RF Shield with Openings for MR Scanner Vibration Control
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Solution Overview
Problem
Electronic devices operating within or near magnetic resonance (MR) scanners face interference from static magnetic fields and time-varying magnetic field gradients, leading to mechanical vibrations and heating due to eddy currents, which compromise their functionality and measurement accuracy.
Innovation Solution
The use of radio frequency shielding with electrically conductive materials featuring openings to suppress time-varying magnetic field gradient-induced vibrations, combined with multiple layers of conductive sheets spaced by insulators, effectively reduces mechanical vibrations and heating while maintaining effective radio frequency shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If radio frequency shielding is used to protect electronic devices from B1 field interference, then radio frequency shielding effectiveness is improved, but mechanical vibration and heating occur due to eddy currents induced by time-varying magnetic field gradients
Solution Approach 1:
The continuous conductive shield is divided into multiple discrete conductive elements arranged in a pattern, which interrupts the formation of large eddy current loops while preserving radio frequency shielding effectiveness through the distributed structure
Solution Approach 2:
The shield is designed with a porous or mesh-like structure consisting of conductive elements with gaps between them, allowing the shield to block radio frequencies while reducing eddy current-induced vibrations and heating by limiting current path continuity
2Object-affected harmful factors
If conductive shielding materials are used to shield electronic devices, then radio frequency interference protection is improved, but eddy currents are induced by time-varying magnetic field gradients causing vibration and heating
Solution Approach 1:
The conductive shield is segmented into discrete elements that limit the size and continuity of eddy current paths, thereby reducing the magnitude of induced currents and associated heating while maintaining radio frequency shielding performance
Solution Approach 2:
The porous structure of the shield creates multiple small current loops instead of large continuous paths, reducing eddy current density and heat generation while preserving the overall shielding effectiveness against radio frequency interference
3Reliability
If continuous conductive shielding is used to protect against radio frequency fields, then radio frequency shielding is effective, but time-varying magnetic field gradients induce strong eddy currents causing mechanical vibration
Solution Approach 1:
The continuous conductive shield is divided into discrete conductive elements arranged in a pattern, which interrupts the formation of large eddy current loops that cause mechanical vibration while preserving radio frequency shielding effectiveness through the distributed structure
Solution Approach 2:
The shield employs a porous or mesh structure with conductive elements spaced apart, reducing eddy current-induced mechanical vibration by limiting current path continuity while maintaining adequate radio frequency shielding performance
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 solution reduces mechanical vibrations and heating in MR environments, enhances radio frequency shielding, and minimizes measurement errors in electronic devices, such as patient monitors, by dissipating gradient energy and increasing electrical resistance.
Implementation Method 1
The time-varying magnetic field gradients present a fast changing magnetic field that induces eddy currents in conductors. These eddy currents interact with the B0 and other electromagnetic fields in the MR bore and can cause conductors to mechanically vibrate.
Implementation Method 2
The time-varying magnetic field gradients present a fast changing magnetic field that induces eddy currents in conductors
Implementation Method 3
The influence of the B1 radiofrequency field can be reduced by employing radio frequency shielding techniques such as soldering an on-board shield to a printed circuit board in order to shield sensitive electronics
Data Source
AI summary
An apparatus comprises an electrical device or component (40) and a radio frequency shield arranged to shield the electrical device or component. The apparatus is disposed in a radio frequency (Bi) field generated by a magnetic resonance scanner and in time varying magnetic field gradients generated by the magnetic resonance scanner (10). The radio frequency shield includes an electrically conductive sheet or layer having openings suppressing time varying magnetic field gradient induced vibration of the radio frequency shield.