Optical heart rate measurement at the earbud: Page 6 of 6

November 18, 2019 // By Christoph Kämmerer
heart rate
Advancements in sensor technology have transformed how and where people diagnose their vitals and health. Portable, noninvasive measurement techniques permit fast and simple measurements that can be performed while we go about our daily lives. But although this diagnostic technology has become very popular in the fitness industry, there were limits to its accuracy that we have only recently overcome.

To better evaluate the need for a motion sensor, Scenario 5 tested measurement technology both with and without an accelerometer. Figure 8 shows a comparison of the additive spectrum without corrected accelerometer data (left) and with corrected accelerometer data (right). The improvement of the signal becomes visible in the identification of the heart rate, which was not possible without an accelerometer’s support.

Fig. 8: A comparison between additive spectrum without accelerometer data (left) and with
accelerometer data (right). With the use of an accelerometer, the user’s heart rate can be

From the test cases, it can be concluded that in most cases, the heart rate can be determined very accurately with an integrated sensor in the earbuds. In the case of local or slow translational motions, the heart rate could even be determined without the use of accelerometer data. However, in the limiting case of abrupt and rapid motions, the comparison with motion-corrected data also permits interpretation of the data. The infrared signals were stronger than the red signals were in all cases.

In comparison to wrist measurements, the signal in the ear is stronger and thus enables more accurate measurements to be made. In addition, the use of red or infrared light allows for measurement of blood oxygen levels.


About the Author

Christoph Kämmerer is field applications engineer at Analog Devices, specialized in emerging applications – www.analog.com. He can be reached at christoph.kaemmerer@analog.com

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