Fibre-Optic Hydrophone With Internal Fluid Filter
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Solution Overview
Problem
Existing fibre-optic hydrophones are bulky and heavy, making them less suitable for compact applications in water, and they often require external housings that reduce sensitivity due to stiffness, while also being prone to noise interference.
Innovation Solution
A compact fibre-optic hydrophone design featuring a stiff tubular body with a deflectable outer wall and internal fluid passages acting as a mechanical low-pass filter, allowing direct exposure to water and optimizing frequency response between 2kHz and 10kHz for enhanced sensitivity and noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hydrophone housing with deflectable wall part and hydraulic coupling is used, then the hydrophone can be protected during handling and installation, but the stiffness of the outer wall material reduces the overall sensitivity
Solution Approach 1:
The patent uses a thin-walled cylindrical housing with a deflectable wall part that allows acoustic pressure to cause radial displacements. The wall is made thin and flexible (while still providing protection) to maximize the transmission of acoustic pressure to the hydrophone sensing element, thereby maintaining high sensitivity while providing necessary mechanical protection.
2Strength
If the hydrophone house is made relatively large and heavy to withstand installation process, then it can be buried in the sea floor, but a more compact hydrophone would be advantageous for use in water
Solution Approach 1:
The patent applies local quality by making the housing thin-walled and lightweight for use in water, while still providing sufficient strength through strategic reinforcement at critical locations. The deflectable wall part is designed with specific local properties to allow acoustic pressure transmission while maintaining structural integrity during installation.
3Measurement precision
If the area of the deflectable wall part is much larger than the area of the sensitive element, then small displacements of housing cause larger displacements at the hydrophone sensing element, but the housing requires larger size to achieve this
Solution Approach 1:
The patent employs a cylindrical (curved) geometry for the deflectable wall part, which provides mechanical advantage through its curved structure. The cylindrical shape allows efficient transmission and amplification of radial displacements from the housing wall to the hydrophone sensing element, achieving displacement amplification without requiring excessive housing size.
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 achieves high sensitivity and compactness by directly exposing the hydrophone mandrel to water, while the internal filter effectively reduces noise bandwidth, resulting in a more reliable and efficient acoustic sensing system.
Implementation Method 1
A hydrophone typically involves the following elements: a hydrophone sensing element for generating a signal when subject to pressure changes
Implementation Method 2
The first duct may optionally be dimensioned to act as a mechanical, acoustic low-pass filter in the form of a Helmholtz tube or filter
Data Source
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AI summary
A fibre-optic hydrophone comprising a substantially incompressible tubular body, the tubular body generally having a geometry of a cylindrical shell defining an axis, and a deflectable outer wall, arranged to surround the tubular body in a distance thereof, and defining an axis that is arranged to substantially coincide with the axis of the tubular body. The hydrophone further comprising an optical fibre coil arranged on an outer surface of the outer wall, and a first and a second end lid arranged to seal the tubular body and the outer wall at a first end and a second end thereof, respectively, the first end lid and the second end lid being substantially incompressible. Additionally, the hydrophone comprising an outer cavity defined by an inner surface of the outer wall, an outer surface of the tubular body, the first lid, and the second lid; and an inner cavity defined by an inner surface of the tubular body, the first lid, and the second lid. The outer cavity is in fluid communication with the inner cavity via one or more passages in the tubular body, the outer cavity and the inner cavity being filled with a fluid, wherein the passages are configured to contribute to a function as a filter defining a low pass filter response with high cut-off frequency. In some embodiments the deflectable outer wall is cylindrical.