[en] Nonlinear damage such as fatigue crack often occurs in some engineering structures, which brings challenges in structural damage diagnosis. A nonlinear damage diagnosis method based on ARMA/GARCH model is proposed to extract the nonlinear characteristic caused by cracks. First, the background description of ARMA/GARCH model is given and a damage diagnosis index based on this model is proposed to detect nonlinear damage location. The main advantage of ARMA/GARCH model is that this hybrid model can well simulate structural time domain acceleration response and effectively extract the nonlinear damage feature. An experiment of three-storey frame structure, which utilized a mechanism constituted of a bumper and a center column to model breathing crack, is studied. The results show that the damage diagnosis index based on ARMA/GARCH model exhibits good accuracy. (paper)

[en] An online measurement method is introduced to ensure the reflectivity of an arbitrary grating in a large-scale ultra-weak fiber Bragg grating (FBG) array. The measurement errors were investigated by theoretical analysis and experiment. In the proposed method, the reflected spectrum of one single FBG was addressed and obtained from the grating array by time domain interrogation, and the FBG reflectivity was calculated by the reference of the end-face reflection in anhydrous ethanol. A measurement error of less than 0.5 dB and a 20 dB dynamic range were obtained in a larger-scale array of 1000 FBGs with an average peak reflectivity of −43 dB, which demonstrated the feasibility of this online measurement method. (paper)

[en] A surface ionization (SI) source is designed and prepared for ion mobility spectrometer (IMS). The source acts not only as an emitter but also an ion injector which can inject ions periodically into the drift region of drift tube. Using the dual-role source, the dimension of the drift tube can be decreased and the circuit for high voltage can be simplified efficiently. The IMS with the SI source has a response range of ∼4 orders of magnitude and a good reproducibility to tri-ethylamine. Compared with radioactive ionization (RI), the ultra-short time for ion injection and the zero level base line of ion mobility spectrum are characteristics of the surface ionization