Fiber-integrated NV Magnetometer with Microcontroller-based Lock-in Technique Enables Low-Cost Magnetic Resonance Detection

Nitrogen-vacancy (NV) magnetometers offer exceptional sensitivity for detecting weak magnetic fields, yet their widespread adoption in industry remains limited by the size and cost of associated electronics. Now, Qilong Wu, Xuan-Ming Shen, Yuan Zhang, and colleagues have developed a compact and affordable solution, fabricating a fiber-integrated NV magnetometer coupled with a microcontroller-based software lock-in technique. This innovative approach efficiently coordinates microwave generation and signal conversion, achieving a sensitivity of 93 nT/Hz^1/2, comparable to that of professional-grade instruments. By demonstrating both high sensitivity and real-time magnetic field detection with a standard deviation of 488 nT, this work represents a significant step towards miniaturising NV magnetometer systems and unlocking their potential for broader industrial applications.

NV Magnetometer Fabrication and Hardware Details

This document provides a comprehensive overview of the hardware and fabrication processes used in the research, strengthening the main publication and aiding reproducibility. It details the construction of the fiber-integrated NV magnetometer, including components like the STM32F103ZET6 microcontroller and the ADF4351 frequency synthesizer. The fabrication process emphasizes cost-effective 3D printing for miniaturization. The inclusion of code implementing the software lock-in technique is valuable, allowing readers to understand the implementation and potentially adapt it for their own applications.

The system demonstrates performance comparable to commercial equipment, with a magnetic field sensitivity of 421 nT/√Hz, while offering advantages in cost and portability. The document is well-organized and comprehensively covers all key aspects of the setup. To further enhance clarity, figure captions could include details about the materials used in 3D-printed components. Adding comments to the code snippet would improve accessibility. Briefly describing the calibration procedure and potential error sources in the magnetic field sensitivity measurement would also strengthen the analysis. The document includes a link to the supplier of the microdiamond particles and specifies the 3D printing material. Overall, this is an exceptionally well-written and informative supplementary document, providing a level of detail rarely seen and significantly enhancing the credibility and reproducibility of the research.

Microcontroller Emulates Lock-in for NV Magnetometry

This research pioneered a low-cost, microcontroller-based software lock-in technique for fiber-integrated nitrogen-vacancy (NV) magnetometry, addressing a key limitation in the practical application of these sensitive devices. Scientists engineered a system where a microcontroller coordinates a microwave source chip and an analog-to-digital converter, mimicking the function of a traditional lock-in amplifier at significantly reduced cost and size. This technique realizes microwave frequency-modulated optically detected magnetic resonance, allowing for sensitive detection of weak magnetic fields. The core of the method involves simultaneously recording voltage series from a photodiode using the microcontroller’s analog-to-digital converter, mirroring the phase-locking mechanism of conventional lock-in amplifiers.

Researchers then calculated averaged voltages and their differences to mimic low-pass filtering, effectively isolating the magnetic signal from noise. By varying the voltage sampling time, the detection bandwidth was precisely controlled. The team achieved a magnetic field sensitivity of 93 nT/Hz 1/2, comparable to performance obtained with bulky, professional devices. To further optimize performance, scientists systematically investigated the impact of frequency modulation depth on magnetic field sensitivity. Experiments revealed that increasing the modulation depth initially enhanced the lock-in voltage and narrowed the linewidth of the detected signal, leading to improved sensitivity.

However, beyond a certain point, increasing the modulation depth led to a broader linewidth, limiting the achievable sensitivity. Real-time magnetic field detection was successfully demonstrated, achieving a standard deviation of 488 nT, confirming the system’s suitability for dynamic measurements. Detailed analysis of noise sources revealed a noise-limited sensitivity of 38 nT/Hz 1/2 when the laser and microwave were switched off, establishing a fundamental performance benchmark.

Fiber Magnetometry with Microcontroller Lock-in Technique

Scientists have developed a new technique for detecting weak magnetic fields using nitrogen-vacancy (NV) centers in diamond, achieving a sensitivity of 93 nT/Hz 1/2. This performance is comparable to that of bulky, professional-grade magnetometers, but utilizes a significantly miniaturized and cost-effective system. The research team fabricated a fiber-integrated NV magnetometer and implemented a microcontroller-based software lock-in technique to detect these subtle magnetic variations. The core of the breakthrough lies in mimicking the functionality of a traditional lock-in amplifier using a microcontroller, a microwave source chip, and an analog-to-digital converter.

By rapidly switching between two microwave frequencies, the system modulates the fluorescence emitted by the NV centers, creating a measurable signal proportional to the external magnetic field. The microcontroller then processes this signal, filtering out noise and amplifying the magnetic field information. Experiments demonstrate the ability to detect real-time magnetic fields with a standard deviation of 488 nT. The team achieved this sensitivity by carefully characterizing the frequency modulation of the NV center fluorescence. The system’s performance was validated by obtaining a frequency-modulated optically detected magnetic resonance (FM-ODMR) spectrum, closely matching results obtained using conventional, high-precision equipment. Theoretical calculations, combined with experimental data, estimate the magnetic field sensitivity, revealing a noise floor comparable to established technologies. This innovative approach paves the way for widespread adoption of NV magnetometry in diverse industrial applications, offering a compact, affordable, and high-performance solution for magnetic field sensing.

Compact NV Magnetometry with Nanotester Sensitivity

This research demonstrates a new approach to fiber-integrated nitrogen-vacancy (NV) magnetometry, achieving performance comparable to that of significantly more complex and expensive systems. Scientists successfully fabricated a compact magnetometer and developed a microcontroller-based software lock-in technique to detect weak magnetic fields. This technique efficiently coordinates a microwave source and an analogue-to-digital converter, enabling frequency-modulated optically detected magnetic resonance. The resulting system achieves a magnetic field sensitivity of 93 nanotesters per root Hertz, and real-time magnetic field sensing with a standard deviation of 488 nanotesters.

This achievement represents a significant step towards miniaturizing NV magnetometers and reducing their cost, potentially accelerating their adoption in industrial applications. The authors acknowledge that the current sensitivity is limited by the system’s components, and future work could improve performance by optimizing the diamond sample, laser source, and analogue-to-digital converter. They envision further miniaturization into a credit-card sized board, paving the way for widespread deployment of this technology.