Microstrip Hybrid Coupler T/R Switch for Dual-Field MRI
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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 3T and 7T magnetic resonance imaging.
Innovation Solution
A hybrid coupler-based transmit/receive switch using microstripline hybrid couplers and PIN diodes, designed on dielectric substrates, which operates at both 3T and 7T magnetic field strengths, enabling broadband frequency operation and short rise time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PIN diode T/R switches are used to achieve low insertion loss and high isolation, then signal quality is improved, but rise time increases and power handling is limited
Solution Approach 1:
The patent divides the T/R switch function into separate modules: a hybrid coupler for signal splitting/combing and a PIN diode switch for switching control. This segmentation allows each component to be optimized independently - the hybrid coupler handles signal processing with minimal rise time requirements, while the PIN diode switch focuses on isolation and insertion loss performance.
Solution Approach 2:
The hybrid coupler acts as an intermediary component between the RF amplifier and the PIN diode switch. It pre-processes the signal by creating orthogonal combinations of transmit and receive modes, which reduces the switching time requirements of the subsequent PIN diode switch and improves overall rise time performance while maintaining signal quality.
2Object-affected harmful factors
If PIN diode switches are used to provide isolation between transmit and receive paths, then interference is reduced, but power handling capability is limited
Solution Approach 1:
The patent separates the isolation function from the power handling function. The hybrid coupler handles high power signal processing and mode conversion, while the PIN diode switch provides isolation only when needed. This segmentation allows the system to achieve both high power handling capability and effective interference isolation without being limited by the power handling constraints of the PIN diode switch alone.
Solution Approach 2:
The hybrid coupler performs power handling and signal conditioning before the signal reaches the PIN diode switch. By pre-processing the signal and creating orthogonal modes in advance, the system protects the PIN diode switch from high power stress while maintaining its isolation function, effectively cushioning against power handling limitations.
3Adaptability or versatility
If coplanar waveguide lines are used to achieve high frequency broadband, then frequency range is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex coplanar waveguide structures with a simplified hybrid coupler design using standard microstripline technology. The hybrid coupler achieves broadband frequency performance through its orthogonal mode conversion capability rather than through complex waveguide geometries, significantly reducing structural complexity while maintaining frequency adaptability.
Solution Approach 2:
The hybrid coupler serves multiple functions simultaneously: it acts as a signal splitter, a mode converter, and a broadband matching network. This multi-functionality eliminates the need for separate components for each function, reducing overall device complexity while achieving high frequency broadband performance through a single integrated structure.
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 fast switching times, ensuring high-quality MRI images with minimal distortion by isolating transmit and receive paths.
Implementation Method 1
The multi-bended microstripline is configured to receive RF electrical signals at the first port and transmit RF electrical signals at a resonance frequency of about 127.8 MHz at each of the second port and at the fourth port
Implementation Method 2
The hybrid coupler also includes a first pair of parallel resonant circuits connected to the junction between the first arm and the fourth arm
Data Source
AI summary
A transmit/receive switch for magnetic resonance imaging (MRI) of a 1H atomic nucleus at 3T (tesla) and 7T 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 3T and at a third harmonic frequency of about 298 MHz at 7T.