First evidence of detecting surface nuclear magnetic resonance signals using a compact B-field sensor

The noninvasive detection and characterization of subsurface aquifer structures demands geophysical techniques. Surface nuclear magnetic resonance (surface NMR) is the only technique that is directly sensitive to hydrogen protons and, therefore, allows for unambiguous detection of subsurface water. Traditionally, surface NMR utilizes large surface coils for both transmitting excitation pulses and recording the groundwater response. Recorded data is thus a voltage induced by the time derivative of the secondary magnetic field. For the first time, we demonstrate that the secondary magnetic field in a surface NMR experiment can be directly detected using a SQUID magnetometer. Conducting measurements at a test site in Germany, we demonstrate not only the ability to detect surface NMR signals on the order of femtoTesla, but that we are able to satisfy the observed data by inverse modeling. This is expected to open up completely new applications for this exciting technology.