• 센서학회지
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• 제31권2호
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• pp.120-124
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• 2022

With advancements in underwater stealth technology for naval vessels, new sensor configurations for detecting targets have been attracting increased attention. Latest underwater mines adopt multiple sensor configurations that include electric field sensors to detect targets and to help acquire accurate ignition time. An underwater electric field sensor consists of a pair of electrodes, signal processing unit, and preamplifier. For detecting underwater electric fields, the preamplifier requires low-noise amplification at ultra-low frequency bands. In this paper, the specific requirements for low-noise preamplifiers are discussed along with the experimental results of various setups of matched transistors and chopper stabilized operational amplifiers. The results showed that noise characteristics at ultra-low frequency bands were affected significantly by the voltage noise density of the chopper amplifier and the number of matched transistors used for differential amplification. The fabricated preamplifier was operated within normal design parameters, which was verified by testing its gain, phase, and linearity.

• 센서학회지
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• 제31권1호
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• pp.45-50
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• 2022

Multi-rod type Ag-AgCl electrodes have been developed for use in underwater electric field sensors. The developed cylindrical electrode had a diameter of 50 mm and a height of 130 mm. The electrode had five Ag-AgCl rods with a diameter of 2 mm and a height of 80 mm to enlarge the reaction surface area. Each Ag-AgCl rod was fabricated under the same conditions as the usual anodizing method in an electrolyte. The two developed electrodes were placed in the center of a 500-mm long, 400-mm wide, and 300-mm high acrylic tank filled with artificial seawater, at an interval of 100 mm, to evaluate their characteristics as uniaxial underwater electric field sensors. The underwater external electric field was generated using titanium plate electrodes installed at both ends of the tank. The noise level at 1 Hz of the developed electrode was approximately 3.7 nV/√Hz. The reception of the underwater electric field signal using the developed electrode was linear, within an error of approximately 0.6 %, in the range of 1-10000 ㎶/m at 1 Hz. In addition, its frequency response was flat within an error of 1.1 % in the range of 1-1000 Hz at 10000 ㎶/m.

• 센서학회지
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• 제31권5호
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• pp.330-336
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• 2022

This paper proposes a method to calibrate the electrode misplacement in underwater electric field sensor arrays (EFSAs) for accurate measurements of underwater electric field signatures. The electrode misplacement of an EFSA was estimated by measuring the electric field signatures generated by a known electric source and by comparing the measurements with the theoretical calculations under similar measurement conditions. When the EFSA measured the electric field signatures induced by an unknown electric source, the electric properties of the unknown electric source were approximated by considering the optimized estimation of the electrode misplacement of the EFSA. Finally, the measured electric field signatures were calibrated by calculating the theoretical electric field signatures to be measured with an ideally installed EFSA without electrode misplacement; the approximated electric properties of the unknown electric source were also taken into account. Simulations were conducted to test the proposed calibration method. The results showed that the electrode misplacement could be estimated. Further, the electric field measurements and the electric field-based localization of underwater vessels became more accurate after the application of the proposed calibration method. The proposed method will contribute to applications such as the detection and localization of underwater electric sources, which require accurate measurements of underwater electric field signatures.