Near-Field Microwave Imaging Method of Monopole Antennas Based on Nitrogen-Vacancy Centers in Diamond

At a Glance

Metadata	Details
Publication Date	2024-05-22
Journal	Micromachines
Authors	Xuguang Jia, Yue Qin, Zhengjie Luo, Shining Zhu, Xin Li
Institutions	North University of China
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: Near-Field Microwave Imaging using NV Diamond

This document analyzes the research paper “Near-Field Microwave Imaging Method of Monopole Antennas Based on Nitrogen-Vacancy Centers in Diamond” and outlines how 6CCVD’s specialized MPCVD diamond materials and processing capabilities can support and advance this quantum sensing technology.

Executive Summary

This research successfully demonstrates a novel, non-invasive method for near-field microwave imaging of monopole antennas using Nitrogen-Vacancy (NV) centers in Single Crystal Diamond (SCD).

Non-Invasive Sensing: The diamond acts as a wide-field probe, eliminating the coupling and interference effects inherent in traditional mechanical metal probes, leading to highly accurate microwave field mapping.
High Efficiency & Stability: By using the entire diamond as a sensor and camera, the system avoids mechanical scanning, resulting in fixed, rapid measurement times (20 s) regardless of imaging resolution.
High Resolution Achieved: The system demonstrated a spatial resolution of 3 µm and successfully characterized 3D field distribution and dynamic phase tracking.
Quantum Sensing Core: The technique relies on measuring the contrast of the Optically Detected Magnetic Resonance (ODMR) spectrum, requiring high-purity, low-strain SCD material for optimal performance.
Phase Tracking Capability: Achieved an optimal input microwave phase resolution of 0.52° at 0.8494 W, validating the system’s ability to track dynamic antenna characteristics.
6CCVD Value Proposition: 6CCVD specializes in the high-quality SCD required for these quantum sensing applications, offering custom dimensions, precision polishing (Ra < 1 nm), and integrated metalization services to accelerate research development.

Technical Specifications

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

Parameter	Value	Unit	Context
Sensing Material	NV Center Diamond	N/A	Non-invasive quantum probe
Diamond Chip Size (Used)	4 x 4	mm	Square chip used in the experimental setup
Field of View (FOV)	5 x 5	mm	Area successfully imaged
Spatial Resolution	3	µm	Achieved imaging detail
Imaging Bandwidth	2.7 to 3.2	GHz	Frequency range characterized
Optimal Phase Resolution	0.52	°	Achieved at optimal microwave power
Optimal Input Microwave Power	0.8494	W	Power level for best phase resolution
Excitation Wavelength	532	nm	Green laser source
Fluorescence Readout	637	nm	Red light emission from NV centers
Measurement Time (Diamond Method)	20	s	Fixed time for resolutions up to 150 x 150
Traditional Method Time (80 x 80)	112	s	Comparison showing speed advantage

Key Methodologies

The near-field microwave imaging system utilizes a combination of optical excitation, microwave interaction, and quantum readout (ODMR) on a diamond substrate.

Diamond Placement: A high-quality diamond chip containing NV centers is positioned in close proximity to the monopole antenna under test.
Uniform Optical Excitation: A 532 nm laser is expanded, collimated, and passed through a fly-eye homogenizer to ensure uniform illumination across the 4 mm x 4 mm diamond surface.
Microwave Interaction: The microwave field generated by the monopole antenna drives transitions between the NV center quantum spin states (m_s = 0 to m_s = ±1).
Fluorescence Acquisition: The resulting red fluorescence (637 nm) is collected and captured by a CMOS camera, generating a wide-field image reflecting the local microwave intensity distribution.
Data Processing and ODMR: The captured image is segmented into multiple units (M=50 pixels per unit). The ODMR spectral contrast is calculated for each unit by comparing fluorescence intensity before and after microwave excitation.
Field Reconstruction: A characteristic curve relating ODMR contrast to microwave power is established through calibration. This curve is used to inversely solve for the microwave field intensity and phase distribution across the diamond surface.
3D Imaging: Layered scanning is performed by precisely adjusting the vertical distance (z-axis) between the diamond probe and the antenna to reconstruct the three-dimensional field profile.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification diamond materials necessary to replicate and advance this cutting-edge quantum sensing research. The success of NV-based imaging hinges entirely on the quality, purity, and surface finish of the Single Crystal Diamond (SCD) substrate.

Research Requirement / Challenge	6CCVD Solution & Capability	Technical Advantage
High-Performance Quantum Sensing Material	Optical Grade Single Crystal Diamond (SCD): We supply high-purity SCD wafers optimized for low strain and controlled NV center density.	Ensures maximum quantum coherence time (T₂) and high ODMR spectral contrast, which is critical for achieving the reported high spatial (3 µm) and phase (0.52°) resolutions.
Custom Dimensions & Scaling	Custom Plates/Wafers: While the paper used 4 mm x 4 mm, 6CCVD offers SCD plates up to 500 µm thick and can supply Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter for large-area imaging applications.	Supports scaling the field of view (FOV) for characterizing larger antenna arrays or integrated circuits, expanding the application range of the system.
Ultra-Smooth Surface Finish	Precision Polishing (Ra < 1 nm): Our SCD material is polished to an industry-leading surface roughness of Ra < 1 nm.	Minimizes optical scattering and ensures highly uniform laser illumination across the wide field of view, maximizing the efficiency of the fly-eye homogenizer and CMOS camera readout.
Integration of On-Chip Microwave Structures	Custom Metalization Services: Internal capability for depositing thin films including Au, Pt, Pd, Ti, W, and Cu.	Allows researchers to integrate complex microwave delivery structures (e.g., coplanar waveguides or microstrip lines) directly onto the diamond surface, enhancing localized field control and enabling focused near-field imaging structures mentioned for future work.
Mechanical Stability for 3D Scanning	Substrates up to 10 mm Thickness: We provide robust diamond substrates suitable for integration with precision triaxial translation tables.	Ensures the mechanical stability and rigidity required for accurate, repeatable z-axis scanning necessary for reliable 3D microwave field reconstruction.

Engineering Support: 6CCVD’s in-house PhD team can assist with material selection, including optimizing NV concentration and crystal orientation, for similar near-field antenna characterization and quantum sensing projects. We offer global shipping (DDU default, DDP available) to ensure rapid delivery of custom materials worldwide.

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

View Original Abstract

Visualizing the near-field distribution of microwave field in a monopole antenna is very important for antenna design and manufacture. However, the traditional method of measuring antenna microwave near field distribution by mechanical scanning has some problems, such as long measurement time, low measurement accuracy and large system volume, which seriously limits the measurement effect of antenna microwave near field distribution. In this paper, a method of microwave near-field imaging of a monopole antenna using a nitrogen-vacancy center diamond is presented. We use the whole diamond as a probe and camera to achieve wide-field microwave imaging. Because there is no displacement structure in the system, the method has high time efficiency and good stability. Compared with the traditional measurement methods, the diamond probe has almost no effect on the measured microwave field, which realizes the accurate near-field imaging of the microwave field of the monopole antenna. This method achieves microwave near-field imaging of a monopole antenna with a diameter of 100 µm and a length of 15 mm at a field of view of 5 × 5 mm, with a spatial resolution of 3 µm and an imaging bandwidth of 2.7~3.2 GHz, and an optimal input microwave phase resolution of 0.52° at a microwave power of 0.8494 W. The results provide a new method for microwave near-field imaging and measurement of monopole antennas.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi15060679

References

2005 - A small wideband microstrip-fed monopole antenna [Crossref]
2022 - A Bayesian Compressive Sensing Approach to Robust Near-Field Antenna Characterization [Crossref]
2022 - An Effective Antenna Pattern Reconstruction Method for Planar Near-Field Measurement System [Crossref]
2022 - An Adaptive Data Acquisition Technique to Enhance the Speed of Near-Field Antenna Measurement [Crossref]
2014 - Fast Antenna Testing with Reduced Near Field Sampling [Crossref]
2022 - Single-Cut Phaseless Near-Field Measurements for Fast Antenna Testing [Crossref]
2022 - Photonics-Based Near-Field Measurement and Far-Field Characterization for 300-GHz Band Antenna Testing [Crossref]