Ocean electric field electrode

Category: Industrial Measurement and Ocean Exploration

Time：2025-12-18

Fueled by national marine development strategies and international expansion drives, China’s marine science and technology have seen rapid progress in recent years. As an emerging technique for marine geological research and resource exploration, marine electromagnetic exploration has gained growing attention among domestic research circles.

Marine electric field electrodes are the key sensing elements for this technology. Their sensitivity and stability directly govern the in-situ performance of electromagnetic exploration systems.

Electrodes are indispensable to marine electric field detectors. Thanks to their high stability and low self-noise, Ag/AgCl electrodes are widely adopted for marine signal detection.

Figure 1: Marine Electromagnetic Exploration

Mechanism of Ocean Electric Field Generation
An electric field is defined as a voltage gradient along a given direction within a medium. In marine environments, flowing seawater currents generate electric fields. Owing to the electrical resistance of seawater, a stable voltage gradient forms naturally. Currently, measurable ocean electric fields range from quasi-DC to several kilohertz in frequency. Such fields derive from a variety of natural and anthropogenic sources.
Natural Sources
Seawater movement
Large-scale seawater movements produce electric fields of varying amplitude and frequency. Ocean turbulence and internal waves also contribute to electric field generation.
Geomagnetic field variations
The Earth’s magnetic field consists of static and time-varying components. Changes in the geomagnetic field induce currents in seawater and further generate electric fields.
Submarine mineral deposits
Seabed minerals trigger electrochemical reactions on their surfaces, which give rise to electric fields.
Seismic activity
Electric fields occur during the entire process of earthquakes. However, the exact mechanisms behind earthquake-related electric field generation have not been fully clarified.
Marine biological activity
Among all natural sources, marine biological activities produce the weakest electric fields with the smallest coverage.
Anthropogenic Sources
Human activities at sea are the main source of artificial marine electric fields, including subsea pipeline deployment, offshore oil exploration and maritime transportation. Vessels are sophisticated engineered systems equipped with extensive technical devices. Whether stationary or underway, their hulls and propellers interact with seawater and induce electric fields, known as ship-generated electric fields. These fields mainly result from electrochemical corrosion, passive and active cathodic protection systems, magnetic line cutting during navigation, and fluctuations in spatial magnetic flux.
Overview of Ocean Electric Field Sensors
An ocean electric field sensor comprises two core parts: sensing electrodes and a signal acquisition and processing system. The performance of sensing electrodes directly determines the accuracy of electric field measurements.
The detection principle is to capture electric field signals by measuring the potential difference between two sensing electrodes. The acquired signals are amplified and denoised before being transmitted to data acquisition devices.
Like the Earth’s inherent electric field, ocean electric fields propagate through physical contact. Seawater acts as a weak electrolyte, where electric current is carried by ion migration. Lower-frequency signals suffer less energy attenuation, so most detectable ocean electric field signals fall within the low and extremely low frequency ranges.
Ocean electric field signals are extremely weak, typically measured in microvolts (μV). Moreover, sensing electrodes are deployed in marine environments for long-term operation. For this reason, marine electric field electrodes must meet the following requirements:
Low noise
Low inherent noise improves electrode resolution and signal-to-noise ratio. Excessively high intrinsic noise may obscure target signals or distort signal waveforms. Electrode drift is a vital indicator for evaluating the practicality of electric field sensors and a key metric of electrode sensitivity.
High pressure resistance
Subsea electrodes operate under far higher hydrostatic pressure than land-based electrodes. Pressure increases by 101 kPa with every 10 meters of water depth. Electrodes must maintain stable performance under high pressure; inadequate mechanical strength will easily cause structural damage.
Long-term stability
Marine environments are complex, and signal collection often lasts for extended periods. Attachment of microorganisms, algae and other marine organisms can lead to signal fluctuations. Poor electrode stability will further aggravate measurement errors.
High measurement sensitivity
Electrodes need high sensitivity to low and extremely low frequency electric field signals, while minimizing signal attenuation on the electrode surface.
Advantages of Greentek’s Ocean Electric Field Electrodes
In response to the rigorous requirements for subsea electric field detection, Greentek has developed dedicated ocean electric field sensors based on its independently patented technology. These sensors feature low self-noise, high measurement sensitivity, excellent durability and reliable long-term stability.
Manufactured via powder compaction and sintering, the electrodes form a micrometer-scale porous microstructure. This structure greatly expands the electrochemical interface and delivers superior overall performance. Sintered solid electrodes offer high mechanical strength and good machinability, making them much better suited than traditional glass electrodes for monitoring in high-pressure seawater environments.
1. Low Self-Noise and High Sensitivity
A two-electrode system under open-circuit conditions is used to test differential potential and baseline drift stability. Given the ultra-weak nature of ocean electric field signals, each pair of sensors must maintain stable differential potential. Otherwise, useful signals will be completely overwhelmed by noise.
Electrochemical noise refers to random non-equilibrium fluctuations of electrochemical parameters such as electrode potential and external current density over time. Such fluctuations stem from changes in electrode potential and current caused by interfacial reactions during sensor operation.
Intrinsic noise originates from within the electrochemical system. Its main causes include uneven activity of local anodic and cathodic reactions, ambient temperature changes, damage and restoration of surface passivation films, varying thickness of the diffusion layer, and bubble formation on electrode surfaces. Intrinsic electrochemical noise dominates at low frequencies and gradually declines as frequency increases.
Silver-silver chloride (Ag/AgCl) is a widely used reference electrode material, featuring high exchange current density, low polarization tendency, low impedance and slight potential drift. Traditional Ag/AgCl electrodes are produced through electrochemical or direct chlorination, yet their surface silver chloride coating is prone to wear, which impairs electrode stability and shortens service life.
Greentek’s powder-sintered electrodes adopt a specialized manufacturing process that greatly enlarges the effective active surface area and electric double-layer interface. The electrodes maintain stable reaction equilibrium even when measuring ultra-weak signals, ensuring consistent long-term potential stability. The uniform and well-distributed Ag/AgCl interface formed by our unique sintering process also effectively reduces electrochemical self-noise.

2. High compressive strength and excellent water tightness stability

Based on the application characteristics of the marine underwater environment, Greentek’s marine electric field electrode products ensure superior performance from multiple angles:

(1) By using encapsulation materials that are highly pressure-resistant, corrosion-resistant, and possess strong mechanical properties, as well as high-strength polytetrafluoroethylene as the outer casing material, we ensure that there will be no cracking or damage even in the high-pressure environment of the deep sea.

(2) Silver rods are used as the signal transmission bridge, with no other materials introducing new electrochemical reaction interfaces.

(3) The special structural design ensures both the relative stability of the electrode surface in the seawater environment, which helps maintain stable electrochemical performance characteristics, and the fluidity of the solution exchange between the inside and outside of the encapsulating shell.

GreenTech’s ocean electric field electrodes have received unanimous praise from users.

Greentek specializes in the development and design of non-polarized electrode sensors. The powder silver-silver chloride electrodes independently developed and designed by Greentek boast stable performance and hold an international leading edge in multiple key indicators—including extreme potential, self-noise, stability of electrode base drift, and electrode impedance. These electrodes are widely used by numerous marine and geophysical surveying organizations and have consistently received high praise from users.