Hybrid Opto-Mechanical Current Sensor Based on a ... - IEEE Xplore

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IEEE SENSORS JOURNAL, VOL. 14, NO. 4, APRIL 2014

Hybrid Opto-Mechanical Current Sensor Based on a Mach-Zehnder Fiber Interferometer Agliberto Melo Bastos, Jose Wally Mendonça Menezes, Alexei A. Kamshilin, and Antonio Sergio Bezerra Sombra

Abstract— In this paper, a new optical sensor based on a Mach-Zehnder interferometer, constructed with single mode optical fibers operating at 1.55 µm has been proposed and studied. The current sensing is obtained by mechanical perturbation applied to one of the single mode fiber, which constitutes the interferometer. This disturbance leads to an optical interference detected in the output of the interferometer and it is proportional to the magnitude of the current in the driver, measured with a reference sensor. The sensor has been tested with ac (60 Hz) up to 110 A. The obtained calibration curve presents a sensitivity between 0.8 and 1.54 mV/A. With a variation on the experimental arrangement, the sensor can be used in the monitoring of low and high amplitude currents. This new sensor can be efficiently used for monitoring the alternating electrical current in both small and large electric power suppliers and consumers.

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Index Terms— Optical sensor, Mach-Zehnder, interferometer.

I. I NTRODUCTION

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PTICAL current sensors (OCS) are achieving increased acceptance and use in high voltage substations due to their superior accuracy, bandwidth, dynamic range and inherent isolation. All-fiber current sensors (OCSs) are in general based on the Faraday magneto-optic effect and are more attractive considering that they present better optical integration than other OCSs solutions [1]–[3]. The all-fiber current sensor technology presents a simple experimental setup for fabrication and operation [4]. However, one disadvantage of the all-fiber current sensor is its low current sensitivity because of the Manuscript received May 31, 2013; revised November 21, 2013; accepted November 22, 2013. Date of publication November 27, 2013; date of current version February 14, 2014. This work was supported in part by CAPES, in part by CNPQ, and in part by ENDESA. The author A. A. Kamshilin thanks the Academy of Finland for financial support in the frames of the project 136881. The associate editor coordinating the review of this paper and approving it for publication was Dr. Anna G. Mignani. A. M. Bastos is with the Laboratory of Telecommunications and Materials Science and Engineering, Universidade Federal do Ceara, Fortaleza 60020, Brazil, and also with the Departamento de Teleinformatica, Laboratório Especializado em Sistemas de Telecomunicações e Ensino, Fortaleza 30000, Brazil (e-mail: [email protected]). J. W. M. Menezes is with the Departamento de Teleinformatica, Laboratório Especializado em Sistemas de Telecomunicações e Ensino, Fortaleza 30000, Brazil (e-mail: [email protected]). A. A. Kamshilin is with the University of Eastern Finland, Department of Applied Physics, Kuopio FIN-70211, Finland (e-mail: [email protected]). A. S. B. Sombra is with the Laboratory of Telecommunications and Materials Science and Engineering, Universidade Federal do Ceara, Fortaleza 60020, Brazil (e-mail: [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2013.2293180

(b) Fig. 1. (a) Experimental setup of the Hybrid Opto-Mechanical Current Sensor based in a Mach-Zehnder Fiber Interferometer. (b) Detail of the permanent magnet, optical fiber and the wire.

conventional silica fiber has a very low Verdet constant, and thus, a very long fiber is necessary to achieve a comparable sensitivity. Another problem is that the linear birefringence affects the sensor performance: since it reduces the Faraday effect in the fiber, which limits the maximum usable fiber length and therefore dimiinishes the sensitivity of the sensor. Another method of enhancing the sensitivity is the use of a doped fiber (Tb or Eu doping), which has a higher Verdet constant [5]. However, the use of a doped fiber increases the cost of the sensor as well as the temperature sensitivity because the Verdet constant is highly dependent on the temperature [6]. In this paper, we demonstrate a new current sensor setup based in a Hybrid Opto-Mechanical Mach-Zehnder Fiber Interferometer. The Mach-Zehnder Interferometer is constructed with single-mode optical fiber operating at 1.55 μm, where the current sensing is obtained by mechanical perturbation in

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BASTOS et al.: HYBRID OPTO-MECHANICAL CURRENT SENSOR

Fig. 2. Photograph of the experimental setup: permanent magnet is driven in a perpendicular direction to the magnetic inductive coil turns (6 mm diameter). The optical fiber (each arm of 18 cm of length) is fixed in the permanent magnet.

the single- mode fiber in one of the arms of the Interferometer. This disturbance leads to an optical interference detected in the output of the interferometer and it is proportional to the magnitude of the current in the wire, measured with a reference current sensor [7]–[12]. II. E XPERIMENT The experimental layout, is shown in Fig. 1, and it comprises a 1.55 μm CW diode laser (THORLABS S1FC1550 at 1.55 μm), two 3dB fiber couplers (OPTOLINK Co., Ltd.), one detector (Photodetector THORLABS Model PDA50B-EC, 800–1800nm ) and a system for digital signal processing. The choice of the laser operating at 1.55 μm is associated to the low loss of the optical fibers to this particular wavelength. The signals from the photodetector are measured and displayed by a Tektronix digital oscilloscope (TDS 2022B, 200 MHz, 2GS/s). The range of the alternating current (AC) in the experiment is 0–110 A. The light from the laser diode is divided between two arms of the interferometer by the first fiber coupler. In one of the arms, the fiber is fixed to a vibrating metal plate which is positioned in a distance D from the wire which is conducting the AC current (see Figs. 1 and 2). The perturbation is enhanced by a small permanent magnet attached to the vibrating plate (see Fig. 1). The mechanical perturbation imposed to the fiber is leading to an optical interference detected in the output of the interferometer and it is proportional to the magnitude of the current in the wire, measured with a reference sensor. III. T HEORETICAL R EVIEW The sensor performance was studied using a magnetic field, which was induced by a sinusoidal current (60Hz) which flowed in a copper magnetic inductive coil in a cone shape (Figs. 1 and 2). The magnetization of the permanent magnet is driven in a perpendicular direction to the magnetic inductive coil turns. Considering the distance D between the magnet and coil, the Lorentz force applied to the magnet is given by I ar , (1) 2π D 2 where I is the current flowing in the coil that induces the magnetic field in the radial direction from the turns of the coil. F = V B M

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V and B M are the volume and magnetization of the permanent magnet, respectively. The equation 1 gives us the expression of the Lorentz force that acts on the permanent magnet, as a function of current I and distance D. The oscillations of the metal plate which holds the magnet are induced by modulation of the Lorentz force, and they lead to periodical mechanical stress of the fiber. These mechanical deformations cause an axial tension which lead to a change of the fiber length in a non-uniform way. Therefore, the mechanical deformations cause a phase change in the light which propagates in the single-mode fiber (SMF) [13]. Since the length of the sensitive section of the SMF is much longer than the amplitude of forced cantilever oscillations, we may suggest that the strains (l/l) induced in the SMF are very small and elastic, and they are directly proportional to the force F applied to the cantilever. (2) l/l = K F . Here the proportionality coefficient K , considers the mechanical properties of the cantilever beam and SMF. It depends on: (i) the Young’s modulus of the fiber; (ii) static tensile stresses applied to SMF; (iii) the length l of the sensitive part of the fiber (between clamps); and (iv) the resonance frequency of the cantilever beam (the metallic plate with the attached permanent magnet and the SMF. The phase difference (φm ) induced into the propagating light through SMF is directly proportional to gl: 2πn (3) φm = K F l λ where n is the refractive index of the fiber and λ is the light wavelength. When an alternating current oscillating at the frequency fi induces a magnetic field, the force F which acts on the cantilever beam produces dynamic strains in the SMF with a periodicity of 1/ f I . The relevant equation for alternating current is I = I0 Si n (2π f i t) ,

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where I0 is the amplitude of the current and t is the time. After substituting Eq. 4 in Eq. 1 and then Eq. 1 in Eq. 3 we obtain 2πn sin (2π f i t) (5) φm = K I 0 V B M l λ D2 Considering V and B M as invariable parameters, one can deduce from Eq. 5, that the efficient conversion of AC current into the phase transient φm depends on the distance D and on the coefficient K . In our sensor small phase transients given by Eq. 4–5 are measured by means of the Mach-Zehnder interferometer. In any interferometer variations of the intensity of interfering beams PD (measured by the photo-detector) are proportional to the sinusoidal phase difference between the two arms: PD = PO + PR + 2 PO PR Cosφ With φ = φ0 + φm

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where PO and PR are the intensities of the transmitted object and the diffracted reference waves, respectively, and φ0 is the

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Fig. 4. Optical sensor response as a function of D (for current of 40A) and theoretical fitting according with equation 1 (hyperbolic profile). Parameters of the hyperbolic fitting are A = 418 and B = 4.71.

Fig. 3. (a) Optical sensor response compared with the conventional sensor for currents (15 to 110A) as a function of D (D = 1.5cm (black square), 2.5cm (red circle) and 4.0cm (green triangle) for currents between 10A to 60A and D = 2.4cm (blue triangle) and 5,0cm (blue square) for currents between 65A and 110A) Solid lines show the linear fitting with the experimental data. (b) sensor sensitivity associated to Fig. 3(a). TABLE I S ENSOR S ENSITIVITY AS A F UNCTION OF D ISTANCE D Fig. 5. Temporal profile of the optical pulses obtained with the optical sensor for the current of 40A as a function of the distance D (1.5cm, 2.5cm, 4.0cm).

mean phase shift between the two arms. Therefore according to Eq. 6, small transients φm are transferred into the intensity variations if the cosine function can be approximated by its argument. IV. R ESULTS AND D ISUSSION In Figs. 1 and 2 one can observe the experimental setup of Mach-Zehnder sensor, where one can identify the fiber couplers (3dB) and the laser diode (1.55 μm). The magnetic field of the AC current modulates the periodical strains of the SMF in the signal arm of the interferometer. This disturbance leads to an optical interference detected in the output of the interferometer and it is proportional to the magnitude of the current in the wire. In Fig. 3 and Table I one has a calibration curve for different currents and distances D between the cantilever beam and the electric wire. The calibration curves were obtained using a conventional current sensor with resolution of 1mA. In Fig. 3 one has the theoretical fitting of the measured points of the sensor, with an uncertainty around 0.5% of the full scale with different sensitivities (see Table I). The highest

sensitivity measured was of 1.54mV/A (see Fig. 3 and Table I). From Table I one can observe the obtained values of the sensitivity obtained from the linear fitting. In Fig. 3 one has the sensor operating in the range of 15 to 60A for three different values of D (D = 1.5cm, 2.5cm and 4.0cm). For all the studied distances the experimental data were well fitted with linear dependences. The sensitivity of the sensor is 1.54mV/A for D = 1.5cm and decreases to 1.27mV/A and to 0.79mV/A for D = 2.5 and D = 4.0cm. When operating in the range of 65 to 110A for three different values of D (D = 2.5cm and 5.0cm) the sensitivity of the sensor is 1.06mV/A (D = 2.5cm) and 0.77mV/A (D = 5.0cm). The decrease of the sensor sensitivity is expected considering the diminishing of the induced magnetic field with the distance between the wire and the optical fiber. Fig. 4 shows that the detected optical amplitude is a decreasing function of the distance from the sensor to the current line, as expected. In this figure one has readings for a current of 40A with the variation of distance D (1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 cm). It is observed that the curve presents a profile (Y α D −2 ), as expected (see equation 1). This is an indication that we can use the sensor for measurements of very high currents without any saturation effect, only increasing the distance from the sensor to the wire. In Fig. 5 one has the time profile of AC signal obtained from the sensor for a current of

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R EFERENCES

Fig. 6. Temporal profile of the optical pulses obtained with the optical sensor for different electric currents of 15A, 25A and 50A at the distance D = 4.0cm.

40A with variation of the distance D (1.5cm, 2.5cm, 4.0cm). One can observe that the amplitude of the signal modulation is diminishing when the distance between the wire and the sensor is increasing. Fig. 6 presents the temporal profiles of the detected signal, for a fixed distance (D = 4.0cm) but, for three different values of current (15, 25 and 50A). This is an indication that our sensor is capable for monitoring variations and fluctuations of the electric current which may occur in the power lines at real time. V. C ONCLUSION In conclusion, a new optical sensor based on a MachZehnder Interferometer, constructed with single mode optical fiber operating at 1.55 μm has been proposed and studied. The current sensing is obtained by a mechanical perturbation in the single mode fiber in one of the arms of the interferometer. This disturbance leads to an optical interference detected in the output of the interferometer and it is proportional to the magnitude of the current in the driver. The sensor has been tested with AC (60Hz) electric current up to 110A. The obtained calibration curve presents a sensitivity up to 1.54mV/A. The sensitivity is a decreasing function of the distance between the power line and the sensor, which is expected considering the variation of the induced magnetic field with the distance from the wire to the optical fiber sensor. The signal amplitude of the sensor is a decreasing function of the distance from the sensor to the current line. This is an indication that we can use the sensor for measurements of high currents without any saturation effect, only increasing the distance from the sensor to the current wire. The sensor provides a time profile of the signal in real time. One can observe that the sensor is very sensitive to the signal shape as a function current intensity and the current wire distance to the sensor. This is an indication of the sensitivity of the sensor in monitoring transients and fluctuations that may exist on the line at real time. With a variation on the experimental arrangement, the sensor can be used in the monitoring of low and high amplitude currents. This new hybrid opto-mechanical current sensor could be efficiently used for monitoring the time profile of periodic and/or aperiodic electrical current in both small and large electric power suppliers and consumers.

[1] Y. N. Ning, Z. P. Wang, A. W. Palmer, K. T. V. Grattan, and D. A. Jackson, “Recent progress in optical current sensing techniques,” Rev. Sci. Instrum., vol. 66, no. 5, pp. 3097–3111, May 1995. [2] K. Malmedal and P. K. Sen, “Potential of massively deployed sensors applications in substation engineering,” in Proc. IEEE 39th NAPS, Oct. 2007, pp. 259–265. [3] P. Zu, C. C. Chan, W. S. Lew, Y. Jin, Y. Zhang, H. F. Liew, et al., “Magnetooptical fiber sensor based on magnetic fluid,” Opt. Lett., vol. 37, no. 3, pp. 398–400, Feb. 2012. [4] J. D. P. Hrabliuk, “Optical current sensors eliminate CT saturation,” in Proc. IEEE PES Winter Meeting, vol. 2. Jan. 2002, pp. 1478–1481. [5] L. Sun, S. Jiang, and J. R. Marciante, “All-fiber optical magnetic-field sensor based on Faraday rotation in highly terbium-doped fiber,” Opt. Express, vol. 18, no. 6, pp. 5407–5412, Mar. 2010. [6] E. MacLean and V. K. Jain, “A power transmission line fault distance estimation VLSI chip: Design and defect tolerance,” in Proc. IEEE Int. Symp. DFT VLSI Nanotechnol. Syst., Oct. 2011, pp. 243–251. [7] R. Langenhorst, M. Eiselt, W. Pieper, G. Grosskopf, R. Ludwig, L. Kuller, et al., “Fiber loop optical buffer,” J. Lightw. Technol., vol. 14, no. 3, pp. 324–335, Mar. 1996. [8] F. A. Viawan, J. Wang, Z. Wang, and W.-Y. Yang, “Effect of current sensor technology on distance protection,” in Proc. IEEE PSCE, Mar. 2009, pp. 1–7. [9] C. Wang and S. T. Scherrer, “Fiber loop ringdown for physical sensor development: Pressure sensor,” Appl. Opt., vol. 43, no. 35, pp. 6458–6464, Dec. 2004. [10] H. Guerreiro, R. Pérez del Real, R. Fernández de Caleya, and G. Rosa, “Magnetic fiel biasing in Faraday effect sensors,” Appl. Phys. Lett., vol. 74, no. 24, pp. 3702–3704, Jun. 1999. [11] X.-J. Ni and M. Huang, “Faraday effect optical current/magnetic field sensors based on cerium-substituted yttrium iron garnet single crystal,” in Proc. IEEE APPEEC, Mar. 2010, pp. 1–4. [12] F. Maystre and A. Bertholds, “Magneto-optic current sensor using a helical-fiber Fabry–Pérot resonator,” Opt. Lett., vol. 14, no. 11, pp. 587–589, Jun. 1989. [13] M. Haapalainen, S. Di Girolamo, A. S. B. Sombra, and A. A. Kamshilin, “Novel fiber-optic sensor of high electrical alternating currents,” in Proc. AIP Conf., May 2013, pp. 107–114.

Agliberto Melo Bastos was born in Itapagé, Brazil. He received the B.Sc. degree in mathematics and the M.Sc. degree in electrical engineering from the Federal University of Ceará in 1983 and 2004.

Jose Wally Mendonça Menezes born in BaturitéCeará, Brazil, in 1970. He received the Ph.D. degree in physics from the Federal University of Ceará (UFC). He is a Professor of telecommunication engineering and the Graduate Program in telecommunications engineering from the Federal Institute of Education Science and Technology, Ceara (IFCE). He was a Researcher of LESTE/IFCE, GFAD/IFCE, and LOCEM/UFC. He works with applied physics to telecommunications, electromagnetics and optical devices.

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Alexei A. Kamshilin received the M.D. degree from Leningrad State University and the Ph.D. degree from the A.F. Ioffe Physical Technical Institute, Leningrad, Russia, in 1974 and 1982, respectively. His academic carrier started in 1974 in Russia, continued in Brazil, from 1990 to 1992, and since 1992, he has been researching and teaching in different universities of Finland. Since 2004, he has been a Professor with the University of Eastern Finland, Kuopio. His research interest includes nonlinear and coherent optics, photorefractive and photogalvanic effects, optical sensors technology, and adaptive interferometry and multispectral imaging for biomedical and industrial applications. He has published more than 160 papers in peer-reviewed journals and one monograph.


Antonio Sergio Bezerra Sombra was born in Jaguarauana, Brazil. He received the B.Sc. and M.Sc. degrees in physics from the Federal University of Ceará in 1981 and 1984, respectively, and the Ph.D. degree from the Federal University of Pernambuco in 1990. He is the Head of the Telecommunications and Materials Science and Engineering Laboratory, Physics Department, Federal University of Ceara. His research interest includes research and development in optical fiber and planar devices for optical networks. He is involved in the study of electric, dielectric, and piezoelectric properties of new ceramics and films for microwave and radio-frequency applications.