Optical Sensor Spatial Separation for Flow Measurement
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Solution Overview
Problem
Current methods for determining the flow characteristic of movable objects, such as blood flow, suffer from low accuracy and depth sensitivity due to the predominance of back-scattered light and random velocity values of blood cells, leading to unclear frequency shifts and poor Doppler effect measurements.
Innovation Solution
A sensor device with a light emitting unit, a light detecting unit, and an optical unit that spatially separates the light incidence and detection elements, utilizing self-mixing interferometry and polarizing beam splitters to enhance depth sensitivity and accuracy by reducing interference and increasing the signal-to-noise ratio, allowing for the determination of flow characteristics based on Doppler shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional laser Doppler flowmetry is used to measure blood flow, then the measurement can be performed, but the accuracy and depth sensitivity are low due to predominance of back-scattered light and random velocity values
Solution Approach 1:
The patent segments the light path into distinct incidence and detection paths using separate optical fibers. The light incidence fiber delivers light to a specific location while the light detection fiber collects light from a different location, spatially separating the illumination and detection functions to reduce back-scattered light interference from the incidence path.
Solution Approach 2:
The patent extracts and removes the harmful back-scattered light component by using polarizing beam splitters to separate polarized light (which includes much of the back-scattered light) from the detection path. This extraction of the harmful component improves the signal-to-noise ratio for flow velocity measurements.
2Measurement precision
If light is incident on the element to detect back-scattered light, then flow characteristics can be determined, but depth sensitivity remains low due to interference from surface reflections
Solution Approach 1:
The patent introduces polarizing beam splitters as intermediary optical components between the light source and detector. These intermediaries selectively transmit or reflect light based on polarization state, allowing the system to filter out surface reflections while transmitting the desired back-scattered light from deeper tissue layers.
Solution Approach 2:
The patent changes the polarization parameter of the light using wave plates and polarizing beam splitters. By manipulating the polarization state of incident and detected light, the system can differentiate between surface reflections and deeper tissue scattering, thereby improving depth sensitivity.
3Measurement precision
If optical components are added to separate light paths and improve depth sensitivity, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent combines multiple optical functions into integrated components. The polarizing beam splitters and wave plates are configured to perform both light path separation and polarization filtering in a compact arrangement, reducing the overall number of discrete components needed while maintaining measurement accuracy.
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 sensor device achieves high sensitivity and accuracy in determining flow characteristics, particularly in deeper layers, by separating light paths and using polarizing beam splitters to enhance signal intensity and reduce noise, thereby improving the determination of flow velocities and directions.
Implementation Method 1
Coherent laser light 102 emitted by a laser unit is incident on a skin portion 104 of a skin 106 of the person. The light 102 penetrates into surface layers of the skin 106 beneath the skin portion 104, and is amongst others scattered at blood cells 108a-e moving in the skin 106. The detector 112 detects all incoming light 110a-d with the detected light comprising a frequency distribution centered around the frequency ω0 of the light 102
Implementation Method 2
The light 102 penetrates into surface layers of the skin 106 beneath the skin portion 104, and is amongst others scattered at blood cells 108a-e moving in the skin 106. Multiple scattering events of the light 102 at different blood cells 108a-c, e as well as a single scattering event of the light 102 at one blood cell 108d are illustrated
Implementation Method 3
A polarizer of the apparatus is arranged between the laser sensor and the skin portion, in order to suppress fractions of the reflected light which comprises a different polarization compared to the emitted light
Implementation Method 4
Due to the self mixing effect the back-scattered light gives rise to power fluctuation of the laser
Implementation Method 5
The light path separation element is configured as a polarizing beam splitter
Implementation Method 6
The light redirecting element is configured as a mirror and/or a prism
Data Source
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AI summary
A sensor device (340) for determining a flow characteristic of an object (341) being movable in an element (342) comprises a light emitting unit (344) configured for emitting light towards the element (342) and a light detecting unit (344) configured for detecting light scattered back from the element (342). The sensor device (340) comprises an optical unit (346) configured for spatially separating a light incidence element portion (348) of the element (342) and a light detection element portion (350) of the element (342) from one another, wherein the light incidence element portion (348) is associated with the emitted light inciding on the element (342) and the light detection element portion (350) is associated with the back-scattered light scattered back from the element (342) for detection. The sensor device (340) comprises a determining unit (358) configured for determining the flow characteristic of the object (341) being movable in the element (342) based on light indicative of the emitted light and the detected back-scattered light. The sensor device (340) allows for an accurate and easy determination of the flow characteristic of the object (341).