Burst eddy current testing with diamond magnetometry
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-02-21 |
| Journal | Applied Physics Letters |
| Authors | Chang Xu, Jixing Zhang, Heng Yuan, Guodong Bian, Pengcheng Fan |
| Institutions | Beihang University |
| Citations | 7 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research demonstrates a significant advancement in non-destructive testing (NDT) using a novel Burst Eddy Current Testing (BEC) technique coupled with a diamond Nitrogen Vacancy (NV) center magnetometer utilizing the Hahn Echo (HE) sequence.
- Sensitivity Breakthrough: The HE-based NV magnetometer achieved a magnetic sensitivity of 4.3 nT/√Hz, and a volume-normalized sensitivity of 3.6 pT/√Hz.mm-3.
- Performance Gain: This volume-normalized sensitivity is approximately five times better than existing NV eddy current testing methods under the same conditions.
- High Resolution NDT: The system achieved a minimum detectable sample size smaller than 300 µm and a high measurement accuracy of 9.85 µm.
- Wide Frequency Band: The enhanced sensitivity is maintained over a broad frequency range, spanning from 100 kHz to 3 MHz.
- Thermal Mitigation: The use of a burst (single-cycle) excitation magnetic field, rather than continuous-wave (CW), avoids adverse eddy current thermal effects, making it suitable for temperature-sensitive materials.
- Versatile Application: The technology is promising for deformation monitoring, security screening, quality control, and extending electromagnetic testing into biocompatible materials and microelectronics due to its nanoscale resolution potential.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Magnetic Sensitivity (HE) | 4.3 | nT/√Hz | Measured at 300 kHz (optimal working point). |
| Volume-Normalized Sensitivity | 3.6 | pT/√Hz.mm-3 | Achieved using HE sequence. |
| Sensitivity Improvement | ~5 | Times | Compared to existing methods (volume-normalized). |
| Minimum Detectable Sample Size | < 300 | µm | Limited by the 3 mm excitation coil diameter. |
| Measurement Accuracy (u) | 9.85 | µm | Calculated using two-point scanning at 300 kHz. |
| Optimal Operating Frequency (HE) | 300 | kHz | Frequency providing the best scale factor K. |
| Frequency Bandwidth | 100 kHz to 3 | MHz | Range over which enhanced sensitivity is maintained. |
| Excitation Coil Diameter | 3 | mm | 18 turns, used to generate the primary magnetic field. |
| Detection Volume | ~7 x 10-7 | mm3 | Estimated volume of the NV center detection region. |
| Diamond Fabrication Method | CVD | N/A | Chemical Vapor Deposition. |
| Nitrogen Impurity Concentration | 50 | ppm | Used during CVD growth. |
| Electron Irradiation Dose | 1 x 1018 | e/cm2 | Used for NV creation. |
| Annealing Temperature/Time | 800 °C for 2 | h | Post-irradiation processing. |
| NV Density | ~3 | ppm | Resulting NV concentration in the diamond sample. |
| Scanning Step Size | 0.3 | mm | Used for 2D imaging of metallic specimens. |
| Averaging Time per Point | 5 | s | Used for accuracy measurement (Fig. 3(d)). |
Key Methodologies
Section titled “Key Methodologies”The NV-BEC testing scheme integrates diamond quantum sensing with pulsed magnetic excitation and advanced signal processing (Hahn Echo sequence).
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Diamond Preparation:
- Diamond samples were fabricated using the Chemical Vapor Deposition (CVD) method.
- Nitrogen impurity was introduced at 50 ppm concentration.
- The sample underwent 10 MeV electron irradiation at a dose of 1x1018 e/cm2.
- Post-processing involved annealing at 800 °C for a total period of 2 hours, resulting in an NV density of approximately 3 ppm.
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Excitation and Sensing Setup:
- A bias magnetic field was generated by a permanent magnet fixed on a translation stage.
- The primary magnetic field was generated by a 3 mm diameter, 18-turn coil driven by an arbitrary waveform generator in burst mode (single-cycle excitation).
- Microwaves were applied to the NV centers via a ring-shaped antenna.
- A confocal scheme was used for the optical path to collect fluorescence.
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Hahn Echo (HE) Sequence Implementation:
- The HE sequence was utilized for BEC testing, consisting of an array of microwave pulses (π/2 pulse, π pulse, and another π/2 pulse) separated by a sensing time τ.
- A single-cycle sinusoidal magnetic field (frequency f = 1/τ) was applied during the sensing time to induce an accumulated phase shift in the NV centers.
- The HE sequence refocuses dephasing caused by inhomogeneous static fields, significantly enhancing sensitivity to AC signals compared to the Continuous-Wave (CW) scheme.
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Imaging and Analysis:
- Specimens (Copper and Lead) were scanned point-by-point using a motorized translation stage.
- Fluorescence signals were recorded at each point, and the data was fitted using a Gaussian function to determine contours and edges.
- For penetration testing, a lower frequency (200 kHz) was used to increase the skin depth, allowing the detection of a hidden copper triangle beneath a lead sheet.
Commercial Applications
Section titled “Commercial Applications”This technology offers high-resolution, non-contact electromagnetic testing capabilities, particularly benefiting fields requiring high sensitivity and thermal stability.
| Industry/Field | Application Focus | Key Benefit |
|---|---|---|
| Non-Destructive Testing (NDT) | Quality control, security screening, defect detection in conductive materials. | Sub-mm resolution and high accuracy (9.85 µm) for identifying small flaws. |
| Micro/Nano-electronics | Inspection of integrated circuits, microelectronic devices, and layered structures. | Ability to penetrate conductive masks and detect hidden internal structures (layer structure imaging). |
| Biomaterials & Biomedical Imaging | Electromagnetic testing of biological tissues and temperature-sensitive samples. | Biocompatibility and avoidance of thermal effects due to burst excitation mode. |
| Structural Health Monitoring | Real-time deformation monitoring of metallic structures and components. | High magnetic sensitivity (4.3 nT/√Hz) enables detection of subtle changes in eddy current patterns. |
| Advanced Sensing | Identification and classification of various targets when combined with machine learning techniques. | Enhanced sensitivity and wide operational frequency band (100 kHz to 3 MHz). |
| Quantum Technology Integration | Promotion of integrated or on-chip NV magnetometry technologies. | Demonstrates a robust, high-performance quantum sensing platform suitable for miniaturization. |
View Original Abstract
In this work, a burst eddy current testing technique based on the employment of a diamond nitrogen vacancy (NV) center magnetometer with the Hahn echo (HE) sequence is demonstrated. With the confocal experiment apparatus, the HE-based NV magnetometer attains a magnetic sensitivity of 4.3 nT/Hz and a volume-normalized sensitivity of 3.6 pT/Hz mm−3, which are ∼five times better than the already existing method under the same conditions. Based on the proposed magnetometer configuration, a burst eddy current testing prototype achieves a minimum detectable sample smaller than 300 μm and a spatial resolution of 470 μm, which is employed to image different metallic specimens and detect layered internal structures. Since this prototype comprises remarkable high sensitivity, it exhibits various potential applications in the fields of security screening and quality control. Moreover, its biocompatibility and promising nanoscale resolution pave the way for electromagnetic testing in the fields of biomaterials.