Cholesteric Liquid Crystal Band Pass Filter for High SN Ratio Sensor
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Solution Overview
Problem
Existing distance-measuring sensors face challenges in achieving high accuracy due to external light interference, which degrades the signal-noise ratio (SN ratio) and measurement precision.
Innovation Solution
A sensor configuration that includes a light source, a band pass filter with a first and second cholesteric liquid crystal layer, and a light-receiving element, where the band pass filter uses a discontinuous layer to selectively reflect light within a specific wavelength range, thereby reducing external light interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional light-receiving element is used without special filtering, then the sensor can receive all wavelengths of light including external light, but external light becomes noise that decreases the signal-noise ratio and measurement accuracy
Solution Approach 1:
The band pass filter is segmented into multiple functional layers: a first cholesteric liquid crystal layer for reflecting specific wavelengths, a discontinuous layer with controlled thickness to modulate light transmission, and a second cholesteric liquid crystal layer for additional wavelength selection. This segmentation allows precise control over which wavelengths reach the light-receiving element, blocking external light while transmitting measurement light.
Solution Approach 2:
The band pass filter acts as an intermediary component between the light source and the light-receiving element. It selectively transmits only the measurement light wavelength range while blocking external light, thereby protecting the light-receiving element from harmful wavelengths without affecting the measurement function.
2Measurement precision
If a band pass filter with multiple layers is introduced to block external light, then measurement accuracy improves, but the device structure becomes more complex
Solution Approach 1:
The patent optimizes specific parameters of the discontinuous layer, including its thickness (controlled within a specific range) and optical properties, to achieve the desired light transmission characteristics. By carefully controlling these parameters, the filter achieves effective external light blocking while maintaining a relatively simple structure that can be integrated into existing sensor designs.
3Measurement precision
If the discontinuous layer thickness is increased to block more external light, then the signal-noise ratio improves, but the transmission of measurement light may be affected
Solution Approach 1:
The thickness of the discontinuous layer is precisely controlled within a specific range to achieve optimal performance. This parameter optimization ensures that the layer is thick enough to block external light effectively while remaining thin enough to allow sufficient transmission of measurement light, thereby balancing noise reduction with light transmission efficiency.
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 proposed sensor configuration effectively prevents external light from entering the light-receiving element, thereby enhancing measurement accuracy and maintaining a high SN ratio.
Implementation Method 1
the band pass filter includes a first cholesteric liquid crystal layer and a second cholesteric liquid crystal layer that are layers obtained by immobilizing a cholesteric liquid crystalline phase
Implementation Method 2
in the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer, helical twisted directions and helical pitches of the cholesteric liquid crystalline phases are the same
Data Source
AI summary
Provided is a sensor having a high SN ratio. The sensor includes a light source, a band pass filter, and a light-receiving element, in which the band pass filter includes two cholesteric liquid crystal layers and a discontinuous layer disposed between the two cholesteric liquid crystal layers, in the two cholesteric liquid crystal layers, helical twisted directions and helical pitches are the same, and in a case where the discontinuous layer is a layer other than a cholesteric liquid crystal layer and a wavelength having a lowest reflectivity in a selective reflection wavelength range of the band pass filter is represented by λm [nm], a thickness [nm] is in a range of “30×(λm/550) to 150×(λm/550)”.