Tiny magnetic sensor tracks human heartbeat

The experiments were carried out at the Physikalisch Technische Bundesanstalt (PTB) in Berlin, Germany, in a building described as having the world’s best magnetic shielding − necessary to stop the Earth’s magnetic field and other external sources from interfering with the measurements taken by the NIST sensor.

The sensor − a tiny container of about 100 billion rubidium atoms in gas form, a low-power infrared laser, and optics − measured the heart’s magnetic signature in picoteslas.

In the experiments at PTB, the NIST sensor was placed 5mm above the left chest of a person lying face up on a bed, whereupon it successfully detected the weak but regular magnetic pattern of the heartbeat.

The same signals were recorded using the ’gold standard’ for magnetic measurements, a SQUID (superconducting quantum interference device). A comparison of the signals confirmed that the NIST mini-sensor correctly measured the heartbeat and identified many typical signal features.

The NIST mini-sensor generated more interference in the signal, but has the advantage of operating at room temperature, whereas SQUIDs work best at -269°C and require more complicated and expensive supporting apparatus.

The researchers suggest that NIST mini-sensors could be used to make magnetocardiograms, a supplement or alternative to electrocardiograms. Further tests of the NIST sensors at PTB are planned.