MRI Balun Circuit Topology for Stable Common-Mode Noise Blocking
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Solution Overview
Problem
In MRI apparatuses, unbalance in the characteristic impedance of coaxial cables leads to variations in balun reactance, causing the resonance frequency to shift, which reduces the balun's ability to effectively block common mode noise, and increasing the number of baluns can degrade performance and occupy space, weight, and cost.
Innovation Solution
A balun configuration with multiple serial resonance circuits connected in parallel, where each circuit's resonance frequency is adjustable to fall within a range that includes the common mode noise frequency, ensuring effective noise blocking even with impedance unbalance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single balun is used in the coaxial cable, then the structure is simple, but the resonance frequency shifts when impedance unbalance occurs, reducing noise blocking effectiveness
Solution Approach 1:
The balun is segmented into multiple independent parallel resonance circuits, each with its own resonant frequency. This segmentation allows the system to maintain effectiveness across a broader frequency range even when impedance variations occur, as at least one circuit remains tuned to the operating frequency.
Solution Approach 2:
The invention changes the frequency parameter by introducing multiple resonance circuits with different resonant frequencies. By adjusting the inductance and capacitance values of each circuit, the system ensures that at least one circuit remains effective at the operating frequency despite impedance unbalance, thereby maintaining noise blocking reliability.
2Reliability
If multiple baluns are connected in series to maintain noise blocking, then the noise blocking effectiveness is improved, but the weight, volume, and cost increase
Solution Approach 1:
Multiple resonance circuits are merged into a single parallel configuration within one balun structure. This combining approach achieves the noise blocking effectiveness of multiple baluns while consolidating them into a single unit, thereby reducing overall weight, volume, and cost compared to using multiple separate baluns in series.
3Reliability
If multiple baluns are connected in series to maintain noise blocking, then the noise blocking effectiveness is improved, but the device complexity increases
Solution Approach 1:
Multiple resonance circuits are merged into a single parallel configuration within one balun structure. This combining approach achieves the noise blocking effectiveness of multiple baluns while consolidating them into a single unit, thereby reducing overall weight, volume, and cost compared to using multiple separate baluns in series.
Solution Approach 2:
The single balun structure performs multiple functions by incorporating multiple parallel resonance circuits that can handle different frequency conditions. This multi-functionality allows one balun to replace what would traditionally require multiple separate baluns, simplifying the overall system architecture.
4Object-affected harmful factors
If the resonance frequency is tuned to the nuclear magnetic resonance frequency, then the common mode noise blocking is maximized, but the performance degrades when impedance unbalance causes frequency shift
Solution Approach 1:
The balun is segmented into multiple independent parallel resonance circuits, each with its own resonant frequency. This segmentation allows the system to maintain effectiveness across a broader frequency range even when impedance variations occur, as at least one circuit remains tuned to the operating frequency.
Solution Approach 2:
The invention changes the frequency parameter by introducing multiple resonance circuits with different resonant frequencies. By adjusting the inductance and capacitance values of each circuit, the system ensures that at least one circuit remains effective at the operating frequency despite impedance unbalance, thereby maintaining noise blocking reliability.
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 configuration maintains effective common mode noise blocking with improved RF coil performance, reducing resonance frequency shifts and allowing for a simpler, cost-effective design.
Implementation Method 1
multiple serial resonance circuits having different resonance frequencies are connected in parallel... at least one of the resonance frequencies of the multiple serial resonance circuits is adjusted to be lower than a frequency at which the balun blocks the common mode noise, and at least one of the resonance frequencies is adjusted to be higher than the frequency at which the balun blocks the common mode noise
Data Source
AI summary
The present invention provides a technique for maintaining a function for effectively blocking common mode noise with a simple configuration, even in the case where unbalance occurs in characteristic impedance of a coaxial cable in an MRI apparatus, and improving the performance of an RF coil. In a circuit where a balun is established by parallel connection with the coaxial cable, multiple serial resonance circuits having different resonance frequencies are connected in parallel. A value of each constitutional element of each of the serial resonance circuits is adjusted in such a manner that the frequency for blocking the common mode noise of the entire balun falls into a range between the resonance frequencies of these serial resonance circuits.