• Title/Summary/Keyword: harmonic generation

Search Result 438, Processing Time 0.023 seconds

Image Enhancement for Sub-Harmonic Phased Array by Removing Surface Wave Interference with Spatial Frequency Filter

  • Park, Choon-Su;Kim, Jun-Woo;Cho, Seung Hyun;Seo, Dae-Cheol
    • Journal of the Korean Society for Nondestructive Testing
    • /
    • v.34 no.3
    • /
    • pp.211-219
    • /
    • 2014
  • Closed cracks are difficult to detect using conventional ultrasonic testing because most incident ultrasound passes completely through these cracks. Nonlinear ultrasound inspection using sub-harmonic frequencies a promising method for detecting closed cracks. To implement this method, a sub-harmonic phased array (PA) is proposed to visualize the length of closed cracks in solids. A sub-harmonic PA generally consists of a single transmitter and an array receiver, which detects sub-harmonic waves generated from closed cracks. The PA images are obtained using the total focusing method (TFM), which (with a transmitter and receiving array) employs a full matrix in the observation region to achieve fine image resolution. In particular, the receiving signals are measured using a laser Doppler vibrometer (LDV) to collect PA images for both fundamental and sub-harmonic frequencies. Oblique incidence, which is used to boost sub-harmonic generation, inevitably produces various surface waves that contaminate the signals measured in the receiving transducer. Surface wave interference often degrades PA images severely, and it becomes difficult to read the closed crack's position from the images. Various methods to prevent or eliminate this interference are possible. In particular, enhancing images with signal processing could be a highly cost-effective method. Because periodic patterns distributed in a PA image are the most frequent interference induced by surface waves, spatial frequency filtering is applicable for removing these waves. Experiments clearly demonstrate that the spatial frequency filter improves PA images.

Noise Harmonic Reduction of IPMSM Based Next Generation High Speed Railway System using RCF-PWM (RCF-PWM을 이용한 IPMSM 기반 차세대 고속철도 구동 인버터 시스템의 소음원 고조파 저감)

  • Kim, Sung-Je;Jin, Kang-Hwan;Lee, Sang-Hyun;Kim, Yoon-Ho
    • Journal of the Korean Society for Railway
    • /
    • v.15 no.3
    • /
    • pp.244-250
    • /
    • 2012
  • In this paper, The next Generation High Speed Railway Inverter system using RCF-PWM(Random Carrier Frequency Pulse Width Modulation) was developed to reduce electromagnetic noise. RCF-PWM method is randomized the switching frequency in the range between Semiconductor switching devices' maximum switching frequency and minimum switching frequency, Simulation program has been built using MATLAB/Simulink to verify the validity of study. Finally, the simulation results of Next Generation High Speed Railway inverter system using the RCF method was compared with the conventional SVPWM method.