矿井瞬变电磁探测中空芯线圈传感器的研制

Research and development on the air-core coil sensor for mine transient electromagnetic exploration

针对矿井瞬变电磁法中探测空间的有限性及探测目标分布的全空间性,研制一种适合该方法的感应式空芯线圈传感器.根据矿井瞬变电磁探测需要,确定了感应式空芯线圈传感器的基本技术指标.通过对空芯线圈的物理结构和前置放大电路的等效噪声电路进行分析,获取了引入噪声的主要来源.构建感应式空芯线圈传感器的等效模型,实现传感器的幅频特性及低噪声的分析,给出影响传感器噪声水平的各噪声源随频率变化的规律,设计矿井瞬变电磁中降低传感器噪声的方法,采用该优化方法,传感器的总噪声在谐振频率处信噪比提高了15.6dB.测试结果表明:感应式空芯线圈传感器噪声性能和输出特性优于加拿大Geonics公司的3D-1HF-coil传感器,满足矿井瞬变电磁探测需要.

The interior space of mine is narrow,and many roadways′width and height are less than 2meters.At present,overlapping multi-turn device is mainly used in the mine transient electromagnetic method,of which the shape and area is not fixed,so it can not guarantee the correctness of the received signal.Its data processing and geological interpretation are essentially based on ground half-space transient electromagnetic method,which has many technical problems to be solved at the application level.For the limitation of the detection space and the whole space distribution of detected target in the mine transient electromagnetic method,this paper developed a kind of inductive air-core coil sensors suitable for this method.The effective area of the sensor at home and abroad meets the requirements of the mine,but the bandwidth is too narrow.And the blind spot is too long,which limits the scope of the mine transient electromagnetic detection.So it is significant to develop a kind of inductive sensor suitable for the mine transient electromagnetic detection.According to the needs of the mine transient electromagnetic detection,the basic technical indicators of the inductive air-core coil sensor are determined.By analyzing the physical structure ofthe air-core coil and the equivalent noise circuit of the pre-amplifier circuit,the main source of introduced noise is obtained.Constructing the equivalent model of inductive air-core coil sensor,we realize the analysis of the amplitude-frequency characteristics and low noise of the sensor,and give the regular pattern of each noise source which affects the noise level of sensor with frequency.The method of reducing the sensor noise in the mine transient electromagnetic detection is designed,with which the SNR（signal to noise ratio）of the sensor at the resonant frequency improves 15.6dB.Test results showed that the noise performance and output characteristics of inductive air-core coil sensor surpasses 3D-1HF-coil sensor of Canada′s Geonics,which meets the needs of mine transient electromagnetic detection.Inductive sensor has been used as a key component of transient electromagnetic receiving system,and its noise level determines the minimum resolution of the received signal directly,which affects the result of the detection.In the production of the air-core coil,a LCR equivalent model is established.Winding the coil hierarchically and segmentally can reduce the distributed capacitance and inductance of the coil,which thereby increases the resonant frequency and broadens the response bandwidth.Small size,wide bandwidth,large effective area and low noise inductive aircore coil sensors are designed for the whole space response of limited space inside the mine.In this paper,a air-core coil sensor with mean diameter of 0.6m,equivalent area of 30m2,bandwidth of700 kHz is produced based on the study of the equivalent model,frequency characteristics,and the noise model.