Design Of Probe For Effective Permittivity Measurement Of Chemical Reaction In Dilute Solution

The effective permittivity of chemical reaction in dilute solution always changes with many physical parameters, such as temperate, frequency and concentration. This causes the great difficulty in study on dielectric propriety of chemical reaction in dilute solution, but it is important for many research fields to measure exactly effective permittivity of chemical reaction. In this paper, tow types of high-sensitive probe are designed for precisely measuring effective permittivity of chemical reaction in dilute solution.First, we calculate the field distribution near the end of slotted open-ended coaxial-line probe with resonant cavity structure by the numerical method of finite difference time domain (FDTD), and study the relationship between reflection coefficient of probe and effective permittivity. In order to determine the influence of ah- bubble on measurement of effective permittivity, we calculate the field distribution with the air bubble, and study the relationship between the size of bubble and reflection coefficients. Through the calculated results we find that air bubble in resonant cavity can disturb the field distribution significantly. We can see that it is necessary to design correctly the coaxial-line probe with resonant cavity structure.A lot of experiments have been done to measure S11 with slotted open-ended coaxial-line probes at the different temperate solution. The reflection coefficients changing via frequency calculated by numerical computation are good agreement very well with the above experimental results. Meanwhile, we analyse the influence of different size of air bubble on reflection coefficient in the frequency domain. The reflection coefficients at different temperate and at 2.45GHz with the two probes are calculated by FDTD and compared with the experimental results.Four types of coaxial-line probe with different end structure are used to measurethe effective permittivity of chemical mixture in dilute solution. From the experiments, we can see that S11 parameter measured by slotted open-ended coaxial-line probe with resonant cavity structure and strip-ended coaxial-line probe changes evidently near the resonant frequency. Through these experiments, it could be conclude that two types of probe with different resonant structure proposed in this paper have high sensitivity to the change of effective permittivity of chemical reaction in dilute solution.The effective permittivity of chemical reaction can be obtained by the inverse calculation by using the measured reflection coefficients and genetic algorithm (GA). In this paper, many numerical simulations with different random error have been done by the above inverse method. We calculate the effective permittivity of pure water at different temperature with the reflection coefficient measured by slotted open-ended coaxial probe. The calculated results are good agreement with the obtained value from Debye's formula.