Single-sided NMR sensors combine open magnets and surface rf coils to generate a sensitive volume external to the sensor and inside the object. The shape of the sensitive volume – fully determined by the geometry of the magnet system – defines the best spatial resolution attainable with the sensor. Recently a novel magnet was developed that improves the resolution by almost three orders of magnitude. The profiling procedure requires repositioning of the sensor with respect to the sample. For this purpose a high-precision lift was built (Fig 1). It has an acrylic plate, where the sample is placed, and a movable plate to control the position of the sensor (in blue). To quantify the improvement in the spatial resolution the point spread functions for a typical sen¬sor (1 mm) and the new sensor (2.3 mm) were measured (Fig. 2). As an example the profile through the wall of a PE fuel tank is shown Fig. 3. The material is made of a multiplayer structure on HDPE, EVOH including a barrier layer that blocks the diffusion of the liquid to outside.

Fig. 2: Point spread function.

Fig. 3: Profile of a PE tank wall.