Sensitivity of superconducting quantum RF magnetic field receivers for NMR spectroscopy and tomography

The contribution gives a theoretical analysis of noise properties of high-frequency magnetic field receivers for NMR systems with low magnetic field (low-field-NMR-RF band). Parameters achievable by using superconducting quantum magnetometers (SQM) with resonance mode of the antenna coil are analyzed. Derived relations for the equivalent spectral sensitivity of the magnetic induction cover the influence of the active elements noise, the influence of losses due to resistances of the antenna circuit and measured sample, and the influence of their noise temperatures. An example points at their connection with the sensitivity of the receiver and the achievable signal-to-noise ratio on the receiving channel output intended for the frequency band of 2.2 × 106 Hz (Bo ∼ 0.05 T). The computed values of the equivalent spectral sensitivity for the antenna coil with the diameter of 24 cm are in the range of 10−19-10−17 T Hz−1/2, which corresponds to the minimum measurable magnetic induction of 10−18-10−16 T for the transmission channel bandwidth of 100 Hz.