New Closed Form Analysis of Resonances in Microwave Power for Material Processing.

A new closed form material invariant analysis on resonances of microwave induced power absorption is presented. It is shown that resonances in average power is confined within two asymptotic limits of thin and thick samples, and the resonances occur if λ_m ≤ 1.5D_p.m for λ_m ≈ λ₀ and λ_m ≤ 3D_p.m for λ_m ≉ λ₀. Here λ_m and D_p.m denote the wavelength and penetration depth within the sample, respectively, and λ₀ is the wavelength within the free space. It has been shown that average absorbed power does not exhibit resonance for one side incidence if λ_m ≈ λ₀, while the occurrence of resonance is independent of φ_l for λ_m ≉ λ₀. Here, φ_l is the fractional power input from the left side. The amplitudes of subsequent resonating peaks are also shown to decay monotonically with sample length for λ_m ≈ λ₀, while they vary nonmonotonically for λ ≉ λ₀ and φ_l ≉ 0, 1 or ½ due to suppressions of odd (for λ_m < λ₀), or even (for λ_m > λ₀) resonating peaks, which increase as φ_l approaches ½ from either 0 or 1. Finally, at φ_l ≈ ½ with λ_m ≉ λ₀ odd (for λ_m < λ₀), or even (for λ_m > λ₀) resonating peaks of average absorbed power vanish reducing the number of resonating points by a factor of two from one side incidence (φ_l ≈ 0 or 1), to both side incidence with equal power input from left and right sides (φ_l ≈ ½). This work provides correlations (corresponding to λ_m ≈ λ₀ and λ_m ≉ λ₀) for predicting the locations of resonating peaks as function of λ_m/λ₀, λ_m/D_p.m, and φ_l. The theoretical prediction on average power characteristics have been shown to be useful in forecasting the heating patterns for efficient material processing. [ABSTRACT FROM AUTHOR]