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Particle loaded polymers and elastomers have been largely used in different ultrasonic applications like backing materials and matching layers because composite properties (velocity, attenuation, density and impedance) can be easily engineered by changing the filler concentration. Recently, the use of magnetic particles has been theoretically proposed as a means to produce active matching layers whose response can be modified upon the application of magnetic fields. In this paper, we propose to introduce modifications of the composite properties by using magnetic particles and applying magnetic fields during curing to establish well defined patterns in the spatial distribution of the particles within the elastomer that induce material anisotropy that effectively modify ultrasonic properties.

The possibility to inspect laminates of prepreg carbon fiber reinforced polymer (CFRP) laminates during lay-up fabrication is studied. First ultrasonic properties of the uncured material are determined, this information is used to design an inspection system that is tested during the fabrication of laminates with up to 30 layers, following different compaction schemes and including some Teflon insertions to simulate the presence of delaminations. The paper shows that for the chosen selection of parameters (transducers sensitivity, centre frequency and mold configuration), the inspection is possible, opening a new field of application of air-coupled ultrasonic techniques.