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Microstrip Patch Sensor for Salinity Determination

Research Institute, Kyungwon Co. Ltd., Siheung 15084, Korea
Department of Ocean System Engineering, Jeju National University, Jeju 690-756, Korea
Department of Electrical Engineering, National University of Computer and Emerging Sciences, Foundation for Advancement of Science and Technology (NUCES-FAST), H 11/4, Islamabad 44000, Pakistan
Author to whom correspondence should be addressed.
Sensors 2017, 17(12), 2941;
Received: 21 November 2017 / Revised: 11 December 2017 / Accepted: 15 December 2017 / Published: 18 December 2017
(This article belongs to the Section Physical Sensors)
PDF [5145 KB, uploaded 18 December 2017]


In this paper, a compact microstrip feed inset patch sensor is proposed for measuring the salinities in seawater. The working principle of the proposed sensor depends on the fact that different salinities in liquid have different relative permittivities and cause different resonance frequencies. The proposed sensor can obtain better sensitivity to salinity changes than common sensors using conductivity change, since the relative permittivity change to salinity is 2.5 times more sensitive than the conductivity change. The patch and ground plane of the proposed sensor are fabricated by conductive copper spray coating on the masks made by 3D printer. The fabricated patch and the ground plane are bonded to a commercial silicon substrate and then attached to 5 mm-high chamber made by 3D printer so that it contains only 1 mL seawater. For easy fabrication and testing, the maximum resonance frequency was selected under 3 GHz and to cover salinities in real seawater, it was assumed that the salinity changes from 20 to 35 ppt. The sensor was designed by the finite element method-based ANSYS high-frequency structure simulator (HFSS), and it can detect the salinity with 0.01 ppt resolution. The designed sensor has a resonance frequency separation of 37.9 kHz and reflection coefficients under −20 dB at the resonant frequencies. The fabricated sensor showed better performance with average frequency separation of 48 kHz and maximum reflection coefficient of −35 dB. By comparing with the existing sensors, the proposed compact and low-cost sensor showed a better detection capability. Therefore, the proposed patch sensor can be utilized in radio frequency (RF) tunable sensors for salinity determination. View Full-Text
Keywords: microstrip patch sensor; salinity; relative permittivity; resonance frequency; sensitivity microstrip patch sensor; salinity; relative permittivity; resonance frequency; sensitivity

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Lee, K.; Hassan, A.; Lee, C.H.; Bae, J. Microstrip Patch Sensor for Salinity Determination. Sensors 2017, 17, 2941.

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