Magnetron Lower End Shield Optimization for EMI Reduction
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Solution Overview
Problem
The existing magnetron for microwave ovens generates excessive electromagnetic interference (EMI) beyond the 2.5 GHz to 5.725 GHz frequency range, exceeding the 92 dB μV/m prevention standard, leading to potential malfunctions in other electronic devices due to unnecessary noise, and has reduced output and oscillation efficiency.
Innovation Solution
The magnetron design incorporates a smaller outer diameter lower end shield, positioned to prevent electron deviation, and a shield disc with optimized hole positions and angles to efficiently guide electron beams, reducing noise and improving output and oscillation efficiency, while maintaining the electromagnetic interference prevention standard.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a conventional magnetron design is used, then the microwave generation function is achieved, but excessive electromagnetic interference (EMI) is generated beyond the ISM band
Solution Approach 1:
The patent extracts and eliminates the source of harmful electromagnetic interference by optimizing the electron beam path and magnetic field distribution. Specifically, the invention modifies the cathode structure and magnetic pole arrangement to confine electron emission and movement within the ISM band frequency range, preventing the generation of out-of-band EMI while maintaining reliable microwave operation.
Solution Approach 2:
The patent applies parameter changes by adjusting the magnetic field strength distribution and electron beam velocity characteristics. By controlling the magnetic flux density in different regions and modifying the cathode heating parameters, the invention tunes the electron cyclotron resonance frequency to stay within the ISM band, thereby reducing EMI generation while ensuring stable operation.
2Power
If the magnetron operates at high power, then the microwave output is sufficient, but the EMI prevention standard is exceeded
Solution Approach 1:
The patent applies local quality by creating non-uniform magnetic field distribution and localized electron beam confinement. The magnetic pole pieces are designed with varying shapes and positions to concentrate magnetic flux in specific regions, which locally controls electron beam trajectories. This allows high power microwave generation in the ISM band while suppressing electron movements that would generate out-of-band noise, thus meeting EMI standards.
Solution Approach 2:
The patent introduces intermediary structures such as magnetic shielding plates and optimized cathode geometries that mediate between the high-power electron beam and the surrounding environment. These intermediaries redirect electron paths and absorb excess energy that would otherwise generate harmful EMI, enabling high power operation while maintaining compliance with noise regulations.
3Loss of energy
If the existing magnetron structure is used, then the basic function is maintained, but the oscillation efficiency is reduced
Solution Approach 1:
The patent applies dynamics by making the magnetic field distribution adjustable and the electron beam path controllable. The magnetic pole pieces are designed with dynamic field concentration capabilities, allowing the magnetic flux to adaptively follow electron beam movements. This dynamic control optimizes the interaction between electrons and magnetic field, improving oscillation efficiency without requiring complex mechanical adjustments or additional components.
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 design effectively minimizes EMI generation, enhances output and oscillation efficiency, and ensures compliance with the electromagnetic interference prevention standard, improving the reliability and performance of microwave ovens, while reducing manufacturing costs and defective rates.
Implementation Method 1
a magnetic field formed by the permanent magnets forms a magnetic circuit along an upper magnetic pole and a lower magnetic pole, so that a magnetic field is generated in a working space between a vane and a filament
Implementation Method 2
the magnetron generates microwaves of 2.45 GHz by being applied a high-voltage power to radiate the microwaves to a cooking chamber
Implementation Method 3
The filament emits thermal electrons at a temperature of about 2000K while an external power is applied to the filament. In the working space, an electron group is formed by the emitted thermal electron
Implementation Method 4
a strong electric field is formed in the working space by the anode voltage applied to the anode and the magnetic field acts in a vertical direction of the electric field. By the electric field and the magnetic field, the electron group proceeds to the vane while performing a cycloid movement
Implementation Method 5
a high frequency having a resonance frequency corresponding to the speed at which the electron group rotates is induced to the vane
Data Source
AI summary
A magnetron for a microwave oven is provided that decreases noise in an ISM band by minimizing a size of a lower end shield, and thus, minimizing EMI generation. In the magnetron for the microwave oven, as a midpoint of a side lead hole is positioned inside a virtual circle formed by points positioned at a predetermined distance from a midpoint of the shield disc and a side lead is connected in a straight line, there are advantages that a further bending process is not generated and a defective rate that occurs in the manufacturing process of the shield disc may be decreased.