| Based on the magnetotelluric theory, HSMT takes the manual electromagnetic field source to complement the weak signal of natural electro-magnetic field source, which can be used to detect resistivity information of underground from several meters to about one kilometer depth applying frequency range 0.1-75kHz. This method only needs one or several receiving system working synchronization to obtain deep resistivity structure utilizing low frequency natural electromagnetic field, while being used shallow exploration for engineering it can utilize low power manual field source to enhance high frequency signal quality so that the detection reliability is improved. The HSMT has excellent character of portability application high reliability and good stabilization etc. As one of the geophysical exploration method, HSMT has important application value in metal mine exploration, underground water exploration and so on. In this paper, it expatiated on magnetotelluric exploration theory by natural electromagnetic field origin from electromagnetic wave theory and researched transmission principle of manual magnetic and electric field source. Based on the researching instrument system key technology, HSMT system was designed. The main research working and achieved working fruits are as following:1,Based on approximate equivalent of electromagnetic wave transmission principle between manual magnetic and electric field source and natural field source. The form of the manual field source can be ignored comparing with transmission-receiving distance so that manual magnetic and electric field source can be approximately considered magnetic and electric dipolar to the receiving system. Based on the electromagnetic field expression in the arbitrariness space, it mostly researched how to get the relationship between electromagnetic field expression and medium resistivity in uniformity medium by argument approach expression of Besell function with the condition of approximately quiescence, which was the foundation theory of HSMT. 2,Combined manual field source. Based on the geologic conditions difference and the requirement of availability in application of HSMT, it was put forward and designed a kind of combined manual field source system which could transmit magnetic field source and electric field source. According to the theory of electromagnetic wave skinned depth and field intensity attenuation rule, it was researched to select the appropriate transmitting frequency point of magnetic source and transmitting magnetic moment, and then designed the structure of the magnetic transmitting system. Based on the multi-frequency wave produced principle, realized method of multi-frequency electric field source transmitting was researched utilizing the transmitting system controlling part. It was designed the software and hardware structure of manual field source transmitting controlling part and the method of optimization transmitting frequency obtained.3,Multi-channel synchronization receiving system and data pretreatment. Based on the represent form of electromagnetic field information at the receiving point, it was designed the working layout in the field of multi-channel electromagnetic receiving system. After researched the receiving system precision demand to suffice the weak signal produced by natural field acquisition, multi-channel data acquisition system was designed utilizing the technology of 24-bit A/D converting, precision amplifier and synchronization based on the GPS. For the LabView development platform has the characters of abundance function and interface amity, it was used to design processing software. To the data acquired by HSMT, One of the most factors of influence data quality was the industry frequency. The basic frequency of industry power has character of most stable so that industry signal deduction technology based on iterative method was researched. Power estimate to the acquired signal was realized by utilizing the method of flatness periodic figure average method.4,Research and design of magnetic induction sensor. Based on the model of hollow induction coil, the character of sensor frequency response and the method to enhance the ratio of signal and noise of senor were researched. The distribution capacitance of the intertwist coil itself affected the coil's frequency response directly, so it was particularly researched calculating method of the capacitance among circles of the induction coils, the capacitance among winding slots, the capacitance between coil and magnetic core and the capacitance between coil and electromagnetic shield layer and then the method to reduce the most parameter among the several kinds of capacitances. Another important part of the magnetic induction sensor was magnetic core, which could increase two order of the sensor induction voltage. In the condition of similar circles of coils, appropriate magnetic core could make the senor output maximum voltage. In this paper, the influence of the assumed length magnetic core shape to the induction sensitivity and the change of relatively magnetic permeability in the magnetic core with the position variety were emphasized researched and selected appropriate parameters. At last, preamplifier circuit structure with frequency character compensation of the induction coil was researched and designed.5,Calibration to system channels and magnetic induction sensor. System channel calibration could gain the frequency characters of the channels to avoid signal aberration caused by system channels. Besides getting sensor frequency characters, magnetic induction sensor calibration could also obtain the voltage value corresponding to magnetic field intensity in a frequency point and the phase shift degree of the magnetic field intensity caused by sensor. Based on the calibration theory of deconvolution in frequency domain, the calibration system structure was researched and designed. After confirming square wave as exciting signal by analysis characters of different exciting signal, it confirmed frequency selection method of square wave to obtain enough calibration precision based on researching the harmonic frequency characters of the square wave after Fourier transform and the frequency band of the system. After analysis magnetic field character produced by different coils, it confirmed the solenoid coil as the exciting coil and according to different calibration circumstance outside, electromagnetic wave shield was researched when the sensor was calibrating. Because of the two channel serial A/D convertor and high magnetic permeability material, influence of sample point to phase shift and influence of shield barrel to the calibration sensitivity of sensor.Real data of testing parameters and experiments in the field in fact has good coherence with the researching results, which shows that the researching fruits are availability and dependability.The main innovation works are as followings:1. Hybrid-source Magnetotelluric exploration method based on combined manual field source was put forward. By utilizing the method, it can improve the system application ability to the complex landform by selecting different manual field source, which makes the theory system be more multiform.2. Based on high permeability nanocrystalline alloy, induction weak magnetic sensor was developed. The frequency band was broadened to about six orders. The detection sensitivity of the sensor was improved and then the weak magnetic detection level was enhanced.3. The self-calculation system of HSMT instrument was constructed. Utilizing digital deconvolution principle, it provided new method and structure of self-calculation for induction magnetic sensor based on the research of induction magnetic sensor dynamic sensitivity test and calculation by the exiting magnetic field produced by solenoid. The self-calculation system of the sensor's dynamic sensitivity and instrument channel's frequency response characters can be referenced by other electro-magnetic method instruments.The work of this thesis will have following function:1. The researched fruits will play important roles to the underground resource exploration and will be much application value to the oil and gas resource, oil sand and oil shale, coal, metal mine resource, relay resource of the crisis mine and etc. prospecting for celerity continuable development of our country.2. The succeed development and design of the HSMT system can break the few developed country monopolization in the electromagnetic field so that the situation of importation many electromagnetic instrumentation by costliness price in many associations of our country such as oil, metallurgy, geologic, traffic and so on can be changed. It is important for the improving the international rivalrousness of our country in the electromagnetic field, enhancing furnishment researching ability and saving foreign exchange.3. The research method and strategy can be used to researching and design of other electromagnetic instruments directly such as magnetotelluric, IP, electromagnetic in time domain and so on.
|
PDF Full Text Request