Antenna Coil With Bobbin Buffer For Inductance Stability
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Solution Overview
Problem
Conventional bar antennas for smart key systems face issues with inductance value fluctuations due to thermal stress and reduced productivity, particularly in molding type antennas where heat from the molding process causes expansion or shrinkage of potting materials, leading to deflection and changes in the inductance value.
Innovation Solution
A coil design featuring a bar-shaped core enveloped by a bobbin with a resin molded body, where the bobbin is longer than the core and covers the most susceptible surface to deflection, minimizing thermal stress impact on the core and allowing for inductance adjustment by sliding the core within the bobbin, and using thermosetting or UV-setting resin to reduce drying time and enhance production efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a bar-shaped core is used in a molding type antenna, then production time is short because there is no drying process, but the heat during the molding process creates thermal stress on the core and the inductance value may change
Solution Approach 1:
A resin layer is introduced as an intermediary substance between the bar-shaped core and the molded resin. This resin layer absorbs and distributes the thermal stress generated during the molding process, preventing direct stress concentration on the core. The resin layer acts as a buffer that protects the core from deflection while still allowing the molding process to proceed without a drying step, thus maintaining high productivity while improving inductance value stability.
2Reliability
If potting material is used to fill gaps in a potting type bar antenna, then the core is protected from external influences, but significant amount of time is required to dry the resin which reduces productivity
Solution Approach 1:
Instead of using traditional potting material that requires extensive drying time, a resin layer is used that can be applied and cured quickly. This resin layer provides sufficient protection to the core from external influences during the critical period, after which the molded resin provides long-term protection. The resin layer serves as a temporary protective measure that enables faster production cycles.
3Quantity of substance
If the bobbin is made shorter to reduce material usage, then manufacturing cost decreases, but the core becomes more susceptible to deflection under thermal stress
Solution Approach 1:
The bobbin is designed with asymmetric length relative to the core, extending beyond one end of the core while potentially being shorter at the other end. This asymmetric design allows the bobbin to provide maximum protection at the critical end where thermal stress concentration occurs, while minimizing material usage in less critical areas. The asymmetric configuration optimizes the balance between material efficiency and core protection.
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 coil design achieves minimal inductance value fluctuation and increased production rate by distributing thermal stress to the bobbin rather than the core, maintaining inductance stability across temperature changes and reducing production time.
Implementation Method 1
the heat during the molding process creates a thermal stress on the core and the inductance value may change. The problems about the stress on the core and the change of the inductance value is caused by expantion or shrinkage of the potting material and molded resin according to environmental temperature.
Implementation Method 2
by generating an AC magnetic field from a reader that is connected to a power supply, a voltage will be induced in a coil inside the key and an electric current will occur
Data Source
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AI summary
The present invention is to provide a coil for an antenna with small inductance fluctuation and high productivity. According to the invention, an antenna coil 1 includes: a bar-shaped core 10, a bobbin 20 which is structured as to at least cover the most deflectable face of the bar-shaped core 10, a coil 30 which is wound around the surface of the bobbin 20, and a resin molded body 3 which covers the bobbin 20 around which the coil 30 is wound.