MINES DETECTION USING THE EMIR METHOD
Patrick Levesque, Daniel Balageas*
Office National d'Etudes et de Recherches Aérospatiales (ONERA)
Structure and Damage Mechanics Department
29, avenue de la Division Leclerc, 92320 Châtillon
* Tél. 01 46 73 48 73, Fax : 01 46 73 48 91, émail, balageas@onera.fr
ONERA has been developing for more than fifteen years a quantitative
imaging technique for electromagnetic fields called EMIR (ElectroMagnetic
InfraRed). The technique consists in observing a thin film (typically 25 m) of
controlled electrical conductivity with an infrared camera in presence of an
electromagnetic field. In the film a photon-heat conversion occurs (photothermal
effect). The temperature distribution on the film is an image of space distribution in
the plane of the film of the photon flux density, and consequently of the intensity of
the electric field [1]. Generally the technique is used in the microwave range
(centimetre to millimeter wavelengths).
The technique has been continuously improved, being presently capable of
measuring both intensity, phase and polarization of the waves [2].
Among the various possible applications, the non destructive evaluation of
electromagnetic materials has been explored [3]. In particular, single-ended
configurations have been proposed for NDE [4]. Such configuration would apply to
the buried mines. The schematic configuration for the mines detection using EMIR
technique is presented, as shown in figure 1.
Figure 1 : Schematic configuration for detection of buried mines using the EMIR technique
In the second part of the paper a comparison of the different ways to use
infrared thermography for mines detection is made, including the EMIR technique.
The discussion leads to the conclusion that this technique must be a priori the best
one.
In the last part of the paper first results obtained by the technique are
presented. They were obtained with metallic and dielectric discs simulating real
mines, embedded at various depth in sand. The influence of various parameters are
studied : nature of the mine, lift-off of the set-up, humidity of the soil, depth/size ratio
of the mine. Some typical results are presented in figure 2 .
a
b
c
Figure 2 : Detection of a metallic mine (100 mm in dia.) located at a depth of 50 mm into dry sand.
EMIR technique at 2.45 MHz. a) EMIR Image of the soil without mine, b) EMIR image of the soil with a
mine, c) EMIR image resulting from the subtraction of the two previous images and showing the
position and size of the mine.
The results presented in the paper are interesting but they must be considered
just as a first validation of the principle of the technique. There is now a need to
optimise the configuration and the frequency used and to compare the performance
to other established techniques, in particular those using infrared cameras. Finally,
the interest of the method will only be established after tests on realistic soils.
References
[1] BALAGEAS D., LEVESQUE P., “EMIR : a photothermal tool for electromagnetic
phenomena characterization“, Revue Générale de Thermique, 37, 1998, p 725-739
[2] LEVESQUE P., LEYLEKIAN L., and BALAGEAS D., “Vectorial characterisation of
electromagnetic fields by infrared thermography “, 5th Quantitative InfraRed Thermography
(QIRT’2000), Reims (France), 2000.
[3] BALAGEAS D., LEVSEQUE P., NACITAS M., KRAPEZ J.-C., GARDETTE G., and
LEMISTRE M., “Microwave interferometry revealed by photothermal films and lock-in IR
thermography . Application to NDE electromagnetic materials “, SPIE Proc. Series, vol. 2944,
SPIE, 1996, pp. 55-66.
[4] LEVESQUE P., BALAGEAS D., “Single-ended interferometric EMIR method for NDE of
radar absorbing structures “, QIRT’98, pp. 36-42, 1998.
Keywords
Buried Mines, EMIR technique, Infrared Thermography, Photothermal Techniques