Frequently asked questions

Discover how NV-center diamond magnetometry can address industrial NDT challenges, from crack and grinding burn detection to microstructural characterization.
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NV-center diamond quantum magnetometry is a magnetic sensing technique that uses nitrogen-vacancy (NV) centers inside diamond as magnetic-field probes.
An NV center is a defect in the diamond crystal lattice consisting of a nitrogen atom adjacent to a vacant carbon site. Its electronic spin can be initialized and read optically. When a magnetic field is applied, the NV spin energy levels shift through the Zeeman effect. This shift can be measured using optically detected magnetic resonance (ODMR), providing a quantitative measurement of the magnetic field.
A bulk diamond contains NV centers oriented along 4 crystallographic directions. Measuring these orientations provides vector information about the magnetic field rather than only a scalar amplitude.
For non-destructive testing (NDT), the diamond sensor can therefore map magnetic fields generated or modified by defects, microstructural changes or induced eddy currents in metallic components.

A diamond NV magnetometer detects defects by measuring local changes in the magnetic response of a metallic component.
In ferromagnetic materials, cracks, microstructural transformations, grinding burns and other material variations can modify local magnetization. These changes generate variations in the stray or leakage magnetic field above the component. A diamond quantum magnetometer can scan this field and produce a spatial magnetic map, or C-scan.
For conductive materials, the same magnetic sensor can also measure alternating fields associated with eddy currents. An AC excitation induces electrical currents in the component; a crack or material variation perturbs their flow and therefore modifies the secondary magnetic field detected by the NV sensor.
Kwan-tek NDT solution deliver simultaneously both approaches: static magnetic-field measurements and eddy-current measurements using NV-center magnetometry. This allows different magnetic signatures of a defect or material state to be investigated with the same sensing technology.

NV diamond magnetometry combines high spatial resolution and magnetic sensitivity, quantitative measurement, a compact sensing head, robustness to harsh environments, and ease of operational deployment. These properties make it particularly relevant for demanding NDT applications involving small defects, complex geometries or challenging operating conditions.
NV centers provide quantitative magnetic-field measurements through the Zeeman effect, with high sensitivity and spatial resolution. Multiple NV orientations can also provide vector magnetic-field information, enabling detailed magnetic C-scans rather than only qualitative defect indications.
Kwan-tek’s fiber-coupled architecture enables a compact sensing head with no electronics at the sensing point: the diamond is optically interrogated through the fiber, while the electronics remain remote. This facilitates inspection of complex and hard-to-reach geometries, as well as integration with robotic systems, automated scanners and in-line inspection.
Diamond is intrinsically robust to demanding environmental conditions, including high temperatures and radiation, making NV sensing particularly relevant for harsh-environment inspection.
From an operational perspective, NV magnetometry is contactless and requires no surface preparation, simplifying inspection workflows and facilitating automated or in-line deployment.
Finally, NV magnetometry can measure both DC magnetic leakage fields and AC fields associated with eddy currents, providing complementary inspection information through a single sensor architecture.

NV magnetometry can complement conventional eddy-current testing (ECT) by using the NV diamond sensor as a high-resolution magnetic receiver.
As in conventional ECT, a coil generates an alternating magnetic field that induces eddy currents in the conductive component. Defects disturb the current flow and the associated magnetic field. Instead of relying only on the electrical response of a conventional receiving probe, the NV sensor directly measures the resulting AC magnetic field, including amplitude and phase.
A key advantage of this architecture is that the same NV sensor can simultaneously measure AC eddy-current fields and DC magnetic leakage fields, providing complementary AC and DC C-scans from a single inspection.
NV magnetic sensing can also operate with lower eddy-current excitation frequencies, which can support greater inspection depth depending on the material and application. In addition, Kwan-tek’s fiber-coupled architecture enables a compact sensing head, facilitating inspection of complex geometries and hard-to-reach areas.
NV magnetometry therefore extends conventional eddy-current inspection by adding high-resolution direct magnetic-field measurement and simultaneous AC/DC information.

The NV sensor itself provides an intrinsically referenced magnetic-field measurement and does not rely on empirical field calibration in the same way as conventional sensors.
The magnetic field is derived from the shift of the NV resonance frequencies through the Zeeman effect. Because this relationship is governed by fundamental physical constants, the sensor provides a direct quantitative magnetic-field readout. This makes the measurement less dependent on empirical sensor calibration and potentially less prone to sensor-response drift over time.
However, the NDT response of a defect is not intrinsic. Signal amplitude and spatial signature depend on parameters such as sensor lift-off, magnetic or eddy-current excitation, material properties, defect geometry and inspection configuration. These conditions therefore need to be controlled or calibrated when quantitative and repeatable defect assessment is required.
The key distinction is between calibrating the sensor and calibrating the inspection: the NV center provides an intrinsically referenced magnetic-field measurement, while the relationship between that field and the defect being inspected remains application-dependent.

Yes. Kwan-tek has experimentally demonstrated non-destructive detection of grinding burns in a 16NiCrMo13 steel gearwheel using NV diamond magnetometry.
Grinding burns are thermally induced material changes created during grinding. They can alter microstructure, residual stresses and mechanical properties, potentially reducing the fatigue life of critical mechanical components.
Because these changes also affect the magnetic properties of ferromagnetic steel, the resulting magnetic signatures can be measured after magnetization. In Kwan-tek’s published study, the NV magnetometer detected all investigated grinding burns on the tested gearwheel, including the weakest burns in the experimental dataset.
A preliminary magnetization of approximately 20 mT was sufficient to obtain a signal-to-noise ratio of at least 10 for the weakest tested burns. Higher magnetization increased the magnetic contrast.
The method is contactless and does not require the chemical etchants used in nital etching, making NV magnetometry a relevant digital and contactless approach for grinding-burn inspection.

Yes. NV magnetometry can detect defects in electrically conductive non-ferromagnetic materials when combined with eddy-current excitation.
While static magnetic flux leakage is naturally suited to ferromagnetic materials, eddy-current excitation extends NV-based inspection to conductive materials. An alternating magnetic field induces eddy currents in the component; cracks disturb their flow and modify the resulting magnetic field. The NV diamond acts as a high-resolution magnetic receiver, directly measuring these AC field variations in amplitude and phase.
Kwan-tek demonstrated this principle on austenitic 304L stainless steel using an artificial crack approximately 2 mm long, 100 µm wide and 300 µm deep, with eddy currents excited at 1.5 kHz.
A key benefit of the NV approach is that the same sensor can simultaneously acquire AC eddy-current and DC magnetic-field information, providing complementary C-scans from a single inspection architecture.
This capability extends NV magnetometry beyond ferromagnetic materials and makes it relevant for crack inspection across a broader range of conductive metals.

Yes. NV-center magnetometry has demonstrated sensitivity to the formation and spatial distribution of ferromagnetic α′-martensite in plastically deformed 316L austenitic stainless steel.

Undeformed austenitic 316L is predominantly non-ferromagnetic, whereas deformation-induced α′-martensite is ferromagnetic. This magnetic contrast creates a measurable signal that can be mapped using magnetic flux leakage and an NV-center magnetometer.

In a study comparing NV magnetometry with magnetic Barkhausen noise, magnetic incremental permeability and eddy-current testing, NV-center measurements were compared with near-surface X-ray diffraction measurements. For the investigated dataset, NV magnetometry showed a corrected Pearson correlation coefficient of r = 0.99 with α′-martensite volume fraction.

The result demonstrates strong sensitivity to martensitic transformation under the tested conditions.

NV diamond magnetometry offers a digital, contactless alternative to LPT for selected surface-defect inspection applications.. Unlike penetrant testing, the NV approach detects magnetic or electromagnetic signatures associated with a defect and can provide a digital spatial map of the measurement.

Liquid penetrant testing requires a defect to be open to the surface so that penetrant can enter it by capillary action. The inspection process typically involves surface preparation, penetrant application, dwell time, excess penetrant removal and developer application.

Kwan-tek has demonstrated NV magnetometry on reference defects representative of penetrant-testing applications. On a NiCr reference sample compliant with EN ISO 3452-3 Type 1, defects including a 47.5 µm-deep discontinuity with a 2 µm opening and a 10 µm-deep discontinuity with a 0.5 µm opening were detected.

The NV approach is contactless and produces digital magnetic data that can be mapped as a C-scan. The same sensor architecture can also access magnetic flux leakage and eddy-current information, opening the possibility of detecting defects through different electromagnetic signatures.

These results demonstrate the potential of NV magnetometry as an alternative or complementary approach to penetrant testing for selected applications.