Abstract
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.
Highlights
Low-salinity water inflow into seawater has been a problem in the mass stranding of conch, abalone, farming fishes, etc
The ANSYS high-frequency structure simulator (HFSS) was utilized for full wave analysis of the proposed sensor design
The reflection coefficients were below −20 dB, which indicates that the load
Summary
Low-salinity water inflow into seawater has been a problem in the mass stranding of conch, abalone, farming fishes, etc. Sensors 2017, 17, 2941 sensors based on the alteration of electromagnetic field for measuring water conductivity are reported, which avoids periodic calibration [8]. These sensors have lower sensitivity and accuracy as compared to CTD, and suffer from erroneous data due to heat and small changes in the position of the sensor. Microstrip patch antennas are low-cost, low profile, lightweight, and easy to fabricate They have narrow bandwidth and sharp frequency response as well, which is useful for measuring a physical quantity when it is used as a sensor.
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