The Design Of Transient Electromagnetic Receiver Based On Sample Integral Method

Transient electromagnetic method, also known as time-domain electromagneticmethod, is a method based on electromagnetic induction principle to prospect thedistribution of geologic structures in the subsurface. The transmitter transmitspulsed magnet field to the underground which is called the primary field. Meanwhile,the receiver observes the secondary field during the emission gap, which is theresponse excited by the primary field. The secondary field contains rich informationabout the geologic structures in the subsurface. Through extraction processing andanalysis of the secondary field information, the distribution can be detected. TEM iswidely used in the field of mineral exploration due to its high efficiency and littlerequirement on the terrain.This paper aimed to design a transient electromagnetic receiver, which couldeffectively extract the late transient electromagnetic signals drowned in noise.Through the research and analysis of the transient electromagnetic signals and noisecharacteristics, sample integral has been chosen to detect weak signals in latetransient electromagnetic signals, combined with other means in order to furtherreduce the effects of noise. The core of this receiver was sample integral circuitwhich the design of this transient electromagnetic receiver based on. This receiverhas adjustable magnification,4integral channels,8kinds of integral resistance andother characteristics. FPGA was applied as a controller to this receiver, and thecontrol logic was explained in the paper. USB was applied as a communicationinterface between the device and the host.The paper described the method of usingdevelopment kit to write the USB firmware and driver. The host computer interfacewas written in NI-VISA functions based on LABVIEW platform. It could control thedevice, receive and save the data through the interface.Finally, the receiver has been tested including the hardware test and the PCsoftware test. The test results were analyzed and explained the influence on theresults of sample integral with different parameters. According to the test results, itis feasible and efficient to extract the late signal of transient electromagnetic methodby using the sample integral. The design of this receiver was accomplished andachieved the desired goals through learning theories, designing hardware circuit,programming software and testing the whole system.