| With the rapid development of microwave system solid miniaturize and study on tealthy technology absorbing wave material and communication and electromagnetic countermeasure, the study on the measurement and mechanics of microwave dielectric constant of solid material become the topic of many people concerned. The measurement of opposite complex dielectric constant εr of dielectric material or absorbing wave material become more and more important. In the last years, people found that remote sensing technique by microwave could obtain more information than by infrared wave and visible light in detecting land, ocean and air. Remote sensing technique by microwave can work anytime and it can realize dynamic states detect real time, it can penetrate some objects and obtain specific parameters of measurand and it can quantitative measurement. These merits make it in play an important role on military and civil, so it becomes the focal point used and studied and development in our times in the remote sensing field. Study dielectric constant of target and background has important function on solving interpretation and conversion of microwave. The microwave plays an important role in the stiff oil exploitation. Electromagnetic wave transmission well logging is used for measuring the dielectric constant of stratum mainly. Because of the difference of dielectric constant between water and oil, this is an important well logging method of partition oil-water layer and water layer. Microwave petroleum job site spread, design of radiation antenna under well, study on penetrate depth of microwave in reservoir and the rate of the utility of microwave based on the measurement of dielectric constant of thick oil. The measurement of dielectric constant of medium material has very important meaning about microwave characteristic of material, design of microwave device, obtaining structure information of material, promoting the study and manufacture of new material and promoting modern high technology. So the study of dielectric constant of medium material has very important meaning. There are many methods of measurement of dielectric constant. There are the method of flat capacitance and the method of low frequency spectrum in low frequency. There are the method of transmission line, the method of resonance cavity and the method of space wave in microwave frequency. In third and fourth section of this article, we introduce these methods. What this article introduced especially is the perturbation method of resonant cavity. There are extensive applications in the field of quantum mechanics to deal with state of microscopic particle and in the field of theoretical mechanics to deal with planetary perturbation and so on. It is one of the effective methods to deal with many-body problems in quantum mechanics field and mechanics field. In electromagnetic wave field, the problem we will deal with is a field distributing in the space, so we can't adopt the method, which can solve the particle problem in mechanics. But with the aid of the treatment method of "state"in quantum mechanics, we can regard parameters that influencing field and boundary condition as perturbation, and regard the state of field unchanged as ground state ofzero-level approximate. This method has very high use value in calculating frequency and Q-factor approximatively. Because electric magnetic field itself have fluctuation and superposition, so perturbation has superposition for the whole area, so this kind of method have certain limitation in the field of electromagnetic wave. But, for the quasistatic, namely, the range of the field is smaller than the situation of the wavelength far, would not have the problem that likes this. In this article, we had introduced the whole process of this experiment from theory, equipment to data processing. When putting the small sample into the resonant cavity. It will cause the changes of the resonance frequency and Q-factor of the resonant cavity. If the sample is very small, and supposes: 1. the relative change that causes after putting into the sample is very small. 2. After putting into the sample, except that the electric magnetic field of the place of the sample changes, the electric magnetic field of other places keeps intact (In fact change is very small, can neglect.), it can regard as a perturbation, and can get perturbation formulae a little of resonant cavity. Put the sample into the proper position in the resonant cavity, can make the magnetic effect of the sample separated from electric effect of the sample, so we can measure the dielectric constant and permeability respectively. If put the sample into the middle of rectangle resonant cavity of type of TE10p (p is for the odd number) (this electric field the strongest, the magnetic field is zero), can obtain the electric effect in this way, can be used for measuring the dielectric constant. According to resonant cavity perturbation formula, measure resonancefrequency and half power frequency when puts the sample when not putting sample, respectively in the experiment. When get the frequencies into the formula, we can calculate the dielectric constant of sample. This experimental system adopt klystron as microwave source, klystron reflector voltage exert the saw-tooth wave modulate, use the detection transistor of square rate. We can observe the resonance curve of the reflecting type resonant cavity on the oscilloscope. With the aid of "instruction mark"("gap" caused by absorbing some power of wavelength meter) of the absorbing type wavelength meter, can determine resonance frequency f0 and corresponding half power frequencies f1 and f1 on the resonance curve. According to QL=f0/|f1-f2| Can calculate QL. Through observing the reflecting type resonance curve before and after putting samples into resonant cavity, according to formula can calculate real par and imaginary part of dielectric constant and the tangent of the loss angle. Because the instruction gap of the wavelength meter and the resonance curve show in one signal channel, the instruction gap of the wavelength meter certainly will cause influence on the resonance curve, increase the error of frequency measures. For propose high sensitivity of frequency measure, we show the instruction gap of wavelength meter alone in a signal channel in this experiment. For design of rectangle resonant cavity of reflecting type, the simple one is come to say, add the metal sheet with coupling hole on one end of a section standard rectangle wave guide, and another end adds the close metal sheet, form a reflecting type resonant cavity. The rectangle resonant cavity that this experiment adopted was... |
PDF Full Text Request