Intensity-Based Fiber Optic Sensor Head ... - OSA Publishing

JTu4A.13.pdf

Advanced Photonics Congress (IPR, Networks, NOMA, PS, Sensors, SPPCom) © OSA 2017

Intensity-Based Fiber Optic Sensor Head Characteristic Using Twist Dual Cycling Bending Loss Sang-Jin Choi, Seong-Yong Jeong, and Jae-Kyung Pan Dept. of Electrical Eng. and Smart Grid Research Center, Chonbuk National Univ., Jeonju, Jeonbuk, 54896, Republic of Korea [email protected], [email protected], [email protected]

Abstract: Intensity-based fiber optic sensor (FOS) head consisting of steel wires and twist dual cycling bending optical fiber is proposed and experimentally demonstrated. The tensile strain and three-point flexural tests for the proposed FOS head are given. OCIS codes: (280.4788) Optical sensing and sensors; (060.2370) Fiber optics sensors

1. Introduction Intensity-based fiber optic sensors (FOSs) are important due to their simplicity and potential low cost, low weight, small size and electromagnetic immunity, as well as from a historical perspective as the first to be developed. They need a self-referencing characteristic to minimize the influences of long-term aging of source characteristics and to handle short-term fluctuations and their sensor head which converted measurands such as strain, pressure, or force into a corresponding optical intensity change [1,2]. Many intensity-based FOSs utilized the attenuation of optical power caused by bending induced mode conversion [3,4]. T. Abe et al. reported a strain sensor using twisted optical fibers which utilizes the optical power loss due to fiber curvature to measure the strain applied to fibers [5]. Recently, we had proposed a self-referencing intensity-based FOS with multipoint sensing characteristics [2] and a twist dual cycling bending structure for ingenerating an optical fiber bending loss, and simple structure [6]. In this paper, seven cases of the intensity-based FOS heads using twist dual cycling bending loss are made with the fiber reinforced plastic (FRP) coupon based on our previous work [6]. The performance of the manufactured FOS heads through the tensile strain and three-point flexural tests are given. Experimental results show that the sensitivities and the lengths of the proposed FOS with twist dual cycling bending structure could be adjustable by changing the steel wire radius, the number of steel wires, and the distance between steel wires. 2. Twist dual cycling bending loss for an optical fiber A macro-bending loss of an optical fiber includes the pure bending loss and the transitional bending loss. Based on our previous work [6], Fig. 1 shows the optical fiber bending length, 𝐿𝑤𝑖𝑟𝑒 , passing above and below the steel wire for the twist dual cycling bending structure, which is given by 𝐿𝑤𝑖𝑟𝑒 = 𝑅𝜃. When we have a twist dual cycling bending structure with steel wires of 𝑁𝑤𝑖𝑟𝑒 , optical fiber bending length 𝐿 is given as follows: 𝐿 = 2𝐿𝑤𝑖𝑟𝑒 𝑁𝑤𝑖𝑟𝑒 = 2𝑅𝜃𝑁𝑤𝑖𝑟𝑒 = 4𝑅𝑁𝑤𝑖𝑟𝑒 sin−1 (2𝑅/𝑑𝑤𝑖𝑟𝑒 )

(1)

where 𝑅 is the bending radius adding the steel wire radius, 𝑅𝑤𝑖𝑟𝑒 , and optical fiber radius, 𝑅𝑓𝑖𝑏𝑒𝑟 , 𝜃 = 2 sin−1 (2𝑅/𝑑𝑤𝑖𝑟𝑒 ), and 𝑑𝑤𝑖𝑟𝑒 is the distance between steel wires. The optical fiber pure bending loss, 𝐿𝑠 , according to 𝐿 and 𝑅 is given as follows [3]: 𝐿𝑠 =

𝐴𝐿 √𝑅

× exp(−𝐵𝑅)

(2)

where A and B are determined by optical fiber parameters [3]. Equations (1) and (2) show that the optical fiber pure bending loss increases with increasing R𝑤𝑖𝑟𝑒 and 𝑁𝑤𝑖𝑟𝑒 and with decreasing 𝑑𝑤𝑖𝑟𝑒 . Optical fiber

Steel wire /2 /2

Fig. 1. Schematic diagram of the twist dual cycling bending structure for an optical fiber.

/2

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Table I. Manufactured seven cases of the proposed FOS heads and measured sensitivities through tensile strain and three-point flexural tests. Tensile strain test Three-point flexural test Sensor Insertion R𝑤𝑖𝑟𝑒 𝑑𝑤𝑖𝑟𝑒 Average Average Average Average Average Average FOS heads length 𝑁𝑤𝑖𝑟𝑒 loss (dB) sensitivity (mm) (mm) sensitivity error sensitivity sensitivity error (mm) (dB/kN) (dB/mm) (dB/𝜇𝜀) (N, 𝜇𝜀) (dB/𝜇𝜀) (𝜇𝜀) Case 1-1 1.00 6 14 110 2.43 1.33 0.00294 34.2, 15.5 1.76 0.00300 26.6 Case 1-2 1.00 6 14 110 2.89 1.35 0.00299 24.9, 11.3 1.78 0.00301 23.1 Case 2-1 0.75 6 14 110 1.17 0.70 0.00155 45.1, 20.4 0.94 0.00160 22.6 Case 2-2 0.75 6 14 110 1.65 0.76 0.00168 30.1, 13.6 0.93 0.00159 20.4 Case 3-1 1.50 6 14 110 9.93 3.99 0.00883 41.1, 18.6 6.27 0.01068 18.2 Case 3-2 1.50 6 14 110 9.98 3.83 0.00847 46.9, 21.2 6.55 0.01117 22.9 Case 4-1 1.00 4 14 82 2.43 1.00 0.00221 42.0, 19.0 1.38 0.00235 42.6 Case 4-2 1.00 4 14 82 2.56 1.02 0.00226 21.9, 9.9 1.45 0.00247 16.9 Case 5-1 1.00 8 14 138 2.80 2.40 0.00531 32.1, 14.5 2.98 0.00507 16.3 Case 5-2 1.00 8 14 138 3.35 2.35 0.00520 20.4, 9.2 3.09 0.00526 21.3 Case 6-1 1.00 6 12 100 5.24 2.58 0.00571 57.7, 26.1 3.29 0.00562 23.9 Case 6-2 1.00 6 12 100 5.27 2.50 0.00553 51.8, 23.4 3.24 0.00553 17.6 Case 7-1 1.00 6 16 120 1.42 1.05 0.00232 57.5, 26.0 1.12 0.00191 17.1 Case 7-2 1.00 6 16 120 1.61 1.09 0.00241 55.1, 24.9 1.19 0.00202 24.8

3. Experiments and results To evaluate the proposed FOS head performance, we made two samples for seven cases of the intensity-based FOS heads shown in Table I, which consist of the steel wires and the standard single mode optical fiber on the FRP coupon surface based on our previous work [6]. We measured the manufactured FOS heads bending loss according to the tensile strain and the flexural strain as follows. 3.1 Tensile strain test To test the tensile strain performance for the manufactured FOS heads, we measured the optical power loss versus the applied load five times for every manufactured FOS heads. Tensile strain test was done under load control mode using an universal testing machine (UTM) with tensioning at a constant loading rate of 20 N/s and the maximum load of 4.5 kN. The tensile load of 4.5 kN is equivalent to approximately tensile strain of 2,000 𝜇𝜀 for our FRP coupons. Fig. 2 shows the measured optical power loss versus applied load for the manufactured FOS sensor heads from Table I at three conditions as follows: (a) R𝑤𝑖𝑟𝑒 = 0.75, 1.00, and 1.50 mm, 𝑁𝑤𝑖𝑟𝑒 = 6, 𝑑𝑤𝑖𝑟𝑒 = 14 mm; (b) 𝑁𝑤𝑖𝑟𝑒 = 4, 6, and 8, R𝑤𝑖𝑟𝑒 = 1.00 mm, 𝑑𝑤𝑖𝑟𝑒 = 14 mm; (c) 𝑑𝑤𝑖𝑟𝑒 = 12, 14, and 16 mm, R𝑤𝑖𝑟𝑒 = 1.00 mm, 𝑁𝑤𝑖𝑟𝑒 = 6. Fig. 2 (a), (b), and (c) show that the average sensitivities increase with increasing steel wire radius, with increasing number of steel wires, and with decreasing the distance between steel wires, respectively, as expected in equations (1) and (2). The measured average sensitivities and errors for seven cases of the manufactured FOS heads are shown in Table I. The average errors of measured tensile strain are less than 26.1 με, which shows the feasibility of the proposed intensity-based FOS sensor head. From Fig. 2 and Table I, we can see that the sensitivities and the lengths of the proposed FOS heads could be adjustable by changing the steel wire radius, the number of steel wires, and the distance between steel wires. 3.2 Three-point flexural strain test To test the flexural strain performance for the FOS heads in Table I, we measured the optical power loss versus the applied cyclic loads with triangle shaped deflection for every FOS heads. The flexural strain test was performed under cyclic loading mode using an UTM with loading roller move at a constant loading rate is 0.04 mm/s and the maximum Case 1-2 reference curve

Case 2-1 reference curve




(b)

10.0

15.0

= 1.50 mm

10.0

= 1.00 mm

= 0.75 mm

5.0

12.0







(c)

10.0

=8

8.0

=6

6.0

12.0

Optical power loss (dB)



20.0


(a)

4.0

2.0







= 12 mm

8.0

6.0

= 14 mm 4.0

2.0

=4 0.0

= 16 mm

0.0 0.5

1.0

1.5

2.0

2.5

3.0

Applied load (kN)

3.5

4.0

4.5

0.0 0.5

1.0

1.5

2.0

2.5

3.0

Applied load (kN)

3.5

4.0

4.5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Applied load (kN)

Fig. 2. Measured optical power loss versus applied load (tensile strain) for the manufactured FOS sensor heads from Table I. (a) R𝑤𝑖𝑟𝑒 = 0.75, 1.00, and 1.50 mm, 𝑁𝑤𝑖𝑟𝑒 = 6, 𝑑𝑤𝑖𝑟𝑒 = 14 mm; (b) 𝑁𝑤𝑖𝑟𝑒 = 4, 6, and 8, R𝑤𝑖𝑟𝑒 = 1.00 mm, 𝑑𝑤𝑖𝑟𝑒 = 14 mm; (c) 𝑑𝑤𝑖𝑟𝑒 = 12, 14, and 16 mm, R𝑤𝑖𝑟𝑒 = 1.00 mm, 𝑁𝑤𝑖𝑟𝑒 = 6.

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10.0 9.0

16.0

8.0

14.0

12.0 10.0

= 0.75 mm

= 1.00 mm

= 1.50 mm

8.0 6.0 4.0 2.0

(c) =4

7.0

=8

=6

6.0 5.0 4.0 3.0 2.0 1.0

0.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0

Deflection of the FRP coupon (mm)

Deflection of the FRP coupon (mm)

Case 1-1 ref erence curve Case 2-2 ref erence curve



10.0

= 12 mm

8.0

= 14 mm 6.0

= 16 mm 4.0 2.0

0.0

0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0

0.0

12.0




0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0 1.0 2.0 3.0 2.0 1.0 0.0

(b)

18.0


20.0



(a)


Deflection of the FRP coupon (mm) Case 1-1 ref erence curve Case 6-2 ref erence curve



Fig. 3. Measured optical power loss versus deflection of the FRP coupon (three-point flexural strain) for the manufactured FOS sensor heads from Table I. (a) R𝑤𝑖𝑟𝑒 = 0.75, 1.00, and 1.50 mm, 𝑁𝑤𝑖𝑟𝑒 = 6, 𝑑𝑤𝑖𝑟𝑒 = 14 mm; (b) 𝑁𝑤𝑖𝑟𝑒 = 4, 6, and 8, R𝑤𝑖𝑟𝑒 = 1.00 mm, 𝑑𝑤𝑖𝑟𝑒 = 14 mm; (c) 𝑑𝑤𝑖𝑟𝑒 = 12, 14, and 16 mm, R𝑤𝑖𝑟𝑒 = 1.00 mm, 𝑁𝑤𝑖𝑟𝑒 = 6.

deflection of 3.0 mm. Both of the loading and supporting rollers have diameters of 10 mm and the loading roller moves to the vertical direction. When the deflection is applied to the FRP coupon up to the maximum of 3.0 mm, the calculated flexural strain is 1,760 𝜇𝜀 for our FRP coupons. Fig. 3 shows the measured optical power loss versus deflection of the FRP coupon for the manufactured FOS sensor heads from Table I at three conditions as follows: (a) R𝑤𝑖𝑟𝑒 = 0.75, 1.00, and 1.50 mm, 𝑁𝑤𝑖𝑟𝑒 = 6, 𝑑𝑤𝑖𝑟𝑒 = 14 mm; (b) 𝑁𝑤𝑖𝑟𝑒 = 4, 6, and 8, R𝑤𝑖𝑟𝑒 = 1.00 mm, 𝑑𝑤𝑖𝑟𝑒 = 14 mm; (c) 𝑑𝑤𝑖𝑟𝑒 = 12, 14, and 16 mm, R𝑤𝑖𝑟𝑒 = 1.00 mm, 𝑁𝑤𝑖𝑟𝑒 = 6. Also, Fig. 3 (a), (b), and (c) show that the average sensitivities increase with increasing steel wire radius, with increasing number of steel wires, and with decreasing the distance between steel wires, respectively, as shown in Fig. 2. From Fig. 3 and Table I we can see that the sensitivities and the lengths of the proposed FOS heads could be adjustable by changing the steel wire radius, the number of steel wires, and the distance between steel wires. 4. Conclusions An intensity-based FOS head using twist dual cycling bending loss was proposed and experimentally demonstrated. To get the performance of the proposed FOS heads, two samples for seven cases of the intensity-based FOS heads shown in Table I were manufactured. The manufactured FOS heads bending loss according to the tensile strain and the flexural strain were measured with using an UTM. Also, the bending loss characteristics according to the interval between steel wires, wire radius, and number of steel wires were given. From the tensile strain and the flexural strain tests, we can the average sensitivities of the manufactured FOS heads increase with increasing steel wire radius, with increasing number of steel wires, and with decreasing the distance between steel wires. So, the sensitivity and sensor length of the proposed FOS structure could be adjustable by changing the steel wire radius, the number of steel wires, and the distance between steel wires. 〈Acknowledgment〉 This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2016R1D1A1A09917117) 5. References [1]

S. S. Yin, P. B. Ruffin, and F. T. S. Yu, Fiber optic sensors 2nd ed. (CRC Press: Boca Raton, Fla, USA, 2008), Chap. 1

[2]

S. J. Choi, Y. C. Kim, M. Song, and J. K. Pan, “A self-referencing intensity-based fiber optic sensor with multipoint sensing characteristics,” Sensors 14, 12803-12815, (2014)

[3]

J. Qiu, D. Zheng, K. Zhu, B. Fang, and L. Cheng, “Optical Fiber Sensor Experimental Research Based on the Theory of Bending Loss Applied to Monitoring Differential Settlement at the Earth-Rock Junction,” Journal of Sensors 2015, 1-13, (2015)

[4]

W. H. Lu, L. W. Chen, W. F. Xie, and Y. C. Chen, “A Sensing Element Based on a Bent and Elongated Grooved Polymer Optical Fiber,” Sensors 12, 7485-7495 (2012)

[5]

T. Abe, Y. Mitsunaga, and H. Koga, “A Strain Sensor Using Twisted Optical Fibers,” J. of Lightwave Technology 7, 525-529 (1989)

[6]

S. J. Choi and J. K. Pan, “Twist Dual Cycling Bending Loss Characteristic for FRP Sensing Element,” in OSA Advanced Photonics Congress 2016 (Optical Society of America. Vancouver, Canada, 2016), pp. JTu4A-20.