Non-Invasive Detection Of Hazardous Liquids

Non-invasive detection of hazardous liquids is a key technology in the field of liquid security check, which enables detection of hazardous liquid in a vessel without opening it. However, since this technology is still underdeveloped at the moment, people are still often prohibited from bringing any liquid with them in some situations, which leads to great inconvenience.Thus, in this thesis, non-invasive detection of hazardous liquids based on complex permittivity method was investigated. A detection sensor was designed using a dielectric resonator which has a resonant frequency of 3GHz and works on TEois mode. By penetrating the vessel with the evanescent field of the dielectric resonator, the complex permittivity of the liquid in the vessel can be measured, and based on the huge difference on complex permittivity between water and hazardous liquids, detection of hazardous liquids can be realized. Besides, an analytical model based on second-order Cohn's model of dielectric resonators and equivalent transmission line method was proposed, which was proved through simulation and experiment to be an efficient tool for evaluating the performance of the sensor. Combining theoretical analysis and simulation, the relationship between complex permittivity of liquid and resonant frequency was investigated, and a non-monotonic characteristic was found. Next, the influence from vessel on detection was analyazed, including diameter, wall thickness, material, shape and liquid level, which shows that wall thickness has the largest influence among the five parameters related to the vessel, and the conclusion was experimentally verified. Last, the performance of the designed sensor was investigated through experiment.