Google has made significant progress in enhancing the technology for true wireless earbuds. By simply updating the software, these earbuds can now incorporate heart rate monitoring, no additional hardware required. The only condition is that the earbuds must possess active noise cancellation, as it uses a similar method to noise cancellation technology.
A research paper authored by Xiaoran Fan, Experimental Scientist at Google, alongside Longfei Shangguan from the University of Pittsburg and Richard Howard from Rutgers University, provides details on the revolutionary technology. The paper, named 'APG: Audioplethysmography for Cardiac Monitoring in Hearables', explains how a low intensity ultrasound probing signal is transmitted through the active noise cancellation headphone's microphone and speakers, and then the echoes are received by onboard feedback microphones. This probing signal bounces off the wearer’s ear canal and the ambient sound-detecting microphone in the earphones or headphones captures the skin surface response to blood flow.
While Photoplethysmography (PPG) is commonly used in fitness and health tracking wearables, it relies on light pulses to measure blood activity. In contrast, APG's low-intensity ultrasound signal bounces off the ear canal and uses the earphone's microphone to detect skin surface perturbations caused by blood flow.
According to the researchers, APG has fewer limitations compared to existing alternatives, making it a promising technology for health tracking in ear wearables. The technology is resistant to factors such as skin tone, seat or fit of the wearable, and the material of the eartips does not affect the readings. Google's study, conducted over an eight-month period with 153 participants, achieved heart rate readings with a median error of 3.21% in all scenarios, while heart rate variability reported a median error of 2.70% in interbeat interval.
Despite its potential, there are limitations to APG, including distorted signal readings in noisy environments. However, the researchers are working on using multiple frequencies and software to capture the most accurate signal. It is important to note that while Google has made significant progress, there is still considerable testing and refinement to be done before this technology can be integrated into real-world applications.
It is possible that Google may embed this technology in their Pixel wireless earbuds in the future. Nevertheless, for other brands' headphones and true wireless earphones, integration would require approval in the companion app software for these audio products. Although there is still a long road ahead, if successful, this innovation could introduce a relevant health tracking method for outdoor fitness routines.