Microwave Passive Direction-Finding Method Based on NV Color Center in Diamond

At a Glance

Metadata	Details
Publication Date	2023-03-30
Journal	Micromachines
Authors	Qi Wang, Yusong Liu, Yue Qin, Hao Guo, Jun Tang
Institutions	North University of China
Citations	1
Analysis	Full AI Review Included

Technical Analysis: Microwave Passive Direction-Finding Based on NV Color Centers

This document analyzes the research paper “Microwave Passive Direction-Finding Method Based on NV Color Center in Diamond” (Micromachines 2023, 14, 774) and outlines how 6CCVD’s advanced MPCVD diamond materials and processing capabilities can support, replicate, and scale this quantum sensing technology.

Executive Summary

This research successfully demonstrates a compact, high-precision passive microwave direction-finding system utilizing the nitrogen-vacancy (NV) color center in diamond.

Core Achievement: Established a passive direction-finding scheme based on quantum precision sensing, measuring microwave frequency, intensity, and angle in a small form factor.
Precision Metrics: Achieved high angular accuracy with an average angle error of 0.24° and a maximum error of 0.48° at a 5 cm distance.
Sensitivity: Demonstrated a minimum detectable microwave intensity resolution of -20 dBm using the closed-loop detection system.
Key Methodology: Utilized continuous microwave excitation Optical Detection Magnetic Resonance (ODMR) combined with the Coherent Population Oscillation (CPO) effect to convert microwave intensity changes into measurable frequency shifts.
Stability Control: Implemented a high-stability microwave closed-loop frequency PID locking system via FPGA, optimizing parameters (Kp=120, Ki=90, Kd=180) for enhanced system stability and sensitivity.
Material Requirement: The experiment relied on Type Ib diamond (HPHT synthesized) treated with electron irradiation and high-temperature annealing to create NV centers with a low nitrogen content (< 200 ppm).
Application Potential: Provides a basis for future quantum sensors in military and civilian applications requiring small equipment size, low power consumption, and high concealment (e.g., UAV detection, multi-platform passive detection).

Technical Specifications

The following hard data points were extracted from the experimental results and methodology:

Parameter	Value	Unit	Context
Diamond Type Used	Type Ib (HPHT)	N/A	Precursor material for NV creation.
Diamond Dimensions	1.5 x 1.5 x 1.5	mm	Cube volume used in the experiment.
Nitrogen Concentration	< 200	ppm	Post-treatment concentration.
Zero Field Splitting (D)	2.87	GHz	Energy gap between
Applied Magnetic Field	1.5	mT	Used to obtain optimal ODMR contrast.
Microwave Carrier Frequency (f_LO)	2.9063	GHz	Frequency set for measurement.
FM Modulation Depth (f_dev)	3	MHz	Used in the detection source microwave.
Minimum Intensity Resolution	-20	dBm	Lowest detectable microwave intensity.
Microwave Emission Range (P)	12 to 26	dBm	Power range of the analog source.
Average Angle Error	0.24	°	Measured at 5 cm distance.
Maximum Angle Error	0.48	°	Measured at 5 cm distance.
Optimal PID Parameters	Kp=120, Ki=90, Kd=180	N/A	Parameters for closed-loop frequency locking.

Key Methodologies

The direction-finding scheme relies on precise material preparation and advanced signal processing:

NV Center Creation: A Type Ib diamond cube (1.5 mm) was subjected to 4 hours of electron irradiation followed by 2.5 hours of high-temperature annealing to convert substitutional nitrogen into NV centers, achieving a nitrogen content below 200 ppm.
ODMR Excitation: The NV centers were excited using a 532 nm laser and subjected to a continuous microwave signal (approx. 2.9 GHz) and a 1.5 mT magnetic field applied along the <111> crystal axis.
Intensity Detection via CPO: The microwave intensity detection scheme utilized the two-channel microwave Coherent Population Oscillation (CPO) effect, which converts changes in microwave resonance peak intensity into a measurable shift of the microwave frequency spectrum.
Closed-Loop PID Locking: An FPGA control system performed a first-order differential operation on the ODMR spectral curve. Microwave closed-loop frequency PID locking was used to stabilize the zero position of the differential curve, providing the feedback signal for intensity measurement.
Direction Calculation: Microwave field intensity distribution was sampled at five cross points in space. The unknown microwave source direction was calculated using the weighted global least squares method (WGLS) based on the spatial distribution data.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality diamond materials and custom processing required to advance this research, particularly for scaling the NV sensor arrays into practical devices.

Applicable Materials

The paper utilized Type Ib diamond followed by post-processing. For next-generation quantum sensors requiring superior coherence and higher NV density control, 6CCVD recommends:

Material Grade	Specification	Application Relevance
Single Crystal Diamond (SCD)	Electronic Grade (Ultra-Low Nitrogen)	Ideal precursor for creating high-coherence NV centers (maximizing T₂ time) through controlled nitrogen implantation or in-situ doping during MPCVD growth.
SCD Substrates	Thickness: 0.1 µm to 500 µm	Allows precise control over the active sensing volume and integration into complex micro-systems (e.g., on-chip microwave circuits).
Optical Grade SCD	Polishing: Ra < 1 nm	Essential for minimizing optical scatter and maximizing fluorescence collection efficiency during ODMR measurements.

Customization Potential

6CCVD’s in-house engineering and fabrication capabilities directly address the requirements for miniaturization and integration necessary for passive direction-finding systems:

Custom Dimensions & Geometry: While the paper used a 1.5 mm cube, 6CCVD can supply SCD wafers and plates cut to any custom dimension required for array integration, including laser cutting services for complex geometries.
Large-Scale Array Development: For multi-platform detection systems, 6CCVD offers Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter, enabling the fabrication of large-area NV sensor arrays.
Integrated Microwave Delivery: The experiment required external microwave sources and coils. 6CCVD offers custom metalization services (Au, Pt, Pd, Ti, W, Cu) to deposit on-chip microwave antennas (e.g., coplanar waveguides) directly onto the diamond surface, significantly improving microwave field efficiency and localization.
Substrate Thickness Control: We provide substrates up to 10 mm thick for robust sensor packaging, or ultra-thin SCD layers (0.1 µm) for integration into photonic structures.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond quantum defects. We offer comprehensive engineering consultation to researchers and developers working on similar projects:

NV Optimization: Assistance with material selection and optimization of post-growth processing (irradiation and annealing protocols) to achieve specific NV concentrations and desired spin coherence properties (T₂).
Interface Engineering: Support in designing and fabricating optimal diamond surfaces, including ultra-low roughness polishing (Ra < 1 nm for SCD) critical for efficient optical coupling in ODMR setups.
Integration Planning: Consultation on integrating diamond sensors with external electronics, including metalization schemes for robust electrical contacts and microwave delivery structures.

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

View Original Abstract

In this study, we established a passive direction-finding scheme based on microwave power measurement: Microwave intensity was detected using microwave-frequency proportion integration differentiation control and coherent population oscillation effect converting the change in microwave resonance peak intensity into a shift of the microwave frequency spectrum, for which the minimum microwave intensity resolution was −20 dBm. The direction angle of the microwave source was calculated using the weighted global least squares method of microwave field distribution. This lay in the 12~26 dBm microwave emission intensity range, and the measurement position was in the range of (−15°~15°). The average angle error of the angle measurement was 0.24°, and the maximum angle error was 0.48°. In this study, we established a microwave passive direction-finding scheme based on quantum precision sensing, which measures the microwave frequency, intensity, and angle in a small space and has a simple system structure, small equipment size, and low system power consumption. In this study, we provide a basis for the future application of quantum sensors in microwave direction measurements.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi14040774

References

2011 - High-sensitivity diamond magnetometer with nanoscale resolution [Crossref]
2011 - Electric-field sensing using single diamond spins [Crossref]
2013 - High-precision nanoscale temperature sensing using single defects in diamond [Crossref]
2015 - Subpicotesla Diamond Magnetometry
2013 - Anomalous modulation of a zero-bias peak in a Hybrid nanowire-superconductor device [Crossref]
2012 - Gyroscopes based on nitrogen-vacancy centers in diamond [Crossref]
2017 - Performance evaluation of wideband microwave direction of arrival estimation using Luneburg lens [Crossref]
2021 - A Low SNR and Fast Passive Location Algorithm Based on Virtual Time Reversal [Crossref]
2019 - Passive radar delay and angle of arrival measurements of multiple acoustic delay lines used as passive sensors [Crossref]
2021 - The possibility of integrating NV magnetometer array by using wireless microwave excitation and its application in remote heart sound records [Crossref]