said second prism having a partially reflective exterior surface, a totally reflective interior surface and a non-reflective exterior surface wherein said partially reflective exterior surfaces of said first and second prisms are parallel and adjacent to each other such that the air gap wedge angle therebetween is less than 5 seconds; (e) a light source for projecting a collimated beam of light through said prisms; and (f) detector means for detecting changes in light intensity of light transmitted through said prisms as caused by angular movement of the prisms relative to each other which is a result of strain in the underlying structure, said movement resulting in a changed air gap wedge angle therebetween wherein said detector means is relatively insensitive to non-angular relative movement between said prisms and said light source so that the sensor is particularly sensitive to strain in the underlying structure.