[1] [1] H. Canbolat, “A novel level measurement technique using three capacitive sensors for liquids,” IEEE Transactions on Instrumentation and Measure, 2009, 58(10): 3762-3768.

[2] [2] B. Kumar, G. Rajita, and N. Mandal, “A review on capacitive-type sensor for measurement of height of liquid level,” Measurement and Control, 2014, 47(7): 219-223.

[3] [3] V. E. Sakharov, S. A. Kuznetsov, B. D. Zaitsev, I. E. Kuznetsova, and S. G. Joshi, “Liquid level sensor using ultrasonic lamb waves,” Ultrasonics, 2003, 41(4): 319-322.

[4] [4] F. Lucklum and B. Jakoby, “Non-contact liquid level measurement with electromagnetic-acoustic resonator sensors,” Measurement Science and Technology, 2009, 20(12): 314-317.

[5] [5] D. Royer, L. Levin, and O. Legras, “Liquid level sensor using the absorption of guided acoustic waves,” IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 1993, 40(4): 418-421.

[6] [6] D. Li, Y. Gong, and Y. Wu, “Tilted fiber Bragg grating in graded-index multimode fiber and its sensing characteristics,” Photonic Sensors, 2013, 3(2): 112-117.

[7] [7] A. F. Obaton, G. Laffont, C. Wang, A. Allard, and P. Ferdinand, “Fiber Bragg gratings and phase sensitive-optical low coherence interferometry for refractometry and liquid level sensing,” Sensors and Actuators A Physical, 2013, 189(2): 451-458.

[8] [8] C. W. Lai, Y. L. Lo, W. F. Liu, and J. P. Yur, “Simultaneous measurement of liquid level and specific gravity based on fiber Bragg grating sensors,” Proc. SPIE , 2009, 7503: 75033T.

[9] [9] C. Yu, L. Liu, X. Chen, Q. Liu, and Y. Gong, “Fiber-optic Fabry-Perot hydrogen sensor coated with Pd-Y film,” Photonic Sensors, 2015, 5(2): 142-145.

[10] [10] T. Lü and S. Yang, “Extrinsic Fabry-Perot cavity optical fiber liquid-level sensor,” Applied Optics, 2007, 46(18): 3682-3687.

[11] [11] W. Wang and F. Li. “Large-range liquid level sensor based on an optical fiber extrinsic Fabry-Perot interferometer,” Optics and Lasers in Engineering, 2014, 52(1): 201-205.

[12] [12] J. N. Wang and C. Y. Luo, “Long-period fiber grating sensors for the measurement of liquid level and fluid-flow velocity,” Sensors, 2012, 12(4): 4578-4593.

[13] [13] A. A. Kazemi, C. Yang, and S. Chen, “Fiber optic cryogenic liquid level detection system for space applications,” Proc. SPIE, 2009, 7314: 73140A.

[14] [14] Y. Huang, B. Chen, G. Chen, H. Xiao, and S. U Khan, “Simultaneous detection of liquid level and refractive index with a long-period fiber grating based sensor device,” Measurement Science and Technology, 2013, 24(9): 95303-95312.

[15] [15] M. Bottacini, N. Burani, M. Foroni, F. Poli, and S. Selleri, “All-plastic optical-fiber level sensor,” Microwave and Optical Technology Letters, 2005, 46(6): 520-522.

[16] [16] H. Golnabi, “Design and operation of a fiber optic sensor for liquid level detection,” Optics and Lasers in Engineering, 2004, 41(5): 801-812.

[17] [17] Y. L. Hou, W. Y. Liu, S. Su, H. X. Zhang, J. W. Zhang, J. Liu, et al., “Polymer optical fiber twisted macro-bend coupling system for liquid level detection,” Optics Express, 2014, 22(19): 23231-22241.

[18] [18] A. W. Snyder and J. D. Love, “Optical waveguide theory,” Chapman and Hall, 1983, 12(3): 1-37.

[19] [19] G. Durana, J. Zubia, J. Arrue, G. Aldabaldetreku, and J. Mateo, “Dependence of bending losses on cladding thickness in plastic optical fibers,” Applied Optics, 2003, 42(6): 997-1002.

[20] [20] F. P. Zanella, D. V. Magalhaes, and M. M. Oliveira, “Frustrated total internal reflection: a simple application and demonstration,” American Journal Physics, 2003, 71(5): 494-496.

[21] [21] K. Rahnavardy, V. Arya, A. Wang, and J. M. Weiss, “Investigation and application of the frustrated-total-Internal-reflection phenomenon in optical fibers,” Applied Optics, 1997, 36(10): 2183-2187.

[22] [22] A. A. Stahlhofen, “Photonic tunneling time in frustrated total internal reflection,” Physical Review A, 2001, 98(62): 1108-1115.

[23] [23] J. Y. Han, “Low-cost multi-touch sensing through frustrated total Internal reflection,” in ACM Symposium on User Interface Software and Technology, Seattle, U. S. A., pp. 115-118, 2005.

[24] [24] M. Lomer, A. Quintela, M. Lopez-Amo, J. Zubia, and J. M. Lopez-Higuera, “A quasi-distributed level sensor based on a bent side-polished plastic optical fibre cable,” Measurement Science and Technology, 2007, 18(7): 2261-2267.

[25] [25] C. Zhao, L. Ye, J. Ge, J.Zou, and X. Yu, “Novel light-leaking optical fiber liquid-level sensor for aircraft fuel gauging,” Optical Engineering, 2013, 52(1): 177-182.

[26] [26] K. E. Romo-Medrano and S. N. Khotiaintsev, “An optical-fiber refractometric liquid-level sensor for liquid nitrogen,” Measurement Science and Technology, 2006, 17(5): 998-1004.

[27] [27] B. Dong, Q. Zhao, J. Lu, T. Guo, L. Xue, S. Li, et al., “A digital liquid level sensor system based on parallel fiber sensor heads,” Proc. SPIE, 2007, 6595: 659541.