Broadband MRI T/R Switch With Hybrid Microstripline Coupler
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Solution Overview
Problem
Existing magnetic resonance imaging (MRI) technologies lack a broadband switch capable of detecting magnetic resonance signals from nuclei with resonant frequencies below 320 KHz at 3T and 7T field strengths, such as 1H, 19F, 31P, 23Na, and 13C, due to narrowband characteristics of conventional couplers.
Innovation Solution
A broadband hybrid microstripline coupler with a multi-bended structure and mirror image geometry, operating at three frequency ranges (25 MHz to 55 MHz, 61 MHz to 128 MHz, and 250 MHz to 317 MHz), utilizing PIN diodes for switching between transmission and reception states, and a phase inverter to achieve wideband operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional quadrature hybrid coupler is used, then narrowband characteristics are achieved, but broadband operation is not possible
Solution Approach 1:
The hybrid coupler is divided into multiple sections (first section and second section) with different electrical lengths. Each section operates optimally at different frequency ranges, allowing the overall device to achieve broadband operation from 25 MHz to 317 MHz while maintaining stable performance across the entire band.
Solution Approach 2:
The patent introduces a multi-dimensional approach by using couplers with different electrical lengths (90 degrees at 61 MHz for first section, 90 degrees at 298 MHz for second section) and different impedance values (50 ohms and 70.7 ohms). This dimensional variation in electrical characteristics enables broadband operation while maintaining performance stability.
2Adaptability or versatility
If broadband operation is achieved, then multiple frequency ranges are covered, but isolation between ports deteriorates
Solution Approach 1:
Each section of the hybrid coupler is designed with specific local characteristics optimized for different frequency ranges. The first section (50 ohm impedance, 90 degree electrical length at 61 MHz) provides optimal isolation for lower frequencies, while the second section (70.7 ohm impedance, 90 degree electrical length at 298 MHz) provides optimal isolation for higher frequencies, achieving overall isolation greater than 40 dB across the broadband range.
3Device complexity
If narrowband coupler is used, then simple structure is maintained, but insertion loss increases at broadband frequencies
Solution Approach 1:
The hybrid coupler employs dynamic design where the electrical characteristics of different sections are optimized for different operating conditions (frequencies). The first section is optimized for 25-55 MHz and 61-128 MHz ranges, while the second section is optimized for 250-317 MHz range, allowing the device to adaptively minimize insertion loss across the entire broadband spectrum with insertion loss less than 0.8 dB.
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 provides high isolation (>40 dB), low insertion loss (<0.8 dB), and wideband operation for MRI at 3T and 7T, enabling detection of multiple nuclei frequencies with improved signal processing efficiency.
Implementation Method 1
The multi-bended microstripline is configured to receive electrical signals at the first port and resonate the electrical signals at frequencies of about 95 MHz and about 285 MHz at the second port and at the fourth port
Implementation Method 2
broadband hybrid magnetic coupler for magnetic resonance imaging (MRI) of atomic nuclei
Data Source
AI summary
A hybrid microstripline transmit/receive switch and methods for use in magnetic resonance imaging of X-atomic nuclei at 3T and 7T magnetic field strengths. A first and second dielectric substrate each include a broadband hybrid magnetic coupler formed on the top side and a ground plane formed on the bottom side. An RF electrical signal is input to a first port and a second port transmits the signal when a first pin diode and a second pin diode are forward biased. A third port is isolated and a fourth port receives signals when the first and second pin diodes are reversed biased. Tuning capacitors are connected to the ports. The T/R switch is configured to operate in broadband frequency ranges of about 25 MHz to about 55 MH, of about 61 MHz to about 128 MHz, and of about 250 MHz to about 317 MHz.