Daniel Kiefer (Institut Langevin, ESPCI) - Mechanical guided and quasi-guided waves for modeling ultrasonic devices

Guided elastic waves find numerous applications in nondestructive testing, ultrasonic sensing and telecommunications. In this talk I will present guided-wave based modeling approaches in two fields: transit-time ultrasonic flow metering and resonant testing of structures. 

The former devices measure the fluid flow rate through a pipe by exploiting the non-reciprocity due to flow. The pipe's interior can conveniently be insonified from the outside, in which case the pipe wall acts as a mechanical waveguide. The interaction with the fluid medium results in quasi-guided waves in the sense that their energy is no longer strictly confined within the pipe wall – an effect that is desired in this context. After exploring the mentioned solutions, I will present how these waves can be used to conveniently model such devices, thereby including the effects of convection as well as temperature. Compared to conventional meters, we find a strongly decreased cross-sensitivity to temperature. 

The second application, resonant testing of structures, is based on so-called zero-group-velocity (ZGV) resonances. This widespread testing technique relies on the measurement of the ZGV frequency. Being able to predict them is of correspondingly high relevance. However, this problem turns out to be particularly hard to solve. To overcome this difficulty, I will present rather unconventional numerical methods to reliably and efficiently locate all ZGV frequencies of generic waveguides.

Finally, I will conclude with an overview of accompanying projects: Schlieren photography of ultrasound, electromagnetic-acoustic transducers for waveguide excitation, a dip-stick sensor for fluid characterization and ultrasonic holography.