There are three main principles of instruments for detecting liquids in the subway.
1. Raman spectroscopy. The instrument emits a single laser beam into the liquid, measures the light scattered by the liquid, and uses the chemical fingerprint it produces to determine the composition of the liquid. This method is suitable for the detection of clear liquids.
Raman spectroscopy is based on the Indian scientist Cv.Raman is an analytical method that analyzes the scattering spectrum with different frequencies of incident light to obtain information about molecular vibration and rotation, and is applied to the study of molecular structure.
2. Fluorescence quenching technology. Using molecularly imprinted fluorescent polymer sensing technology, these polymer sensing materials fluoresce under ultraviolet light under normal conditions, but if there are explosive molecules adsorbed to the sensing material, the fluorescence will be quickly quenched and detected by the instrument, and the sensitivity is very high.
3.GPR (Ground Penetrating Radar) technology as well as dielectric constant and conductivity detection. Knowing that the absorption of microwaves by a medium is directly proportional to the dielectric constant of the medium, we can use this property to determine the type of liquid by judging its dielectric constant.
In addition, for some metal containers, X-ray methods can also be utilized.