Using NV centers in diamond to detect DC to very-low frequency magnetic fields

The article presents a compact tabletop magnetometer using NV centers in diamond to detect magnetic fields generated by electrical currents. The magnetometer is capable of sensing low-frequency magnetic fields, offering high sensitivity for applications such as electric current measurements and magnetic communication.

Key points:

1. Experimental Setup:

• The setup utilizes optically detected magnetic resonance (ODMR) and a dual-resonance detection approach to measure magnetic fields. This technique allows for detecting two ODMR transitions simultaneously, enhancing the measurement accuracy.

• The system includes a 532 nm green laser for excitation and a microwave antenna for driving the NV centers, with magnetic fields being sensed through red fluorescence emission.

2. Sensing Electrical Currents:

• The device was tested by measuring magnetic fields from electric currents flowing through a test wire, showing sensitivity to low electrical currents (0-0.4 A) and a higher current (50 A).

• Results indicate that the system can detect changes in magnetic fields with a standard deviation of 281.3 nT at 50 A and 85.2 nT at 0 A, demonstrating its ability to monitor electrical current variations.

3. Noise Floor and Sensitivity:

• The system’s noise floor was measured to be around 2.3 nT/√Hz, and the shot-noise-limited sensitivity was estimated at 585 pT/√Hz when using continuous-wave laser excitation at 0.5 W power.

• The device demonstrated low-frequency magnetic field detection over a distance of up to 10 m and was compared to a commercial magnetoresistive sensor, showing better performance in certain frequency ranges.

4. Magnetic Field Remote Signal Detection:

• The system successfully detected low-frequency magnetic field signals transmitted over distances of up to 10 meters, showcasing potential for magnetic field communication in environments where electric field propagation is not feasible, such as in underwater or underground conditions.

5. Encoding Information in Magnetic Signals:

• The system was used to detect discrete frequency modulations of magnetic fields, enabling low-frequency magnetic field communication. Using frequency-shift keying (FSK), the device was able to receive encoded information bits, demonstrating its application in magnetic data transmission.

6. Long-Term Stability:

• Allan deviation analysis revealed that for low electrical currents, the system exhibits flicker-dominated noise. At higher currents, a random-walk noise behavior is observed, which is attributed to thermal fluctuations in the test wire.

7. Improvements and Future Work:

• The study notes that improvements in microwave delivery and active temperature stabilization could help reach the shot-noise-limited sensitivity. The alignment of the NV axis with respect to the test wire could further improve sensitivity for magnetic field changes due to the wire.

Conclusion:

This work demonstrates a compact, portable NV diamond-based magnetometer capable of precise, non-invasive measurements of electrical currents and magnetic fields. It shows great potential for applications in magnetic field communication, especially in RF-attenuating environments, and offers a robust platform for high-sensitivity field measurements. Further developments could enhance its practical applications in wireless communication and environmental sensing.