The Future of Hearables: APG for In-Ear Health Sensing
The market for true wireless stereo (TWS) active noise-canceling (ANC) earbuds and headphones has been growing rapidly in recent years. In fact, by 2023, the global shipment volume of these devices is expected to double that of smart wristbands and watches.
People use hearables not only for listening to music, but also for exercising, focusing, and adjusting their mood. However, when it comes to health monitoring, the potential of hearables is largely untapped.
At MobiCom 2023, we presented a new technology called Audioplethysmography (APG) for monitoring a user’s physiological signals, like heart rate and heart rate variability, with ANC earbuds. The great thing about APG is that it doesn’t require any additional sensors or compromise battery life.
So how does APG work? It sends a low-intensity ultrasound through the speakers of the ANC earbuds and collects the echoes with the feedback microphones. These echoes are modulated by the minute vibrations in the ear canal caused by the heartbeat.
The result is an APG waveform that resembles a photoplethysmogram (PPG), but with more detailed information about the user’s cardiac activities. APG can provide insights into the central artery system and blood pressure through features like dicrotic notches.
What makes APG even more impressive is its resilience to motion artifacts and its ability to work regardless of the quality of the earbud seal. It also adheres to safety regulations and is suitable for all skin tones.
In comparison to other health sensing methods like PPG, APG has several advantages. PPG sensors require multiple diodes to send and receive light frequencies, which adds complexity and cost. On the other hand, APG can easily use multiple audio tones, making it a low-cost and low-power solution.
We have found that using multiple frequencies in APG signaling enhances the quality of the data and makes it more resilient to motion. By transmitting different frequencies simultaneously and using coherent detection, we can separate the signals related to cardiac activities from those related to motion.
Through our experiments, we have demonstrated that APG can accurately measure heart rate and heart rate variability, even during activities like running. By applying blind source separation techniques, we can further enhance the signal quality and improve the accuracy of the measurements.
The potential applications of APG in hearables are vast. It can enable sleep monitoring, heart rate tracking, and even help with the diagnosis of ear diseases. With the advancement of ANC technology and the integration of APG, hearables will not only provide an immersive audio experience but also become powerful health monitoring devices.
In conclusion, APG is a groundbreaking technology that brings health sensing capabilities to ANC earbuds and headphones. It eliminates the need for additional sensors, offers high-quality data, and is resilient to motion artifacts. With APG, the future of hearables looks bright, and we are excited to see how it will revolutionize the consumer market.