A new retroreflector named "quatriplan" based on the corner-cube principle, for advanced ultrasonic telemetry applications.

Telemetry consists in remotely detecting and locating an object. For applications in immersed structures as in nuclear primary vessel, ultrasonic waves are well adapted. Moreover, fixing a target on the structures of interest maximizes the signal-to-noise ratio and provides a reference point. Classical Corner-Cube Retroreflector (CCR) demonstrated high performance in this framework (1D and 2D measurements) but does not allow knowing the full (3D) positioning of the structure. This paper proposes an innovative compact target named "quatriplan", based on the CCR principle, and which must allow the ability to determine the orientation of the target in addition to its distance to the transducer. The simple design of the quatriplan is first explained, then its performances are investigated with modelling and experimentations. The results highlight its strong performance and benefit for advanced telemetry applications in industrial systems where complex design can impede easy and efficient access for inspection of specific parts.

Multi-modal leaky Lamb waves in two parallel and immersed plates: Theoretical considerations, simulations, and measurements.

Leaky Lamb waves have the potential to be used to perform non-destructive testing on a set of several parallel and immersed plates. Short-time Fourier transform and two-dimensional Fourier transform have both been successfully used to measure the propagation properties: phase and group velocity, and leaky attenuation. Experimental measurements were validated by comparison between theory, experimentation and finite-element simulations (using comsol multiphysics® software) in the case of one immersed plate in water. These signal processing techniques proved to be efficient in the case of multi-modal propagation. They were applied to two immersed plates to identify the leaky Lamb mode generated in the second plate. Dispersion curves of the system composed by two immersed and parallel plates are computed. When plates have the same thickness, leaky Lamb modes propagate from the first to the second plate without any mode change, with the apparent attenuation being weaker in the second plate. Considering that the second plate is continuously supplied in energy by the first one, an energy-based model is proposed herein to estimate the apparent attenuation in the second plate. Despite our extremely simplifying assumption, this model proved to be in good agreement with both finite-element modelling and experimentation.