Gradient Magnetic Sheet for Foldable RFID Antenna
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Solution Overview
Problem
Magnetic sheets used in portable communication devices face challenges with folding resistance and magnetic characteristics due to differences in linear expansion coefficients between the magnetic sheet and the antenna main body, leading to potential crack formation and reduced reliability under temperature changes.
Innovation Solution
A magnetic sheet with a gradient of magnetic powder to resin binder content ratio in the thickness direction, where one surface has a higher magnetic powder content and the other a higher resin binder content, is produced using a copolymer of epoxy resin and acrylic rubber, allowing for different folding resistances without compromising magnetic characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a magnetic sheet with uniform composition is used, then magnetic characteristics are maintained, but folding resistance deteriorates due to crack formation under temperature changes
Solution Approach 1:
The magnetic sheet employs a gradient composition where the content ratio of magnetic powder to resin binder varies through the thickness direction. Specifically, one surface has a higher magnetic powder content (70-90 wt%) while the opposite surface has a higher resin binder content (30-10 wt%), creating intermediate layers with gradual transitions. This local variation in composition allows the sheet to maintain magnetic characteristics near the antenna while providing flexibility and crack resistance at the resin-rich surface, thereby resolving the contradiction between magnetic performance and folding resistance.
2Reliability
If magnetic powder content is increased to improve magnetic characteristics, then communication performance is enhanced, but flexibility and folding resistance deteriorate
Solution Approach 1:
The invention applies local quality by creating a spatial gradient in magnetic powder concentration. The magnetic powder content is highest (70-90 wt%) at one surface that contacts the antenna main body, ensuring optimal magnetic coupling and communication performance. As depth increases, the magnetic powder content gradually decreases while resin binder content increases, reaching 30-10 wt% magnetic powder at the opposite surface. This gradient structure provides high flexibility and folding resistance at the resin-rich outer surface while maintaining excellent magnetic characteristics at the antenna interface.
3Strength
If resin binder content is increased to improve folding resistance, then flexibility is enhanced, but magnetic characteristics deteriorate
Solution Approach 1:
The invention strategically concentrates resin binder at specific locations rather than distributing it uniformly. The resin binder content is highest (30-10 wt%) at one surface that does not contact the antenna, providing enhanced flexibility, adhesion, and resistance to folding-induced cracks. The intermediate layers show gradual transitions in resin content, while the antenna-contacting surface maintains low resin content (10-30 wt%) to ensure strong magnetic coupling. This localized resin distribution resolves the contradiction by providing flexibility where needed while preserving magnetic characteristics where required.
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 magnetic sheet maintains good magnetic characteristics and reliability while improving resistance to folding and temperature-induced deformation, ensuring stable communication performance across varying environmental conditions.
Implementation Method 1
The RFID system is based on the principle of electromagnetic induction, in which the magnetic flux generated from a reader/writer's loop antenna is magnetically coupled to a transponder's loop antenna through inductive coupling
Implementation Method 2
the magnetic flux generated from a reader/writer's loop antenna is magnetically coupled to a transponder's loop antenna through inductive coupling
Data Source
AI summary
The present invention provides a magnetic sheet with improved resistance to folding while maintaining good magnetic characteristics and reliability; a method for producing the magnetic sheet; an antenna; and a portable communication device.A magnetic sheet of the present invention includes a flat magnetic powder, and a resin binder capable of dissolving in a solvent, wherein the magnetic sheet has a gradient of the content ratio of the magnetic powder to the resin binder in a thickness direction thereof, wherein, in use, the magnetic sheet is folded so that, of the front and back surfaces thereof, one surface whose magnetic powder content is lower than that of the other is folded inward, and wherein the difference in glossiness measured at a light-incident angle of 60° between the front and back surfaces is 9.4 or more.