Optical Fiber Hydrophone With Low-Modulus Core for Deep-Water Sensing

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Solution Overview

Problem

Existing hydrophones face challenges in achieving high sensitivity and cost-effective manufacturing while maintaining resistance to high hydrostatic pressures and acoustic detectability, particularly in deep-water applications.

Innovation Solution

A hydrophone design featuring a mandrel with a core of solid material having a low bulk modulus, a cylindrical cavity, and passages for fluid communication, combined with an optical fiber wound on the mandrel, allowing for sensitive pressure variation measurements and resistance to high hydrostatic pressures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a sealed gas filled interior is used to increase sensitivity to pressure variations, then the hydrophone becomes more acoustically detectable

Engineering Contradiction:

Improvesensitivity to pressure variationsVSAvoidacoustic detectability

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent uses a liquid-filled interior instead of gas, exploiting the incompressibility of liquids to transmit pressure variations directly to the optical fiber while avoiding the acoustic resonance issues associated with gas-filled chambers. The liquid coupling allows sensitive pressure measurement without creating acoustic signatures.

Inventive Principle:

Principle #29Pneumatics and hydraulics

Solution Approach 2:

The patent changes the physical state parameter from gas to liquid in the interior filling, which fundamentally alters the acoustic properties while maintaining pressure transmission capability. This parameter change eliminates acoustic detectability while preserving sensitivity.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If a compliant structure is used to increase sensitivity to pressure variations, then the hydrophone becomes more vulnerable to damage from high constant hydrostatic pressures

Engineering Contradiction:

Improvesensitivity to pressure variationsVSAvoidresistance to high hydrostatic pressures

Core Design Contradiction:

Measurement precisionVSStrength

Solution Approach 1:

The patent applies different material properties to different parts of the structure: the shell and internal components use high bulk modulus materials for strength and pressure resistance, while the optical fiber winding provides the necessary compliance for sensitivity. This local differentiation allows simultaneous achievement of strength and sensitivity.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The hydrophone employs a composite structure combining rigid materials (for the shell and core) with optical sensing elements. The rigid core provides structural integrity against high hydrostatic pressure, while the optical fiber winding detects pressure variations through strain effects.

Inventive Principle:

Principle #40Composite materials

3Reliability

If complex internal structures are used to achieve both sensitivity and pressure resistance, then the manufacturing cost and complexity increase

Engineering Contradiction:

Improveperformance under deep-water conditionsVSAvoidmanufacturing simplicity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent divides the hydrophone into simple functional segments: a cylindrical shell, an internal core structure, fluid passages, and an optical fiber winding. Each component can be manufactured separately using standard processes and assembled through simple operations, reducing overall manufacturing complexity while maintaining deep-water performance.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The design provides enhanced sensitivity to pressure variations, resistance to high hydrostatic pressures, and reduced acoustic detectability, enabling accurate acoustic and seismic measurements at great depths with simplified manufacturing.

Implementation Method 1

an optical fiber comprising an optical sensing section that is at least partially wound on the mandrel, the optical sensing section having an optical characteristic that varies as a function of a radial dimension of the mandrel

Methodology Applied

Scientific EffectOptical sensing: Optical Fibre

Implementation Method 2

the mandrel comprises a core of solid material having a bulk modulus lower than 0.1 GPa, the cylindrical cavity being comprised between the core and the shell

Methodology Applied

Scientific EffectBulk modulus: Elasticity

Implementation Method 3

the passage in the mandrel makes that a relatively large constant hydrostatic pressure that is exerted on an outside surface of the shell is also exerted on an inside surface of the shell

Methodology Applied

Scientific EffectHydrostatic pressure: Pressure Gradient

Data Source

PatentUS12405157B2Optical fiber-based hydrophone

Publication Date: 2025.09.02 OPTICS11 BV

AI summary

A hydrophone has a mandrel with a shell and a cylindrical cavity inwardly adjacent to the shell. A passage provides fluid communication between the cylindrical cavity and an exterior environment surrounding the mandrel. The hydrophone further has an optical fiber having an optical sensing section that is at least partially wound on the mandrel. The optical sensing section has an optical characteristic that varies as a function of a radial dimension of the mandrel. The mandrel has a core of solid material having a bulk modulus lower than 0.1 GPa. The cylindrical cavity is between the core and the shell.