SQUID Systems for Geophysical Time Domain Electromagnetics (TEM) at IPHT Jena
SQUID Systems for Geophysical Time Domain Electromagnetics (TEM) at IPHT Jena
复制标题
DOI：
10.1587/transele.e98.c.167
复制
发表时间：
2015-03
期刊：
影响因子：
--
通讯作者：
A. Chwala;R. Stolz;M. Schmelz;V. Zakosarenko;M. Meyer;H. Meyer
中科院分区：
文献类型：
--
作者：
A. Chwala;R. Stolz;M. Schmelz;V. Zakosarenko;M. Meyer;H. Meyer
超导量子干涉仪（SQUID）首次应用于地球物理目的40年后，它们最近已成为矿产勘探的重要工具。最常见的应用之一是时域（或瞬态）电磁学（TEM），这是一种有源方法，测量从地面到表面回路中变化电流（主要是矩形）的感应响应。在发射器线圈中的电流被切换之后，在地面中激发涡电流，涡电流以取决于下面的地质结构的导电性的方式衰减。在关闭时间期间，通过接收器线圈（感应电压）或磁力计（例如SQUID或磁通门）测量表面处产生的次级磁场。通过叠加正、负衰减，改善了记录的瞬态信号质量。或者，TEM结果可以被反转，并给出地面在深度上的电导率。由于SQUID以高灵敏度和恒定频率传递函数测量磁场，因此与传统感应线圈相比，SQUID显示出上级性能，尤其是在存在强导体的情况下。由于初级场，特别是其转换速率，是相当大的，SQUID系统需要有一个大的转换速率和动态范围。任何通量跳跃都将使标准叠加算法无法使用。IPHT和Supracon正在开发和生产基于低温超导体（LTS，在我们的案例中是铌）的SQUID系统，这是目前最先进的技术。由于需求量大，我们还提供高温超导体（HTS，在我们的案例中是YBCO）系统。虽然低温SQUID系统具有更好的性能（噪声和转换速率），但高温SQUID系统更容易在现场操作。与感应线圈相比，SQUID的上级性能是探测大深度良导体或导电覆盖层下矿体的最重要因素。
SUMMARY Forty years after the first application of Superconducting Quantum Interference Devices (SQUIDs) [1], [2] for geophysical purposes, they have recently become a valued tool for mineral exploration. One of the most common applications is time domain (or transient) electromagnetics (TEM), an active method, where the inductive response from the ground to a changing current (mostly rectangular) in a loop on the surface is measured. After the current in the transmitter coil is switched, eddy currents are excited in the ground, which decay in a manner dependent on the conductivity of the underlying geologic structure. The resulting secondary magnetic field at the surface is measured during the off-time by a receiver coil (induced voltage) or by a magnetometer (e.g. SQUID or fluxgate). The recorded transient signal quality is improved by stacking positive and negative decays. Alternatively, the TEM results can be inverted and give the electric conductivity of the ground over depth. Since SQUIDs measure the magnetic field with high sensitivity and a constant frequency transfer function, they show a superior performance compared to conventional induction coils, especially in the presence of strong conductors. As the primary field, and especially its slew rate, are quite large, SQUID systems need to have a large slew rate and dynamic range. Any flux jump would make the use of standard stacking algorithms impossible. IPHT and Supracon are developing and producing SQUID systems based on low temperature superconductors (LTS, in our case niobium), which are now state-of-the-art. Due to the large demand, we are additionally supplying systems with high temperature superconductors (HTS, in our case YBCO). While the low temperature SQUID systems have a better performance (noise and slew rate), the high temperature SQUID systems are easier to handle in the field. The superior performance of SQUIDs compared to induction coils is the most important factor for the detection of good conductors at large depth or ore bodies underneath conductive overburden.