Enhancement effect of cumulative second-harmonic generation by closed propagation feature of circumferential guided waves
Gao Guang-Jian1, Deng Ming-Xi2, †, Hu Ning2, Xiang Yan-Xun3, ‡
       

(a) Time-domain signal detected at the probe point θ = π/2, (b) the corresponding spectrogram, (c) the slice at the fundamental frequency (line H1), and (d) the slice at the second-harmonic frequency (line H2).