Ultrasonic wavefront integration using optical fibre sensors

Ultrasound has been demonstrated to be a perfect tool for NDT. There are several optical detectors that can be applied in NDT, for example fibre Bragg grating, interferometry, etc. Here we concentrate in polarimetric optical fibre detection. In this paper we develop a simple but realistic analysis of the ultrasonic wavefront integration technique along an optical fibre for acoustic detection. Our model considers the perturbation caused by the acoustic wave as an isotropic change in the effective refractive index of the sensing fibre used as the detection system and neglects the polarization modulation. Also we assume the stress homogeneous through the section of the fibre. The theoretical analysis has been simulated in MATLAB. In this program we have analysed the relation between the length of the sensing fibre, its distance to the ultrasound source and its sensitivity to ultrasound detection, for different orientations of the source with respect to the sensing fibre. The results indicate that optimum ultrasonic detection may be achieved through careful positioning and orientation of the optical fibre. These results may be applied, for example in NDT, where scattered ultrasound from defects introduces new effective sources that may be characterized by arrays of these integrating sensors.