A Study On The Special Phenomenon In Permittivity Measurements Of Electrolyte Solutions By Different Microwave Powers

Microwave energy has already been extensively applied to industry and agriculture productions and scientific researches. But so far, the interaction mechanism between microwave and biological tissues or a chemical reaction system has not been deeply understood yet, the special effect produced in interaction remains the focus that people dispute. It has been discovered that the permittivity of a material will often change when the high power interact with the material and cause the absorption of the microwave system to suddenly increase, and as result the larger change of temperature enable to burns even damages to the microwave system. From this phenomenon, a study and analysis of the relation between the material permittivity and microwave powers can offer a helpful reference with purpose of researching further the special effect. The special phenomenon that the permittivity varies with powers also can be found in the permittivity measurements by the microwave powers of the several up to dozens of watts.As kinds of the simplest biological tissue and chemical reaction system, three electrolyte solutions have been considered. Three main contents and innovation points of this thesis are as follows:First, reflection coefficients of the deionized water and NaCl and the Na₂C₂O₄ solutions have been measured under different microwave powers by using the open-ended coaxial probe; the permittivity of each kind of electrolyte solution in the 34℃thermostatically water bath has been calculated according to the Capacitive Model under the microwave frequency of 915MHz. The experiment and result of calculation indicate that the microwave power of several watts and dozens of watts will exert an influence on the measurement value of the permittivity of electrolyte solution.Second, because microwave heating is a quick course, and the electrolyte solution dispelling the heat is a relatively slower course, in order to reducing the heat effect in experiments, the order of power test points has been changed. The optical fiber thermometer has written down the change of the temperature each position of solutions. The experiment and result of calculation indicate that the main reason why the permittivity of the electrolyte solution varies with powers is not caused by the microwave heat effect. Then it has been explained that why the phenomenon happens place from the electrolyte solution ion conductance theory, and it is showed that the special phenomenon should belong to the microwave non-heat effect.third, due to longer measurement time and the electric chemical reaction it has been observed that the NaCl solution will often produce bubbles that adhere to the surface of probe when measuring the permittivity of the electrolyte solution by using the open-ended coaxial probe; the region of the probe and solution and bubbles has been simulated numerically by using the Finite Element Method, and the electromagnetic field distribution of the simulation region has been calculated and the reflection coefficient has been become to known and the equivalent permittivity of the electrolyte solution also can be calculated too according the Capacitive Model. Results of the calculation indicate that the bubbles have less influence on the real part of the permittivity, but the influence on the imaginary part is relevant to the position, size and number of the bubbles, and the use of the Capacitive Model also can brings to errors because the solution is not uniform.