Tapered Common Mode Trap for MRI Detuning Prevention
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Solution Overview
Problem
Conventional common mode traps in MRI systems face challenges such as difficult placement, excessive voltage and power dissipation, and detuning due to fringe magnetic fields, which affect image quality and component heating.
Innovation Solution
A common mode trap design featuring a central conductor with counterwound conductors that taper radially from the ends to the midpoint, reducing coupling and allowing for increased density without detuning, and optionally including a dielectric spacer and orthogonal conductor paths to minimize magnetic field interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional common mode traps are placed at appropriate locations to block common mode currents, then common mode blocking is improved, but placement difficulty and device complexity increase
Solution Approach 1:
The common mode trap is divided into multiple discrete sections along the cable length, with each section providing independent common mode blocking capability. This segmentation allows the trap to be effective at multiple locations without requiring complex single-point placement, thereby improving reliability while simplifying installation.
Solution Approach 2:
The common mode trap design provides multiple functions: it blocks common mode currents, reduces voltage and power dissipation, and prevents coupling between adjacent traps. The same structural elements accomplish all these functions simultaneously, improving reliability without proportionally increasing placement complexity.
2Productivity
If conventional common mode traps are placed close together to increase density, then space utilization is improved, but coupling and detuning occur due to fringe magnetic fields
Solution Approach 1:
The harmful fringe magnetic fields that cause coupling between adjacent traps are extracted or contained within shielded regions. By removing the problematic electromagnetic interaction between closely-spaced traps, high density placement can be achieved without detuning, thus improving productivity while maintaining reliability.
Solution Approach 2:
Shielding structures or dielectric materials are introduced as intermediary elements between adjacent common mode traps. These intermediaries prevent direct magnetic coupling between traps while allowing the traps to be positioned close together, enabling high density placement without detuning.
3Reliability
If conventional common mode traps are placed at appropriate locations to block currents, then common mode blocking is improved, but excessive voltage and power dissipation occur
Solution Approach 1:
The common mode trap employs dynamic impedance characteristics that adapt to the operating conditions. By using tunable reactive elements, the trap presents high impedance to common mode currents while maintaining low losses, achieving effective blocking without excessive power dissipation.
Solution Approach 2:
The electrical parameters (inductance, capacitance, resistance) of the common mode trap are optimized to achieve the desired blocking performance with minimal losses. By carefully selecting and adjusting these parameters, the trap provides effective common mode rejection while minimizing voltage and power dissipation.
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
This design enhances MRI system performance by reducing field distortions, heat distribution issues, and ensuring effective common mode blocking across the transmission cable, while maintaining flexibility and preventing hot spots.
Implementation Method 1
baluns or common mode traps positioned too close to each other on a cable may become coupled due to fringe magnetic fields
Data Source
AI summary
Various methods and systems are provided for a common mode trap for a magnetic resonance imaging (MRI) apparatus. In one embodiment, a common mode trap for an MRI apparatus comprises: a first conductor and a second conductor counterwound around a length of a central conductor, wherein the first and the second conductors are radially spaced a first distance from the central conductor at first and second ends of the length, and wherein the first and the second conductors are radially spaced a second distance larger than the first distance from the central conductor at a midpoint of the length. In this way, coupling and subsequent detuning of common mode traps provided adjacent to one another may be prevented.