Scanning Miniaturized Magnetometer Based on Diamond Quantum Sensors and Its Potential Application for Hidden Target Detection

At a Glance

Metadata	Details
Publication Date	2025-03-17
Journal	Sensors
Authors	Wookyoung Choi, Chanhu Park, Dongkwon Lee, Jaebum Park, Myeongwon Lee
Institutions	LG (South Korea), Korea University
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond NV Magnetometry for Hidden Target Detection

This document analyzes the research paper “Scanning Miniaturized Magnetometer Based on Diamond Quantum Sensors and Its Potential Application for Hidden Target Detection” to provide technical specifications and align the findings with 6CCVD’s advanced MPCVD diamond capabilities.

Executive Summary

This research successfully demonstrates a miniaturized, scanning magnetic sensor utilizing ensemble Nitrogen-Vacancy (NV) centers in diamond for millimeter-scale imaging of concealed magnetic targets.

Core Achievement: Development of a compact, two-dimensional scanning magnetometer based on ensemble NV centers for detecting hidden magnetic objects (simulating landmines or concealed industrial targets).
Material Basis: Single Crystal Diamond (SCD) Type 1b ($3 \text{ mm} \times 3 \text{ mm} \times 0.3 \text{ mm}$) was used, prepared via electron irradiation and annealing to achieve an NV concentration of $\sim 2 \times 10^{14} \text{ cm}^{-3}$.
Performance: Optimal DC magnetic field sensitivity reached $406 \pm 2 \text{ nT}/\sqrt{\text{Hz}}$ using a fiber-coupled laser setup.
Methodology: The system employs Optically Detected Magnetic Resonance (ODMR) combined with lock-in detection and a Double Split-Ring Resonator (DSRR) for efficient microwave delivery.
Key Finding & Challenge: Magnetic images are susceptible to distortion based on the magnitude of the stray magnetic field and the choice of fixed carrier frequency ($f_c$). The study proposes vector magnetometry to compensate for target tilt angles, significantly improving localization accuracy (reducing errors from $\Delta x \approx 2.1 \text{ cm}$ to $\Delta x \approx 0.05 \text{ mm}$).
Future Requirements: Achieving practical sensitivity levels (order of nT/$\sqrt{\text{Hz}}$) and improved sensor integration (microwave filtering) are necessary for real-world military and industrial applications.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Type	Single Crystal (SCD) Type 1b	N/A	Commercial source (Element Six)
Diamond Dimensions	$3 \times 3 \times 0.3$	mm	Sensor plate size
Crystal Orientation	<100>	N/A	Used for NV creation
Nitrogen Concentration	<200	ppm	Initial concentration in SCD
Irradiation Dose	$1.8 \times 10^{15}$	electrons	At 2 MeV, for vacancy creation
Annealing Temperature	900	°C	For 2 hours, to form NV centers
NV Concentration (N)	$\sim 2 \times 10^{14}$	$\text{cm}^{-3}$	Resulting ensemble density
Optimal Sensitivity ($\eta_{\beta}$)	$406 \pm 2$	$\text{nT}/\sqrt{\text{Hz}}$	Achieved with fiber-coupled laser sensor
ESR Zero-Field Splitting	2870	MHz	Ground state separation ($m_s = 0$ to $m_s = \pm 1$)
Intrinsic Strain Splitting ($\delta$)	2.26	MHz	Pre-existing non-zero strain
DSRR Resonance Frequency	2.87	GHz	Microwave delivery frequency
DSRR Quality Factor (Q)	160	N/A	Tuned value (reduced from 395)
Excitation Wavelength ($\lambda$ )	532	nm	Continuous Wave (CW) Green Laser/LED
Detection Volume	$\sim 0.36$	$\text{mm}^{3}$	Estimated volume in the diamond
Total Scan Area	$24.38 \times 18.75$	cm	Area scanned over the diorama
Spatial Step Size	3.75	mm	Resolution of the scanning stage
Target Localization Error (Corrected)	$\Delta x \approx 0.05, \Delta y \approx -0.08$	mm	Achieved via vector magnetometry correction

Key Methodologies

The miniaturized scanning magnetometer relies on precise material preparation and integration of microwave and optical components:

Material Selection and Preparation: Commercial Single Crystal Diamond (SCD) Type 1b ($3 \text{ mm} \times 3 \text{ mm} \times 0.3 \text{ mm}$) with low nitrogen concentration (<200 ppm) was selected to serve as the host material for NV centers.
NV Center Creation: The diamond was irradiated with $1.8 \times 10^{15}$ electrons at 2 MeV to create vacancies, followed by annealing at $900^\circ \text{C}$ for 2 hours to mobilize vacancies and form ensemble NV centers ($\sim 2 \times 10^{14} \text{ cm}^{-3}$).
Microwave Delivery System: A Double Split-Ring Resonator (DSRR) fabricated on a Printed Circuit Board (PCB) was used to efficiently deliver microwave fields at the 2.87 GHz Electron Spin Resonance (ESR) frequency. The DSRR resonance was fine-tuned using a $60 \text{ µm}$ thick copper plate.
Optical Excitation and Collection: NV centers were excited using a 532 nm CW green laser or LED. Photoluminescence (PL) was collected via a GRIN lens, passed through a dichroic mirror and optical filter (630-800 nm), and detected by a silicon photodetector (PD).
Signal Processing: The PL signal was fed into a lock-in amplifier and demodulated at 5 MHz, utilizing the lock-in detection technique to enhance the Signal-to-Noise Ratio (SNR).
Scanning and Imaging: The miniaturized sensor was mounted on a two-dimensional motorized stage (24.38 cm by 18.75 cm scan area) to map magnetic fields from concealed Nd magnets in a diorama.
Image Analysis and Correction: Magnetic simulations (OOMMF) were used to model the non-linear response of the lock-in signal to varying magnetic field magnitudes. Vector magnetometry was proposed and simulated to compensate for target tilt angles, minimizing localization errors.

6CCVD Solutions & Capabilities

The research highlights the critical role of high-quality SCD material and precise sensor integration—areas where 6CCVD provides industry-leading expertise and customization.

Applicable Materials for Replication and Extension

To replicate and extend this high-sensitivity NV ensemble magnetometry research, 6CCVD recommends the following materials, optimized for high-density, high-coherence NV creation:

High-Purity Single Crystal Diamond (SCD):
- Requirement: The paper used Type 1b SCD with N <200 ppm. For next-generation sensors requiring higher coherence and lower strain, 6CCVD offers Optical Grade SCD with nitrogen concentrations precisely controlled down to <5 ppb (for high-coherence single NV applications) or controlled doping (for optimized ensemble NV density).
- Benefit: Tighter control over initial nitrogen concentration allows researchers to optimize the final NV density ($\sim 2 \times 10^{14} \text{ cm}^{-3}$ in this study) for maximum sensitivity ($\eta_{\beta}$) while managing coherence time ($T_2$).
Custom Substrates:
- Requirement: The paper used a $0.3 \text{ mm}$ thick plate. 6CCVD can supply SCD plates in thicknesses ranging from $0.1 \text{ µm}$ up to $500 \text{ µm}$ for integration into compact DSRR/PCB setups, or Substrates up to $10 \text{ mm}$ for robust sensor packaging.

Customization Potential for Miniaturized Sensors

The study emphasizes the need for miniaturization and precise integration, particularly concerning the DSRR and optical components. 6CCVD directly addresses these needs:

Research Requirement	6CCVD Custom Solution	Technical Advantage
Custom Dimensions	Plates/wafers up to $125 \text{ mm}$ (PCD) and custom SCD sizes.	Enables scaling of the scanning area or integration into specific sensor housings (e.g., UAV/drone platforms).
Surface Quality	Polishing: Ra < 1 nm (SCD) and < 5 nm (PCD).	Essential for minimizing optical scattering and maximizing PL collection efficiency through the GRIN lens and photodetector.
Microwave/Electrical Integration	Custom Metalization: Internal capability for depositing Au, Pt, Pd, Ti, W, and Cu layers.	Allows for direct fabrication of microwave structures (like the DSRR or tuning plates) onto or adjacent to the diamond surface, improving coupling efficiency and reducing noise.
Vector Magnetometry	Laser Cutting & Shaping: Precise laser cutting services.	Enables the creation of complex diamond geometries or arrays necessary for separating the four NV crystal axes (NV1, NV2, NV3, NV4) required for accurate 3D vector field measurement (Equations 8-11).

Engineering Support

The paper identifies complex challenges related to magnetic field analysis, non-linear response, and vector magnetometry correction.

Material Optimization: 6CCVD’s in-house PhD team can assist researchers in optimizing the initial material specifications (N concentration, crystal orientation) and post-processing parameters (irradiation dose, annealing temperature) to achieve the target sensitivity of nT/$\sqrt{\text{Hz}}$ required for similar Hidden Target Detection projects.
Integration Consultation: We provide technical consultation on minimizing spurious coupling effects and optimizing optical coupling, addressing the observed sensitivity degradation when microwave power exceeded 8 mW due to proximity effects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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 NV’s 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 sample’s 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.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s25061866

References

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]