Trapezoidal Prism Authentication Light Source Placement
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Solution Overview
Problem
Existing living body authentication apparatuses using a prism method face challenges with light source placement, where disposing light sources below the prism secures light but results in reflection issues, and placing them on the side reduces light intensity and increases apparatus size.
Innovation Solution
A trapezoidal prism design with an expanded side face for imaging, where the visible light source is positioned below the imaging face and near the expanded side, allowing for minimal light source influence and reduced apparatus size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If light sources are disposed below the prism, then light amount is sufficient, but light sources are reflected on the mirror face and appear in the image, making authentication impossible
Solution Approach 1:
The patent changes the spatial arrangement by using a trapezoidal prism where the light source is disposed below the imaging face but offset toward one side, rather than being centered or directly below the authentication face. This dimensional repositioning allows sufficient light illumination while preventing the light source from appearing in the captured image through total internal reflection.
2Object-affected harmful factors
If light source is disposed on the side face side of the prism, then light source reflection does not occur, but light amount for capturing authentication image cannot be secured and apparatus size increases
Solution Approach 1:
Instead of placing the light source on the side face, the patent positions it below the imaging face but offset toward one side. The trapezoidal geometry with its inclined faces creates total internal reflection that directs light appropriately while preventing source reflection in the image, and the offset positioning ensures sufficient light amount without increasing apparatus size.
3Object-affected harmful factors
If light source is disposed on the side face side of the prism, then light source reflection does not occur, but apparatus length in lateral direction becomes large
Solution Approach 1:
The patent repositions the light source from a side-face location (which would increase lateral length) to a position below the imaging face. The trapezoidal prism geometry with inclined faces enables the light to reach the authentication surface effectively while keeping the apparatus compact in the lateral direction.
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 configuration enables effective capture of high-contrast and natural images with reduced light source interference, allowing for accurate authentication while minimizing the apparatus's size.
Implementation Method 1
employ a method using a critical angle of total reflection by a triangular prism
Data Source
AI summary
An authentication apparatus comprises a prism member, an imaging unit, and a visible light source configured to radiate visible light to a living body. The prism member has a substantially trapezoidal shape with at least one side face thereof formed in an expanded shape from a living body authentication face against which an authentication portion of the living body is put, toward an imaging face that is parallel to the living body authentication face. The visible light source is disposed below the imaging face and near a side of an expanded side of the imaging face. The imaging unit is disposed below the imaging face.