Flexible PCB Shim Coils for Compact MRI Gradient Cooling
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Solution Overview
Problem
Existing gradient and shim coil assemblies for MR-devices face challenges in achieving compactness, efficient cooling, precise positioning, and simplified manufacturing, with issues related to space utilization, heat dissipation, and complex wire coil manufacturing.
Innovation Solution
A combined gradient and shim coil assembly using flexible printed circuit boards with a heat-conductive filler and vacuum casting, allowing for precise positioning and efficient cooling, reducing space requirements, and simplifying the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wire coils with variable pitch or arrangements of several wire coils are used to generate higher field orders, then field characteristics with quadratic, cubic or other dependence on spatial coordinates can be achieved, but the coils become complex and delicate to manufacture with complex frame coil bending and exact positioning requirements
Solution Approach 1:
The patent replaces traditional mechanical wire coil winding and frame bending with a flexible printed circuit board (FPCB) system. The FPCB carries conductor traces that form the shim coils, eliminating the need for manual wire winding, frame bending, and precise mechanical positioning. The FPCB can be precisely manufactured using standard PCB fabrication processes, and its flexibility allows it to conform to the cylindrical gradient tube surface without complex mechanical structures.
Solution Approach 2:
The patent changes the physical state and properties of the coil support structure from rigid wire and frame materials to flexible printed circuit board material. This parameter change enables the coil structure to be manufactured with standard PCB processes rather than delicate wire winding operations, significantly simplifying manufacturing while maintaining precise geometric control through the FPCB's inherent dimensional stability.
2Power
If the inner diameter of the gradient tube is reduced to increase the magnetic field strength, then higher field orders can be achieved, but the space available for gradient coils, shim coils and cooling is limited
Solution Approach 1:
The patent utilizes the radial dimension by positioning the FPCB-based shim coils on the outer surface of the cylindrical gradient tube, concentric with the inner bore. This dimensional arrangement allows the shim coils to occupy the radial space outside the gradient tube rather than competing for the limited axial or circumferential space within the tube's inner diameter, effectively utilizing previously unused spatial volume.
Solution Approach 2:
The patent implements a nested configuration where the FPCB-based shim coil system is positioned on the outer surface of the gradient tube, with the cooling channels embedded within the gradient tube structure itself. This nested arrangement allows multiple functional systems (gradient coils, shim coils, cooling) to occupy different radial zones, maximizing space utilization without increasing the overall device footprint.
3Temperature
If plastic or copper heat exchangers are used with chill casting to remove heat from the coils, then active cooling can be achieved, but the manufacturing process becomes complex and the thermal conductivity may be insufficient
Solution Approach 1:
The patent employs a composite material system where the FPCB substrate (typically polyimide or similar flexible polymer) is combined with copper conductor traces and embedded cooling channels. The FPCB itself serves as both the structural support for the shim coils and the thermal management medium, with copper traces providing electrical conductivity and the FPCB material providing thermal conduction pathways to the embedded cooling channels, eliminating the need for separate copper or plastic heat exchanger components.
Solution Approach 2:
The FPCB serves multiple functions simultaneously: it provides the structural support for the shim coil conductors, acts as an electrical insulator between adjacent conductors, serves as a thermal conduction medium to transfer heat from the coils to the cooling channels, and provides mechanical flexibility for installation. This multi-functionality eliminates the need for separate components for each function, significantly simplifying the manufacturing process.
4Manufacturing precision
If the outer diameter of the gradient tube is increased to accommodate more shim coils, then higher field orders can be generated, but the bore diameter is limited upward
Solution Approach 1:
The patent moves the shim coil structure from the internal volume of the gradient tube to the external surface, utilizing the radial dimension outward from the tube. This allows multiple concentric layers of FPCB-based shim coils to be positioned on the tube's outer surface, each layer contributing to different field order corrections, without increasing the tube's outer diameter or encroaching on the bore space.
Solution Approach 2:
The patent divides the shim coil system into multiple independent FPCB layers, each carrying specific conductor patterns for different shim coil windings. These segmented FPCB layers can be manufactured separately and then assembled concentrically on the gradient tube, allowing systematic addition of different field order corrections without requiring a single large, complex coil structure that would increase the tube diameter.
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 solution enables a compact, efficiently cooled, and precisely positioned coil assembly with reduced assembly steps, high thermal conductivity, and improved dielectric strength, suitable for pre-clinical MRI systems.
Implementation Method 1
a sealing compound with a fluid reaction resin augmented with a heat conductive filler enclosing the components of the assembly to form a cylindrical tube and filling the cavities of the gradient and the shim coil systems and between the coils and the carrier tube
Data Source
AI summary
A combined gradient coil and shim coil assembly for use in MR-devices, comprising a cylindric carrier tube, a gradient coil system arranged concentrically onto the carrier tube, a cooling tube assembly positioned around the gradient coils, and an active shim coil system, is characterized in that the active shim coil system is constructed on a flexible printed circuit board, and the assembly further comprises a sealing compound with a fluid reaction resin augmented with a heat conductive filler enclosing the components of the assembly to form a cylindrical tube and filling the cavities of the gradient and the shim coil systems and between the coils and the carrier tube. Such a combined gradient and shim coil assembly is particularly compact having an efficient cooling system allowing a precise positioning of the coils and a time-saving manufacturing.