Transient Electromagnetic Transmitting System Design Based On Multi-turn And Small Coil

In the process of tunnel construction of highways, railways and mineral extraction, water and mud outburst is the major geological disasters that affect the speed of construction and threat the engineering safety of construction.The Transient Electromagnetic Method(TEM) is commonly used as forecasting methods in ahead electromagnetic detection of tunnels and mines’ complex and small space. It has important engineering application value.For tunnels and mines’ complex and small space, the environment is crowded that it has difficulties for coil laying and construction. We tend to use a multi-turn and small coil technology, to ensure transient electromagnetic emission’s magnetic moment unchanged, by increasing the number of emission turns to achieve the reduction of transmit coil’s side. However, the small size and multi-turn of the coil is often associated with larger inductance. It results that the off-time of emission current in the coil is longer, the off-edge is poor linearity, and the current tail is often accompanied by overshoot or shock. These phenomenon led to the inaccurate data for the shallow interpretation. Therefore, how to design a transient electromagnetic transmitting system based on multi-turn and small coil is essential.In the application of small multi-turn coil antenna, the existing transient electromagnetic transmitters often have problems. Emission current’s frequency is single. Off-time is very long. Waveform tail has overshoot or shock. It couldn’t be well compatible with different receivers machine in the requirements of synchronization signal. The measurement of off-time is inaccurate And it couldn’t observe the emission current’s waveform in the real-time. They can not meet the actual requirements of the project as large volume and low protection level.This paper presents a transient electromagnetic transmitting system based on multi-turn and small coil. Analysis the theory of constant voltage clamping and damping matching absorption. We designed an emission current waveform shaping circuit. A launching bridge parallel across power regulator. The transmitter coil ends are in parallel with adjustable matching resistor. By certain clamping voltage and load coils, adjusting the matching resistance’s value, we can achieve emission current has a short turn-off time, good linearity, no overshoot or shutdown purposes shock. For MSP430F149 MCU system’s problems, we designed a low-power embedded PC as the core of operation control, LabVIEW as the development software, programmable logic devices CPLD as a timing generator unit. The USB capture card collect the emission current to ensure the accuracy of the timing signal, friendly of the man-machine interface. While meeting the real-time observation of the emission current waveform, we can easily adjust the matching resistance value in different environments, to improve the emission current waveform. We designed a new synchronization circuit, so as to be compatible with the internal and external trigger synchronization signal. solve the above-mentioned deficiencies of the prior art. At the same time we design the structure of the instrument system, so as to have the light volume and high degree of protection features.After designing the transient electromagnetic transmitting system based on multi-turn and small coil, this paper make a comparison test for the instrument systems and indoor and outdoor test verification. Test results show that the design of the transient electromagnetic transmitting system is reasonable. The performance has been improved over existing instrument systems, to meet the multi-turn and small coil application’s requirement.