Lock-in infrared thermography applied to the characterization of electromagnetic fields

Abstract

Lock-in infrared thermographic systems developed since more than ten years allow the measurement of both amplitude and phase of periodic temperature fields. They have been essentially used for mechanical testing, mainly for stress field analysis, and for NDE. The present system is applied to the quantitative characterization of electromagnetic fields. The modulated amplitude of the temperature leads to the intensity of the field. The purpose of such a system is to eliminate both radiato-convective and conductive effects which produce a blurring of the thermal image and hence degrade the accuracy of the measurement. Experiments demonstrate the real enhancement of the technique when compared to classical steady state measurements. The interest of the thermal phase image is also presented.

Vectorial Characterisation of Electromagnetic Fields by Infrared Thermography

“…This method, mainly used for non destructive evaluation of dielectric or absorbing materials, antenna radiation pattern characterisation and mapping of the electric field around objects or inside cavities, consists in measuring by means of an IR camera the temperature increase of a thin photothermal film, which is proportional to the intensity of the electric field component tangential to the film [2]. In order to avoid the distortion of the temperature field due to the natural convection, and to increase the spatial resolution, the amplitude of the EM field is modulated at a low frequency (some Hz), and a lock-in thermographic system is used [3].…”