Fabry-Perot Speed Sensor Resists EMI in Harsh Environments
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Solution Overview
Problem
Inductive coil-based speed sensors in harsh aircraft engine environments are prone to degradation from high temperatures and corrosive chemicals, making them sensitive to electromagnetic interference and difficult to predict when they fail.
Innovation Solution
A Fabry-Perot cavity system using a magnet and magnetostrictive material, where the rotation of a toothed wheel modulates the magnetic field, causing changes in the cavity dimension and allowing light wavelength detection to determine rotation frequency, thereby providing a robust and insensitive speed measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inductive coils are used for speed sensing, then electromagnetic field changes can be detected, but the sensor becomes sensitive to electromagnetic interference and degrades in harsh environments
Solution Approach 1:
The patent replaces the electromagnetic inductive coil system with an optical Fabry-Perot interferometer system. Instead of detecting electromagnetic field changes directly with coils, the system uses light waves passing through a cavity whose dimensions are modulated by magnetostrictive material. This substitution of electromagnetic detection with optical detection eliminates sensitivity to electromagnetic interference while maintaining the ability to detect rotational speed through optical path length changes.
Solution Approach 2:
The patent introduces magnetostrictive material as an intermediary between the magnetic field and the optical measurement system. The magnetostrictive material converts magnetic field changes into mechanical dimension changes of the Fabry-Perot cavity, which then modulate the optical path. This intermediary conversion chain (magnetic field → mechanical deformation → optical modulation) protects the sensing system from direct electromagnetic interference while preserving the measurement capability.
2Ease of operation
If inductive coils are located in high-temperature and corrosive environments, then speed sensing can be performed, but the coils and components degrade and fail
Solution Approach 1:
The patent changes the physical state and material composition of the sensing system from electromagnetic coils to optical components. The Fabry-Perot interferometer uses optical waves instead of electromagnetic coils, and the magnetostrictive material provides a solid-state mechanism that is inherently more resistant to thermal and chemical degradation. This parameter change in the fundamental sensing mechanism enables operation in high-temperature and corrosive environments where inductive coils would fail.
3Measurement precision
If inductive coils are used in harsh environments, then speed measurement can be achieved, but failure prediction becomes difficult and warning is minimal
Solution Approach 1:
The replacement of inductive coils with an optical Fabry-Perot interferometer system provides more stable and predictable performance in harsh environments. Optical components and magnetostrictive materials have more predictable degradation characteristics compared to inductive coils, enabling better failure prediction and maintenance scheduling while maintaining measurement precision.
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 system effectively determines rotation frequency with improved resistance to electromagnetic interference and environmental degradation, offering reliable operation in harsh conditions.
Implementation Method 1
The second mirror is bonded to a magneto-strictive material having a thickness dimension that changes in response to changes in the magnetic field caused by rotation of the rotatable member
Implementation Method 2
A cavity dimension between the first mirror and the second mirror changes in response to movement of the second mirror with respect to the first mirror. A wavelength of light reflected by the Fabry-Perot cavity changes in response to changes in the cavity dimension
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
Apparatus and associated methods relate to optically determining rotation frequency of a rotatable member using a Fabry-Perot cavity (16) formed between a partly reflective mirror (26) and a movable reflective mirror (28). A cavity dimension between the mirror and the movable reflective mirror changes in response to movement of the movable reflective mirror. The movable reflective mirror is bonded to a magneto-strictive material (30) having a thickness dimension that changes in response to changes in a magnetic field. A magnet (14) generates the magnetic field, which changes in response to rotation of the rotatable member. The detectable field variations are caused e.g. by teeth of a rotating target, moving within the magnetic field of a stationary permanent magnet.