Improved Active Non-destructive Inspection Using Periodic Binary Heating Sequences

Most widespread non-destructive techniques like ultrasonic waves, radiography, magnetic testing, etc., which are effective for metallic parts, have shortcomings regarding the evaluation of composite parts. Active infrared inspection or thermography has proven to be a valid alternative. An important aspect of thermographical inspection is the analysis (image processing) of the recorded infrared footage. The quality of the analysis results is strongly depending to the heating sequence used during inspection. In this paper the use of optimized periodic binary sequences to drive the heating device(s) will be investigated. Periodic binary (on/off) sequences are easy to apply: a relay switch (low cost and lightweight) can be used instead of power amplifiers. This results in a reliable, low cost and portable solution allowing in-field inspections. The design of optimized periodic binary sequences and the processing of the resulting thermal images will be discussed in detail and illustrated by means of measurement results.