Fig.1 Basic Structure and Principle Diagram of the Deep-Sea Current Sensor Based on TENG

 Triboelectric Nanogenerator (TENG) Technology

The principle of TENG is that when different materials come into contact and then separate, charges accumulate on the surfaces of the materials, resulting in a voltage. This voltage difference causes a current to flow through an external circuit, converting the mechanical energy of the ocean currents into electrical energy. By designing the structure so that the voltage, current, and phase of the generated electricity correlate with the flow velocity, the device can measure flow velocity simultaneously with power generation. Using magnetic coupling for power transmission and a super-pressure-resistant casing design, they have developed the DS-TENG (Deep-Sea Triboelectric Nanogenerator) for deep-sea measurements.

This research was published online in the journal Nature Communications (Springer Nature, London) on Sunday, July 21, 2024.

https://doi.org/10.1038/s41467-024-50581-w

Background:

The deep sea (below 200 meters) is a world of darkness and extreme pressure, with currents that are deeply connected to various natural phenomena, making detailed observations extremely difficult. Therefore, the deep sea is often referred to as an enigmatic, unknown realm akin to outer space. A typical behavior of the deep sea is the conveyor belt-like circulation of seawater, where deep water formed in the North Atlantic and the Southern Ocean travels around the world's deep oceans over approximately 1500 years, rising to the surface in the North Pacific and Indian Oceans, and returning to the Polar Regions. This circulation plays a crucial role in natural phenomena such as global temperature and climate change, making it essential to understand the three-dimensional flow of ocean currents, including their vertical movement.

Moreover, in the abyssal zone (4000 ~ 6000 meters), there is a mechanism called the biological pump. This process involves the transport of microparticles and dissolved organic carbon from the atmosphere and ocean surface to the seabed. The biological pump significantly contributes to the transportation of nutrients necessary for the survival of deep-sea organisms. Understanding the direction, strength, and transport volume of the biological pump can help elucidate the mechanisms behind the birth, survival, and evolution of deep-sea life.

Furthermore, it is essential to understand the actual conditions of deep-sea currents for various applications, such as elucidating the spread of pollutants like plastics in the ocean, achieving carbon neutrality through the protection and restoration of blue carbon deep-sea ecosystems, and more.

Current issue:

To understand the actual conditions of deep-sea currents, direct velocity observations are effective, but comprehensive measurements on a global scale are extremely challenging. Therefore, numerical simulations are the most practical approach. However, creating numerical models requires basic data on deep-sea current velocities and their spatial distribution at various points. By constructing models based on this data and performing simulations, they can predict the behavior of deep-sea currents. To establish accurate numerical models, it is necessary to increase the number of measurement points and fully understand the assumed velocities and spatial distribution of deep-sea currents.

Previous research on ocean current sensing and monitoring has primarily utilized electromagnetic, acoustic, and mechanical instrumentation. However, electromagnetic sensors are easily disturbed by environmental magnetic factors, acoustic sensors are limited by rigid geometric structures, and current mechanical sensors have low pressure resistance and a narrow measurement range. Additionally, all these existing sensors require external power supplies, further limiting their ability to perform long-term measurements with high spatiotemporal resolution.

Therefore, to accurately elucidate the actual conditions of deep-sea currents, it is necessary to develop measurement devices that can operate autonomously for extended periods, at a lower cost, and with sufficient spatiotemporal resolution.

Proposed method:

To solve above issues, they aim to develop low-cost, compact, and long-term autonomous measurement devices for deep-sea current measurement on a global scale, especially in deep-sea environments where power supply is challenging. By utilizing the principles and structure of the TENG power generation devices they previously developed【1】【2】, they have successfully developed the DS-TENG, housed in an ultra-pressure-resistant casing of about 20 cm (45 MPa-75 MPa). The developed DS-TENG can measure flow velocity while generating power, correlating voltage and current with flow velocity. Since it enables autonomous power generation and measurement, it allows for long-term current velocity measurement and data accumulation as long as ocean currents are present.

1. https://doi.org/10.1016/j.matre.2024.100280
2. https://doi.org/10.1016/j.nanoen.2023.108240

Significance of this research:

The DS-TENG deep-sea current sensor developed in this study enables long-term high spatiotemporal-resolution simultaneous measurements and autonomous energy supply in deep-sea environments. This advancement is expected to play a crucial role in deep-sea research and environmental monitoring. Specifically, it can contribute to solving various marine issues, such as elucidating deep ocean circulation, advancing deep-sea life sciences, and understanding the dynamics and storage mechanisms of deep-sea blue carbon