| Metadata | Details |
|---|
| Publication Date | 2025-03-17 |
| Journal | Sensors |
| Authors | Wookyoung Choi, Chanhu Park, Dongkwon Lee, Jaebum Park, Myeongwon Lee |
| Institutions | Korea University, LG (South Korea) |
| Citations | 2 |
| Analysis | Full AI Review Included |
This research details the development and validation of a miniaturized scanning magnetometer utilizing ensemble Nitrogen-Vacancy (NV) centers in diamond for high-resolution magnetic imaging of hidden targets.
- Core Achievement: Demonstrated millimeter-scale magnetic imaging (3.75 mm resolution) over a large area (24.38 cm x 18.75 cm) using a compact NV-based sensor integrated with a 2D scanning stage.
- Sensitivity: Achieved an optimal DC magnetic field sensitivity of 406 ± 2 nT/âHz using a fiber-coupled laser configuration.
- Detection Method: Utilized fixed-frequency lock-in detection on the Optically Detected Magnetic Resonance (ODMR) signal to significantly expedite the scanning process compared to full spectrum acquisition.
- Image Distortion Analysis: Identified that magnetic images are susceptible to distortion based on the choice of carrier frequency (fc) and the magnitude of the local magnetic field, especially when transitioning between linear and non-linear response regimes.
- Localization Correction: Proposed and simulated a method based on NV vector magnetometry to compensate for unknown target tilt angles (e.g., 20° and 30°), reducing target localization errors from centimeters (Îx â 1.5 cm) to sub-millimeter (Îx â 0.05 mm).
- Application Simulation: Simulated real-world scenarios, such as remote detection of landmines or concealed objects, using a toy diorama with embedded permanent magnets.
| Parameter | Value | Unit | Context |
|---|
| Optimal DC Field Sensitivity | 406 ± 2 | nT/âHz | Fiber-coupled laser sensor |
| LED Sensor Sensitivity | 628 ± 3 | nT/âHz | LED sensor configuration |
| NV Concentration (N) | ~2 x 1014 | cm-3 | After 2 MeV electron irradiation |
| Diamond Crystal Type | Single crystal 1b | N/A | Nitrogen concentration <200 ppm |
| Diamond Dimensions | 3 x 3 x 0.3 | mm | Sensor chip size |
| Crystal Orientation | <100> | N/A | Diamond growth direction |
| ESR Frequency (Ground State) | 2.87 | GHz | Room temperature operation |
| Intrinsic Splitting (ÎŽ) | 2.26 | MHz | Due to crystal strain |
| Excitation Wavelength (λ) | 532 | nm | CW Green Laser/LED |
| Max Laser Power | ~24 | mW | Fiber-coupled laser source |
| DSRR Quality Factor (Q) | 160 | N/A | Tuned resonance (originally 395) |
| Lock-in Demodulation Frequency | 5 | MHz | Used for microwave modulation |
| Effective NV Count | ~3 x 1013 | N/A | Within detection volume (~0.36 mm3) |
| Total Scan Area | 24.38 x 18.75 | cm | Maximum imaging dimensions |
| Scan Step Size | 3.75 | mm | Spatial resolution of the scan |
| Total Imaging Duration | 6000 | s | For 1200 steps (40 x 30) |
| Sensor-to-Target Distance (z) | â 10 | cm | Distance to diorama surface |
- Diamond Synthesis and Preparation: Used commercial single crystal Type 1b diamond (<100> orientation). NV centers were created by 1.8 x 1015 electron irradiation at 2 MeV, followed by annealing at 900 °C for 2 hours, resulting in an NV concentration of ~2 x 1014 cm-3.
- Microwave Delivery: The diamond plate was affixed to a Double Split-Ring Resonator (DSRR) fabricated on a Printed Circuit Board (PCB). The DSRR was tuned using an additional copper plate to align its resonance (Q=160) with the NV Electron Spin Resonance (ESR) frequency (2.87 GHz).
- Optical Excitation and Readout: NV centers were excited using continuous wave (CW) green light (532 nm) from either an LED (~16 mW) or an external fiber-coupled laser (~24 mW). Photoluminescence (PL) (630-800 nm) was collected via a Gradient-Index (GRIN) lens, dichroic mirror, and optical filter, and measured by a silicon photodetector (PD).
- Signal Processing: Optically Detected Magnetic Resonance (ODMR) was measured using a lock-in detection technique (demodulated at 5 MHz) to enhance the Signal-to-Noise Ratio (SNR).
- Scanning Protocol: The miniaturized sensor was mounted on a 2D motorized stage controlled by stepper motors. The scanning sequence allocated 5 s per step: 1 s for measurement, 2 s for position adjustment, and a critical 2 s pause to allow stepper motor vibrations to dissipate before measurement commenced.
- Magnetic Imaging: Magnetic field changes were tracked by monitoring the lock-in signal at a constant carrier frequency (fc) near the NV ESR. Background magnetic noise (including Earthâs field) was eliminated by subtracting pre- and post-magnet placement scans.
- Image Analysis and Simulation: Magnetic field profiles were simulated using the Object-Oriented Micromagnetic Framework (OOMMF) software. The measured lock-in signal was modeled as a function of the magnetic field (BNV) to account for non-linear responses and image distortion observed when the field magnitude exceeded the ESR linewidth.
- Vector Magnetometry (Tilt Correction): Magnetic field components (Bx, By, Bz) were extracted by measuring the Zeeman shifts across the four distinct NV crystal axes. These components were used to calculate and minimize the âTotal residueâ between measured and simulated fields, accurately determining and correcting the targetâs tilt angles (Ξx, Ξy).
| Sector | Application | Relevance to NV Magnetometer |
|---|
| Military & Defense | Remote detection of hidden magnetic targets (e.g., landmines, UXO). | Compact size, high sensitivity (nT/âHz scale), and ability for vector magnetometry to accurately localize targets even when tilted or buried. |
| Industrial Inspection | Non-invasive location of concealed metallic objects in infrastructure or construction sites. | Millimeter-scale resolution scanning over large areas (tens of centimeters) at ambient temperature. |
| Quantum Sensing | Development of next-generation magnetic sensors. | NV centers offer simultaneous high magnetic field sensitivity and atomic spatial resolution, functioning at room temperature. |
| Aerospace/UAV | Drone-mounted magnetic surveys (e.g., geological prospecting, infrastructure monitoring). | The miniaturized, compact sensor design is suitable for integration onto Unmanned Aerial Vehicles (UAVs) or drones, complementing existing OPM and fluxgate systems. |
| Materials Science | Mapping magnetic domains and current distributions in materials. | While this work focuses on mm-scale, the underlying NV technology is crucial for nanoscale imaging of ferromagnetic materials and graphene devices. |
View Original Abstract
We have developed a miniaturized magnetic sensor based on diamond nitrogen-vacancy (NV) centers, combined with a two-dimensional scanning setup that enables imaging magnetic samples with millimeter-scale resolution. Using the lock-in detection scheme, we tracked changes in the NVâs spin resonances induced by the magnetic field from target samples. As a proof-of-principle demonstration of magnetic imaging, we used a toy diorama with hidden magnets to simulate scenarios such as the remote detection of landmines on a battlefield or locating concealed objects at a construction site, focusing on image analysis rather than addressing sensitivity for practical applications. The obtained magnetic images reveal that they can be influenced and distorted by the choice of frequency point used in the lock-in detection, as well as the magnitude of the sampleâs magnetic field. Through magnetic simulations, we found good agreement between the measured and simulated images. Additionally, we propose a method based on NV vector magnetometry to compensate for the non-zero tilt angles of a target, enabling the accurate localization of its position. This work introduces a novel imaging method using a scanning miniaturized magnetometer to detect hidden magnetic objects, with potential applications in military and industrial sectors.
- 2017 - Quantum Sensing [Crossref]
- 2020 - Sensitivity Optimization for NV-Diamond Magnetometry [Crossref]
- 1979 - Performance of a Resonant Input SQUID Amplifier System [Crossref]
- 2021 - Quantum-Enhanced Nonlinear Microscopy [Crossref]
- 2010 - Ultrahigh Sensitivity Magnetic Field and Magnetization Measurements with an Atomic Magnetometer [Crossref]
- 2008 - Nanoscale Imaging Magnetometry with Diamond Spins under Ambient Conditions [Crossref]
- 2018 - Probing Condensed Matter Physics with Magnetometry Based on Nitrogen-Vacancy Centres in Diamond [Crossref]
- 2021 - Mapping Current Profiles of Point-Contacted Graphene Devices Using Single-Spin Scanning Magnetometer [Crossref]
- 2019 - Nanotesla Sensitivity Magnetic Field Sensing Using a Compact Diamond Nitrogen-Vacancy Magnetometer [Crossref]