为了研究冷金属与脉冲复合焊(cold metal transfer and pulse,CMT+P)的焊接行为,使用PCI数据采集卡、高速相机、红外成像仪及声发射采集系统对焊接过程进行同步监测.发现脉冲射滴过渡发生前,焊机输出电流突增,同时焊丝尖端释放猛烈电弧...为了研究冷金属与脉冲复合焊(cold metal transfer and pulse,CMT+P)的焊接行为,使用PCI数据采集卡、高速相机、红外成像仪及声发射采集系统对焊接过程进行同步监测.发现脉冲射滴过渡发生前,焊机输出电流突增,同时焊丝尖端释放猛烈电弧光,随后熔滴滴入焊道,熔池温度增加,声发射(acoustic emission,AE)信号显示出1个波峰.发生CMT短路过渡时,焊机输出电流同时为焊丝熔化和焊丝伸出提供能量,待到焊丝尖端接触基板瞬间形成短路,熔池温度持续降低,AE信号微弱,伴随着熔滴因过热收缩而爆断,熔滴短路过渡完成.对AE信号进行离散傅里叶变换(discrete Fourier transform,DFT)后,可通过特征频率对CMT+P各个周期及阶段进行过程识别.结果表明,575 kHz和415 kHz可作为脉冲电弧周期和CMT短路周期的特征频率,推断180 kHz是脉冲电弧的特有频率,575 kHz的频率则是基础电弧提供,415 kHz处的频率则在CMT短路接触瞬间产生.展开更多
A widely-wavelength-tunable Brillouin fiber laser(BFL)with improved optical signal-to-noise ratio(OSNR)based on parity-time(PT)symmetric and saturable absorption(SA)effect is present.This novel BFL realizes PT symmetr...A widely-wavelength-tunable Brillouin fiber laser(BFL)with improved optical signal-to-noise ratio(OSNR)based on parity-time(PT)symmetric and saturable absorption(SA)effect is present.This novel BFL realizes PT symmetry and SA effect through polarization-maintaining erbium-doped fiber(PM-EDF)Sagnac loop,which is composed of a PM-EDF,a coupler and two polarization controllers(PCs).By using the inherent birefringence characteristic of PM-EDF,two feedback loops in orthogonal polarization state are formed when the Strokes signal in injected.One of these loops provides gain in the clockwise direction with in the Sagnac loop,while the other loop generates loss in the counterclockwise direction.By adjusting the PCs to control the polarization state of the PM-EDF,a single-longitudinal-mode(SLM)BFL can be achieved,as the PT symmetry is broken when the SA participating stimulated Brillouin scattering(SBS)gain and loss are well-matched and the gain surpasses the coupling coefficient.Compared to previous BFLs,the proposed BFL has a more streamlined structure and a wider wavelength tunable range,at the same time,it is not being limited by the bandwidth of the erbium-doped fiber amplifier while still maintaining narrow linewidth SLM output.Additionally,thanks to SA effect of the PM-EDF,the PT symmetric SBS gain contract is enhanced,resulting in a higher optical signal-to-noise(OSNR).The experimental results show that the laser has a wide tunable range of 1526.088 nm to 1565.498 nm,an improved OSNR of 77 dB,and a fine linewidth as small as 140.5 Hz.展开更多
文摘为了研究冷金属与脉冲复合焊(cold metal transfer and pulse,CMT+P)的焊接行为,使用PCI数据采集卡、高速相机、红外成像仪及声发射采集系统对焊接过程进行同步监测.发现脉冲射滴过渡发生前,焊机输出电流突增,同时焊丝尖端释放猛烈电弧光,随后熔滴滴入焊道,熔池温度增加,声发射(acoustic emission,AE)信号显示出1个波峰.发生CMT短路过渡时,焊机输出电流同时为焊丝熔化和焊丝伸出提供能量,待到焊丝尖端接触基板瞬间形成短路,熔池温度持续降低,AE信号微弱,伴随着熔滴因过热收缩而爆断,熔滴短路过渡完成.对AE信号进行离散傅里叶变换(discrete Fourier transform,DFT)后,可通过特征频率对CMT+P各个周期及阶段进行过程识别.结果表明,575 kHz和415 kHz可作为脉冲电弧周期和CMT短路周期的特征频率,推断180 kHz是脉冲电弧的特有频率,575 kHz的频率则是基础电弧提供,415 kHz处的频率则在CMT短路接触瞬间产生.
文摘A widely-wavelength-tunable Brillouin fiber laser(BFL)with improved optical signal-to-noise ratio(OSNR)based on parity-time(PT)symmetric and saturable absorption(SA)effect is present.This novel BFL realizes PT symmetry and SA effect through polarization-maintaining erbium-doped fiber(PM-EDF)Sagnac loop,which is composed of a PM-EDF,a coupler and two polarization controllers(PCs).By using the inherent birefringence characteristic of PM-EDF,two feedback loops in orthogonal polarization state are formed when the Strokes signal in injected.One of these loops provides gain in the clockwise direction with in the Sagnac loop,while the other loop generates loss in the counterclockwise direction.By adjusting the PCs to control the polarization state of the PM-EDF,a single-longitudinal-mode(SLM)BFL can be achieved,as the PT symmetry is broken when the SA participating stimulated Brillouin scattering(SBS)gain and loss are well-matched and the gain surpasses the coupling coefficient.Compared to previous BFLs,the proposed BFL has a more streamlined structure and a wider wavelength tunable range,at the same time,it is not being limited by the bandwidth of the erbium-doped fiber amplifier while still maintaining narrow linewidth SLM output.Additionally,thanks to SA effect of the PM-EDF,the PT symmetric SBS gain contract is enhanced,resulting in a higher optical signal-to-noise(OSNR).The experimental results show that the laser has a wide tunable range of 1526.088 nm to 1565.498 nm,an improved OSNR of 77 dB,and a fine linewidth as small as 140.5 Hz.
