High-Dynamic-Range Integrated NV Magnetometers

At a Glance

Metadata	Details
Publication Date	2024-05-18
Journal	Micromachines
Authors	Tianning Wang, Zhenhua Liu, Yankang Liu, Bo Wang, Yuanyuan Shen
Institutions	North University of China
Citations	2
Analysis	Full AI Review Included

Executive Summary

This analysis focuses on a high-dynamic-range (HDR) integrated Nitrogen-Vacancy (NV) magnetometer utilizing a frequency-tracking scheme for real-time measurement of time-varying magnetic fields.

Core Achievement: The system successfully extended the measurable dynamic range (DR) of the NV center to 6.4 mT, achieving a 34-fold increase over the intrinsic DR (±384 µT).
Tracking Performance: Demonstrated efficient detection of rapidly changing magnetic fields with a maximum tracking rate of 0.038 T/s.
Sensitivity: Maintained a competitive magnetic noise figure of 3.58 nT/Hz^1/2 and a system bandwidth of 40 Hz.
Methodology: Implemented an innovative frequency-tracking feedback loop where the resonant frequency shift (caused by the external field) is fed back to continuously adjust the microwave source frequency, locking the signal within the linear demodulation range.
Integration and Portability: The magnetometer probe is highly integrated using fiber optics and self-focusing lenses, resulting in a compact size of 2.9 x 2.1 x 2 cm³.
Theoretical Limit: Theoretical calculations suggest the dynamic range can be extended up to 28.8 mT (150 times the intrinsic range), limited by the slope of the demodulated signal approaching zero at high fields.

Technical Specifications

Parameter	Value	Unit	Context
Extended Dynamic Range (Achieved)	6.4	mT	34 times the intrinsic range.
Intrinsic Dynamic Range (Linear)	±384	µT	Range where the demodulated signal is linear.
Theoretical DR Limit	28.8	mT	Maximum calculated extension limit (150x intrinsic range).
Maximum Tracking Rate (V_max)	0.038	T/s	Based on 10 ms cycle time for frequency adjustment.
Magnetic Noise Figure (Sensitivity)	3.58	nT/Hz^1/2	Measured via Amplitude Spectral Density (ASD).
System Bandwidth	40	Hz	Determined by normalized peak-to-peak amplitudes.
Probe Volume	2.9 x 2.1 x 2	cm³	Physical size of the integrated NV magnetometer probe.
Laser Wavelength	532	nm	Excitation source.
Laser Power (P_L)	80	mW	Power used for ESR signal acquisition.
Microwave Power (P_MW)	20	dBm	Power used for ESR signal acquisition.
ESR Contrast	7.5	%	Measured contrast of the Electron Spin Resonance signal.
FWHM (ODMR)	13	MHz	Full Width at Half Maximum of the ODMR signal.
Optimal Modulation Depth (V_dev)	5	MHz	Used for optimal slope value in demodulated signal.
Optimal Modulation Frequency (V_mod)	500	Hz	Used for optimal slope value in demodulated signal.
Gyromagnetic Ratio (γ)	2.8 x 10¹⁰	Hz/T	Standard value for NV center calculations.

Key Methodologies

The system integrates a compact NV probe with a frequency-tracking feedback loop to achieve HDR measurement of time-varying fields:

Integrated Probe Design: A highly compact probe was designed using micro-nano fabrication techniques. It incorporates a 532 nm laser coupled via single-mode optical fiber and self-focusing lenses to excite the NV centers in the diamond sample.
Signal Acquisition: Red fluorescence (637-800 nm) emitted by the NV centers is filtered and collected by a photodiode, converting the optical signal into an electrical signal (Optically Detected Magnetic Resonance, ODMR).
Microwave Modulation: A microwave source provides the sweep frequency via a circular copper wire antenna (1 mm diameter) to induce spin transitions. The ODMR signal is modulated using a reference signal.
Demodulation and Calibration: The electrical signal is processed by a lock-in amplifier. The demodulated signal provides a linear relationship between voltage output (V) and frequency shift (Δf) within the intrinsic dynamic range (±384 µT). The conversion coefficient (slope) is pre-calibrated.
Frequency Tracking Implementation: When the external magnetic field causes the resonant frequency to shift outside the intrinsic linear range, the system initiates frequency tracking.
Feedback Control: The upper computer program continuously monitors the resonant frequency shift and calculates the necessary frequency offset. This offset is fed back to the microwave source, dynamically adjusting its center frequency to keep the resonance peak locked within the linear range of the demodulated signal.
Rate Limitation: The tracking rate is limited by the time required for the computer to collect, calculate, and adjust the microwave source frequency (approximately 10 ms per cycle), resulting in a V_max of 0.038 T/s.

Commercial Applications

The high dynamic range, high sensitivity, and integrated nature of this NV magnetometer technology make it suitable for demanding applications in dynamic magnetic environments:

Electric Vehicle (EV) Technology: High-precision, robust monitoring of charge and discharge currents in EV batteries over wide dynamic ranges, crucial for battery management systems.
Geomagnetic Survey and Navigation: Portable vector magnetometers for calibrating geomagnetic anomalies and providing stable, accurate magnetic heading data in complex environments (e.g., shipboard or aerial platforms).
Industrial Non-Destructive Testing (NDT): Real-time detection and monitoring of magnetic flux leakage or subtle field changes associated with material defects, stress, or corrosion in pipelines and infrastructure.
Quantum Sensing and Miniaturization: Provides a blueprint for miniaturizing conventional quantum sensing platforms, enabling the deployment of high-sensitivity magnetometers in field settings or integrated circuits.
Biomagnetism: High spatial resolution magnetic imaging for biological research, including monitoring neuron activity or detecting reactive oxygen species concentrations.
Electromagnetic Compatibility (EMC) Testing: Measuring rapidly changing or high-intensity magnetic fields generated during complex electromagnetic interference tests.

View Original Abstract

High-dynamic-range integrated magnetometers demonstrate extensive potential applications in fields involving complex and changing magnetic fields. Among them, Diamond Nitrogen Vacancy Color Core Magnetometer has outstanding performance in wide-range and high-precision magnetic field measurement based on its inherent high spatial resolution, high sensitivity and other characteristics. Therefore, an innovative frequency-tracking scheme is proposed in this study, which continuously monitors the resonant frequency shift of the NV color center induced by a time-varying magnetic field and feeds it back to the microwave source. This scheme successfully expands the dynamic range to 6.4 mT, approximately 34 times the intrinsic dynamic range of the diamond nitrogen-vacancy (NV) center. Additionally, it achieves efficient detection of rapidly changing magnetic field signals at a rate of 0.038 T/s.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi15050662

References

2008 - High-sensitivity diamond magnetometer with nanoscale resolution [Crossref]
2008 - Nanoscale magnetic sensing with an individual electronic spin in diamond [Crossref]
2008 - Nanoscale imaging magnetometry with diamond spins under ambient conditions [Crossref]
2011 - Real time magnetic field sensing and imaging using a single spin in diamond [Crossref]
2011 - Avoiding power broadening in optically detected magnetic resonance of single NV defects for enhanced dc magnetic field sensitivity [Crossref]
2011 - Electric-field sensing using single diamond spins [Crossref]
2010 - High sensitivity magnetic imaging using an array of spins in diamond [Crossref]
2018 - Circularly polarized zero-phonon transitions of vacancies in diamond at high magnetic fields [Crossref]
2022 - Long spin coherence times of nitrogen vacancy centers in milled nanodiamonds [Crossref]
2013 - Solid-state electronic spin coherence time approaching one second [Crossref]