Transient Electromagnetic Special Signal Generator Development

Transient electromagnetic method(TEM), also known as domain electromagnetic method, is an artificial source electromagnetic detection method in time domain based upon law of electromagnetic induction, It is mainly applied to the field of geological exploration. The transient electromagnetic receiver is the primary approach of data collection and storage, its performance directly affects the later data processing and interpretation. Therefore, people put forward much higher requirements for the performance of the transient electromagnetic receiver. The continuous development of modern electronic technology and computer technology makes high resolution, high sensitivity and high interference rejection transient electromagnetic instrument to become the main direction of researchers. During the development of instrument, every testing experiment is in the field and consumes much time, labor cost and material. The testing experiment can be done in indoor if transient electromagnetic signal can be simulated, which can not only reduce the cost of the experiment and improve performance of the instrument, but also calibrate the instrument before field operation. It is difficult to simulate the transient electromagnetic original signal waveform for general signal generator. Therefore, this dissertation designs a special signal source that provides the reference signal for the development of transient electromagnetic instrument.The dissertation is based on the project “half airborne transient electromagnetic exploration technology research based on UAV”(project number:201311037) which is supported by public welfare project of Ministry of Land and Resources of China. The main contents of the dissertation are as follows:Chapter 1 introduces the research background of TEM and the research significance of transient electromagnetic special signal source. Then,the development history and technology of signal generator are discussed. Finally,according to the requirements of this subject, the design index of the system is put forward.In chapter 2, we analyse theoretically the principle and characteristics of transient electromagnetic signal, establish the simulation model of transient electromagnetic signal, analyse the characteristics of the main noise affecting the transient electromagnetic signal, and research the effects of unmanned helicopter on transient electromagnetic receiver through the analysis of field measured data, establish the corresponding matlab simulation model, which lays a theoretical foundation for the development of transient electromagnetic special signal source.Chapter 3 introduces the principle of DDS, proposes the system design scheme based on SOPC by scheme comparison. We expound the design of phase accumulator and SRAM controlling switch, design the DAC and LPF circuit with high speed D/A ISL5961 and high slew rate amplifiers THS4271, and elaborate the design of power supply circuit.In chapter 4, PC software based on LabVIEW is designed and we introduce the function and design method of waveform data module, display module and dealing with parameters module.In chapter 5, firstly, the test scheme of the system is proposed. We test the ripple of the power supply and execute the function simulation of FPGA internal module with the principle of bottom-up. Finally, we test the whole system. The experimental results show that the anticipated function is achieved.Through these researches that is beneficial to reduce the cost of testing experiment of transient electromagnetic receiver and it is of great significance to improve the receiver’s performance index and calibrate the receiver.