Research Of The Performance Improvement Of Coil-moving Geophone

As the development of technology of geophysical prospecting and the extension of prospecting scopes, especially the application of technology of high resolution prospecting and the study of Q technology and the lithology exploration, the requirement of the quality of seismic data is higher and higher, low distortion,high S/N ratio and wide band become very important. The quality of seismic data is mainly decided by the specification of the data acquisition system. The data acquisition is combined with instrument and geophone, as the development of electronic technology, the specification of instrument is much better than the geophone's. As a result , the quality of seismic data is mainly decided by the performance of geophone. So the study of application of geophone is important.The development of computer technology and the constant renewal of seismic instruments, as well as the seismic exploration of new technologies and new methods is closely related to the enhancement and improvement of geophone type performance. Generally speaking, the development of geophones experienced three periods.Before 1978, the geophone were a narrow band (14 ~ 60Hz), low sensitivity (30dB) and pattern are also single.In the mid 80's, seismic instruments is digital and computer data processing technology had also been development.More importantly, technology such as three.dimensional geophone, high-resolution geophone and VSP seismic logging technology had expanded the field of seismic exploration, great change happened to the pattern and the performance of seismic detectors as well as the shape of seismic detectors, a large number of high-pass geophones with different technical indicators appeared, the sensitivity, natural frequency, distortion factor, spurious frequency of geophone were modified greatly, which greatly increased the performance and the use scope of the geophone, geophones used in well and piezoelectric detectors used in the sea had been developed successfully.From the late 80's to present, three-dimensional seismic, high-resolution seismic have become more and more sophisticated. With the development of new technology such as four-dimensional seismic, multi-wave and multi-component exploration, seismic and other new technologies and new methods, the type and series of geophone become more and more abundant, such as three-component detector, four-component detectors, eddy-current detector, high-performance-piezoelectric detector. According to preliminary statistics, there were a total of 12 series, each series contained 25 types of geophones used in seismic exploration. In this paper, the structure, working principle and the advantages and disadvantages of geophone were discussed exhaustively, which were widely used ,named move-coil geophone . And some jobs were done to improve the performance of this kind of geophone.Firstly, a brief introduction was made to the working principle of geophone, and some problems which existed in practical application were discussed. The kinematics differential equations of geophone were establish, what's more, combined with Faraday's law of electromagnetic, the relationship between the input speeds and output voltage were induction, amplitude and phase frequency curve under different damping coefficient were mapped. The natural frequency, damping coefficient and sensitivity of geophone were discussed. By calculated, the overall detector coefficient and sensitivity calculation expression of geophone group were given, discussed how to select the combination group to make the best geophone performance. The results shows, the ideal style is the p = q = m, adapting this combination style, sensitivity was increased q times and the damping coefficient h was unchanged. That is to say, as long as a single geophone achieved the best value of damping coefficient, the damping coefficient detector combination is also the best value.Generally magnetic boots are made by high-quality pure iron, magnetic permeability can be regarded as infinite, so we simplify the magnetic boots, use the two-dimensional scalar field to calculate this field, give the Laplace equation which meet the boundary conditions and use numerical method to solve the magnetic intensity.This paper briefly introduces the development of computational electro magnetic. Analysis and compare the finite element method and finite difference method, discuss how to deal with the boundary conditions of this two kinds of methods. The numerical solution equation is derived using the finite element method and finite difference method.By calculating, we know how the magnetic field homogeneity effects the output signal distortion of magnetic fields, which lay a theoretical basis. According to the characteristics of the magnetic field of geophone, the simulation model is established. The results show that the scope of a uniform magnetic field is limited; It is to say that there is necessary to improve the magnetic field homogeneity. Under the conditions of ensuring the overall size of the geophone unchanged, the major dimension of permanent magnet and magnetic boots are analysis .Analysis results shows, the magnetic field homogeneity is proportional to the radial dimension of the permanent magnet, but it is a non-linear relationship with the axial dimension of the permanent magnet. According to Ansofe Maxwell, the new dimension of geophone is determined .The scope of the magnetic field homogeneity had a great improvement.To further increase the region of homogeneity magnetic field, we redesign the shape of magnetic boots. We use empirical equation to reshape the magnetic boots, the surface of magnetic boots is processed by rogalsky curve. And then, we made some improvements to the shape of magnetic boots. The result shows that the magnetic field uniformity and strength of this kinds of magnetic boot are stronger than before optimization.In this paper, we discuss how the spider spring influent the performance of geophone. Totally, there are two aspects which effects the performance of geophone. One hand, the non-linear stiffness of spider spring will cause the distortion of output signal, and this also effect the accuracy of the data acquisition; On the other hand, the structure of geophone cause the spurious frequency ,which caused by spider spring. To analysis the non-linear characteristic of spider spring, we adapt pseudo rigid body methods to research the spider spring which are used to analysis the large deflection beams in compliant mechanisms. The results got by traditional methods are compared with which got by pseudo rigid body methods. The result shows that the stiffness of spider spring cannot be treated as a constant. By using pseudo rigid body methods ,the degree of non-linear can be measured more accurately ,which lay the way for the further study.