The Circuit Design Of Proton Precession Magnetometer

With the development of society and the progress of science and technology, therequest for the accuracy of measurement of magnetic field becomes higher and higher.Proton precession magnetometer is such an instrument with high accuracymeasurement of the geomagnetic. Now the proton precession magnetometer is widelyused in geomagnetic measurements, local metal conductor measurement and otheraspects.The basic principle of proton precession magnetometer is: when the solution in theprobe rich in hydrogen proton is polarized by external magnetic, the proton in thesolution will form a magnetic strength in a direction along the polarization. When thepolarization field suddenly disappeared, the magnetic strength will do the precessionmotion around the earth, and the frequency of the precession of magnetic strength isdirectly proportional to the strength of the magnetic field. We make use of coil toreceive strength and the movement, so we can calculate the signal frequency to get thesize of the magnetic field. This measurement method needs few seconds to severalseconds to measure a point, which is a kind of intermittent measurement method ofmagnetic field, and this method can only measure scalar value of the magnetic field,so we need to add a Helmholtz coil to the probe for vector measurement.As the proton precession magnetometer has simple structure and high precision,small size, high maintainability, moderate price, it is widely popular. This paperstudies the proton precession magnetometer which starts mainly from the use ofelectronic components to realize the basic function of the proton precessionmagnetometer, and studies the basic methods to realize the polarization, shut off,amplification, signal conditioning and other aspects of the proton precessionmagnetometer. The main contents of this paper are as follows:This paper discusses the basic principle of proton precession in detail firstly, and makes a discussion of the process of polarization of proton’s precession. Then wediscuss the formation of the magnetic strength from the classical theory and quantummechanics theory, and concept of depolarization, and give a quantitative descriptionof the related parameters of magnetic strength rotating around the magnetic field. Atthe same time, we give the basic structure of the probe and the related parameters ofproton precession magnetometer. Finally, we simulate the attenuation process andacquisition signal ideal form of the magnetic strength with MATLAB.Then the article discusses the function and design of the polarization circuit for theproton precession. The changing of current in the coil is discussed when the switch isturned on and turned off. When the polarization circuit is opened, the current in thecoil rises to the maximum value exponentially. When the circuit is cut off, the voltageon the coil keeps constant at first, and then declines exponentially. However, thecurrent in the coil declines linearly firstly, and then exponentially by the action ofmatching resistor. A relay is used to switch the coil between the polarization circuitand preamplifier circuit, which ensures that each part of the circuit can work properly.Receiving circuit includes coil matching, preamplifier and signal conditioning. Thecoil is matched at the resonant frequency by matching capacitor and is equivalent to aresistor. The output signal is amplified Q times to the input signal. We calculate theinfluence of matching resistor under this model. Signal conditioning is composed ofamplifier, filter and signal adjustment. We use four amplifiers to build a broadbandfilter amplifier, so that the signal is limited in a limited range. The MAX260is used asnarrowband filtering to improve the signal-to-noise ratio. Finally, two amplifiers areused to realize low-pass filter and change the range of the signal, to prepare for theAD sample.The last part of this article studies the signal form measured outside. We find thatdifferent solutions get different proton precession signal. We study the characteristicsof proton decay in different solutions to obtain better result.