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Acoustic detection of thin films in ­fluid-­filled hoses and pipes


  • Deposition monitoring in fluid conduits
  • Non-invasive online monitoring
  • Sensors well suited for IIOT applications


The propagation of surface acoustic waves along the surface of a substrate is very sensitive, in both its amplitude and velocity, to any deposition on the surface. Their miniaturized ­design, high thermal stability, and possibility of wireless integration make surface acoustic wave ­sensors very promising devices for Internet of Things applications. Specifically, in the context of industrial automation the continuous monitoring of the infrastructure becomes ­absolutely crucial. The continuous monitoring enables targeted and predictive maintenance measures, which promise significant cost reductions compared to time-based preventive maintenance and failure-based corrective maintenance. A significant problem in a wide range of industrial applications, such as in the chemical, medical, and process industries, is the deposition of thin films on the inside of hoses and pipes conducting fluids.

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The inventors suggest a method and device, based on Lamb-wave propagation along solid walls1. Exploiting this approach, the piezoelectric sensor elements can be mounted on the ­outside of liquid filled conduits made from any structural material, i.e. glass, plastics, and ­metal. This allows for non-invasive measurement of thin films2 with a sensitivity down well below 100 µm. The inventors have suggested a number of ways that enable easy retrofitting of existing conduits for these measurements, including measurement collars for flexible hoses with soft walls and clamp-on devices for solid pipes with circular cross sections.


Use cases include the detection and thickness monitoring of deposition layers in a ­fluid-filled conduit, such as biofilm, limescale, and polymer layers. Enabling a wide variety of ­industrial applications, as well as applications in supply engineering and medical devices, e.g. ­catheters. Additionally, the invention also allows for monitoring of conduit properties, such as ­embrittlement, and measurements of the filling level in partially filled horizontal pipes.

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