Recording the heart beat of cattle using a differential system of optically pumped magnetometers

Livestock farming occupies about 30% of the Earth’s habitable surface area with a global value around £1 trillion. This important economic entity relies to a large extend on the health and wellbeing of the animals involved. Besides economic pressure there is also a growing interest of the consumer in the ethical keeping of livestock. Seeking physiological parameters that allow a close assessment of animal wellbeing has identified the animals’ heart beat as a possible parameter to monitor.
The electric signal of the heart muscle excitation and relaxation does also carry a magnetic field component. Reading the magnetic field to query heart beat information does avoid the need for contact electrodes. We use two QuSpin Total Field Magnetometers (QTFM®) in a differential set-up to cancel common mode noise. Using the background noise to time-shift the two signals we optimize signal to noise ratio and record the magnetic heart signal over a noise floor close to 1 pT Hz-1/2 in the 1–100 Hz frequency band. By means of a correlation search algorithm we retrieve the heart rate and the shape of the magnetic heart excitation. Comparison to electro cardiograms shows good correlation.