Moisture Sensor Using Polarized Light for Paper
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Solution Overview
Problem
Conventional moisture sensors face challenges in accurately detecting moisture content in paper due to noise components from distance instability and surface characteristics, making it difficult to achieve high-precision measurements, especially in thin paper with varying smoothness and coatings.
Innovation Solution
A moisture sensor system utilizing linearly polarized light with a polarization direction rotated 90 degrees from the incident light to selectively detect internally scattered light, which has a longer optical path and is less affected by surface noise, combined with a processor for correcting outputs based on paper type determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional moisture sensors are used to detect moisture content in paper, then the measurement can be performed, but the precision is degraded due to noise components from distance instability and surface characteristics
Solution Approach 1:
The patent extracts and isolates internally scattered light from surface reflected light by detecting light at a specific angle (not directly toward the sensor) and using polarization filtering. This separates the useful signal (internally scattered light carrying moisture information) from the harmful surface noise, thereby improving measurement precision
Solution Approach 2:
The patent changes the detection parameter from direct reflected light intensity to polarized light intensity at a specific scattering angle. By measuring light that has been scattered internally within the paper at angles other than the incident direction, and applying polarization filtering, the system transforms the measurement approach to eliminate sensitivity to distance and surface variations
2Measurement precision
If light scattering detection is used to measure moisture content, then moisture detection is enabled, but surface noise from varying smoothness and coatings degrades the measurement accuracy
Solution Approach 1:
The patent extracts internally scattered light that penetrates into the paper by detecting light at scattering angles rather than direct reflection. This extraction method isolates the light carrying internal moisture information from surface-reflected light that contains noise from surface smoothness variations and coatings
Solution Approach 2:
The patent introduces polarization filtering as an intermediary mechanism to separate internally scattered light from surface reflected light. The polarization filter acts as a mediator that allows only the desired light component to pass through, blocking surface noise while transmitting the moisture-carrying signal
3Measurement precision
If a simple optical sensor is used, then the device size remains small, but the ability to distinguish internally scattered light from surface reflected light is insufficient
Solution Approach 1:
The patent makes the optical sensor multi-functional by combining moisture detection, paper type determination, and light scattering separation capabilities in a single integrated device. The same optical system detects both the intensity of polarized light for moisture measurement and the characteristics of scattered light for paper type identification, eliminating the need for separate dedicated sensors
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
This approach enhances the detection precision of moisture content in paper by isolating internally scattered light and correcting for paper type variations, resulting in improved sensitivity and accuracy.
Implementation Method 1
a light source to emit light having an infrared wavelength that is absorbed by water
Implementation Method 2
an optical system to receive the light from the light source and output linearly polarized light having a first polarization direction
Implementation Method 3
a photodetector to receive the linearly polarized light having the second polarization direction output from the optical system
Data Source
AI summary
A moisture sensor for detecting moisture content of an object includes a light source to emit light having an infrared wavelength that is absorbed by water; an optical system to receive the light from the light source and output linearly polarized light having a first polarization direction in a direction toward the object, and to receive light scattered from the object and output linearly polarized light having a second polarization direction perpendicular to the first polarization direction in another direction other than the direction toward the object; and a photodetector to receive the linearly polarized light having the second polarization direction output from the optical system.