LPAC acquires the EVITA X-ray phase contrast imaging system

EVITA X-ray phase contrast imaging system © 2022 EPFL LPAC

EVITA X-ray phase contrast imaging system © 2022 EPFL LPAC

Run with the help of ENAC’s PIXE, EVITA allows non-destructive testing of low-density samples such as composites, plants, biological material, and many others

While multiple non-destructive testing methods such as acoustic emission or infrared analysis are available for composite structures, conventional X-ray absorption imaging is generally unable to detect microscopic details such as defects in fibrous media, or cracks in laminates, due to a lack in contrast.

In the recent years, the development of phase-contrast imaging, based on Talbot-Lau grating interferometry, has allowed to overcome some of the limitations of standard X-ray absorption [1]. The resulting refraction (or differential phase) images can yield a good distinction between regions in a sample with relatively similar densities but different refractive properties. The same system was also shown to be adequate for the analysis of ultra-small angle scattering [2]. These scattering (or dark-field) images are sensitive to the presence of microscopic heterogeneities within the sample, and can bring out small details with sizes below the detector resolution.

Examples of images obtained with EVITA
Examples of images obtained with EVITA in absorption, scattering, and refraction. Scattering helps distinguishing between the skin and the flesh of a banana; refraction reveals the orientation of the stem fibers. In the middle, an impact crack in a palm/flax/epoxy composite is displayed clearly by scattering. Below, an impacted palm/epoxy composite part shows how scattering clearly reveals the fibrous network © 2022 EPFL LPAC

Developed by CSEM in Alpnach, EVITA has successfully allowed to apply these principles for the testing of composite parts. Recently installed in LPAC, EVITA is now up and running at EPFL, and has already started delivering its imaging capabilities for the analysis of composites. Large samples can be analyzed in 2D (up to 1 square meter), and computed tomography allows the 3D reconstruction of absorption, scattering and refraction images.

These CT renderings of an impacted palm fiber/flax composite show how EVITA can provide complementary information on the internal structure of a sample © 2022 EPFL LPAC

New applications have also been tested, like the in-situ imaging of flow fronts in partially saturated fibrous media [3]. Further use cases are now considered and expected, such as imaging dynamic effects in plants or other biological material.

Flow profile in a partially saturated UD carbon fabric. Left to right: absorption, scattering and refraction images. © 2022 EPFL LPAC

Beyond these examples, other potential applications are welcome for exploration, thanks to the support of EPFL Platform Technical Advancement Seed Fund, with LPAC and PIXE which would connect researchers from different fields, and help stimulating transdisciplinary studies. Please reach out to Prof. Michaud (LPAC) or Dr Turberg (PIXE) to discuss the feasibility of a prospective study.


[1] Pfeiffer, F., Weitkamp, T., Bunk, O., David, C., 2006. Phase retrieval and differential phase-contrast imaging with low-brilliance X-ray sources. Nature Phys 2, 258–261. https://doi.org/10.1038/nphys265

[2] Pfeiffer, F., Bech, M., Bunk, O., Kraft, P., Eikenberry, E.F., Brönnimann, C., Grünzweig, C., David, C., 2008. Hard-X-ray dark-field imaging using a grating interferometer. Nature Mater 7, 134–137. https://doi.org/10.1038/nmat2096

[3] Teixidó, H., Caglar, B., Revol, V., Michaud, V., 2021. In-operando dynamic visualization of flow through porous preforms based on X-ray phase contrast imaging. Composites Part A: Applied Science and Manufacturing 149, 106560. https://doi.org/10.1016/j.compositesa.2021.106560