Hybrid Coupler MRI T/R Switch for Broadband High-Power Isolation
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Solution Overview
Problem
Existing T/R switches for MRI systems face limitations such as long rise time, limited power handling, and narrow frequency range, which hinder their performance in high-field MRI applications like 3 T and 7 T magnetic resonance imaging.
Innovation Solution
A hybrid coupler-based transmit/receive switch utilizing microstripline hybrid couplers and PIN diodes, designed for 3 T and 7 T MRI, with a multi-bended microstripline configuration and parallel resonant circuits, enabling broadband frequency operation and fast switching between transmission and reception modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If PIN diode T/R switch uses many sections of coplanar waveguide lines to achieve high frequency broadband, then frequency range is improved, but device complexity increases
Solution Approach 1:
The patent divides the T/R switch into multiple functional sections, each with specific coplanar waveguide line configurations optimized for different frequency ranges. This segmentation allows the overall device to achieve broadband operation while keeping each individual section relatively simple and manageable.
Solution Approach 2:
The patent transitions from traditional planar circuit layouts to a three-dimensional integrated structure where coplanar waveguide lines are arranged in multiple layers and orientations. This dimensional change enables compact integration of broadband matching networks without proportionally increasing device footprint or complexity.
2Reliability
If PIN diode switch is used for T/R switching, then isolation between transmit and receive paths is improved, but power handling capability deteriorates due to limited power handling and damage from high power pulses
Solution Approach 1:
The patent introduces intermediate matching networks and impedance transformation stages between the PIN diode switch and the high-power transmit path. These intermediary components gradually transform the impedance levels, allowing the PIN diode to handle high power indirectly while maintaining effective isolation between transmit and receive paths.
Solution Approach 2:
The patent incorporates protective matching networks and impedance transformation stages before the high-power pulses reach the PIN diode switch. These pre-positioned components cushion the impact of high-power pulses by gradually transforming the power levels, preventing direct exposure of the PIN diode to full transmit power while maintaining isolation performance.
3Adaptability or versatility
If PIN diode T/R switch is designed for high frequency broadband, then frequency range is improved, but rise time increases causing delay in switching
Solution Approach 1:
The patent segments the broadband matching network into multiple discrete stages, each optimized for specific frequency ranges and switching characteristics. This segmentation allows different sections to operate at optimized speeds for their respective frequency bands, achieving overall broadband performance without uniformly increasing rise time across the entire frequency range.
Solution Approach 2:
The patent employs parameter optimization techniques where the electrical lengths, characteristic impedances, and geometries of coplanar waveguide lines are carefully tuned to achieve broadband operation. By optimizing these parameters, the patent achieves wide frequency coverage while minimizing the impact on switching rise time through reduced signal propagation delays.
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 switch achieves high-power handling, broadband frequency range, and short rise time, ensuring high-quality MRI images with minimal distortion by providing isolation between transmit and receive paths.
Implementation Method 1
The multi-bended microstripline coupler is configured to receive RF electrical signals at a first port and transmit RF electrical signals at a fundamental frequency of about 127.8 MHz and at a third harmonic frequency of about 298 MHz, which corresponds to a 1H frequency at 3 T and 7 T magnetic field strengths
Implementation Method 2
A third pair of parallel resonant circuits is connected to a fourth junction of the multi-bended microstripline. The third pair of parallel resonant circuits is tuned to a third harmonic frequency of the RF electrical signals, which corresponds to a 1H frequency at 7 T magnetic field strength
Data Source
AI summary
A transmit/receive switch for magnetic resonance imaging (MRI) of a 1H atomic nucleus at 3 T (tesla) and 7 T magnetic field strengths includes a first and second dielectric substrate and a first and a second microstripline hybrid coupler formed on the first and second dielectric substrates respectively. A first port and a second port are connected to a first junction and a second junction respectively of the first microstripline hybrid coupler, a third port and a fourth port are connected to a third junction and a fourth junction of the second microstripline hybrid coupler respectively. Each port is connected by a matching network embodied by a microstripline wire to a pair of parallel resonant circuits. The transmit/receive switch is configured to operate at a fundamental frequency of about 127.8 MHz at 3 T and at a third harmonic frequency of about 298 MHz at 7 T.