Design, Fabrication, and Impedance Characterization of a Capacitance-Based Salinity Sensor for Marine Applications

We report on the fabrication and electrochemical impedance characterization of a parallel plate capacitance sensor for ocean water salinity monitoring. The standard printed circuit board PCB fabricated and assembled sensor shows excellent response to changes in salinity with a sensitivity of 3.3 k /PSU. Use of the standard PCB process, necessitated by the requirement of low cost and ease of fabrication, posed challenges such as electrode corrosion and fouling. We investigated two polymeric materials as possible electrode passivation coatings, Novolac resin polymer Novolac and a proprietary commercial organic polymer Accuflo . By performing electrochemical impedance spectroscopy EIS and electrical equivalent-circuit-based model fitting, we show that Accuflo has better stability and passivation characteristics in comparison with Novolac. The pore resistance of Accuflo was found to be 3 orders of magnitude higher than that of Novolac, which indicates that Accuflo is relatively less porous than Novolac. Optical observations of the Accufloand Novolac-coated sensors after 48 h of immersion in ocean water show that Accuflo maintains its structural integrity, whereas Novolac is severely compromised and the underlying electrode has undergone corrosion, in agreement with EIS analysis. This confirms that Accuflo is a better choice as an electrode coating for underwater applications. © 2008 The Electrochemical Society. DOI: 10.1149/1.2981045 All rights reserved.