研究目的
To develop and validate a non-destructive technique for measuring the complex permittivity of irregularly shaped objects, overcoming the shape dependency in traditional resonant cavity perturbation methods, with applications in archaeology and material identification.
研究成果
The Dielectric Replica Measurement (DRM) technique successfully eliminates shape dependency in resonant cavity perturbation measurements, enabling accurate determination of complex permittivity for irregularly shaped objects. It is non-destructive and has been validated with geometric shapes and archaeological samples, showing good repeatability and the ability to distinguish different materials. The method holds promise for applications in archaeology, customs, and environmental agencies, with potential for further refinement and extension to other materials and frequencies.
研究不足
The technique is currently validated for low-loss dielectric materials; applicability to high-loss materials requires further research. Sample size is limited by the cavity aperture (46mm), and baseline drift can affect accuracy for small objects. The method assumes homogeneous materials and may not be suitable for composites. Thermal drift and experimental uncertainties (e.g., in frequency and Q-factor measurements) can introduce errors, and the need for precise replica creation adds complexity.
1：Experimental Design and Method Selection:
The study uses resonant cavity perturbation (RCP) with a novel Dielectric Replica Measurement (DRM) technique. A resonant cavity is employed to measure perturbations in frequency and Q-factor due to inserted samples. Three orthogonal field directions (x, y, z) are used to eliminate shape effects by comparing perturbations from the object and its replica made from a material with known dielectric properties. Theoretical models are developed and refined with second-order terms for accuracy.
2：Sample Selection and Data Sources:
Samples include geometric shapes (e.g., spheres, cylinders, cones) made from PTFE and 3D-printed acrylic, and irregular archaeological objects (pottery sherd, flint chip). Replicas are created using 3D scanning and printing. Data on dielectric properties are sourced from literature for calibration.
3：List of Experimental Equipment and Materials:
Equipment includes an aluminum resonant cavity (diameter and height 560mm), vector network analyzer (Agilent 8712ET), mechanical coaxial switches, N-type connectors, antennas, sample holder (polypropylene tube), Vernier calipers, electronic balance, and 3D printer (Stratasys Objet 24). Materials include PTFE, acrylic polymer, Perspex, quartz, calcite, terracotta pottery, and flint.
4：4). Materials include PTFE, acrylic polymer, Perspex, quartz, calcite, terracotta pottery, and flint.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The cavity is calibrated with empty measurements. Samples are inserted, and perturbations in frequency and Q-factor are measured for each orthogonal field direction by switching modes and rotating the sample holder. Measurements are repeated for replicas. Data are processed to compute complex permittivity using derived equations, with corrections for volume differences and non-linearity.
5：Data Analysis Methods:
Data analysis involves calculating complex frequency shifts, applying the DRM equations (e.g., equations 8, 9, 10, 11 from the paper), and using polynomial fitting (e.g., in Matlab) for second-order corrections. Statistical analysis includes Monte Carlo simulations to assess uncertainties.
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