Modeling an omnidirectional fiber-optic strain transducer

We present a modeling study devoted to an omnidirectional fiber-optic transducer for elastic ultrasound waves. A coil-wound single mode fiber is attached to the surface of the device under test. The interferometric detection of strains is accomplished with the help of a reference coil, a 3×3 coupler, a laser or superluminescent LED, and two avalanche photodiodes. Since practical coil diameters of 25 mm are comparable to typical wavelengths of the mechanical excitation, we deal with distinct spatially distributed transduction. Finite element analyzes (FEA) demonstrate the achievable transducer sensitivity to Lamb waves in thin rigid plates. Moreover, FEA are capable to resolve minor distortions of wave propagation by the attached fiber coil.