ACOUSTIC DETECTION OF THIN FILMS IN FLUID- FILLED HOSES AND PIPES
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.
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.
Functional demonstration with growing biofilms.
Figure: A thin biofilm deposited inside a fluid-filled conduit (top). Photo of the experimental setup for a clamp-on device2 (bottom left). Photo of the experimental setup for a collar-based measurement device for soft hoses (bottom right).
1) G. Lindner, J. Phys. D: Appl. Phys., 41, 123002 (2008); doi: 10.1088/0022-3727/41/12/123002
2) S. Tietze et al., Sensors 2018, 18(2), 526 (2018); doi: 10.3390/s18020526