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3. AC Magnetometry Using Nano-ferrofluid Cladded Multimode Interferometric Fiber Optic Sensors for Power Grid Monitoring Applications.

Author

Karki, Dolendra, Khanikar, Tulika, Mullurkara, Suraj V., Naeem, Khurram, Hong, Jun Young, and Ohodnicki, Paul

Abstract

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. [ABSTRACT FROM AUTHOR]

Published
2024
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8. Pd/PMMA Nanocomposite-Coated Optical Fiber Hydrogen Sensor Operating at Room Temperature With Humidity Tolerance

Author

Khanikar, Tulika, Karki, Dolendra, Su, Yang-Duan, Young Hong, Jun, Wang, Yuankang, Naeem, Khurram, and Ohodnicki, Paul R.

Abstract

A fiber-optic hydrogen sensor coated with a palladium/polymethyl methacrylate (Pd/PMMA) nanocomposite layer is fabricated and benchmarked here. The sensor with Pd/PMMA substituted cladding operates by intensity modulation technique through partial reflection in the sensing region. The in situ thermal reduction method has been adopted for nanocomposite synthesis due to the reduced processing steps required and to avoid material waste. Benefitting from the hydrogen selective response of Pd nanoparticles (NPs) and the filtering ability of the PMMA matrix, the sensor exhibits excellent resistance to humidity and good environmental stability in the presence of interfering gases. Furthermore, it can detect low hydrogen concentrations of down to 0.1%, shows suppressed hysteresis, and has a response time of 25 s to 4% hydrogen. All these features, combined with the feasible and cost-effective sensor preparation protocol, make the sensor a competitive candidate for hydrogen gas monitoring applications that operate at near room temperatures.

Published
2024
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