<title>Numerical System For Infrared Scanners And Application To The Subsurface Control Of Materials By Photothermal Radiometry</title>

Abstract

Non -destructive testing (NDT) of materials can be achieved via proper photonic excitation and radiometric monitoring of the induced thermal changes. The theoretical support for this photothermal conversion in bi-layered materials is proposed, single -pulse and periodically modulated fluxes being considered. Some practical proposals are derived concerning the various aims of NDT: coatings thickness measurements, detection of defective bondings or delaminations, measurements of contact resistances between two layers. Measurements performed with a commercially available infra -red scanner and a digital data acquisition and processing system are reported.

Lockin-Thermography: Principles, NDE-applications and trends

“…The outcome is the compact information known from photoacoustics: One image displays local thermal wave phase, the other one amplitude. Such images have been generated as soon as powerful enough computers were available [17][18][19], and with progress of computer performance the complicated mathematics involved are done almost in real time. This way the information contained in a stack of several thousand thermographic images taken at video frequency while illumination goes on and off, is squeeezed out so that just two images are obtained: One of local amplitude and one of phase.…”

Thermography with excitation by elastic waves: comparison of techniques (pulse, burst, lockin)

“…However, OLT [12,13] provides a map of all thermal structures, and one needs to search deviations from these known structures in order to identify defects.…”

Investigation of resolution in lock-in thermography: theory and experiment

“…Lock-in thermography allowing for rapid inspection is relevant for industrial use [1][2][3][4][5]. Also the study of thermal wave propagation, diffraction, and scattering in materials is becoming a subject of interest for NOE [6][7][8][9][10][11].…”