Citation: Schmieder, L.; Koss, P.A.;
Lambrecht, A.; Kühnemann, F.
Noninvasive
Magnetic-Marking-Based Flow
Metering with Optically Pumped
Magnetometers. Appl. Sci. 2022, 12,
1275. https://doi.org/10.3390/
app12031275
Academic Editors: Arkadiusz Gola,
Izabela Nielsen and Patrik Grznár
Received: 6 December 2021
Accepted: 15 January 2022
Published: 25 January 2022
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Article
Noninvasive Magnetic-Marking-Based Flow Metering with
Optically Pumped Magnetometers
Leonhard Schmieder
1,2,
* , Peter A. Koss
1
, Armin Lambrecht
1
and Frank Kühnemann
1
1
Fraunhofer IPM, Georges-Köhler-Allee 301, 79110 Freiburg im Breisgau, Germany;
peter.koss@ipm.fraunhofer.de (P.A.K.); armin.lambrecht@ipm.fraunhofer.de (A.L.);
frank.kuehnemann@ipm.fraunhofer.de (F.K.)
2
Faculty of Mathematics and Physics, University of Freiburg, Hermann-Herder-Str. 3,
79104 Freiburg im Breisgau, Germany
* Correspondence: leonhard.schmieder@ipm.fraunhofer.de; Tel.: +49-761-8857-277
Featured Application: Noninvasive inline flow-metering procedure with optically pumped
magnetometers.
Abstract:
We present a noninvasive procedure that measures the flow velocity of a fluid by using
polarized hydrogen nuclei in the fluid. The measurement procedure is based on a time-of-flight
method where magnetic information is applied on the fluid with a permanent magnet and an RF-pulse.
In contrast to other methods, this magnetic-marking method works without tracers. The read-out of
the magnetic information is performed by optically pumped magnetometers downstream. In order to
function, the magnetometers have to be operated in a magnetic shield with magnetic field strengths
lower than 100 nT, i.e., in the zero-to-ultra-low-field regime. In this regime, the magnetometers
are capable of detecting induced magnetic signals of 10 pT or less with an inline-flow setup. The
results presented in this paper demonstrate the viability of optically pumped magnetometers for flow
metering. The first metering results yielded an average accuracy of 3% at flow velocities between
13 cm/s and 22.4 cm/s.
Keywords:
ZULF-NMR; flow metering; OPM; time-of-flight measurement; noninvasive; tracer-free;
calibration-free; inline measurement; volumetric flow
1. Introduction
Flow is one of the most important variables in industrial environments, and its precise
measurement is the foundation of process automation. It is an established method in
the production, infrastructure and process industry [
1
]. Electromagnetic flow metering
(EMFM) is widely used for flow monitoring in research and industry [
1
]. However, it
requires a minimum conductivity of 5
µ
S/cm of the fluid of interest. For nonconductive
and multiphase media, which include non-ionized gases, ceramics, fuels or oils, there is no
equivalent volumetric flow-metering technique [2].
NMR-based flow metering has proven to be a viable tool for multiphase flow detection
in clinical applications and does not require a minimum conductivity [
3
,
4
]. Conventional
high-field NMR measuring devices established on the market are rarely used in industry [
5
].
The difficult system integration and the associated costs limit its applicability [
6
]. In the
high field NMR regime, strong alternating magnetic fields are a compromise between
signal strength and field generation effort. For noninvasive flow metering through metal
pipes, the reduced penetration depth of the radiofrequency (RF) signals is an additional
obstacle [7].
For field strengths similar to the Earth’s magnetic field or lower (<50
µ
T), these
disadvantages are significantly attenuated. Low magnetic fields are easy to generate, can
be varied rapidly, and the low frequency RF-signals penetrate deeper through metallic
Appl. Sci. 2022, 12, 1275. https://doi.org/10.3390/app12031275 https://www.mdpi.com/journal/applsci
