Dynamic Frequency Sweep-Resonance Cavity Perturbation Method For Measuring Complex Permittivity And Complex Permeability

In microwave equipments and circuit,particularly in the microwave integrated circuit,the application of electricity and magnetism medium is very abroad.And the electromagnetism characteristic of medium material have very important influence to electromagnetic wave spreading speed, the work wave-length,characteristic resistance,power to exhaust etc.also has consanguineous relation with the technique function of the microwave equipments.From extensive meaning to speak, though the research of characteristic parameter of electricity and magnetism medium material electricity, we can probably make clear some regulation of molecule structure or material structure; The measurement of Complex Permittivity and Complex Permeability 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 Complex Permittivity and Complex Permeabilityof 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.This paper is based on the basal electromagnetic theory,and briefly explains the kindling and transmit theroy,resumptively states the methods to measure Complex Permittivity and Complex Permeability, and resumptively states how to use dynamic frequency sweep -resonance cavity perturbation method to measure complex permittivity and complex permeability,and actualizes one cavity-many modes technique. 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 Complex Permittivity and Complex Permeabilityand 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 Complex Permittivity. If put the sample into the middle of rectangle resonant cavity of type of TE10p (p is for the even number) (this the magnetic field is strongest, the electric field is zero), can obtain the magnetic effect in this way, can be used for measuring the Complex Permeability.According to resonant cavity perturbation formula, measure resonance frequency 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 Complex Permittivity and Complex Permeabilityof sample.This experimental system adopt HP8620C as microwave source, 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 Complex Permittivity and Complex Permeability 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 designed on the basis of adjustable short circuited, its cross-section size is 22.86 mm×10.16mm, adopting a slice of coupling with round coupling hole( the diameter of coupling hole is 7.8mm).We have set up experiment system by using of perturbation method of rectangle resonance cavity. We have obtained very good result.Compared to reflector as microwave resource , We have testified that DynamicFrequency Sweep - Resonance Cavity perturbation method of resonance cavity is a stable feasible method of measurement of Complex Permittivity and Complex Permeability of medium through experiment.