Measurements of Spatial Angles Using Diamond Nitrogen–Vacancy Center Optical Detection Magnetic Resonance

At a Glance

Metadata	Details
Publication Date	2024-04-19
Journal	Sensors
Authors	Zhenrong Shi, Haodong Jin, Hao Zhang, Zhonghao Li, Huanfei Wen
Institutions	North University of China
Citations	2
Analysis	Full AI Review Included

Measurements of Spatial Angles Using Diamond Nitrogen-Vacancy Center Optical Detection Magnetic Resonance

Executive Summary

This research introduces a novel, solid-state system for non-contact spatial angle measurement utilizing ensemble diamond Nitrogen-Vacancy (NV) center Optical Detection Magnetic Resonance (ODMR) imaging.

Core Functionality: Realizes all-optical, wide-field vector magnetic field measurements to determine the spatial angles (yaw, pitch, and roll) of magnetic components.
Sensor Material: Uses a 5 x 5 x 0.5 mm³ (100) oriented CVD diamond plate with an estimated NV concentration of approximately 1.5 ppm.
Methodology: Maps the magnetic field distribution generated by a current-carrying test chip. Angles are calculated based on the spatial relationship between the magnetic field strength and the distance from the current elements.
High Sensitivity: The calculated magnetic sensitivity (η) of the system is 0.26 µT/Hz^1/2.
Angular Accuracy: Achieved high precision in angle detection:
- Yaw Angle (α) average error: 0.95°.
- Pitch Angle (φ) average error: 1.28°.
- Roll Angle (β) average error: 1.41°.
Key Advantage: Eliminates systematic errors associated with sensor misalignment and zero drift common in conventional multi-vector magnetic sensor arrays.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Sensor Size	5 x 5 x 0.5	mm³	(100) oriented CVD plate
NV Concentration	~1.5	ppm	Ensemble NV center concentration
Laser Excitation	532	nm	Used for NV center polarization
Zero-Field Splitting (D)	2.87	GHz	Ground-state electron energy level ³A₂
Bias Magnetic Field (B₀)	~2.84	mT	Applied to separate degenerate ±1 resonance peaks
Microwave Scan Range	2.5 to 3.1	GHz	Step frequency 0.3 MHz
Microwave Power (Resonant)	30	dBm	Input power to the diamond NV center
Magnetic Sensitivity (η)	0.26	µT/Hz^1/2	Calculated minimum detectable magnetic field
ODMR Linewidth (Γ)	~10	MHz	Approximate value
CCD Resolution	1920 x 1080	pixels	Camera resolution
Single Pixel Area	5	µm²	CCD pixel size
Imaging Field Size	960 x 540	µm²	Using 10x objective (NA=0.3)
CCD Frame Rate (FPS)	200	FPS	Camera exposure frequency
Yaw Angle (α) Average Error	0.95	°	Measured accuracy
Pitch Angle (φ) Average Error	1.28	°	Measured accuracy
Roll Angle (β) Average Error	1.41	°	Measured accuracy
Test Current (I)	0.5	A	Current flowed through the 20 Ω resistor chip
Test Distance (R)	2	mm	Distance between sample and diamond

Key Methodologies

The spatial angle detection relies on continuous wave ODMR magnetometry combined with magnetic field imaging and geometric calculation.

NV Center Initialization and Excitation: The ensemble NV centers in the diamond are polarized to the initial state (m_s = 0) using a 532 nm laser focused onto the sensitive layer via a 10x objective (NA=0.3).
Microwave Manipulation: A microwave scanning system (2.5 to 3.1 GHz) provides a homogeneous microwave field (30 dBm power) to manipulate the electron spin states, inducing transitions between m_s = 0 and m_s = ±1.
Fluorescence Detection: Changes in fluorescence intensity, corresponding to the spin state, are collected by the CCD camera (200 FPS), synchronized with the microwave frequency scan. This generates a complete ODMR spectrum for every pixel.
Vector Magnetic Field Extraction:
- The ODMR spectra are fitted using the Lorentz formula to determine the resonant frequencies (v⁺, v^-).
- These frequencies are used to calculate the projection magnetic fields (B₁, B₂, B₃, B₄) along the four NV symmetry axes.
- The Cartesian vector components (B_x, B_y, B_z) of the external magnetic field are then derived from these four projections.
Current Element Positioning: To accurately locate the magnetic source, the magnetic field map is grouped by rows/columns. Lorentz fitting is applied to the magnetic field strength versus pixel position to determine the center of the full width at half maximum, yielding the precise coordinates (i, j) of the current elements.
Angle Calculation (Pitch/Roll): The angular space (θ_n) between adjacent current elements is calculated based on the magnetic field strength (B) and the known distance (d) between elements, leveraging the principle that B is inversely proportional to R (distance). The final angle (θ) is the average of all calculated θ_n.
Angle Calculation (Yaw): The yaw angle (α) is determined by calculating the angle between the positions of two adjacent current elements (i_n, j_n) relative to the X-axis of the laboratory coordinate system.

Commercial Applications

The high-precision, non-contact spatial angle detection capability based on NV magnetometry is valuable across several high-tech sectors:

Quantum Sensing and Metrology: Used in advanced magnetic microscopes for wide-field tomography and vector magnetic field imaging, particularly where high sensitivity (0.26 µT/Hz^1/2) at room temperature is required.
Aerospace and Navigation: Provides robust, solid-state angle detection for inertial measurement units (IMUs) and control systems, offering an alternative to traditional sensors susceptible to wear or environmental constraints.
Electronic Manufacturing and Quality Control: Enables non-destructive testing of encapsulated or concealed magnetic components (e.g., chips, PCBs) to verify precise spatial alignment and detect assembly errors or zero drift without physical contact.
Robotics and Automation: Applicable in systems requiring precise angular feedback for complex motion control, overcoming limitations of contact measurement methods (wear, maintenance).
Materials Science Research: Used for mapping and analyzing magnetic fields generated by novel materials or micro-structures, where spatial orientation is a critical parameter.

View Original Abstract

This article introduces a spatial angle measuring device based on ensemble diamond nitrogen-vacancy (NV) center optical detection magnetic resonance (ODMR). This device realizes solid-state all-optical wide-field vector magnetic field measurements for solving the angles of magnetic components in space. The system uses diamond NV center magnetic microscope imaging to obtain magnetic vector distribution and calculates the spatial angles of magnetic components based on the magnetic vector distribution. Utilizing magnetism for angle measuring enables non-contact measuring, reduces the impact on the object being measured, and ensures measurement precision and accuracy. Finally, the accuracy of the system is verified by comparing the measurement results with the set values of the angle displacement platform. The results show that the measurement error of the yaw angle of the system is 1°, and the pitch angle and roll angle are 1.5°. The experimental results are in good agreement with the expected results.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s24082613

References

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Measurements of Spatial Angles Using Diamond Nitrogen–Vacancy Center Optical Detection Magnetic Resonance

At a Glance