Development Of A Large Dynamic Electromagnetic Signal Receiver Based On Logarithmic Amplification Technology

Ground-air transient electromagnetic method has the advantages of high detection efficiency,wide coverage area and low cost,it is widely used in geophysical exploration,Including ore body resources exploration,mined areas investigation,hydrological exploration,etc.In the development of transient electromagnetic receiving systems,to improve the sampling accuracy of the system and increase the dynamic range of the system measurement,the research on the electrical distribution of underground conductors is extremely important.However,there is a huge contradiction in the dynamic range of transient electromagnetic signals from the original signal to the final use for resistivity interpretation.Traditionally,the pursuit of a large dynamic range acquisition of hardware has led to a dynamic range that is subject to A/D,and data is greatly compressed in software.This design proposes that the large dynamic range signal be first hardware-compressed so that it is not subject to A/D and the dynamic range is increased.The following research was conducted on this technology.1?The influence of the matching resistance of the hollow core coil of the electromagnetic signal acquisition device on the working state was analyzed.At the same time,a measure of the parameters such as the bandwidth of the air-core coil was proposed.In order to increase the amplitude of the electromagnetic signal,a low-noise,gain-adjustable differential amplifier circuit was designed.2?By analyzing the necessity of large dynamic range measurements,reasonable design of logarithmic amplification technique was demonstrated,the logarithmic amplifier characteristics are simulated,the overall design of the bipolar electromagnetic signal logarithmic amplification module was finally realized.3?Three key techniques for logarithmic amplification of bipolar electromagnetic signals in electromagnetic signal acquisition devices were studied,the measurement of the logarithmic amplification module was completed,the final voltage signal was output as a linear change.The paper focuses on the analysis of the formation and calculation of internalnoise,and the acquisition's noise was around 7?V/Hz^1/2.4?The electromagnetic signal acquisition module was designed,the overall hardware design scheme of the electromagnetic signal acquisition module was given,and the key technology for high-precision acquisition of electromagnetic signals was proposed.Each part of the design module to determine the overall structure of the electromagnetic signal acquisition device was integrated.5?The comprehensive testing of large dynamic range electromagnetic signal acquisition devices was completed.The influence of the matching resistor on the working state of the air-core receiving coil was tested.The three parameters of the amplification module's consistency,dynamic range,and output linearity were tested.By analyzing the output error of the logarithmic amplification module,the system output linearity was similar to the theoretical output,and the error was less than 0.4%.The effect of the compensation capacitor on the output response was tested.The difference between the linear amplifier circuit and the logarithmic amplifier circuit was compared and analyzed.