EFPI Pressure Sensor with FBG Reference for Medical Applications
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Solution Overview
Problem
Existing pressure sensors in the biomedical field face issues such as drift, complexity in manufacturing, increased temperature sensitivity, and reduced pressure sensitivity, which hinder their multi-use and compact design.
Innovation Solution
A pressure sensor incorporating an optical fiber with a glass capillary and diaphragm, utilizing an in-fiber Bragg Grating as a reference sensor to cancel out temperature sensitivity, and dynamically controlling the diaphragm thickness through etching to enhance pressure sensitivity, while maintaining a compact and biocompatible all-silica structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an extrinsic Fabry-Perot interferometric pressure sensor is used, then pressure sensitivity is improved, but temperature sensitivity increases
Solution Approach 1:
The sensor is segmented into two independent sensing elements: an EFPI cavity for pressure sensing and an FBG for temperature sensing. Each element independently measures its respective parameter, allowing temperature effects to be measured and compensated separately from pressure measurements.
Solution Approach 2:
The FBG acts as an intermediary reference sensor that measures temperature effects on the optical fiber. This temperature measurement serves as a mediator to compensate for temperature-induced drift in the EFPI pressure sensor, enabling accurate pressure measurements across varying temperatures.
2Object-affected harmful factors
If a reference sensor is added to cancel temperature sensitivity, then temperature cross-sensitivity is reduced, but device complexity increases
Solution Approach 1:
The EFPI cavity and FBG reference sensor are merged into a single integrated sensor head, both being written into the same optical fiber. This combination allows temperature compensation functionality to be added without requiring separate housing or additional complex assembly, minimizing the increase in device complexity.
Solution Approach 2:
A single optical fiber serves multiple functions: it acts as the waveguide for the EFPI pressure sensor and simultaneously contains the FBG temperature reference sensor. This multi-functionality reduces the number of separate components needed, offsetting the complexity increase from adding temperature compensation.
3Measurement precision
If diaphragm thickness is reduced to enhance pressure sensitivity, then pressure sensitivity is improved, but manufacturing precision requirements increase
Solution Approach 1:
The etching process uses feedback control where the EFPI cavity length is continuously monitored during diaphragm thinning. This real-time feedback allows precise control of the diaphragm thickness, ensuring it reaches the optimal thin state for high pressure sensitivity without requiring excessive manufacturing precision from the outset.
Solution Approach 2:
The diaphragm is pre-formed with a thickness closer to the target value before the final precision etching step. This preliminary action reduces the total etching time and minimizes the precision requirements during the critical final thinning phase, as less material needs to be removed with high precision.
4Object-affected harmful factors
If an all-silica structure is used for biocompatibility, then biocompatibility is improved, but manufacturing complexity increases
Solution Approach 1:
The sensor employs homogeneous all-silica construction where the optical fiber, capillary, and diaphragm are all made of silica material. This material homogeneity simplifies manufacturing by eliminating the need for bonding dissimilar materials, as all components can be fusion-spliced together using standard optical fiber joining techniques.
Solution Approach 2:
Mechanical bonding methods (such as epoxy or metal brazing) are replaced with optical fusion splicing to join the all-silica components. This substitution eliminates the need for complex mechanical assembly steps and specialized bonding equipment, reducing manufacturing complexity while maintaining the all-silica biocompatible structure.
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 achieves high pressure sensitivity, reduces temperature cross-sensitivity, and facilitates discrimination between pressure and temperature readings, making it suitable for medical applications with improved manufacturing efficiency and biocompatibility.
Implementation Method 1
the reference sensor includes a Bragg Grating. Preferably, the reference sensor is an in-fiber Bragg Grating (FBG) within said optical fiber
Implementation Method 2
the diaphragm and the end face are arranged for interferometric sensing
Implementation Method 3
the interferometric sensing is of the extrinsic Fabry-Perot interferometric (EFPI) type
Data Source
AI summary
A pressure sensor (10 for medical applications comprises a silica optical fiber extrinsic Fabry-Perot interferometric (EFPI) pressure sensor (2) and an in-fiber Bragg grating (FBG, 3). The cavity of the EFPI pressure sensor (2) is formed by the end face of the FBG (3), a glass capillary (5) and a glass diaphragm (6). The glass diaphragm (6) is secured in place by a fusion splice (7) and the glass capillary (5) by a fusion splice (8). As illustrated, incident light is directed into the FBG 3 and there are reflections in the EFPI pressure sensor (2). Applied pressure causes a deflection of the glass diaphragm (6) and hence modulation of the EFPI sensor (2) cavity. The FBG (3) is used as a reference sensor to eliminate temperature cross-sensitivity of the EFPI pressure sensor (2). The EFPI cavity was fabricated using a 200 μm silica glass fiber, a 133/220 μm (inner/outer diameter) silica glass capillary and a standard telecommunication FBG. Initially, the end faces of the 200 μm silica glass fiber and the silica glass capillary were polished and both planar surfaces were spliced together using a fusion splicer. Then the silica glass capillary was cleaved 5 mm away form the capillary/200 μm fiber splice. After that, the FBG (3) was inserted into the silica glass capillary (5) and both elements were bonded together using the fusion splicer again.