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  • Method of the difference frequency variation for determining the resonance and Q-factor of microwave sensors in the process of microwave curing of thermoset and thermoplastic materials

    In this paper, we present a new two-frequency method for determining the resonant frequency, transmission bandwidth, reflection coefficient, and quality factor of a resonant microwave sensor for monitoring the curing reactions of thermosetting and thermoplastic resins and adhesives. The method was named - the method of variation of the difference frequency. The results show that non-invasive, continuous and continuous monitoring of the dielectric properties of polymers can be realized, which makes it possible to control the adequate evolution of the process of their curing by known initial conditions. The questions of the realization of the method are considered in the case of variations in the difference and mean frequencies of the probing oscillation, as well as the option for fixed sounding, provided that all four components of the two two-frequency oscillations are in the spectral band of the microwave sensor. In addition, an estimate is given for determining the error in measuring the resonance frequency when probing different zones of the spectral characteristics of the sensors from 0.1 to 0.707 of the maximum reflection value. The universality of the method makes it possible to use a measurement system based on it as a means of monitoring both the production of polymers and for laboratory research

    Keywords: Microwave technology, thermosetting and thermoplastic polymers, microwave measurements, resonance sensor, difference frequency variation method, beat envelope, resonant frequency, Q-factor, bandwidth, reflection coefficient, dielectric constant, degree of