JEC COMPOSITES MAGAZINE - Issue #87 - March 2014 Special JEC Europe - 120

NDT

Fig. 2: In this example, the specimen to be characterized is a piece of PA6 with a deliberate defect in the form of a crack. The defect is detected on a frequency band and
shown in colour on the chart © 2013 J.M. Geffrin

waves can improve the penetration
power of the interrogation wave in
the material under consideration,
at the same frequency. This constitutes a major advantage for detecting defects in composite materials,
which often exhibit high permittivity
and dielectric loss. The evanescent
wave coupling used and the improvement in spatial resolution make this
innovative patented technology an
excellent candidate for the testing of
internal defects in dielectric materials such as plastics, glass-fibre- or
carbon-fibre-reinforced composites,
ceramics, wood, glass and cement, for
which this type of testing is usually
difficult.
Due to the use of microwaves, the
new technology is eminently suitable for applications where drying by

natural or artificial means is an issue,
e.g. inspecting for water pockets in
mineral wool or in wood.
The illustration shows the result
of the actual detection of a crack
in a plastic material (a 25-mmlong, <1-mm-wide saw mark on a
50x50x10-mm3 specimen, or λ/3
x λ/25 at 4 GHz). The difference
between the field diffracted by an object with and without a crack shows
an observable far-field difference.
Therefore, it is possible to detect a
defect that is smaller than the half
wavelength in one direction, and
one that is even smaller, in the other
direction. By using the same system
to carry out near-field measurements,
the research scientists were also able
to locate and map the crack. Given
that most other microwave systems

Using microwaves to "interrogate" objects

Rodolphe Vaillon (CETHIL, Lyon) and Jean-Michel Geffrin (Fresnel Institute, Marseille) worked together for a number of years studying the diffusion of particles in
free space. This research is the direct outcome of their collaboration. The notion of
using evanescent waves (which cover higher spatial frequencies) instead of plane
waves (or waves that are treated as such) to "interrogate" objects arose from
discussions with M. Francoeur while he was at the University of Kentucky (he is
now at the university of Utah), where a system using a prism was developed in the
field of optics. A prototype was then defined and built thanks to B. Lacroix (CETHIL),
and finalized by R. Abdeddaim (Fresnel Institute). The results of this research are
revolutionizing the non-destructive testing of dielectric materials, in particular composites.

120 jec composites magazine / No87 March 2014

used in non-destructive testing
are limited to a resolution of a half
wavelength, the fact that the crack
detected using the prototype was so
much smaller than the wavelength
is an indication of the prototype's
competitive potential.

A patented system that opens
up many possibilities in nondestructive testing
Following the initial development
phase (financed by the Carnot STAR
Institute), an application for a French
patent was filed for the technology on behalf of the Aix-Marseille
University and the French scientific
research institute CNRS, the inventor organizations. Technology transfer accelerator SATT Sud Est, whose
role is to help technologies developed in public laboratories to reach
the industrialization stage, started
a bold engineering programme to
optimize the performance of NDT
for composites. The SATT Sud Est
is now looking for a manufacturer to
develop and run the programme. n
More information:
www.sattse-technologies.com/projects/fr/scanner_micro_onde
Contact:
licensing@sattse.com

http://www.sattse-technologies.com/projects/fr/microwave_scanner

JEC COMPOSITES MAGAZINE - Issue #87 - March 2014 Special JEC Europe

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