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High efficiency radiofrequency power amplifier module for parallel transmit arrays at 3 Tesla
Author(s) -
Twieg Michael,
Griswold Mark A.
Publication year - 2017
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.26510
Subject(s) - amplifier , rf power amplifier , duty cycle , materials science , radio frequency , optoelectronics , power (physics) , power added efficiency , electrical engineering , voltage , cmos , physics , engineering , quantum mechanics
Purpose The purpose of this study is to develop an in‐bore radiofrequency (RF) power amplifier (RFPA) module with high power efficiency and density for use in parallel transmit (pTX) arrays at 3 Tesla. Methods The modules use a combination of current mode class D, class S, and class E amplifiers based on enhancement‐mode gallium nitride‐on‐silicon field‐effect transistors. Together the amplifiers implement envelope elimination and restoration to achieve amplitude modulation with high efficiency over a wide operating range. The static nonlinearity and power efficiency of the module were measured using pulsed RF measurements over a 37 dB dynamic range. Thermal performance was also measured with and without forced convection cooling. Results The modules produces peak RF power up to 130 W with an overall efficiency of 85%. When producing 100 W RF pulses at a duty cycle of 10%, maximum junction temperatures did not exceed 80 °C, even without the use of heatsinks or forced convection. Conclusion The small size and low cost of the modules promise lower cost implementation of pTX systems compared with linear RFPAs located remotely. Further work must be done on control of the RF output in the presence of nonlinearities and coupling. Magn Reson Med 78:1589–1598, 2017. © 2016 International Society for Magnetic Resonance in Medicine.