Transverse magnetic field effects on diamond quantum sensor for EV battery monitor

At a Glance

Metadata	Details
Publication Date	2024-09-03
Journal	Frontiers in Quantum Science and Technology
Authors	Yuji Hatano, Junya Tanigawa, Akimichi Nakazono, T. Sekiguchi, Yuta Kainuma
Institutions	Yazaki (Japan), Tokyo Institute of Technology
Citations	2
Analysis	Full AI Review Included

Executive Summary

This research investigates and validates key implementation points for deploying diamond Nitrogen-Vacancy (NV) quantum sensors as high-accuracy Electric Vehicle (EV) battery monitors.

Core Value Proposition: The sensor achieves high accuracy (< 10 mA/√Hz) over an extremely wide dynamic range (up to ±1,000 A), enabling precise State of Charge (SOC) estimation and potentially increasing EV cruising range by 10%.
Critical Challenge Addressed: The study focused on mitigating the transverse magnetic field effect caused by misalignment between the NV-axis and the applied static (B₀) and current (B_I) magnetic fields.
Misalignment Quantification: Misalignment was accurately quantified to within ±1° by analyzing the shift in the resonance frequency midpoint under high bipolar current (±1,000 A).
Simultaneous Measurement: Compensation based on the estimated misalignment successfully decoupled the magnetic field and temperature effects, allowing for accurate simultaneous measurement.
Linearity Improvement: Compensation reduced the current measurement linearity error to less than ±0.3% across the 20-1,000 A range, matching the accuracy of the current source used.
Robustness for Differential Detection: The ability to quantify misalignment contributes directly to accurately aligning dual sensors for differential detection, effectively eliminating external noise as common mode.

Technical Specifications

Parameter	Value	Unit	Context
Current Dynamic Range	±1,000	A	Maximum measurable busbar current.
Current Accuracy (Noise Level)	< 10	mA/√Hz	Achieved sensitivity across -40°C to 85°C.
Post-Compensation Linearity Error	< ±0.3	%	Achieved linearity in the 20-1,000 A range.
Misalignment Estimation Accuracy	±1	°	Accuracy achieved by analyzing resonance midpoint shift.
Static Magnetic Field (B₀)	17	mT	Applied by magnet to sensors A and B.
Diamond Crystal Type	HPHT Type Ib	N/A	2 x 2 x 1 mm³ (111) crystal orientation.
Initial Nitrogen (P1) Concentration	100	ppm	Concentration before irradiation/annealing.
Electron Irradiation Dose	3 x 10¹⁸	cm^-2	Used 2 MeV electron beam.
Annealing Temperature	1,000	°C	Annealing performed for 2 hours in vacuum.
Estimated NV Concentration	5-6	ppm	Concentration after processing.
Sensor A Misalignment (θ_A, φ_A)	3, 21.5	°	Estimated misalignment angles (static B₀, current B_I).
Sensor B Misalignment (θ_B, φ_B)	6, 3	°	Estimated misalignment angles (static B₀, current B_I).

Key Methodologies

NV Center Creation: High-pressure high-temperature (HPHT) Type Ib diamond (2 x 2 x 1 mm³, [111] orientation, 100 ppm P1) was irradiated with a 2 MeV electron beam (3 x 10¹⁸ cm^-2 dose). The crystal was subsequently annealed at 1,000°C for 2 hours in vacuum to form NV centers (5-6 ppm concentration).
Sensor Head Assembly: The diamond sensor surface was adhered to the top of a multimode optical fiber (400 µm core). A microwave guide surrounded the diamond to apply a microwave magnetic field perpendicular to the [111] NV-axis.
Differential Detection Setup: Two sensor holders (A and B) made of Polyetheretherketone (PEEK) were placed on the lower and upper sides of the busbar (25 mm width, 12 mm thickness) for differential detection, cancelling external magnetic noise as common mode.
Resonance Tracking: A closed-loop system utilized 0° and 90° quadrature outputs of a lock-in amplifier fed back to FM modulation terminals of two microwave oscillators, ensuring the microwave frequencies tracked the low- and high-frequency-side resonance frequencies (R_L and R_H).
Misalignment Quantification: The resonance frequency midpoint change, A(R_L + R_H)/2, was measured under bipolar current (±1,000 A). Misalignment angles (θ and φ) were estimated iteratively by comparing the measured midpoint change against theoretical models derived from the longitudinal (ω) and transverse (ω_⊥) magnetic field components.
Transverse Field Compensation: The estimated misalignment angles (accurate to ±1°) were used to calculate and compensate for the transverse magnetic field effects on the resonance frequency difference (R_H - R_L), thereby improving linearity and enabling accurate simultaneous temperature and current measurement.

Commercial Applications

Electric Vehicle (EV) Battery Management: Direct application for high-precision monitoring of charge/discharge currents (up to 1,000 A) and simultaneous temperature tracking, crucial for optimizing battery life and maximizing cruising range.
High-Power Electronics Monitoring: Current sensing in power grids, industrial machinery, and high-voltage DC systems requiring wide dynamic range and high immunity to temperature fluctuations.
Extreme Environment Sensing: Utilization of the diamond sensor’s intrinsic stability from cryogenic temperatures up to 600 K for monitoring systems in harsh environments (e.g., aerospace, deep-sea hydrothermal deposits, high-temperature industrial processes).
Quantum Magnetometry Systems: Development of robust, highly aligned differential sensor pairs for eliminating common-mode noise, applicable in sensitive biomagnetic field measurements (e.g., magnetocardiography) or geophysical surveys.
Metrology and Calibration: Providing highly linear, wide-dynamic-range current standards and calibration tools due to the demonstrated sub-0.3% linearity error.

View Original Abstract

Key implementation points for achieving full accuracy in simultaneous temperature and magnetic field measurement and linearity when applying diamond quantum sensors to electric vehicle (EV) battery monitors were investigated. Both the static and busbar current magnetic field are required to be aligned to the NV-axis. If misalignment should exist, the resonance frequency midpoint move in the direction opposite to the temperature change under a large busbar current due to the transverse magnetic field effect. Misalignment could be quantified with an accuracy of ±1° by analysing the resonance frequency midpoint change under a current of ±1,000 A. The transverse magnetic field effects compensation estimated from misalignment, confirmed that the resonance frequency midpoint changed consistently with temperature changes. Furthermore, linearity over a wide dynamic range also improved. Moreover, it will contribute to accurate alignment of the two sensors for differential detection to eliminate external noise as common mode. These are expected to expand the application of diamond sensors for high-precision measurement in a wide dynamic range.

Tech Support

Original Source

DOI: https://doi.org/10.3389/frqst.2024.1432096

References

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