Magnetostrictive composite–fiber Bragg grating (MC–FBG) magnetic field sensor
Highlights
► A magnetostrictive composite–fiber Bragg grating (MC–FBG) magnetic field sensor based on the direct coupling of the magnetostrictive strain in an epoxy-bonded Terfenol-D particle pseudo-1–3 MC actuator with a FBG strain sensor has been developed. ► The quasistatic peak wavelength has been found to shift appropriately linear in accordance with the quasistatic magnetostrictive strain characteristics of the MC bar and by as much as 0.68 nm under a relatively small magnetic field of 146 kA/m, giving a high quasistatic peak wavelength shift sensitivity of about 4.66 × 10−3 nm/kA/m and a large quasistatic magnetostrictive strain sensitivity of about 3.4 ppm/kA/m. ► A wide extrinsic magneto-optical signal frequency range in excess of 60 kHz has been demonstrated and found to be almost 60 times larger than state-of-the-art MA–FBG magnetic field sensors based on monolithic Terfenol-D MA as a result of reduced eddy-current losses in the MC. ► These attractive quasistatic and dynamic performances, in conjunction with the alleviated brittleness, weight, shape and cost problems intrinsic in the MA–FBG sensors, make our MC–FBG sensor great promise for long-distance and distributed magnetic field or electric current sensing.
Introduction
Fiber Bragg grating (FBG) sensors have become an important class of sensing device for long-distance and distributed sensing of various types of physical parameters such as strain, pressure, temperature, etc. in a broad domain of industrial fields [1], [2]. However, FBG sensors fall short of any magnetic field sensing because of their inherently weak magneto-optical Faraday effect [3]. Recently, it has been demonstrated that a FBG can be bonded onto a monolithic Terfenol-D (Tb0.3Dy0.7Fe1.92) magnetostrictive alloy to form a magnetostrictive alloy–FBG (MA–FBG) sensor for magnetic field or electric current sensing [4], [5], [6], [7], [8]. In the reported sensor design, the MA functions as a magnetic actuator with magnetostrictive strain as the output, while the FBG operates as a strain sensor with the magnetostrictive strain from the MA as the input. Compared to conventional non-optical magnetic field or electric current sensors such as Hall-effect sensors and reluctance coils [9], this type of MA–FBG sensor features a high level of immunity to electromagnetic interference, a great potential for large-scale multiplexing and a large capability for self-reference [4], [5], [6], [7], [8]. Unfortunately, since the monolithic Terfenol-D MA used in the reported sensor design is an excellent conductor with an extremely low electrical resistivity of about 0.6 μΩ cm, operation of monolithic Terfenol-D MA and its associated devices above a few kilohertz is significantly limited by the presence of eddy-current losses [10], [11]. Another crucial problems associated with monolithic Terfenol-D MA are high mechanical brittleness, heavy weight (density as high as 9250 kg/m3), limited shape variety and high material cost [11].
In this paper, we present results on the fabrication and evaluation of a magnetostrictive composite–FBG (MC–FBG) magnetic field sensor developed using an epoxy-bonded Terfenol-D particle pseudo-1–3 MC as a magnetic actuator and a FBG as a strain sensor. This MC-based FBG sensor not only possesses a large quasistatic peak wavelength shift of 0.68 nm at an applied magnetic field of 146 kA/m and a wide extrinsic magneto-optical signal frequency range in excess of 60 kHz, but also alleviates the brittleness, weight, shape and cost problems intrinsic in state-of-the-art MA-based FBG sensors.
Section snippets
Sensor structure and fabrication
Fig. 1 shows the schematic diagram of the proposed MC–FBG magnetic field sensor formed by bonding a FBG onto a bar-shaped MC. The MC bar was fabricated in-house using Terfenol-D magnetostrictive particles with randomly distributed sizes of 10–300 μm in at least one dimension (Gansu Tianxing Rare Earth Functional Materials Co., Ltd., China) as the active phase and Spurr epoxy with a dynamic viscosity of 60 mPa s at room temperature (Polysciences, Inc., PA) as the passive phase. Predetermined
Performance evaluations
Fig. 2 shows the experimental setup for evaluating the quasistatic and dynamic performances of the MC–FBG magnetic field sensor. The MC–FBG sensor was placed between the pole gap of a C-shaped high-frequency electromagnet, and the whole sensor-electromagnet assembly was situated between the pole gap of a C-shaped, water-cooled, low-frequency electromagnet (Mylten PEM-8005 K) to receive the stimulus of magnetic fields in the longitudinal direction of the sensor (also along the length direction of
Results and discussion
Fig. 4 shows the quasistatic peak wavelength of the MC–FBG magnetic field sensor and the corresponding magnetostrictive strain of the MC bar under an applied quasistatic magnetic field (H) with the maximum amplitude of 146 kA/m and a frequency of 1 Hz. In the absence of H, the magnetostrictive strain of the MC bar is essentially zero and there is no shift in the peak wavelength of the FBG in the MC–FBG sensor. When an H is used, the magnetostrictive strain from the MC bar will be directly coupled
Conclusion
We have developed a novel MC–FBG magnetic field sensor consisting of a Spurr epoxy-bonded Terfenol-D particle pseudo-1–3 MC bar as a magnetic actuator and a FBG as a strain sensor. The quasistatic peak wavelength has been found to shift appropriately linear in accordance with the quasistatic magnetostrictive strain characteristics of the MC bar and by as much as 0.68 nm under a relatively small magnetic field of 146 kA/m, giving a high quasistatic peak wavelength shift sensitivity of about 4.66 × 10
Acknowledgments
The work was supported by The Hong Kong Polytechnic University under Central Research Grants (1-ZV7P and G-YE16) and the Research Grants Council of the HKSAR Government (PolyU 5266/08E).
Heliang Liu received the BSc degree in physics from Nankai University, China, in 1997 and the Ph.D. degree in electrical engineering from The Hong Kong Polytechnic University (PolyU) in 2005. He was a research associate in the Department of Electrical Engineering at PolyU from 2005 to 2006, working on fiber Bragg grating (FBG) sensors. He has been a senior optical engineer in the R&D group of JDSU Shenzhen, China. Dr Liu's research interests include erbium-doped fiber amplifiers and lasers,
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Heliang Liu received the BSc degree in physics from Nankai University, China, in 1997 and the Ph.D. degree in electrical engineering from The Hong Kong Polytechnic University (PolyU) in 2005. He was a research associate in the Department of Electrical Engineering at PolyU from 2005 to 2006, working on fiber Bragg grating (FBG) sensors. He has been a senior optical engineer in the R&D group of JDSU Shenzhen, China. Dr Liu's research interests include erbium-doped fiber amplifiers and lasers, reconfigurable optical add/drop multiplexers (ROADMs), micro-electro-mechanical system (MEMS)-based optical devices, and FBG and fiber-optic sensor systems.
Siu Wing Or received the BSc (First Class Honors), MPhil and PhD degrees in engineering physics from The Hong Kong Polytechnic University (PolyU) in 1995, 1997 and 2001, respectively. He was a teaching company associate, a R&D electronic engineer and a senior R&D electronic engineer in ASM Assembly Automation Ltd., Hong Kong, from 1995 to 2001. He then worked as a postdoctoral research fellow in the Mechanical and Aerospace Engineering Department at the University of California, Los Angeles, USA, for 1.5 years before he joined PolyU as a lecturer in the Department of Applied Physics in 2002. Dr Or is currently an associate professor and the director of Multifunctional Materials and Systems Laboratory in the Department of Electrical Engineering at PolyU. He is also a senior member of IEEE and a member of ASME. His research interests include multifunctional materials, smart devices and systems, condition and health monitoring, energy harvesting and storage, ultrasonics and vibrations, and automation and precision equipment. He has published two professional book chapters, 125 SCI journal papers and 45 international conference papers in addition to the award of 39 patents.
Hwa Yaw Tam received the BSc and Ph.D. degrees in electrical and electronic engineering from The University of Manchester, UK, in 1985 and 1990, respectively. He was a research scientist and a senior research scientist in Hirst Research Center of GEC-Marconi Ltd., UK, from 1989 to 1993. He also worked as a consultant to Marconi-Italiana, Italy, in 1992. Prof. Tam joined the Department of Electrical Engineering at the Hong Kong Polytechnic in 1993. He is currently the chair professor of photonics in the Department of Electrical Engineering at The Hong Kong Polytechnic University (PolyU) and the director of Photonics Research Center at PolyU. He is a senior member of IEEE, a member of IET and a Chartered Engineer. His research interests include fabrication of special optical silica and polymer fibers, fiber Bragg gratings (FBGs), FBG- and photonic crystal fiber-based sensor systems, fiber amplifiers, optical fiber communications, and all-optical signal processing. He has published over 450 technical papers and awarded/applied about 20 patents.