Critical Angle Optical Sensor with Multi-Wavelength Segmentation
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Solution Overview
Problem
Existing refractive index sensors face limitations due to the use of single light sources, epoxy encapsulation, thermal expansion mismatches, and incompatibility with certain chemicals, which restrict the range of measurements and resolution, especially at higher temperatures and with short wavelength light.
Innovation Solution
An optical sensor apparatus utilizing a precision-machined, optically transparent light guiding structure with multiple light sources and a photodetector array, allowing for wider wavelength range measurements, direct deposition of reflecting materials, and reduced design complexity, along with a CTE-matched material selection to mitigate thermal expansion issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single light source is used in the sensor, then the device complexity is reduced, but the measurement precision and refractive index range are limited
Solution Approach 1:
The patent divides the single light source into multiple light sources (at least two) with different wavelengths. Each light source contributes to measuring different portions of the refractive index range, thereby extending the overall measurement capability and precision without excessively increasing device complexity
Solution Approach 2:
The sensor apparatus is designed to perform multiple measurement functions using different wavelength light sources. The system can measure refractive indices across a broader range by utilizing the complementary spectral responses from multiple light sources, making the device more versatile
2Device complexity
If epoxy encapsulation is used to house light sources and photodetectors, then the device structure is simplified, but thermal expansion mismatches occur at elevated temperatures
Solution Approach 1:
The patent changes the material parameter (coefficient of thermal expansion) by selecting a housing material that is CTE-matched to the epoxy encapsulation. This ensures that the housing and encapsulation expand at similar rates when temperature increases, preventing structural damage and maintaining measurement reliability at elevated temperatures
3Ease of manufacture
If the sensor housing material is not CTE-matched to the epoxy, then ease of manufacture is improved, but thermal expansion mismatches cause structural issues at high temperatures
Solution Approach 1:
The patent modifies the material selection parameter by choosing a housing material whose coefficient of thermal expansion matches that of the epoxy encapsulation. This CTE-matched material prevents differential thermal expansion at elevated temperatures, avoiding structural failures while remaining manufacturable
4Measurement precision
If short wavelength light is used, then the measurement precision is improved, but the light source and optical path become more sensitive to thermal and chemical environmental factors
Solution Approach 1:
The patent employs a composite approach by using multiple light sources with different wavelengths (including short wavelength sources for precision and longer wavelength sources for environmental stability). This multi-wavelength strategy allows the system to leverage the high precision of short wavelength light while compensating for environmental sensitivities through comparative measurements across different wavelengths
5Measurement precision
If multiple light sources are used, then the refractive index range and resolution are extended, but the device complexity increases
Solution Approach 1:
The patent segments the measurement function across multiple light sources, each contributing to different portions of the refractive index range. This segmentation allows the system to achieve extended measurement capability while managing complexity by assigning specific wavelength ranges to specific light sources
Solution Approach 2:
The sensor apparatus is designed with multi-functionality, where multiple light sources serve both individual and collective purposes. Each light source can operate independently for specific measurements, and together they provide comprehensive refractive index coverage, maximizing the utility of each added component
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 enables extended refractive index range measurements with improved resolution and compatibility with various chemicals, including those at elevated temperatures, and allows for the use of short wavelength light, enhancing the sensor's operational flexibility and accuracy.
Implementation Method 1
When light traveling from a high index medium is incident upon an interface between the high index medium and another medium having a lower refractive index at angles of incidence larger than a critical angle of incidence, total internal reflection may be observed
Implementation Method 2
if the refractive index of one medium is known, the refractive index of the other may be determined from a measurement of the critical angle
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
An optical sensor apparatus includes an optically transmissive structure having planar first, second, and third faces, light sources located outside the structure adjacent the first face, and a photo detector array located outside the prism adjacent the first face. The structure, light sources, and photodetector array are configured such that light from the light sources that is totally internally reflected at an optical interface between the prism and a sample outside the structure proximate the second face is reflected at the third face and incident on a portion of the photo detector array that depends on a refractive index of the sample. The light sources are positioned with respect to the structure and photodetector array such that the totally internally reflected light from each light source corresponds to a different range of refractive index of the sample and maps to a corresponding portion of the photodetector array.