A New Way Of Simultaneously Detecting Magnetic Fields In Various Directions

  • A new tool uses the Nitrogen-Vacancy center defect in diamond to simultaneously detect magnetic fields in different directions. 
  • It creates a 3D picture of magnetic fields in real-time. 
  • The technology could be utilized in various fields including condensed-matter physics and biology. 

The real-time sensing of a dynamic vector magnetic field is required in numerous magnetometry applications, such as magnetic navigation, biomagnetic field detection and imaging, and magnetic anomaly detection.

Scalar magnetometers are capable of measuring only the magnitude of the magnetic field, whereas vector-projection magnetometers can measure the magnetic field projection along a particular axis. But what if you want to measure magnetic fields in different directions all at once.

Recently, researchers at Harvard University have developed a tool that can sense magnetic fields in almost everything from condensed-matter systems to firing neurons. To do this, the tool uses one of the various point defects in diamond called Nitrogen-Vacancy (NV) centers. It’s capable of detecting magnetic fields in different directions simultaneously.

How It Works?

The researchers subjected a small 4-millimeter-square diamond wafer to 4 different microwave signals. Each signal was configured to measure a particular NV orientation and dithered (added white noise to decrease distortion of low-amplitude signals) as per the special frequency-modulation pattern. This allowed them to analyze how individual NV orientation behaved in different magnetic field directions.

Until now, this has been a tedious and time-consuming process of regularly transitioning between microwave frequencies to observe the response of a single NV orientation at a time. The new tool represents significant improvements over previous methodologies.

The old technique doesn’t work for fast processes like biomagnetic fields generated by firing neurons. It would not be able to capture all information, but the new technique can measure magnetic fields in various directions at the same time.

In this study, researchers collected a continuous stream of data from the diamond as the magnetic field is fluctuating. The new tool can process this data faster than it collects it, allowing researchers to observe the amplitude and direction of a magnetic field in real-time.

Reference: APSPhysics | doi:10.1103/PhysRevApplied.10.034044 | The Harvard Gazette

The system is built on a previous research that used diamond’s Nitrogen-Vacancy centers to identify neural signals in marine worms. It was just a proof of principle. An effective neuroscience system must be compatible with neurons of mammals, but since firing neurons generate magnetic fields that are aligned in various directions, making such systems is quite difficult. However, the newly developed tool handles all these issues of neuron magnetic sensing.

Why Did They Use Nitrogen-Vacancy Centers?

For this task, NV centers are arranged perfectly in the diamond lattice. Each NV center is created by replacing one carbon atom with a nitrogen atom and an adjacent vacancy. Since each atom is linked to 4 other atoms, there are 4 possible NV orientations, each is sensitive to magnetic fields oriented in that directions. Thus, one can use 4 kinds of NV centers to determine the direction of magnetic field.

Courtesy of researchers 

In this experiment, researchers placed a wafer of diamond in a magnetic field (produced in the lab) and projected a laser light on it, causing the mineral to shine. When NV centers reacted to magnetic field alterations and unique frequency-modulation pattern, the brightness of the NV center changed significantly.

Researchers tracked the changes in brightness and created a 3D image of the magnetic field. Now it’s possible to observe all 4 NV orientations concurrently and determine the magnetic field in real time. It’s like listening to 4 different radio channels at the same time and they all make sense together.

Read: The Strongest Indoor Pulsed Magnetic Field Ever Generated

Although it’s a small improvement of what other scientists are doing, authors believe that their technology could be utilized in various fields, including condensed-matter physics and biology.

Written by
Varun Kumar

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