Study On Anti-interference Techniques For Overhauser Magnetometer

Magnetic exploration is one of the most widely used exploration methods in geophysical exploration.With the rapid development of all kinds of wireless technologies,the magnetometer with no anti-interference ability can not meet the needs of large-scale construction and emerging technology research,the market urgently needs the magnetic exploration equipment with high measurement precision and strong anti-interference ability.The Overhauser magnetometer is a new type of magnetic field measuring equipment that meets the needs of the market,but the Overhauser magnetometer seen in the domestic market is all imported from abroad.At home,the research and development of Overhauser magnetometer is still in the immature stage,especially in the anti-interference technology of the Overhauser magnetometer,and no relevant personnel or institutions have been studied in China.Therefore,it is very important to study the anti-interference of Overhauser magnetometer.The main process for Overhauser magnetometer: By the high frequency excitation circuit and dc polarization circuit on the probe at the same time;make a proton in the solution free radical system inside the probe do larmor precession motion,thus produce larmor signals;transfer the signal to the signal processing module,the signal filtering plastic to enlarge,the attenuation of the larmor signal processing for the square wave;have a frequency meter for each wave frequency measurement,the results show under the environment of the magnetic field numerical instrument.When the Overhauser magnetometer stops transmitting signals,there are three main types of interference: harmonic noise interference,attenuation signal interference,impulse noise interference.The harmonic noise interference is mainly caused by the residual voltage of the dc polarization signal and the harmonic noise;the signal that the attenuation signal interferes with the instrument is an e exponential attenuated larmor signal,which can interfere with the accuracy of the later measurement frequency;the impulse noise interference is caused by the noise influence of the square wave signal obtained after amplification.This paper focuseson the research of anti-jamming technology:(1)The first kind of interference,this paper designs the light coupling dc polarization switching circuit to isolate residual voltage,prevent them from causing interference of received signal,and put forward and set up a capacitor filter circuit and active band-pass filter circuit two anti-interference methods to eliminate the harmonic interference measuring magnetic field outside the scope of the bandwidth required.Respectively for two kinds of circuits in the Multism software simulation comparison,finally chose the better anti-jamming capability of the capacitor filter circuit as a means of anti-interference,and gives the circuit and the concrete implementation plan of the instrument combination.(2)The second type of interference,In this paper design and build the amplifier shaping circuit to reduce interference,enlarge shaping circuit can enlarge the larmor signal amplitude attenuation,and its effective plastic for square wave,so as to realize the purpose of anti-jamming.In the Multisim software,it simulates the signal of noisy larmor,so that it can observe the output signal by amplifying the shaping circuit.(3)The third kind of interference,select the appropriate method to measure the frequency and carry on the data processing.By designing the FPGA program,the multi-channel frequency measurement of the signal is realized,and the data volume is increased to four times;secondly,selected the five ways to remove the gross error in the Matlab simulation compared to the same set of data,according to the simulation results is finally the two-way mean square error adaptive threshold value method as a anti-jamming measure.Finally,according to the simulation results to build the capacitance harmonic and shaping circuit,and to provide circuit input continuous sinusoidal signals with noise signal,to observe output for the stability of the square wave signal,this circuit was verified in weakening harmonic interference and attenuation signal interference effect is obvious;the measurement frequency and data processing module of the square wave signal generated by the high-precision signal generator are used to verify the effectiveness of the anti-interference scheme.