Innovative Sensor Traces Signature of Human Heartbeat

Researchers from the U.S. National Institute of Standards and Technology (NIST; Gaithersburg, MD, USA) and the German National Metrology Institute (PTB; Berlin, Germany) have micro-fabricated chip-scale atomic magnetometers (CSAMs)--consisting of a container with about 100 billion rubidium atoms in gas form, a low-power infrared laser, and optics--that are capable of detecting faint magnetic fields. The devices, about one square centimeter in size, were taken to the PTB, which possesses the most magnetically isolated building in the world. Using the tiny magnetometers, the investigators were able to detect the magnetic signature of human heartbeats, as measured in picoteslas (pT), perhaps opening up the possibility for a new modality to complement electrocardiograms (ECGs).

In the experiments at PTB, a sensor was placed 5 millimeters above the left side of a person lying face up. The sensor successfully detected the weak but regular magnetic pattern of the heartbeat. The signals were also recorded using a superconducting quantum interference device (SQUID), the current "gold standard" for magnetic measurements, and a comparison between the two signals confirmed that the minisensor correctly measured the heartbeat and identified many typical signal features. While the CSAM generated more signal interference, it works at room temperature, whereas the SQUID device works work best at -269 °C, and requires more complicated and expensive supporting apparatus. The study describing the CSAM sensor and the experiment were published early online on September 28, 2010, in Applied Physics Letters.

The study also demonstrated that atomic magnetometers could offer sensing stability lasting tens of seconds, as needed for an emerging technique called magnetorelaxometry (MRX), used to localize, quantify, and image magnetic nanoparticles inserted into biological tissue for medical applications such as targeted drug treatments.

Related Links:
U.S. National Institute of Standards and Technology
German National Metrology Institute