The Research On Bipolar Gauss Pulse Source And Langmuir Triple Probe

Nineteen sixties, researchers abroad applied the impact of pulse source to GPR forthe first time. The impact of pulse source with very narrow pulse width, ultra wide bandand high voltage greatly improved the effective distance and detection resolution oftargets. The pulse width of impact of pulse source should be nanosecond, the amplitudeshould reach to one thousand voltage, at the same time the amplitude and waveformshould be with higher stability and better frequency characteristics, so there are manydifficulties to solve. At present the research at home mostly concentrated in the unipolarpulse source, the spectrum of which has more proportion of low frequency component,so it is more difficult to radiate out. In the other hand, the spectrum of bipolar pulse hasless low frequency component than unipolar pulse, which is beneficial to improve theradiation efficiency. And in the application of GPR, the type of transmitting antenna isbalanced and symmetrical, so the bipolar pulse is more suitable to the antenna radiation.Now there is no such domestic commercial pulse source, so it has a high value inengineering application in researching on bipolar pulse source.In research of pulse source，the theory was studied at first, analysis was putforward to the waveform of Gauss pulse, compared the pulse generation technology ofseveral of semiconductor switch, the result reflected the avalanche transistor was moresuitable to output the pulse with high voltage and narrow width, the pulse coupledtechnology can generate bipolar pulse. Using the method of pure electronic circuit togenerate bipolar pulse, simulated the circuit with Pspice software, and optimized thecircuit parameters. During the PCB designing, the device and plate selection, and layoutare introduced. According to the scheme of theory optimization, designed andprocessing the pulse source circuit of Marx with16class avalanche transistor. A seriesof measures were put forward to restrain crosstalk phenomenon which appeared duringcircuit debugging process.Through testing in experiment, the output pulse widthbetween positive peak and negative peak was3.05ns, the amplitude was952V, the tail’samplitude was72V. The pulse spectrum was obtained with Fourier transform, whichcovered the range of600MHz, the center frequency was120MHz. The pulse spectrum basic agreement with the simulation results, and verified the feasibility of the scheme.In this paper，in addition to the research of Gauss pulse source, Langmuir tripleprobe was studied too. In low temperature plasma, the spatial distribution of plasmaparameters could be measured by electrostatic probe, this way was proved to be asimple and effective diagnosis method. Scanning power supply was not needed in tripleprobe diagnostic circuit, so it was especially suitable for transient plasmameasurement.In this paper, the basic principle and structure of single probe and doubleprobe were introduced first, and some factors which influenced voltammetric curve ofprobe were analysed. Adding photocoupler to the testing circuit,it can prevent plasmaelectromagnetic interference on the data acquisition systemn effectively. Adding thesampling resistor in current testing circuit,it could convert current to voltage to measure.Experiment result showed that the testing circuit could transfer sinusoidal signal withthe frequency up to1MHz, fully meet the demand of frequency diagnosis for instantplasma in the shock tube.