Sunderland Andrew, Ju Li, Blair David G, McRae Wayne, Veryaskin Alexey V
School of Physics, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia.
Rev Sci Instrum. 2009 Oct;80(10):104705. doi: 10.1063/1.3227237.
Magnetic gradiometers are tools for geophysical exploration. The magnetic gradient is normally calculated by subtracting the outputs of two total field magnetometers which are separated by a baseline. Here we present a unique device that directly measures magnetic gradients using only a single string as its sensing element. The main advantage of a direct string magnetic gradiometer is that only gradients can induce second harmonic string vibrations. A high common mode rejection ratio is thus naturally achieved without any balancing technique. Performance depends on the ability to dissipate heat while minimizing air damping. By combining high current, an elevated temperature and low pressure, we can easily achieve sensitivity of 0.18 nT/m/square root of Hz. Further increases in sensitivity can be attained by optimizing the sensing element. In this paper we present an in-depth study of the most critical parameters of the magnetic gradiometer. We describe the design for the next generation of sensor, which will reach the required sensitivity of 0.01 nT/m/square root of Hz using only 1 W of power. By combining a few single-axis magnetic gradiometer modules, it will be possible to deploy a full tensor magnetic gradiometer with more than sufficient sensitivity for airborne geophysical applications.
磁梯度仪是用于地球物理勘探的工具。磁梯度通常通过减去两个由基线隔开的总场磁力仪的输出值来计算。在此，我们展示了一种独特的装置，它仅使用一根弦作为传感元件就能直接测量磁梯度。直接弦式磁梯度仪的主要优点是只有梯度能引起弦的二次谐波振动。因此，无需任何平衡技术就能自然地实现高共模抑制比。其性能取决于在使空气阻尼最小化的同时散热的能力。通过结合高电流、升高的温度和低压，我们能够轻松实现0.18 nT/m/√Hz的灵敏度。通过优化传感元件可以进一步提高灵敏度。在本文中，我们对磁梯度仪最关键的参数进行了深入研究。我们描述了下一代传感器的设计，该传感器仅使用1瓦功率就能达到所需的0.01 nT/m/√Hz的灵敏度。通过组合几个单轴磁梯度仪模块，将有可能部署一种全张量磁梯度仪，其灵敏度足以满足航空地球物理应用的需求。
