Development Of Hybrid-source Electromagnetics Transmitter EM-â…¡

According to the present situation, there are two main representative research direction that are time-domain electromagnetic method and Frequency–domain electromagnetic method about the electromagnetic method.The main research of Frequency–domain electromagnetic method is the relationship of frequency and response. Using the change of emission frequency and receiving distance, different depth of the target detection can be implement, and changing of the different structure of emission coils and receiving coils ,detection ability and effect can be improved. According to the different field sources, electromagnetic method can be classified into natural source electromagnetic method and man-made source electromagnetic method.Natural source electromagnetic method, namely Magnetotellurics, MTT is for short. That is a geophysical method studied on the underground electrical structure, and Mainly through the observation of internal earth induced electromagnetic field that is generated by electromagnetic waves from high altitude. It is essence that Man-made source electromagnetic method, namely controlled source audio-frequency magnetotelluric (CSAMT), is artificial source kania electrical resistivity. By Changing the frequency of artificial excitation source( field source transmitter) , CSAMT can measure kania electrical resistivity and obtain underground information. Combined with high-new electronic technology , Hybrid-Source Magnetotellurics(HSMT) based on the initial frequency and electromagnetic theory combines natural source(called passive source) with man-made source (called active source) and form a new earth detection method. Combined with the characteristics of MT(or AMT) and CSAMT, HSMT used natural source and man-made source as field source and using electromagnetic induction electromagnetic field and kelvin effect, therefore distributed information of underground different depth resistivity of media can be obtained. Natural source usually use low frequency signals(0.1～1KHz),and frequency range of man-made source is 1K～100KHz. Through detection of underground electrical resistivity(1-1000m),continuous profile of electrical resistivity can be obtained. The of HSMT has a lot of characteristics, include wide range of exploration depth, strong resolution, and high observation efficiency. Besides , it has both depth sounding and profile double features. HSMT will provide a effective method for the study of groundwater-detecting, environment description, geothermal exploration, mineral exploration and engineering geological investigation.The instrument of HSMT was divided into transmitter and receiver, and occurrence of the transmitter used as man-made source played an important part. According to the index requirement of the whole nstrument, based on the transmitter of the EM-ⅠHSMT and around the development process EM-ⅠHSMT, this paper gives detailed design conditions of transmitter of the EM-ⅠHSMT. Firstly, this paper discussed the principle of HSMT, analyze the development of foreign countries and china and proposed the design program of the transmitter of EM-ⅡHSMT. Secondly, the this paper gives detailed exposition of every module design implementation from hardware and software. In the end, this paper analyzed the test results of system in the experiment, and puts forward some suggestions for the improvement of system.In this system, STC89C54 microcontroller used as master controller, CPLD(Complex Programmable Logic Device)used as control sequence and logic occurrence unit; PDA used as the instrument of human-computer interaction controled operation; using the system of serial interface and lower computer microcontroller as Communication; Resonant emission part used MOSFET as inverter bridge circuit switching element; Used GPS synchro-control technique as the work of synchronous transmitter and receiver.In the special environment of HSMT instrument field operation, experiment instrument must be small volume perfect, convenient carrying, clear display, seed setting and durable. PDA, namely Personal Digital Assistant , is small volume perfect, convenient carrying, high processing speed, strong movability and powerful function. with internal powerful embedded operating system, serial port, USB port, infrared port etc. , PDA is convenient connection to desktop, simultaneously provided embedded developed environment of bootstrap design.Considering of the HSMT detection of the requirements of emission current excitation signal, EM-ⅡHSMT, we used APT50M60JN type Power MOSFET that was produced by APT ( Advanced Power Technology)to design transmitter system, and CMOS transmission-gate driving circuit design the power. In order to reach more accurate emission frequency, resonant capacitor used CBB customized polypropylene capacitor as resonant emission part, and solve the problem of inaccuracy and instability of the resonant frequency that caused by the properties of capacitor of the EM-ⅠHSMT. In order to reduce the volume of system, improve integration and obtain pseudo-random signal, we used programmable logic CPLD as control sequence and logical generated unit circuit.Under the compile environment of the Microsoft Visual Studio 2005, User application program of the PDA has completed program.Application program provides friendly, convenient and object-oriented operated window interface, and by clicking the window button users can implement the control of the system of the transmitter.This paper provides test results of experiments, and the system has achieved more satisfied effect and applicable value. In the end, in order to improve the design of the system of transmitter, this paper puts forward some suggestions of follow-up design and research.