SHIELD

Swarm of Energy Harvesting Floaters for the Detection of Vessel threats

A project sponsored by the NATO Science for Peace and Security Programme under grant # G7646

Mission of the project

The acoustic detection of vessels or submarines by small low-cost devices connected to an Internet of Underwater Things (IoUT) offers a distributed sensing opportunity with easy deployment from moorings, vessels or air.

A key technology for IoUT is energy harvesting, as it enables unattended devices to extend their time of operation. We identify high potential in the acoustic ambient noise, which is broadly present in underwater scenarios.

In project SHIELD, we will design a novel swarm of energy-efficient IoUT floaters to detect vessels or submarines while extracting energy from transients of ambient noise via a dense array of polymer-based hydrophones. Our objective is to potentially extend operations time up to multiple months without need to charge batteries along this period, revolutionizing the underwater sensing paradigm.

Security Challenge

We target the security field of threat detection and renewable energy protection.

In particular, we focus on the defense of critical marine infrastructures such as gas rigs and underwater cables by unmanned underwater vehicles or by divers with motorized scooters.

Objectives

Design a passive acoustic monitoring platform in the form of a low-cost floater that efficiently changes its buoyancy while remaining quiet in order to enable passive acoustic monitoring.
Design, implement and test a novel energy harvesting polymer-based circuit that charges the floater’s battery using the ambient noise as a source of renewable energy.
Design and test a low complexity vessel detection algorithm.
Implement protocols for swarm cooperation between floaters to improve ship detection capabilities.
Develop five TRL6 floater prototypes and demonstrate their swarm operation and energy harvesting capabilities in sea trials.

Challenges and Solutions

Floater Design

The SHIELD floater will be capable of one degree of freedom of movement -vertically- by changing the buoyancy of its elongated and bottom-heavy body.

Acoustic interference is avoided by suppressing the noise of the motors themselves and mounting them on vibration-absorbing material that decouples them from the float housing.

Energy Harvesting

We will use the ambient acoustic noise as a source of renewable energy, aiming for a potential power of 1 Watt near ports or around vessels.

The scavenging system will be implemented via polymer-based capacitive micromachined ultrasonic transducers, with low acoustic impedance and large, conformal areas for efficient acoustic energy scavenging.

Acoustic Detection

We will rely on the expected stability of the noise emitted by ships as opposed to the more random statistics of ambient noise.

Our ship detection solution will combine classification and clustering to recognize this stability through a two-step approach.

When a vessel is detected, the direction of arrival is estimated via cross-correlation of signals on a 3-element hydrophone array

SwarM Operation

Our solution for the swarm operation of the floaters is based on the information that the individual floaters collect via the acoustic detection of ships. Based on their acoustic modems, the floaters send this information to reach a consensus on a target depth.

In this process, the acoustic properties of the water will be taken into account using the temperature measurements by the floaters.

International effort

We bring together expertise from three NATO countries and one Partner country. Our co-directors bear a long-standing expertise in communications, networking, signal processing, security, hardware, and field trials.

Theory into practice

We back rigorous theoretical results with sea experiments featuring real hardware, different systems, and complex equipment such as drifters and autonomous underwater vehicles.

Want to know more?

Follow up with the structure, specific activities and time line of our project or consult the list of partners

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