Guided acoustic waves, such as Lamb waves, are widely applied for material characterization, sensing of liquids and the generation of streaming in liquids. There are numerical simulation tools for the prediction of their propagation near a solid-liquid boundary but a demand for complementary measurement techniques for the validation of the simulation results remains. In this contribution it is demonstrated that light refractive vibrometry is a suitable approach for the visualization of the interaction of guided acoustic waves with liquids. For this purpose Lamb waves were excited by piezoelectric transducers on copper plates partially immersed in water. There the fundamental symmetric and antisymmetric modes are converted to compressional waves and quasi-Scholte plate waves below a frequency-thickness product of 1?MHz?mm. From the vibrometry scans the wavelengths, radiation angles and pressure amplitudes of the involved modes could be determined and thus theoretical predictions of the attenuation of the Lamb modes and the energy distribution of quasi-Scholte plate waves between the solid substrate and the liquid environment could be confirmed.

The monitoring of liquid-filled tubes with respect to the formation of soft deposition layers such as biofilms on the inner walls calls for non-invasive and long-term stable sensors, which can be attached to existing pipe structures. For this task a method is developed, which uses an ultrasonic clamp-on device. This method is based on the impact of such deposition layers on the propagation of circumferential guided waves on the pipe wall. Such waves are partly converted into longitudinal compressional waves in the liquid, which are back-converted to guided waves in a circular cross section of the pipe. Validating this approach, laboratory experiments with gelatin deposition layers on steel tubes exhibited a distinguishable sensitivity of both wave branches with respect to the thickness of such layers. This allows the monitoring of the layer growth.

A previous experiment showed that the rate of the electropolishing of a copper anode may be increased by twofold when generating a 60 KHz to 1.7 MHz frequency vibration in the anode. In this work we use theory to elucidate the mechanisms by which the vibration may enhance the transport of ions in the electrolyte solution and support the formation of dents in the anode, which was observed in experiment. We find that in the limit of weak ion convection the transport of ions mainly supports the formation of dents in the anode. However, in the limit of prominent ion convection we find an appreciable contribution of the vibration to the efficiency of the electropolishing process, in accordance with the previous experimental findings. The contribution of the vibration to ion transport is given by 2√PeDkC s /π√π, in which the Pecl ́et number, Pe, quantifies the ratio between the convective and diffusive fluxes of ions, and D, k, and C s are the diffusion coefficient of the ions, the wavenumber of the vibration, and the solubility limit of the ions in the electrolyte.

The kinetics of the charge transport across the solid-liquid interface between the electrode and the electrolyte is controlled by a diffusion boundary layer, which is responsible for the time needed for charging the battery. Therefore a removal of this boundary layer by acoustic streaming induced by surface acoustic waves propagating on the electrodes was considered to be promising approach for a reduction of the charging time. Previous electropolishing experiments have shown that Scholte waves were particularly effective in that respect. This concept has been transferred to a model electrode system representing the core of a lead acid battery, where significant reductions of the charging time and corresponding increases of the charging currents resulting from surface acoustic wave sonication have been observed.