Covering thickness measurement by photothermal method

Abstract

For many industry branches the thickness control of a covering different type, for example, antistain, varnish covering in the process of their coatication on a metal in motor-car industry is actual. Control methods of such type covering must be undestructive and differ by the high fast-acting at covering research on objects that is moving with certain speed.Today for the noncontact measurement of covering thinkness in industry the methods that are based on registration of the induced heat-waves by the powerful laser impulse radiation are widely used. Such methods require the long time of measurement (few seconds) that complicate their use for the covering control on moved objects.In the given work the high speed photothermal method is offered. In this method a photothermal response in time after the irradiation of sample by one short impulse is registered.For method realization the heat distribution theory in sandwich-type systems is developed and software for the design of thermal responce after laser impulse irradiation (with given parameters) on such systems is created. Fig.1 shows the simulated temporal changes of temperature on the surface of steel sample that covered by one varnish layer after its irradiation by 0.1 ps laser impulse with energy density of 1 Dg/sm*. U t; 600 Y \ ! J 0 0.0 0.5 1 P 1.5 1.0 2.5 t* w Figure 1 -Change of temperature on the surface of steel sample covering by one varnish layer after irradiation by 0.1 ps laser impulse with energy density of 1 Dg/sm2 for different covering thinkness: curve 1 ~ steel without covering; 2varnish thickness of Spm; 3 -1Opm; 4 ~ 25pm; S -SopmIJse. of speed detectors for registration of thermal responce from the surface of the explored sample and use of the developed software allows to define its thickness at the known optical and physical parameters of covering.

Thickness measurement by model-based exhaustive analysis in far-infrared

“…Different technologies have been proposed in the relevant literature to obtain such a map: ultrasound [9], eddy currents [10], X-ray fluorescence [11], optical coherence tomography [12], and photothermal methods [13]. For a complete overview of MLS NDE technologies see [14].…”