A compact Class D RF power amplifier for mobile nuclear magnetic resonance systems

Abstract

A 20 MHz Class D amplifier with an output of 100 W of RF power has been developed. The compact size printed circuit board area of 50 cm and efficiency of 73% make it suitable for mobile nuclear magnetic resonance (NMR) systems. Test results show that the rise and ring down times of the amplifier are less than 0.2 μs, and it is capable of producing constant amplitude pulses as short as 2 μs. Experiments using a Carr Purcell Meiboom Gill pulse sequence with a NMR MOUSE sensor confirm that the Class D amplifier is suitable for mobile NMR applications.

Three-dimensional MRI in a homogenous 27 cm diameter bore Halbach array magnet

“…There are several potential advantages of this approach including the use of parallel reconstruction techniques to reduce the imaging time (if the SNR is high enough to allow this), as well as the use of preamplifier decoupling to effectively widen the bandwidth of the coils during receive. In addition there may also be advantages to increasing the number of transmit channels, which would allow the use of higher efficiency class D switched mode amplifiers, which could be made much smaller, more modular and more easily replaceable [36].…”

Design of broadband power amplifier based on loop-shaped filter matching structure

“…At present, the technologies to improve efficiency mainly include envelope tracking (ET) [1,2], envelope elimination and restoration (EER) [3,4], switch-type PAs, etc. ET and EER require peripheral circuits, so the design process is more complicated, while switch-type PAs such as class-E [5,6], class-F [7,8], and class-D [9,10] cannot maintain broadband due to their design characteristics. Continuous mode PA is one of the effective ways to expand its working bandwidth while ensuring high efficiency [11,12,13].…”