Optical Fingerprint Sensor Eliminates EMI via Total Internal Reflection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electronic fingerprint sensors often generate electromagnetic interference (EMI) or stray radio frequency (RF) signals, which can be detrimental to devices such as computers, GPS receivers, and mobile telephones where they are used for security purposes.
Innovation Solution
The use of light beams to detect fingerprints by altering the total internal reflection characteristics of a ridged surface, allowing for the observation of changes in light reflection as a finger is swiped over the sensor, eliminating the need for electrical signals and thus reducing EMI and RF interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electronic fingerprint sensors use electrical signals to detect fingerprints, then fingerprint detection capability is improved, but electromagnetic interference and radio frequency signals are generated that disrupt nearby electronic devices
Solution Approach 1:
The patent replaces the electrical signal-based detection system with an optical system using light beams. The optical fingerprint sensor uses light sources to illuminate the finger and optical detectors to capture reflected light patterns, substituting electrical fields with optical fields to eliminate electromagnetic interference while maintaining fingerprint detection capability
Solution Approach 2:
The patent introduces light as an intermediary medium between the finger and the detection system. Instead of directly measuring electrical properties of the finger, the system uses light reflection patterns as an intermediary to convey fingerprint information, thereby avoiding direct electrical contact and associated electromagnetic interference
2Volume of moving object
If electronic components are placed close to the fingerprint sensor for compact design, then device size is reduced, but electromagnetic interference affects both the sensor and nearby components
Solution Approach 1:
By replacing electrical detection components with optical components, the patent eliminates the source of electromagnetic interference. This allows electronic components to be placed closer to the sensor without interference concerns, as the optical system does not generate electromagnetic fields that would disrupt nearby electronics
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 effectively eliminates EMI and RF interference, enabling secure fingerprint recognition without disrupting the operation of nearby electronic devices and allowing for the placement of electronic components away from the sensor to minimize further interference.
Implementation Method 1
beams of light are directed toward individual regions of the ridged surface so that the light beams will generally be totally internally reflected when a finger is not touching the ridge
Data Source
AI summary
A fingerprint sensor uses beams of light to detect a fingerprint as the finger is swiped over a ridged surface. The beams of light are directed toward individual regions of the ridged surface so that the light beams will generally be totally internally reflected when a finger is not touching the ridge. The total internal reflection characteristics of the ridged surface are altered at regions touched by the ridges on the finger as the finger is swiped over the sensor. This alters the amount of light reflected by the ridged surface. These changes in light reflection as the finger is swiped over the ridged surface can be observed simultaneously over multiple channels, preferably disposed laterally with respect to each other, to provide a fingerprint.