Ultrasonic Sensing Principles in Energy Systems

This work focuses on the application of Ultrasonics or Ultrasound (US) wave propagation in two application scenarios: The first deals with the determination of flow characteristics of fluids in a pipe under harsh environmental conditions. The second scenario concerns the in-situ diagnosis of Li-Ion Batteries (LIBs) to estimate their State of Charge (SOC) and State of Health (SOH). To determine the flow characteristics a novel measurement principle based on US beam steering inside a pipe is introduced. A phased array of US transducers generates a steerable beam within the cross section of the pipe. A fluid flow inside the pipe leads to the formation of a flow field deflecting the US beam. Quantification of the deflection allows to derive parameters of the flow field,namely the flow velocity at the position of US beam. The described sensing mechanism is modeled based on a multiphysical approach. Simulations of this model are used to assess and optimize the sensing principle. In a second step a prototype is conceived and constructed. This includes the mechanical construction, the design of a custom electronic system and the software including the measurement evaluation. Furthermore a new acoustic field measurement methodology based on a membrane free optical microphone is set up to test and verify the prototype’s beamforming capabilities. Finally as a proof of concept the prototype is tested against a dedicated flow test bench. Within this work the results of these steps are discussed including the positive end result of the first flow tests. The second application scenario deals with the determination of mechanical properties of LIBs with Non-Destructive Testing (NDT) methologies employing US. During the operation and also over the lifetime LIBs are changing their mechanical properties. To monitor these changes two different approaches are investigated, at first a mechanical Eigenfrequency study of the cell and secondly the propagation of Surface Acoustic Waves (SAWs). The simulations for this approaches include finite element models for the Eigenfrequency study as well as a semi-analytical model for the estimation of the Time-of-Flight (ToF) of the SAWs between two points at the surface of the LIBs. The results of these simulations as well as the modeling approach are discussed.