A new ultrasonic transducer with multi-belts coil for generating and receiving longitudinal guided wave in ferromagnetic material pipes is proposed.The theory backgrounds and transduction principle of the proposed tra...A new ultrasonic transducer with multi-belts coil for generating and receiving longitudinal guided wave in ferromagnetic material pipes is proposed.The theory backgrounds and transduction principle of the proposed transducer are presented and ana- lyzed.To verify the performance of the transducer,several experiments are performed.The performance of inspecting crack, frequency-tuned characteristic,effect of bias static magnetic field and dynamic magnetic field,lift-off effect and effect of the period number of the exciting current are investigated.The results show that the proposed coils not only could tune the center frequency but also could improve the amplitude and signal-to-noise(SNR)of the detected signals.Bias static magnetic field and dynamic magnetic field are two important factors influencing the amplitude of the longitudinal guided wave.The amplitude of the longitudinal guided wave is exponentially decreased versus the lift-off distance of the transmitter and receiver.Period number of excitation signal could influence the amplitude and wave width of the ultrasonic wave.The proposed transducer could easily control the wave modes and would be a better choice for pipes’monitoring and inspection compared to traditional single-belt coil transducer.展开更多
The authors investigate a kind of degenerate quadratic Hamiltonian systems with saddle-loop. Under quadratic perturbations, it is proved that the perturbed system has at most two limit cycles in the finite plane. The ...The authors investigate a kind of degenerate quadratic Hamiltonian systems with saddle-loop. Under quadratic perturbations, it is proved that the perturbed system has at most two limit cycles in the finite plane. The proof relies on a careful analysis of a related Abelian integral.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.10974115)
文摘A new ultrasonic transducer with multi-belts coil for generating and receiving longitudinal guided wave in ferromagnetic material pipes is proposed.The theory backgrounds and transduction principle of the proposed transducer are presented and ana- lyzed.To verify the performance of the transducer,several experiments are performed.The performance of inspecting crack, frequency-tuned characteristic,effect of bias static magnetic field and dynamic magnetic field,lift-off effect and effect of the period number of the exciting current are investigated.The results show that the proposed coils not only could tune the center frequency but also could improve the amplitude and signal-to-noise(SNR)of the detected signals.Bias static magnetic field and dynamic magnetic field are two important factors influencing the amplitude of the longitudinal guided wave.The amplitude of the longitudinal guided wave is exponentially decreased versus the lift-off distance of the transmitter and receiver.Period number of excitation signal could influence the amplitude and wave width of the ultrasonic wave.The proposed transducer could easily control the wave modes and would be a better choice for pipes’monitoring and inspection compared to traditional single-belt coil transducer.
基金the National Natural Science Foundation of China (No.10101031. No. 10071097). Guangdong Natural Science Foundation (No. 001289)
文摘The authors investigate a kind of degenerate quadratic Hamiltonian systems with saddle-loop. Under quadratic perturbations, it is proved that the perturbed system has at most two limit cycles in the finite plane. The proof relies on a careful analysis of a related Abelian integral.
