高压密封舱与磁场传感器的综合频响变异及其实验验证

大地电磁测深在陆地上的方法技术成熟, 但将其移植到海洋中却遇到了较多的技术问题.其中之一是如何将磁场传感器运抵海底实施测量.为抵御海水的侵蚀和抗衡海下的环境压力, 需要研发装载磁场传感器的密封舱.该舱体需满足测磁的技术要求, 即制造材料的非磁性, 且兼顾海洋作业设备轻便的特点.LC4超硬铝合金在可选的材料中性价比居高, 然而用它制成的高压密封舱并非十分完美.因它的弱磁性, 使得磁场传感器装入舱体后, 整体频率响应发生了部分变异.这种变异虽不影响磁场传感器的使用, 但要对其规律特征予以测定, 方能剔除由此产生的对磁场测量的不良影响.在所构思的实验装置中, 通过人为产生扫频磁场, 对密封和非密封条件下的磁场传感器进行激励.在响应输出端, 测取幅频特性和相频特性, 获得归一化的对比资料和频响异常曲线, 从而对密封前后磁场传感器的性能变化有较清楚的认识.实验结果揭示, 由高压密封舱引起的频响变异发生在中高频区段.实验数据可作为标定资料, 对海底大地电磁探测的实测信号进行校正后, 即可还原出真实的海底场源信息. 

Experimental Verification and Research for the Distortion in the Integrated Frequency Responses of the Sealed Pressure Case and Magnetic Field Sensor

Although the magnetotelluric sounding method applied to land is mature, many technical problems arise when they are transplanted into the seafloor environment, one of which is how to put magnetic field sensors down to the seafloor to complete measurements. To protect magnetic field sensors from intense erosion and high pressure, suitable sealed pressure cases must be designed. Considering the magnetic measurement and seafloor operation, the sealed pressure case should be nonmagnetic and transportable. Among all optional materials, LC4 super-hard aluminum alloy has the highest performance to price ratio. However, it doesn′t mean that the sealed pressure case made by LC4 will be perfect in performance. In fact, because of its weak magnetism, the pressure case made by LC4 has distorting effect on frequency responses of the magnetic field sensors sealed in it. This distorting effect doesn′t affect the use of the magnetic field sensor, but if we want to eliminate its impact, we should study it through experimental measurements. In our experimental tests, we used frequency swept magnetic field as excitation signal, and then measured responses of the magnetic field sensor before and after being loaded into the sealed pressure case. Ultimately, we obtained normalized abnormal curves for the frequency responses, through which we could reveal how the sealed pressure case impacts the responses of the magnetic field sensor. Experiment results suggest that the response distortion induced by the sealed pressure case appears in the mid and high frequency area. Using experiment results as standardized data, the frequency responses collected by seafloor magnetotelluric measurements can be corrected to produce authentic information about the seafloor field source.