The Research On Some Key Technologies And Theory Of Frequency Domain IP Decoupling By Chop-wave

Electromagnetic (EM) effect is a strong interference in frequencydomain induced polarization (IP) survey, especially in the districtscovered with earth in lower resistivity and the electrodes configuration ingreat distance. It influences the depth of exploration, survey accuracy,and it is a great encumbrance to apply the IP method. Nowadays, tosuppress and remove the EM effect has become an important researchproject in frequency domain IP method in the world.This dissertation expounds the principle of EM effect proceedingfrom physics fundament. Systemic study is done on the factors of EMeffect and methods to suppress it. The author consider that there are fourmethods to suppress the EM effect in frequency domain IP survey: 1.Emendate by software; 2. Applicable configuration; 3. Electromagneticshielding; 4. Chop-wave decoupling method. A lot of researches havebeen done by scholars both in and abroad on the 1st method. Commonlyspeaking, correcting based on EM effect of simple models is verydifficult to adapt the complex geo-electric fields. Good configuration cansuppress EM effect, but the efficiency is very limited.In allution to the latter 3 methods, the dissertation expounds thedefection of good collocation of electrodes configuration, and designed alow noise pre-amplifier with cable shield driver, with which can enhanceanti-jamming capability, partially suppress the EM effect in frequencydomain IP survey, especially expounds the principle for chop-wave inhow to suppress and remove the EM in IP survey, and parametersselection of chop-wave, choice and realize the synchronize methods.The author proved the chop-wave decoupling method in dual-freq.waveform, calculated the relative chop-width of the waveform and its EMeffect during frequency domain IP survey.The author lays out a plan to synchronize the transmitter andreceiver of DFIP instruments with the use of GPS receiver at the firsttime. GPS synchronization has many advantages not only high precision,high reliability, low cost, but also easy operation, easy to take and with art design. It is a perfect synchronization method with high precision as wellas suit for fieldwork.Signal for driver of transmitter and synchronizing chop-wavewaveform of receiver are realized by the use of field programmable gatearray (FPGA) devices. In the meantime, manage peripheral cells anddevice of FPGA by the use of system level chip of MCU. It has a verygood man-machine interface, credibility, operability and easy to upgrade.The author studied on several questions such as chop-wave withprecise synchronization and small signal detection, etc. and designed outsome feasible circuits. Except for the low noise pre-amplifier withfunction of suppress EM coupling, ultra-low drop out voltage regulatorwith current-limiting results lower noise, high conversion efficiency, highreliability and security. To simulate IP effect by the use of RC-network,we can make the test quickly and validate the chopping-wave decouplingdevice easily. It has economized a lot of manpower, material resourcesand money.The geo-electric survey system with precise synchronizing ofchop-wave used the satellite clock as the reference at the first time.Transmitter and receiver of DFIP instruments have self-synchronizingfunction, quick acquisition of GPS-time auto synchronously. It has highprecise synchronization even if lost GPS signal for more than 30 minuteswith the use of keeping-time clock of OCXO. The synchronizegeo-electric survey system results very high precision of synchronization,high stability and ultra-low noise in chop-wave. It decouples the EMeffect during the IP effect measurement, no need any extra field work andindoor calculation. Compared with the EM decoupling methods such asdata and software correcting methods, this method has many advantages:high efficiency, convenience and applied widely, which results a veryuseful application.