Stacked Coil Antenna for RFID Resonant Frequency Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Wireless IC devices used in RFID systems face issues with resonant frequency variation due to changes in usage conditions, such as the proximity of a person's hand, leading to inconsistent performance and the need for adjustment during manufacturing.
Innovation Solution
The design involves superposing coil electrodes to form a single ring when viewed from the normal direction, reducing the leakage of electric field lines and minimizing capacitance changes, thereby stabilizing the resonant frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If coil electrodes are arranged side by side in a spiral shape on the substrate surface, then the antenna coil can be formed with simple structure, but the resonant frequency varies with usage conditions due to capacitance changes
Solution Approach 1:
The patent transitions from a two-dimensional planar spiral arrangement to a three-dimensional stacked configuration where multiple coil electrodes are superimposed on different layers separated by insulating sheets. This dimensional change causes electric field lines to extend primarily in the vertical direction between stacked coils rather than horizontally between adjacent spiral turns, preventing hand proximity from affecting capacitance and stabilizing resonant frequency.
2Manufacturing precision
If adjustment capacitors are added to trim resonant frequency, then the resonant frequency can be adjusted during manufacturing, but the device complexity and manufacturing process are increased
Solution Approach 1:
The stacked coil structure inherently provides stable resonant frequency characteristics that do not require external adjustment mechanisms. The design self-regulates by preventing the capacitance variation problem at its source through the three-dimensional configuration, eliminating the need for adjustment capacitors and trimming processes that would otherwise be necessary.
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 suppresses resonant frequency variations with usage conditions, eliminating the need for adjustment capacitors and simplifying the manufacturing process by maintaining a consistent resonant frequency across different usage scenarios.
Implementation Method 1
a non-contact IC card described in Patent Document 1 is known as an example of wireless IC devices used for access management, commuter passes, credit cards and the like
Implementation Method 2
an adjustment resistor (not illustrated in Fig. 19) and an adjustment capacitor 108 are connected to the antenna coil 104
Implementation Method 3
an inductance L100 of the antenna coil 104, a resistance R100 of the IC 106 and a capacitance C100 of the antenna coil 104 are illustrated
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3
AI summary
To provide a wireless IC device for which varying of the resonant frequency with the condition of use can be reduced and a method of manufacturing the wireless IC device. A plurality of insulating sheets (12a to 12d) are stacked on top of one another. Coil electrodes (14a to 14d) are provided so as to sandwich therebetween the insulating sheets (12a to 12d) and form an antenna coil (L) by being connected to one another. The plurality of coil electrodes (14a to 14d) are superposed with one another and thereby form a single ring when viewed in plan from a z-axis direction.