Resin-Coated Coil Antenna With Stable Ferrite-Core Inductance
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Solution Overview
Problem
Resin-molded antennas in keyless entry systems and tire pressure-monitoring systems face issues with temperature-dependent and stress-dependent inductance changes, leading to resonance frequency discrepancies and reduced communication effectiveness.
Innovation Solution
A resin-coated coil device with a Ni ferrite core having specific permeability and crystal grain size characteristics, along with a composition of 47.5-48.4% Fe2O3, 25.0-30.5% ZnO, and 7.0-11.5% CuO, which maintains inductance stability within a wide temperature range and under stress, is used to suppress inductance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ferrite core is used in a resin-molded antenna, then the antenna can achieve the required inductance for LF wave communication, but the inductance changes with temperature and stress, causing resonance frequency discrepancy
Solution Approach 1:
The patent changes the physical parameters of the ferrite core by controlling its average crystal grain size to be 5-9 μm and adjusting its composition (47.5-48.4% Fe2O3, 25.0-30.5% ZnO, 7.0-11.5% CuO). These parameter changes result in a ferrite core with initial permeability of 450 or more and temperature-dependent inductance change ratios of -0.6% to +0.6%, significantly reducing inductance variation with temperature and stress while maintaining communication reliability
Solution Approach 2:
The patent uses a composite ferrite material containing multiple metal oxides (Fe2O3, ZnO, CuO, and NiO) with specific compositional ratios. This composite material structure provides both high initial permeability (μi ≥ 450) and stable inductance characteristics across temperature ranges, resolving the contradiction between achieving required inductance and maintaining inductance stability
2Measurement precision
If the resonance frequency is adjusted to match communication frequency at a specific temperature, then communication works at that temperature, but frequency discrepancy occurs at other temperatures
Solution Approach 1:
The patent changes the temperature stability parameter of the ferrite core by controlling crystal grain size (5-9 μm) and composition, achieving temperature-dependent inductance change ratios of -0.6% to +0.6%. This allows the antenna to maintain accurate resonance frequency across a wide temperature range (-40°C to +80°C), providing both frequency accuracy and temperature adaptability
Solution Approach 2:
The patent makes the ferrite core's magnetic properties dynamically stable across temperature changes. By optimizing the crystal grain size and compositional parameters, the ferrite core automatically maintains stable inductance characteristics throughout the operating temperature range, enabling the resonance frequency to remain accurate without manual adjustment
3Temperature
If a ferrite material with negative temperature coefficient of permeability is used, then temperature-dependent inductance change is reduced, but stress-dependent inductance change remains significant
Solution Approach 1:
The patent simultaneously optimizes multiple parameters: average crystal grain size (5-9 μm), initial permeability (μi ≥ 450), and compositional ratios (Fe2O3: 47.5-48.4%, ZnO: 25.0-30.5%, CuO: 7.0-11.5%). This multi-parameter optimization achieves both temperature-dependent inductance change ratios of -0.6% to +0.6% and stress-dependent inductance change ratios of -0.6% to +0.6%, reducing both temperature and stress sensitivity
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 solution provides a stable resonance frequency and improved communication performance by minimizing inductance changes due to temperature and stress variations, ensuring reliable operation across a broad temperature range.
Implementation Method 1
Because ferrite materials forming the ferrite core have permeability variable with temperature and stress, the inductance of the resin-molded antenna likely changes by ambient temperature changes
Implementation Method 2
Because ferrite materials forming the ferrite core have permeability variable with temperature and stress
Data Source
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AI summary
A coil device comprising a coil, and a ferrite core arranged in a hollow portion of the coil, and a resin covering them; the ferrite core being a Ni ferrite core having initial permeability µi of 450 or more at a frequency of 100 kHz and a temperature of 20°C, and an average crystal grain size of 5-9 µm, both of temperature-dependent inductance change ratios TLa and TLb and stress-dependent inductance change ratios PLa and PLb being -0.6% to +0.6%, and both of the sum of TLa and PLa and the sum of TLb and PLb being more than -1.0% and less than +1.0%; and an antenna comprising it.