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NIST on a Chip

Chip-Scale Atomic Magnetometers

The Technology

NIST scientists have developed inexpensive chip-scale magnetometers that sense very faint magnetic fields. An individual sensor consists of a vapor of atoms in a sealed glass vacuum chamber with a volume of about 1 cubic millimeter. The sensor units are low power and intended to be deployed in large arrays.

Each magnetometer detects changes in a tiny diode laser beam as it passes through a vapor of atoms such as rubidium. The laser light is polarized, aligned in one orientation. When the light interacts with the vapor, it causes the magnetic spins of the trapped atoms to also align. The laser beam then exits the vapor cell and hits a detector.

In the absence of a magnetic field, the atoms’ spins would stay lined up and the polarization of the laser beam would remain unchanged. But when a field is present, it changes the atoms’ spin by some amount. That, in turn, changes the polarization, and hence the amount, of the light entering the detector. The magnitude of that change is a sensitive and accurate measure of magnetic field strength.

Measuring Field Strength with an Optically Pumped Magnetometer — This animation demonstrates the principles behind a new device for measuring the strength of magnetic fields. One potential application for the technology is mapping electrical activity in the brain, for use in diagnosing traumatic brain injuries. Unlike typical instruments used today, the new magnetometer prototypes do not require cooling and can be placed within a few millimeters of the scalp. The prototype consists of a glass cell filled with a cloud of rubidium atoms. First, polarized laser light aligns the rubidium atoms’ spins. Then, an applied magnetic field deflects the atomic spins around the axis of the field, which decreases the amount of laser light that is transmitted through the cloud of atoms. Monitoring the amount of transmitted light provides a measure of the strength of the magnetic field. Animation: Sean Kelley/NIST

Advantages Over Existing Methods

Many current high-end magnetic field measurement applications use superconducting quantum interference devices (SQUIDs), which must be cooled to cryogenic temperatures.

Unlike SQUIDs, the chip-scale NIST sensor operates at room temperature, making it available for medical applications, and it collects data in the form of light, which can be measured more exactly than any other physical property.

Applications

The chip-scale sensor is convenient and practical for biomedical applications. It can measure the weak magnetic fields from the brain and heart. Therefore, it’s potentially useful for monitoring fetal heartbeats and neurological conditions such as epilepsy.

Chip-scale atomic magnetometers may also provide new opportunities for space science. Their small size makes them suitable for the new generation of miniaturized, low-cost satellites called CubeSats, which can be as small as 10 centimeters (4 inches) on a side. Most CubeSats are monitoring Earth, but some have been deployed as far away as Mars.

Further progress is expected to enable deployment of the sensors in a wide range of places where their conventional counterparts cannot go. These devices could someday be placed in battery-powered mobile computers, wireless communications and GPS components, defense systems, and miniaturized sensors and calibration standards for the factory floor.

Key Papers

J. Kitching. Chip-scale atomic devices. Applied Physics Reviews. Published online Aug. 14, 2018. DOI: 10.1063/1.5026238

R. Mhaskar, S. Knappe and J. Kitching. A low-power, high-sensitivity micromachined optical magnetometer. Applied Physics Letters. Published online Dec. 11, 2012. DOI: 10.1063/1.4770361

T.H. Sander, J. Preusser, R. Mhaskar, J. Kitching, L. Trahms and S. Knappe. Magnetoencephalography with a Chip-Scale Atomic Magnetometer. Biomedical Optics Express. Published April 17, 2012. DOI: 10.1364/BOE.3.000981

M.P. Ledbetter, I.M. Savukov, D. Budker, V. Shah, S. Knappe, J. Kitching, D.J. Michalak, S. Xu and A. Pines. Zero-field remote detection of NMR with a microfabricated atomic magnetometer. PNAS. Published Dec. 18, 2007. DOI: 10.1073/pnas.0711505105

V. Shah, S. Knappe, P.D.D. Schwindt and J. Kitching. Subpicotesla atomic magnetometry with a microfabricated vapour cell. Nature Photonics. Published online Nov. 1, 2007. DOI: 10.1038/nphoton.2007.201

P.D.D. Schwindt, B. Lindseth, S. Knappe, V. Shah, J. Kitching and L. Liew. Chip-scale atomic magnetometer with improved sensitivity by use of the Mx technique. Applied Physics Letters. Published online Feb. 21, 2007. DOI: 10.1063/1.2709532

P.D.D. Schwindt, S. Knappe, V. Shah, L. Hollberg, J. Kitching, L. Liew and J. Moreland. Chip-scale atomic magnetometer. Applied Physics Letters. Published Dec. 27, 2004. DOI: 10.1063/1.1839274