Ferromagnetic Shielding for Camera Coil Noise Reduction
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Solution Overview
Problem
The increase in ISO sensitivity of imaging elements in devices like digital cameras leads to image disturbances due to magnetic field noise from coils, which existing non-magnetic conductive members fail to adequately suppress, resulting in larger apparatus sizes to achieve sufficient noise cancellation.
Innovation Solution
A ferromagnetic member with a thickness less than the skin depth is used between the coil and the imaging element, made of high magnetic permeability materials like permalloy, to absorb and redirect magnetic flux, reducing noise without increasing the apparatus size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a non-magnetic conductive member with thickness equal to or greater than the skin depth is used to cancel magnetic field noise, then the magnetic field noise cancellation effect is sufficient, but the apparatus size increases
Solution Approach 1:
The patent changes the magnetic permeability parameter from non-magnetic (μ≈1) to ferromagnetic (μ≫1). This parameter change reduces the skin depth by a factor of √μ, allowing the use of much thinner shielding members while maintaining adequate noise cancellation performance. The ferromagnetic material provides both magnetic flux shunting and eddy current effects simultaneously.
Solution Approach 2:
The patent employs ferromagnetic materials that combine high magnetic permeability and high electrical conductivity in a single material system. This composite property allows the shielding member to function both as a magnetic flux shunt and as an eddy current generator, achieving superior noise cancellation with reduced thickness compared to non-magnetic materials.
2Volume of moving object
If the thickness of the conductive member is reduced below the skin depth, then the apparatus size is reduced, but the eddy current becomes insufficient and magnetic field noise cancellation effect decreases
Solution Approach 1:
By changing the magnetic permeability parameter to a high value (ferromagnetic material), the patent reduces the skin depth threshold. This allows the use of thinner members (thickness < original skin depth) while maintaining sufficient eddy current generation and magnetic flux shunting effects for adequate noise cancellation.
Solution Approach 2:
The patent converts the high magnetic permeability property, which could potentially concentrate magnetic flux and increase noise, into a beneficial effect by using it to shunt magnetic flux away from the imaging element and to enhance eddy current generation at reduced thickness, thereby achieving noise cancellation where it would otherwise be insufficient.
3Object-affected harmful factors
If a ferromagnetic member with high magnetic permeability is used, then the magnetic flux is absorbed and redirected effectively, but the material selection and manufacturing complexity increases
Solution Approach 1:
The patent specifies quantitative parameter ranges for ferromagnetic materials (relative magnetic permeability μr≥100, electrical conductivity σ≥10^6 S/m, thickness 0.01-0.5mm) to standardize material selection and simplify the manufacturing process. These parameter specifications make it easier to select appropriate materials and control manufacturing quality.
Solution Approach 2:
The patent employs thin ferromagnetic sheets or foils that can be easily manufactured, handled, and installed. These thin materials are cost-effective and can be replaced or adjusted if needed, simplifying the overall manufacturing and maintenance process despite the specialized material requirements.
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 ferromagnetic member effectively absorbs and redirects magnetic flux, reducing noise at the imaging element while maintaining a thinner profile than traditional non-magnetic solutions, thus minimizing image disturbances and apparatus size.
Implementation Method 1
a ferromagnetic member (102), which is formed of a ferromagnetic material
Implementation Method 2
magnetic flux generated from the coil may affect the imaging element
Implementation Method 3
a skin depth d caused by a skin effect is expressed by: skin depth d=√(1/(π·f·σ·μ))
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3C
AI summary
A camera includes a ferromagnetic member (102), which is formed of a ferromagnetic material into one of a plate shape and a film shape, and arranged between a coil and an imaging element so that a part of a flat surface is opposed to the coil. The ferromagnetic member (102) has a thickness that is less than a skin depth, which is determined by a drive frequency of a coil (101), magnetic permeability of the ferromagnetic material, and electric conductivity of the ferromagnetic material. Accordingly, with the ferromagnetic member having a smaller thickness than before, an amount of arrival by which magnetic flux generated at the coil arrives at the imaging element may be reduced.