Embedded Solenoid Filter for PCB EMI Reduction
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Solution Overview
Problem
Printed circuit boards (PCBs) face challenges in mitigating electromagnetic interference (EMI) due to the limitations of existing EMI filters, such as discrete components which are costly, consume valuable space, and are sensitive to manufacturing tolerances.
Innovation Solution
Integration of solenoid filters within the PCBs to reduce common-mode RF interference by impeding changes in electric current on DC supply or signal traces, with the filtered frequency range tunable by modifying the number of turns, length, and width of the solenoid, allowing for broadband interference signal reduction without adding series resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discrete components (resistors, capacitors, inductors) are used to build EMI filters, then the filters can be assembled on PCBs, but they consume valuable surface area and are sensitive to manufacturing tolerances
Solution Approach 1:
The patent merges the EMI filter functionality directly into the PCB structure by embedding solenoid traces within the PCB layers. This integration eliminates the need for separate discrete components, thereby conserving PCB surface area while ensuring consistent filter performance through precise manufacturing control of the embedded traces.
Solution Approach 2:
The PCB structure is designed to serve multiple functions: it provides structural support, electrical connectivity through standard traces, and EMI filtering through embedded solenoid traces. This multi-functionality eliminates the need for additional discrete filter components, reducing both surface area consumption and manufacturing complexity.
2Object-affected harmful factors
If ferrite beads are used to attenuate EMI, then EMI suppression is achieved, but they are expensive and result in additional series resistance in power traces
Solution Approach 1:
The patent replaces the ferrite bead mechanism (which relies on magnetic material properties) with an electromagnetic induction mechanism using solenoid traces. This substitution eliminates the need for expensive ferrite materials and avoids the series resistance issues associated with ferrite beads, while achieving comparable or superior EMI suppression through inductive coupling.
3Object-affected harmful factors
If ferrite beads are surface-mounted to combat EMI, then EMI filtering is provided, but they consume valuable space on the PCB
Solution Approach 1:
The patent embeds the solenoid filter traces within the internal layers of the PCB, nesting the filtering functionality inside the existing PCB structure. This approach eliminates the need for external surface-mounted ferrite beads, thereby conserving valuable PCB surface area while maintaining effective EMI suppression through the embedded solenoid configuration.
4Manufacturing precision
If discrete components are used in EMI filters, then the filters can be implemented, but it is difficult and expensive to ensure the intended cutoff frequency due to manufacturing tolerances
Solution Approach 1:
The patent combines the filter traces directly into the PCB manufacturing process, eliminating the need for separate component assembly. This integration ensures precise control over trace dimensions, spacing, and geometry, thereby achieving accurate cutoff frequencies without the variability introduced by discrete component tolerances and manual assembly processes.
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 solenoid filters effectively reduce EMI susceptibility without degrading desired signals, conserve PCB space, and are insensitive to manufacturing tolerances, providing a cost-effective solution for EMI mitigation in various electronic devices.
Implementation Method 1
The solenoid filters reduce common-mode RF interference by impeding changes in the electric current on DC supply or signal traces
Implementation Method 2
Higher-frequency energy couples with the ferrite bead, thereby developing impedance that has inductive and resistive components. The inductive reactance reduces the conducted EMI current
Data Source
AI summary
Disclosed herein are printed circuit boards with embedded solenoid filters through which signal traces pass to filter unwanted noise and electromagnetic interference. A printed circuit board comprises a least three layers, a solenoid embedded within the at least three layers, and at least one trace extending through the solenoid. The insertion loss characteristics of the solenoid filter can be tuned by modifying the number of turns in the solenoid(s) and the width of the solenoid(s). The solenoid filter may comprise multiple solenoids connected in series, with adjacent solenoids having opposite wind directions. Surface components may be included on the board to tune the insertion loss further.