Development Of Time-Domain Borehole Radar Transmitting And Receiving System

High detection efficiency,strong anti-interference ability,and high resolution are provided by borehole radar,a ground-penetrating radar used in boreholes.More intuitive results can also be obtained.Geological information of 10-40m near boreholes can be provided by it and it is widely used in groundwater,mining exploration,nuclear waste disposal,and goaf detection.To improve the two most important indicators of borehole radar,which are detection distance and resolution,the transmitting pulse amplitude needs to be increased to several kV in the transmitting system and the pulse width needs to be changed to the ns level.The echo signal received by the borehole radar system has a large bandwidth and narrow pulse width.If the echo signal is collected using a real-time sampling method,an ADC with a high sampling rate is required.However,this leads to a low resolution of ADC,increased data storage pressure,and development cost.To solve these problems,the following work has been completed through in-depth research from the following three aspects:1)Transmitting System:The research work was mainly completed in three factors.Firstly,the main parameters of the pulse signal were determined by analyzing the pulse signal in the time and frequency domains.Secondly,the working principle of the avalanche transistor circuit was analyzed,and the unipolar pulse generation circuit,bipolar pulse generation circuit,and MARX cascade circuit based on the avalanche transistor were designed and simulated.Finally,after the optimization and simulation of component parameters,the final design index was determined based on the pulse amplitude and bandwidth demand.Thirdly,the circuit schematic diagram was used to draw PCB,and the physical circuit was welded and tested.A bipolar pulse with a peak-to-peak value of 200 V and a pulse width of 20 ns could be generated by the avalanche transistor circuit,whereas a negative vibration with an amplitude of 1500 V and a pulse width of 20 ns could be caused by the MARX cascade circuit.2)Receiving System:The research work was mainly completed in three factors.Firstly,the ADC sampling rate requirements were reduced by using equivalent sampling technology.This helped solve the contradiction between a high sampling rate and low resolution and also reduced the development cost and data storage pressure.Secondly,a receiving system comprising of a four-tube balanced sampling gate circuit,sampling pulse circuit,and stepping delay circuit was designed based on the equivalent sampling technology.The four-tube balanced sampling gate circuit and sampling pulse circuit were analyzed using circuit simulation software.The delay chip required by the stepping delay circuit was then selected,and the program for configuring the internal register of the chip was written.Finally,the circuit schematic diagram was used to draw PCB,and the actual circuit was made and tested.The signal was broadened in the time domain by the sampling gate circuit,while the stepping delay circuit allowed stepping in 1 ns increments.The sampling pulse circuit generated a positive pulse with an amplitude of 8 V and a pulse width of 1.4 ns and a negative pulse with an amplitude of 7.8 V and a pulse width of 1.4 ns.The echo signal function was realized using equivalent sampling technology.3)Front-end Receiving System:A low-pass filter with a cut-off frequency of 164 MHz,a passive bandpass filter with a bandwidth of 54-193 MHz,and a low-noise amplifier module with a bandwidth of 50-750 MHz and gain of 15 dB are made.Finally,a joint practical test was conducted on the transmitting and receiving system.The test results showed that microsecond signals were obtained after the nanosecond range signals were converted using equivalent sampling.These results verified that the transmitting and receiving system developed in this thesis can be applied to borehole radar systems.The developed transmitting and receiving systems in this thesis are designed using discrete components,which greatly reduces the design complexity and development costs compared to digital integrated circuits.The research objective of this thesis is to improve the detection depth and resolution of the transmitting and receiving systems of the borehole radar and solve the problems faced in practical engineering.Through practical testing,good results have been achieved,providing strong technical support for the application and promotion of borehole radar.