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Design Example: Vintage Mixing Console01:17

Design Example: Vintage Mixing Console

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A sound engineer at a music company recently encountered a problem. The output from their newly acquired studio's vintage mixing console was too low for the requirements of modern recording equipment. To rectify this situation, the engineer decided to design an audio pre-amplifier using an operational amplifier (op-amp) to boost the signal level.
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Related Experiment Video

Updated: Nov 26, 2025

Characterization of SiN Integrated Optical Phased Arrays on a Wafer-Scale Test Station
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A retrofit to enable dynamic steering for transmit arrays without multiple amplifiers.

Chenhao Sun1, Kevin Patel1, Matthew Wilcox2

  • 1Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, USA.

Magnetic Resonance in Medicine
|December 14, 2020
PubMed
Summary

This study presents a novel system for dynamic B1 shimming in 7T MRI using only two power amplifiers and digitally controlled phase shifters. This cost-effective solution enables precise B1 field control for improved imaging quality.

Keywords:
body coildynamic shimmingphase shiftertransmit arrayultrahigh-field MRI

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Radiofrequency (RF) Engineering

Background:

  • B1 inhomogeneity is a significant challenge in high-field MRI, impacting image quality.
  • Independent power amplifiers for each transmit element offer precise B1 shimming but are costly.
  • Traditional methods like coaxial cable length adjustment are impractical for dynamic shimming.

Purpose of the Study:

  • To develop a cost-effective system for dynamic, phase-only, eight-channel B1 steering at 7T.
  • To enable precise B1 field control without requiring individual power amplifiers per channel.

Main Methods:

  • Utilized power dividers to split a two-channel signal into eight transmit channels.
  • Implemented digitally controlled phase shifters with 22.5° resolution for independent phase control.
  • Validated the system using an eight-channel body dipole array through simulation, bench measurements, and 7T scanner evaluation.

Main Results:

  • Phase conjugate B1 steering successfully generated homogenous B1 regions at targeted spatial positions.
  • Simulation, bench, and scanner measurements showed consistent results, confirming effective B1 steering.
  • Demonstrated the ability to steer the B1 field to specific regions of interest.

Conclusions:

  • The described system offers a simple retrofit for existing MRI hardware, enabling dynamic B1 shimming.
  • It provides phase control without manual cable adjustments or multiple power amplifiers.
  • This approach increases degrees of freedom for B1 shimming at a significantly reduced hardware cost.