A Measurement Technique Along With Data-Processing Approach Related to Time-Varying Complex Permittivity and Thickness of Materials

Under the circumstance of rapidly fluctuating temperatures, the measurement of electromagnetic parameter of medium becomes notably more challenging due to alterations in the morphology, state of matter, and dimensions of materials resulting from ablation over a brief period. In this article, we focus on exploring a novel approach related to the measurement of time-varying complex permittivity and thickness of material under its several temperature states, with a particular emphasis on the impact of high-temperature ablation on the parameter variation of material. Initially, by measuring three typical reflection coefficients based on built single-antenna measurement system, we propose a novel measurement approach through adoption of a special cancellation technique to mitigate adverse signals that contain inherent reflection information and unknown stray signals. Subsequently, we build an explicit constraint relationship based on the definition of a generalized reflection coefficient, through which the optimization solutions of material under test (MUT) can be obtained in a well-founded manner. Furthermore, utilizing inverse chirp Z transform (ICZT) and quantum-behaved particle swarm optimization (QPSO) as techniques for obtaining the time-domain initial solutions and frequency-domain optimal solutions, respectively, we perform interval estimation of the obtained solutions to ensure their certain confidence by adopting the bootstrap strategy. The calculation results based on simulation and application of actual test data demonstrate that our proposed measurement technique and data-processing methods are effective and reliable for the measurement of time-varying complex permittivity and thickness of materials.