Compact Fingerprint Sensor Using Grating Light Deflection
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Solution Overview
Problem
Conventional fingerprint image acquisition devices are bulky due to the spatial arrangement of the light source, convex lens, and image sensor, which prevents a reduction in device volume.
Innovation Solution
A compact fingerprint image acquisition device design featuring a surface light source with a grating to change the light beam's propagation direction, allowing for a reduced distance between the light source, convex lens, and image sensor, utilizing a transparent plate as the finger touching surface and an OLED array as the light source, with the grating attached to the light output surface to facilitate precise light deflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional spatial arrangement of light source, convex lens and image sensor is used, then the device structure is simple, but the device volume cannot be reduced
Solution Approach 1:
The patent transitions from a conventional linear spatial arrangement to a layered configuration where the light source is positioned below the transparent plate rather than to the side. This dimensional repositioning allows the light beam to travel upward through the transparent plate to the finger contact surface, enabling the convex lens and image sensor to be placed in the space directly below the plate, thus reducing overall device volume while maintaining functional simplicity
Solution Approach 2:
The patent embeds multiple components within a compact vertical stack: the light source is integrated into the casing below the transparent plate, the convex lens is positioned between the plate and image sensor, and all components are arranged in a nested vertical configuration. This nesting approach maximizes space utilization and reduces the device footprint
2Volume of moving object
If surface light source with grating is used, then the device volume is reduced, but the manufacturing precision requirement increases
Solution Approach 1:
The grating is directly integrated with the light output surface of the surface light source, forming a unified optical assembly. This merging eliminates the need for separate mounting mechanisms and reduces the number of interfaces requiring precision alignment, thereby lowering manufacturing precision requirements while achieving compact device volume
Solution Approach 2:
The transparent plate serves as an intermediary optical element that facilitates light transmission from the surface light source to the finger contact surface. By positioning the light source below the plate and using the plate as a light guide, the system achieves compact volume without requiring high-precision alignment of all components, as the plate provides optical coupling and positioning tolerance
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 design achieves a more compact structure and reduced volume of the fingerprint image acquisition device, enabling its application in smaller electronic products like mobile phones or cameras.
Implementation Method 1
the grating is configured to change a propagation direction of the light beam to thereby form a detection light beam
Implementation Method 2
the convex lens is configured to focus the reflected light beam on the image sensor
Implementation Method 3
the finger touching surface is configured for a user to place a finger thereon to reflect the detection light beam and thereby obtain a reflected light beam
Data Source
AI summary
A fingerprint image acquisition device includes: a light source, a finger touching surface, a convex lens, an image sensor and a grating. The light source is a surface light source, and the grating is disposed on a light output surface of the light source. The light source is configured to emit a light beam, the grating is configured to change a propagation direction of the light beam to form a detection light beam, the finger touching surface is configured for a user to place a finger thereon to reflect the detection light beam and thereby obtain a reflected light beam, the convex lens is configured to focus the reflected light beam on the image sensor, and the image sensor is configured to generate a fingerprint image based on the focused reflected light beam. Accordingly, the invention can make the structure of the fingerprint image acquisition device be more compact.