A pulsed current-mode class-D low-voltage high-bandwidth power amplifier for portable NMR systems

Area of Science:

• Nuclear Magnetic Resonance (NMR) spectroscopy
• Radio Frequency (RF) electronics
• Portable sensing technologies

Background:

• Low-field NMR systems are gaining traction for portable applications.
• Low magnet homogeneity necessitates short RF pulses for adequate excitation bandwidth and short echo times.
• High-Q coils, while improving SNR, can prolong RF pulse transients, limiting measurement bandwidth at low Larmor frequencies.

Purpose of the Study:

• To design a novel pulsed current-mode class-D power (PCMCD) transmitter for low-field NMR.
• To address the limitations of pulse transients and transmit bandwidth in portable NMR systems.
• To improve power efficiency and reduce echo times in RF excitation trains.

Main Methods:

• Design and implementation of a pulsed current-mode class-D power (PCMCD) transmitter.
• Incorporation of a charge recycling mechanism for enhanced power efficiency.
• Tuning the transmitter to a sample coil for high power output.

Main Results:

• The PCMCD transmitter achieves a peak RF power of 240 W into a 9.16 μH coil at 4 MHz from a single 12 V supply.
• Short pulse transients and high output bandwidth were maintained.
• Minimum achievable echo times of 70 μs and 25 μs were demonstrated, depending on the operating mode.

Conclusions:

• The developed PCMCD transmitter effectively overcomes bandwidth limitations in low-field NMR.
• The design enables high power transmission with improved efficiency for portable NMR applications.
• This technology facilitates faster measurements and reduced echo times, enhancing NMR system performance.