Fiber Optic MEMS Seismic Sensor with Hinged Beams
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Solution Overview
Problem
Conventional MEMS seismic sensors have a limited operating temperature due to integrated electronic components, restricting their application in high-temperature environments, and their frequency range is not suitable for detecting small seismic displacements effectively.
Innovation Solution
A fiber optic MEMS seismic sensor with a proof mass supported by hinged beams, fabricated using silicon-on-insulator wafers, which allows for optical sensing without electronic components, enabling operation beyond traditional temperature limits and improved frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If integrated electronic components are used in MEMS sensors, then signal conditioning and processing are improved, but the maximum operating temperature is limited to 75°C
Solution Approach 1:
The patent removes electronic components from the high-temperature environment by extracting the signal conditioning function to external electronics located away from the sensor. Only the passive mechanical proof mass and optical fiber remain in the harsh environment, allowing operation at temperatures exceeding 75°C while electronic signal processing is performed remotely where cooling is feasible.
Solution Approach 2:
The patent replaces electronic signal conditioning within the sensor with an optical sensing mechanism. The proof mass displacement is measured optically using fiber optic interferometry, eliminating the need for electronic components at the sensor location and enabling high-temperature operation.
2Measurement precision
If a soft spring is used in geophone sensors, then sub-micrometer resolution for large displacements is achieved, but the frequency range is limited to about 10Hz
Solution Approach 1:
The patent changes the fundamental parameter of the suspension system from a soft spring to a stiff spring with hinged beams. This parameter change shifts the mechanical bandwidth from 10Hz to potentially much higher frequencies while maintaining measurement precision through optical detection of the proof mass position relative to the cartridge.
Solution Approach 2:
The patent replaces the mechanical spring-based displacement measurement with an optical measurement system. The position of the proof mass is detected using fiber optic interferometry, which provides high-resolution measurement without the frequency limitations imposed by soft spring mechanics.
3Speed
If a stiff spring is used in MEMS accelerometers, then the mass moves with the case for acceleration measurement, but the sensor is not suitable for detecting small seismic displacements
Solution Approach 1:
The patent creates a dynamic system where the proof mass is suspended by hinged beams that allow controlled movement. The hinged beams provide a transition between the stiff spring configuration (for acceleration measurement) and the ability to detect small displacements, enabling the sensor to operate effectively in the seismic frequency range.
Solution Approach 2:
The patent introduces an optical field as an intermediary to measure the relative displacement between the proof mass and the cartridge. The fiber optic interferometer detects changes in the optical path length caused by proof mass movement, providing high sensitivity to small displacements while the stiff hinged beam structure maintains good acceleration response.
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 solution extends the operating temperature of seismic sensors beyond 75°C and enhances their sensitivity to small displacements, achieving a broader frequency range for seismic measurements.
Implementation Method 1
The end of the optical fiber is positioned within the interferometric gap such that the position of the proof mass may be measured with the optical fiber
Data Source
Figure 1~2B
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AI summary
The present invention relates to an optic seismic MEMS sensor. More specifically, a proof mass is supported by a frame having supporting beams. The proof mass is positioned within the frame and has a hinged attachment to the beams. The proof mass has a sensor gap having a first reflector and a second reflector positioned at opposing ends of the sensor gap. An optical fiber injects light into the sensor gap and light is reflected to determine seismic movement of the proof mass with respect to the frame. Stops are provided for limiting the movement of the proof mass to minimize strain on the attachment of the beams and the proof mass.