Skewed Antenna Coil Coupling for RFID Systems
Solution Overview
Problem
Existing HF band RFID systems face challenges in achieving sufficient magnetic coupling between the feed coil and the antenna coil, leading to inefficient signal transmission due to large distances and reduced inductance values, which hinder effective communication in communication terminal devices.
Innovation Solution
The antenna device incorporates a feed coil and an antenna coil with a coupler portion that electromagnetically couples, where the winding axes are skewed relative to each other, and magnetic body portions are strategically arranged to enhance coupling efficiency, including a magnetic shielding layer to reduce eddy currents and improve radiation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ferrite sheet is attached on the coil antenna to cover the whole surface, then magnetic coupling is improved, but the distance between feed coil and antenna coil becomes too large resulting in insufficient magnetic coupling
Solution Approach 1:
The patent applies local quality by placing magnetic bodies only at specific locations (both ends of the antenna coil) rather than covering the entire surface with a ferrite sheet. This localized approach maintains magnetic coupling effectiveness while reducing the overall distance and improving signal transmission between the feed coil and antenna coil.
2Device complexity
If the size of the magnetic sheet is reduced to fit the antenna coil, then the inductance value decreases, but sufficient magnetic coupling cannot be obtained
Solution Approach 1:
The patent uses local quality by positioning magnetic bodies at both ends of the antenna coil rather than using a uniformly sized magnetic sheet. This configuration maintains sufficient inductance value while achieving effective magnetic coupling, as the magnetic bodies at the ends concentrate the magnetic flux where it is most needed for coupling with the feed coil.
Solution Approach 2:
The patent employs composite materials by combining magnetic bodies with the antenna coil structure. The magnetic bodies are made of ferrite or other magnetic materials with specific permeability characteristics, creating a composite structure that enhances magnetic coupling while maintaining appropriate inductance values.
3Reliability
If the winding axis of feed coil and antenna coil are aligned parallel, then magnetic coupling is maximized, but eddy currents are induced in conductor layers causing energy loss
Solution Approach 1:
The patent applies asymmetry by skewing the winding axis of the antenna coil relative to the feed coil at an angle between 0 and 90 degrees. This asymmetric configuration reduces eddy current induction in conductor layers while maintaining sufficient magnetic coupling through the strategic placement of magnetic bodies at the antenna coil ends.
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 significantly increases the coupling coefficient between the feed coil and the antenna coil, enhancing transmission efficiency and reducing losses, while allowing for a more compact and flexible antenna design that can be easily integrated into communication terminal devices.
Implementation Method 1
a feed coil connected to a RFID IC chip is mounted on a control board and allows to magnetically couple with an antenna coil
Implementation Method 2
an antenna coil including a coil conductor, a portion of the antenna coil being a coupler portion that electromagnetically couples with the feed coil
Implementation Method 3
at a section of the antenna coil other than the coupler portion, a first magnetic body portion is arranged at a feed coil side of the antenna coil
Data Source
AI summary
An antenna device includes a feed coil including a coil conductor and being connected to a feed circuit, and an antenna coil including a coil conductor, a portion of the antenna coil being a coupler portion that electromagnetically couples with the feed coil. The winding axis of the coil conductor of the feed coil is not parallel to the direction along which the coil conductor of the antenna coil at the coupler portion extends. Further, at other than the coupler portion, a first magnetic body portion is arranged at a feed coil side of the antenna coil, and at the coupler portion, a second magnetic body portion is arranged at a side of the antenna coil opposite to the feed coil.