Optically pumped magnetometers (OPM)

Detect material damage at an early stage

Quantum technologies open up new ways in solving technological problems. This also applies to measurement technology: Quantum-based sensors provide access to ever increasing accuracies and thus to the observation and measurement of previously inaccessible processes. Many materials science applications in particular offer great opportunities for the use of quantum sensors – for example to better understand mechanisms and further optimize processes or to monitor safety-relevant components more reliably.

In industrial quality assurance, magnetic testing methods and sensors have long been established and are used, for example, to detect damage during wire drawing. The basic idea is that material damage causes magnetic »districts« to change in such a way that this change can be detected as an anomaly in the magnetic stray field. However, current methods suffer from low detection sensitivity in combination with reduced spatial resolution. As a result, the stray magnetic fields can only be detected on average over relatively large measurement volumes.

Quantum magnetometer for non-destructive mechanical testing of materials

Quantum sensors, such as optically pumped magnetometers (OPM), open up new possibilities in measurement technology. In a similar way to atomic clocks, they use atomic constants, meaning they do not need to be calibrated. Quantum mechanical principles such as entanglement improve the statistical measurement uncertainty compared with traditional approaches, so that the resulting sensors are robust, highly sensitive and have an extraordinary dynamic range.

Inside microfabricated optically pumped magnetometers (OPM), a laser uses the Larmor precession to measure the magnetic field in about 1 mm³ rubidium gas. This level of sensitivity is sufficient to detect damage due to material fatigue in a sample volume of just 0.1 mm³ based on its magnetization.

Making high measurement sensitivity available for industrial applications

Fraunhofer IPM and Fraunhofer IWM work with additional partners on the development of novel, magnetic measurement systems for materials testing. The extreme sensitivity of OPM – just one millionth of the earth's magnetic field – enables the high-resolution magnetic detection of damage in ferromagnetic materials, such as the stress concentration on imperfect welding connections in steel.

To enable industrial applications to benefit from this level of sensitivity, our team is working on new components such as flux guides as »magnetic prisms« for controlling sensitivity and spatial resolution, suitable actuators and a special shield against interfering magnetic fields from the surrounding area. Critical components can thus be tested to the strictest specifications in terms of functional safety at an early stage of production, even though the ambient conditions are anything but ideal for OPM in this context.