An unshielded radio-frequency atomic magnetometer with sub-femtoTesla sensitivity

Abstract

We demonstrate a radio-frequency potassium-vapor magnetometer operating with sensitivities of 0.3 fT/Hz at 0.5 MHz and 0.9 fT/Hz at 1.31 MHz in the absence of radio-frequency and mu-metal or magnetic shielding. The use of spatially separated magnetometers, two voxels within the same cell, permits for the subtraction of common mode noise and the retention of a gradient signal, as from a local source. At 0.5 MHz the common mode noise was white and measured to be 3.4 fT/Hz; upon subtraction the noise returned to the values observed when the magnetometer was shielded. At 1.31 MHz, the common mode noise was from a nearby radio station and was reduced by a factor of 33 upon subtraction, limited only by the radio signal picked up by receiver electronics. Potential applications include in-the-field low-field magnetic resonance, such as the use of nuclear quadrupole resonance for the detection of explosives.

Atomic Magnetometer Multisensor Array for rf Interference Mitigation and Unshielded Detection of Nuclear Quadrupole Resonance

“…The sensitivity of the atomic magnetometers can easily be taken advantage of in shielded enclosures, but many applications, like NQR used for the detection of illicit substances, would be more fieldable if done unshielded. It has been shown that the superior sensitivity of the RF magnetometer can be retained unshielded if operated with two effective sensors and used as a gradiometer [24]. In that work, however, the two sensors were two channels within a larger cell and represented a baseline of only 2 cm; more recently, a similar gradiometer measurement was made with separate sensors 5.6 cm apart, but at a much lower frequency and worse sensitivity [25].…”

Remote detection of rotating machinery with a portable atomic magnetometer

“…The spectrum is flat when the RF supply is off (V RF =0), while the central peak and sidebands appear as soon as the voltage increases (see top inset). Given the proof-of-principle nature of the present work and taking into consideration data reported in literature on atomic magnetometers [8][9][10][11][12], one can anticipate a great potential for a further increase in detection capability and range.…”

NQR detection of explosive simulants using RF atomic magnetometers

“…However, the use of a gradiometer for interference mitigation inherently lowers sensitivity to the NQR response 24,25 . RF atomic magnetometers offer a unique alternative to coil based gradiometers for RFI mitigation and the potential for significant enhancement in interference cancellation 11 . Since magnetometers act as independent sensors, background subtraction of interference can be performed without suffering any loss in the detected NQR signal.…”

“…The noise floor of an optically pumped atomic magnetometer is limited by the Heisenberg Uncertainty Principle resulting in an order of magnitude improvement in sensitivity over an inductive coil 8,9,10 . Furthermore, multiple magnetometers can be arranged in an array to mitigate RFI by background subtraction of interference without the mutual inductive coupling issues or sensitivity degradation that plagued inductive sensors 11 . In this paper, we present results from a proof-of-principle breadboard experiment utilizing RF atomic magnetometers with sub-femtotesla sensitivity in the 400 kHz to 5 MHz frequency range for detection of NQR signals from explosive simulants.…”