RF Inductor With Permanent Magnet Shielding
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Solution Overview
Problem
Conventional RF inductors face challenges with high losses and low Q values, especially at microwave frequencies, due to eddy current losses and parasitic capacitance, limiting their efficiency and usability in high-frequency applications.
Innovation Solution
A radio frequency (RF) inductor design featuring a non-conductive ferrimagnetic core with a toroidal shape and a wire coil, incorporating a permanent magnet with an electrically conductive shielding layer to reduce losses and increase efficiency, by creating separate magnetic circuits for DC and RF fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional ferrite core or tunable coil slug is used in RF inductor, then inductance can be achieved, but eddy current losses increase and Q values decrease at microwave frequencies
Solution Approach 1:
The ferrite core is segmented into multiple insulated particles or powder grains rather than using a solid bulk core. This segmentation breaks up continuous eddy current paths, reducing eddy current losses while maintaining magnetic properties. The grains are coated with insulative material to further prevent eddy current formation between particles.
Solution Approach 2:
Different regions of the inductor are assigned different properties: the core uses finely divided insulated ferrite particles optimized for high frequency, while the shielding layer uses conductive material for RF field exclusion. Each region's material properties are locally optimized for its specific function.
2Quantity of substance
If solid core of pure iron or steel is placed inside RF inductor, then magnetic permeability increases, but inductance drops due to conductivity
Solution Approach 1:
The core uses a porous or particulate structure consisting of finely divided ferrite particles with insulative coatings. This porous arrangement allows magnetic field penetration while preventing continuous eddy current paths, resolving the contradiction between magnetic permeability and electrical conductivity.
3Ease of manufacture
If printed spiral inductor is used, then fabrication is simplified, but magnetic field circulation through substrate causes eddy-current loss and higher parasitic capacitance
Solution Approach 1:
A conductive shielding layer is introduced as an intermediary element between the RF magnetic field and the substrate. This shielding layer excludes RF fields from the substrate, preventing eddy current losses and parasitic capacitance while allowing the inductor to maintain its printed spiral fabrication advantages.
4Power
If nickel zinc ferrite core is used, then high efficiency is achieved for small inductor, but resistance losses occur as heat due to partial conductivity
Solution Approach 1:
The harmful conductive property is extracted or removed from the ferrite core by using finely divided particles with insulative coatings. This separates the useful magnetic properties from the harmful electrical conductivity, allowing high efficiency while minimizing resistance losses.
5Quantity of substance
If permanent magnet is added to increase magnetic field strength, then inductance is enhanced, but RF field interference and additional losses may occur
Solution Approach 1:
A conductive shielding layer is placed around the permanent magnet to act as an intermediary that excludes RF fields from the magnet while allowing the DC magnetic field to pass through. This prevents RF field interference and additional losses while maintaining the beneficial DC magnetic field enhancement.
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 achieves higher Q and efficiency by reducing core permeability and eddy current losses, allowing the RF inductor to perform better at higher frequencies, suitable for RF communication circuits and antenna couplers.
Implementation Method 1
a permanent magnet with an electrically conductive shielding layer to reduce losses and increase efficiency, by creating separate magnetic circuits for DC and RF fields
Implementation Method 2
due to eddy current losses and parasitic capacitance, limiting their efficiency and usability in high-frequency applications
Implementation Method 3
an electrically conductive RF shielding layer is on the at least one permanent magnet body
Implementation Method 4
RF magnetic materials must be nonconductive or nearly so, for the magnetic fields to penetrate. Yet, if the same material is finely divided into insulated particles then the inductance increases
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The radio frequency (RF) inductor (10,10') includes a core (12,12') being electrically non-conductive and ferrimagnetic, and having a toroidal shape, and a wire coil (16,16') thereupon. At least one permanent magnet body (18,18') is at a fixed position within the interior of the core, and an electrically conductive RF shielding layer (20,20') is on the at least one permanent magnet body. The core may be ferrite for example. The electrically conductive RF shielding layer may be a conductive plating layer or a metal foil surrounding the permanent magnet body, for example. A magnetic field from the permanent magnet is applied to the inductor core to reduce losses, and the permanent magnet may be enclosed within the conductive shield to keep RF fields out. The inductor may be made small and have increased Q and resulting efficiency. The RF inductor may be applicable to RF communication circuits, for example, as an antenna coupler.