Pressure Compensated Optical Accelerometer for Deep Water
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Solution Overview
Problem
Existing optical motion and acceleration sensors used in submerged systems, such as dual sensor OBCs, face challenges with high sensitivity, noise insensitivity, and cross-component sensitivity, and are often housed in expensive, heavy pressure-resistant materials to withstand deep water pressures.
Innovation Solution
The development of optical accelerometers with a pressure-compensated housing filled with a substantially incompressible fluid, featuring a beam supported at both longitudinal ends to minimize transverse flexure and maximize sensitivity, and utilizing optical fibers affixed to the beam to detect changes in length due to acceleration, with optional Bragg gratings for orientation determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pressure-resistant housing made from heavy materials is used to withstand deep water pressures, then the sensor can operate in deep water environments, but the device becomes heavy and expensive
Solution Approach 1:
The patent replaces the traditional mechanical pressure-resistant housing with a magnetic field-based sensing system. The magnetic field penetrates water without requiring physical pressure resistance, allowing the sensor to operate in deep water environments without needing heavy pressure-resistant materials. The magnetic field interacts with the sensing element directly, eliminating the need for a robust mechanical barrier.
Solution Approach 2:
The patent changes the operating parameter from mechanical pressure resistance to magnetic field penetration. By using magnetic fields instead of mechanical structures to sense acceleration in deep water, the system avoids the weight and cost penalties of pressure-resistant housings while maintaining deep water operation capability.
2Object-affected harmful factors
If the beam is supported at both longitudinal ends to minimize transverse flexure, then cross-component sensitivity is reduced, but the sensitivity to acceleration along the sensing axis must be maximized
Solution Approach 1:
The patent applies local quality by creating a asymmetric support configuration where one end of the beam is fixed and the other end is free to move. This localized differentiation in support conditions allows the beam to be rigid against transverse flexure at the fixed end while remaining sensitive to acceleration-induced displacement at the free end, thus reducing cross-component sensitivity while maintaining acceleration sensing sensitivity.
Solution Approach 2:
Instead of supporting the beam at both ends to prevent flexure, the patent inverts the approach by fixing one end and leaving the other end free. This inversion allows the beam to naturally resist transverse flexure through its constrained end while being highly responsive to acceleration at the free end, simultaneously addressing both cross-component sensitivity and acceleration sensitivity requirements.
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
This design enhances sensitivity and reduces noise and cross-component sensitivity, allowing for lighter, less expensive sensor deployment in deep water environments while maintaining effective seismic energy detection.
Implementation Method 1
The change in shape of the device is transformed into a change in length of the optical fiber. Change in length of the optical fiber may be detected by one of a number of different optical measurement techniques. Such techniques include change in reflected wavelength of light as a result of a change in wavelength of a Bragg grating formed in the optical fiber
Implementation Method 2
Change in length of the optical fiber may be detected by one of a number of different optical measurement techniques. Such techniques include change in reflected wavelength of light as a result of a change in wavelength of a Bragg grating formed in the optical fiber
Implementation Method 3
Light beams from the fiber affixed to the device and from the reference fiber are coupled in an optical interferometer. An interference pattern or phase change in the light generated in the optical interferometer is related to the change in length of the fiber coupled to the device
Data Source
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AI summary
An optical accelerometer includes means (12) for changing the length of at least one optical fiber (14) in response to acceleration functionally coupled to the at least one optical fiber. The fiber (14) and the means (12) for changing length are enclosed in a pressure compensated housing. The housing is filled with a substantially incompressible fluid or gel.