Wideband Low-Impedance Receive Interface for Untuned Coils

Conventional MRI and other RF receive coils are designed as high-Q resonant structures, which maximizes sensitivity but inherently restricts their utility for multinuclear imaging or multiband reception. This narrowband dependence necessitates complex retuning circuits or hardware replacement whenever the coil geometry, loading, or target frequency changes. To address this, we present a wideband receive interface that eliminates resonant tuning components by actively damping an untuned loop using a low-impedance differential common-gate pHEMT front end. By synthesizing a broad resistive termination, the circuit treats the coil as a current sensor rather than a resonant tank, effectively suppressing high-Q resonances from 10 MHz to 130 MHz. Experimental results at 3 T demonstrate successful imaging of both ¹H (127.7 MHz) and ³¹P (51.7 MHz) using the same fixed hardware, achieving usable SNR levels relative to tuned reference coils.