A first-order gradiometer is formed from two magnetometers that are separated by a 3-cm baseline. Our magnetically silent sensors measure the total magnetic field by detecting the free-precession frequency in a highly spin-polarized alkali-metal vapor. N2 - We present a method of optical magnetometry with parts-per-billion resolution that is able to detect biomagnetic signals generated from the human brain and heart in Earth's ambient environment. The proof-of-principle demonstrations of the sensor detecting biomagnetic signals were supported by Princeton University and the Fetzer Franklin Fund of the John E. Approved for Public Release, Distribution Unlimited. The views, opinions, and/or findings expressed are those of the authors and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. The sensor development was funded by the Defense Advanced Research Projects Agency (DARPA) Microsystems Technology Office (MTO) under Contract No. T1 - Portable Magnetometry for Detection of Biomagnetism in Ambient Environments This work demonstrates the possibility of a dense array of portable biomagnetic sensors that are deployable in a variety of natural environments. Recording of neuronal magnetic fields is one of a few available methods for noninvasive functional brain imaging that usually requires extensive magnetic shielding and other infrastructure. The gradiometer has a sensitivity of 16 fT/cm/Hz1/2 outdoors, which we use to detect neuronal electrical currents and magnetic cardiography signals. Our gradiometer operates from a laptop consuming 5 W over a USB port, enabled by state-of-the-art microfabricated alkali-vapor cells, advanced thermal insulation, custom electronics, and compact lasers within the sensor head. This work demonstrates the possibility of a dense array of portable biomagnetic sensors that are deployable in a variety of natural environments.Ībstract = "We present a method of optical magnetometry with parts-per-billion resolution that is able to detect biomagnetic signals generated from the human brain and heart in Earth's ambient environment. We present a method of optical magnetometry with parts-per-billion resolution that is able to detect biomagnetic signals generated from the human brain and heart in Earth's ambient environment.
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