IMPROVEMENTS IN AND RELATING TO INSPECTION

摘要

The invention provides a non-destructive test (NDT) method and apparatus for remote detection of ultrasound, particularly from industrial rough surfaces. The technique enables the measurement of ultrasonic velocity, in-plane and out-of-plane ultrasonic displacements within Lamb wave frequencies. The technique is particularly applicable to chemical and nuclear industry process pipes and the like. The system provides high light gathering power, similicity in alignment, vibration tolerance, fibre compatibility and is suitable for use in hazardous environments, giving it particular relevance to NDT in the chemical and nuclear industry. The technique provides a method of investigating an item, the method comprising the steps of: generating ultrasound waves in the item; generating a first laser beam, forming a first probe beam and a first reference beam from the first laser beam, applying the first probe beam to a location on the item to generate a first return beam; applying the first reference beam and the first return beam to first detection means; generating a second laser beam, forming a second probe beam and a second reference beam from the second laser beam, applying the second probe beam to a location on the item to generate a second return beam; applying the second reference beam and second return beam to second detection means; analysing the output of the first and second detector means. The technique can also be implemented using a single probe beam to produce a first and second return beam and first and second reference beams.