瞬变/谐变一体化的大地电磁收发线圈设计

Design of magnetotelluric transmitter and receiver coils with the integration of transient and harmonic electromagnetic method

采用瞬变电磁法和谐变电磁法仪器观测地下空间数据并进行融合处理,能够提高探测成像能力,然而现有的瞬变电磁法和谐变电磁法仪器独立成套,必须配置多套仪器分次采集。设计了一种可满足瞬变/谐变两种模式使用的小型、大带宽、高灵敏度大地电磁收发线圈,为便携、浅层高分辨的瞬变/谐变一体化电磁探测系统开发奠定基础。首先,建立了空心线圈传感器等效电路模型,分析了线圈传感器的灵敏度和噪声特性,制作的传感器经过测试表明,在1125 Hz处,灵敏度为23.12 mV/nT,等效磁噪声9.27 pT/√Hz,传感器带宽1 Hz~100 kHz;然后,通过公式和有限元软件对传感线圈偏心放置时收发耦合进行了计算,确定了收发线圈组合的最佳耦合位置,计算和仿真结果与实际位置分别相差0.21%和0.17%,有效对消了发射磁场(一次场)。构建了时间域和频率域电磁法探测系统,测试表明,设计的瞬变/谐变一体化收发线圈能够满足时间域和频率域电磁法两种探测模式使用。

The use of transient electromagnetic method and harmonious electromagnetic method instrument to observe the underground space data and perform fusion processing can improve the detection imaging ability,but most of the existing transient electromagnetic method and harmonious electromagnetic method instruments are independent sets and must be equipped with multiple sets to separate collection.A small size,large bandwidth and high sensitivity electromagnetism transceiver coil that can meet the use of both transient/harmonic modes is designed to lay the foundation for the development of portable,shallow and high resolution transient/harmonic integrated electromagnetic detection system.First,the equivalent circuit model of the air-core coil sensor is established,and the sensitivity and noise characteristics of the coil-core sensor are analyzed,the test results of the air-core sensor show that at 1125 Hz,the sensitivity is 23.12 mV/nT,the equivalent magnetic noise is 9.27 pT/√Hz and the bandwidth is 1 Hz~100 kHz.Then,the formula and finite element analysis software are used to calculate the transceiver coupling relation when the sensor coils are placed eccentrically,and the optimal eccentric location of the combination of transceiver coil is determined,the calculation and simulation results differ from actual location by 0.21%and 0.17%respectively,which effectively eliminated the launch magnetic field(primary field).Finally,the time-domain and frequency-domain electromagnetic method systems are constructed,and the test results show that the designed transient/harmonic integrated transceiver coil can meet the needs of time-domain and frequency-domain electromagnetic detection modes.