Piezoelectric Sensor Optical Compensation Layer for Birefringence
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Solution Overview
Problem
Piezoelectric sheets used in touch panels and display devices exhibit birefringence when uniaxially stretched, causing changes in image tone when viewed with polarizing sunglasses, especially when the polarization direction of the top polarizing plate and the stretching direction of the piezoelectric sheet are not in a parallel or orthogonal state due to manufacturing and assembly variations.
Innovation Solution
Incorporating an optical compensation layer with a slow axis intersecting the uniaxial direction of the piezoelectric sheet to cancel out the phase difference produced by the stretching, thereby maintaining image tone consistency regardless of the alignment between the polarization direction of the top polarizing plate and the stretching direction of the piezoelectric sheet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a uniaxially stretched piezoelectric sheet is used to detect pressing operations, then pressing force detection capability is improved, but image tone changes when viewed with polarizing sunglasses due to birefringence
Solution Approach 1:
A compensation film is introduced as an intermediary element between the piezoelectric sheet and the external environment. This compensation film has optical properties that counteract the birefringence effect of the piezoelectric sheet, thereby eliminating image tone changes when viewed with polarizing sunglasses while preserving the pressing force detection capability
Solution Approach 2:
The optical parameters of the compensation film are specifically designed to match and counteract the birefringence characteristics of the piezoelectric sheet. By adjusting the retardation and optical axis orientation of the compensation film, the harmful optical effects are neutralized while maintaining the piezoelectric sheet's functional properties
2Object-affected harmful factors
If the polarization direction of the top polarizing plate and the stretching direction of the piezoelectric sheet are aligned parallel or orthogonal, then image tone stability is improved, but manufacturing and assembly precision requirements increase
Solution Approach 1:
The compensation film serves as a mediator that decouples the optical stability requirement from the mechanical alignment requirement. It absorbs and compensates for misalignment errors, allowing the piezoelectric sheet to be positioned without strict parallel or orthogonal alignment while still achieving image tone stability
Solution Approach 2:
The compensation film is designed in advance to provide a buffer against potential misalignment issues. By pre-configuring the compensation film with appropriate optical characteristics, the system becomes tolerant of manufacturing and assembly variations without requiring high-precision alignment
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 optical compensation layer effectively suppresses changes in image tone when viewed with polarizing sunglasses, ensuring consistent image quality even when the polarization direction and stretching direction are not parallel or orthogonal, enhancing the reliability of touch input devices and display systems.
Implementation Method 1
a piezoelectric sheet which is stretched in a uniaxial direction; an electrode which detects an electric charge generated in the piezoelectric sheet
Implementation Method 2
a piezoelectric sheet which is stretched in a uniaxial direction... an optical compensation layer which includes a slow axis disposed on at least one side of the piezoelectric sheet and intersects the uniaxial direction, and optically compensates for a phase difference produced when the piezoelectric sheet is stretched in the uniaxial direction
Data Source
AI summary
A piezoelectric sensor includes: a piezoelectric sheet which is stretched in a uniaxial direction; an electrode which detects electric charges generated in the piezoelectric sheet; and an optical compensation layer which includes a slow axis stacked on at least one side of the piezoelectric sheet and intersects the uniaxial direction, and optically compensates for a phase difference produced when the piezoelectric sheet is stretched in the uniaxial direction.