Karki Dolendra, Khanikar Tulika, Mullurkara Suraj V, Naeem Khurram, Hong Jun Young, Ohodnicki Paul
Mechanical Engineering & Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States.
Electrical and Computer Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States.
ACS Appl Nano Mater. 2024 Nov 23;7(23):26894-26906. doi: 10.1021/acsanm.4c04912. eCollection 2024 Dec 13.
The AC magnetic field response of the superparamagnetic nano-ferrofluid is an interplay between the Neel and Brownian relaxation processes and is generally quantified via the susceptibility measurements at high frequencies. The high frequency limit is dictated by these relaxation times which need to be shorter than the time scale of the time varying magnetic field for the nano-ferrofluid to be considered in an equilibrium state at each time instant. Even though the high frequency response of ferrofluid has been extensively investigated for frequencies up to GHz range by non-optical methods, harnessing dynamic response by optical means for AC magnetic field sensing in fiber-optic-based sensors-field remains unexplored. Instead, the incorporation of nano-ferrofluid as sensing materials has been only limited to DC magnetic field sensing, often citing their long response time as a limiting factor to AC field sensing. This work reports the finding of high frequency (up to 15 kHz) AC magnetic field sensing capability of nanomagnetic fluid as the cladding material of a fiber-optic multimode interferometry (MMI) structure optimized for the fourth self-imaging spectral response. The key parameter enabling high frequency response is the short response time (<1 ms) achieved by optimizing both the sensing structure and nano-ferrofluid solution. Focus has been imparted on 60 Hz line-frequency profiles of various current/magnetic fields to test the efficacy of these sensors in metering and monitoring current and current-induced magnetic fields in the electrical power grid systems. The magnetic field sensitivity of 240 mV/Gauss per dBm of transmitted power was achieved for 60 Hz field applied via Helmholtz coil, whereas the 60 Hz AC current sensitivity of 2.83 mV/A was measured due to magnetic field induced by current in a straight conducting wire.
超顺磁性纳米铁磁流体的交流磁场响应是尼尔弛豫和布朗弛豫过程之间的相互作用，通常通过高频下的磁化率测量来量化。高频极限由这些弛豫时间决定，对于纳米铁磁流体在每个时刻处于平衡状态而言，这些弛豫时间需要短于时变磁场的时间尺度。尽管通过非光学方法对高达吉赫兹范围的频率下铁磁流体的高频响应进行了广泛研究，但利用光学手段在基于光纤的传感器场中进行交流磁场传感的动态响应仍未得到探索。相反，将纳米铁磁流体用作传感材料仅局限于直流磁场传感，通常将其长响应时间视为交流场传感的限制因素。这项工作报道了作为光纤多模干涉仪（MMI）结构包层材料的纳米磁性流体具有高达15 kHz的高频交流磁场传感能力的发现，该结构针对第四次自成像光谱响应进行了优化。实现高频响应的关键参数是通过优化传感结构和纳米铁磁流体溶液实现的短响应时间（<1 ms）。重点关注了各种电流/磁场的60 Hz工频分布，以测试这些传感器在计量和监测电网系统中的电流及电流感应磁场方面的功效。对于通过亥姆霍兹线圈施加的60 Hz磁场，实现了每分贝毫瓦发射功率240 mV/高斯的磁场灵敏度，而由于直导线中电流感应的磁场，测量得到的60 Hz交流电流灵敏度为2.83 mV/A。
