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

Area of Science:

• Electrical Engineering
• Physics
• Biomedical Engineering

Background:

• Mobile nuclear magnetic resonance (NMR) systems require compact, efficient, and high-power radio frequency (RF) amplifiers.
• Existing amplifiers may not meet the size, power, and speed requirements for portable NMR devices.

Purpose of the Study:

• To develop and evaluate a compact 20 MHz Class D amplifier for mobile NMR applications.
• To assess the amplifier's performance characteristics, including power output, efficiency, and pulse fidelity.

Main Methods:

• Design and fabrication of a Class D amplifier on a 50 cm² printed circuit board.
• Characterization of amplifier performance, including rise/ring down times and pulse generation capabilities.
• Testing the amplifier in a mobile NMR setup using a Carr Purcell Meiboom Gill pulse sequence and an NMR MOUSE sensor.

Main Results:

• The developed Class D amplifier achieves 100 W of RF power output at 20 MHz.
• The amplifier exhibits a high efficiency of 73% and a compact PCB area of 50 cm².
• Demonstrated fast switching speeds with rise and ring down times under 0.2 μs and the ability to generate 2 μs pulses.

Conclusions:

• The 100 W, 20 MHz Class D amplifier meets the stringent requirements for mobile NMR systems.
• Its compact size, high efficiency, and rapid pulse capabilities make it a suitable component for portable NMR instrumentation.
• Experimental validation confirms the amplifier's efficacy in mobile NMR applications, particularly with standard pulse sequences.