A distributed optical fiber temperature measurement system based on Raman scatter and optical time domain reflecting (OTDR) was used to detect and locate the leakage of water pipe. Firstly, the temperature resolution of the system and the temperature difference at the leakage point were analyzed in the paper. Secondly, the lengths of 200m sensing fiber was used to locate the leakage of water pipe, and the detection signal was processed by accumulative averaging and wavelet transform. Finally, the location of pipe leakage was identified by comparing threshold signals and leakage signals. The experimental results show that the distributed fiber optic temperature system operation was stable and can identify the water pipe leakage.The system can leak location and the positioning error was less than or equal to 1m.
Polyethylene gas pipe sample with defects was detected by the transmission THz-TDS system. Firstly, the difference of the THz time-domain waveform and corresponding frequency spectra between the defect part and non-defect part was compared. Then, the PE pipe defects were imaged by the maximum value of THz time-domain data and the frequency-domain data. The results show that the existence of defects cause obvious reduction the maximum value of the THz time-domain spectrum. The PE defects can be clearly distinguished from the non-defect part by the transmission THz images. Imaged by the THz timed-domain and the frequency-domain parameter can reveal the defects in the polyethylene gas pipe.
The terahertz spectra of triadimefon has been investigated using time-domain THz spectroscopy (THz-TDS) in the range of 0.4~2.0 THz. Calculations of the vibrational modes and intensities are carried out using solid-state density functional theory (DFT) with periodic boundary condition employing the B3LYP and PW91 density functions. Good agreement between the calculated and experimentally measured spectra has been achieved where isolated-molecule calculations fail to reproduce the observed spectral characters. These simulations reveal that the solid-state DFT calculations provide high quality structural and spectral reproductions. All the experimental THz absorption peaks are assigned utilizing the PW91 and BLYP method.
Terahertz time domain spectroscopy (THz-TDS) is a new kind of nondestructive detection method, frequency of
terahertz wave spans from a few tens of GHz to several THz, which is used to detect material because of its strong
identification, it can supply rich vibration information caused by intermolecular and large intra-molecular. Ammonium
sulfamate (AMS) is a kind of herbicide, it has special value for many woody plants, which can prevent annual weeds.
The excess use of pesticide is a huge threaten for human health in recent years, thus the research on detection of pesticide
has absolutely important meaning, in this paper, pure AMS and mixture samples of AMS and orange are measured using
THz-TDS, and their absorption coefficient are calculated by the model, which is put forward based on Fresnel equation.
We qualitatively analyze the absorption coefficient spectra of pure AMS, which is useful for us to identify the pesticide
in agriculture products. Meanwhile, we measured 14 mixture samples of AMS and orange, the weight ratio of mixtures
are from 0% to 59.9%. Nine samples are considered as calibration set and the other five samples are regarded as
prediction set, to quantitatively analyze the concentration of AMS by the partial least squares (PLS), the result shows that
the prediction error is less then 4.5%, in addition, the relationship of the average absorption and weight ratio are
absolutely linear. The experiment demonstrates that THz-TDS is promising and efficient to quantitatively detect the
component of mixtures, and it has important reference value for the detection of pesticide in agriculture food.
A replacement algorithm used in the calculation of roundness errors by a least regional fitting method has been proposed
in this paper. Using the high fitting precision initial-value, which is calculated by the relative algebraic distance method,
the replacement algorithm needs less iterations and has a higher calculation speed. Simulation tests show the higher
fitting accuracy. The replacement algorithm by using computer programming is applied to measurement software of a
universal tools microscope.