TechKnowmad
Researchers at Google have devised a device that, with the installation of an appropriate software update, may convert true wireless stereo (TWS) active noise canceling (ANC) headphones into heart rate monitors.
Traditional smartwatches typically rely on the measurement of light pulses to track a user’s heart rate. However, Google’s cutting-edge research proposes a groundbreaking alternative approach. Instead of using light-based sensors, they advocate harnessing the power of ultrasound, emitted by the speaker driver of a pair of earphones, to detect incredibly subtle changes in the surface of the ear canal.
Google Introduces APG
Google presented a new method of health sensing at MobiCom 2023 with the title “APG: Audioplethysmography for Cardiac Monitoring in Hearables.” The abstract for this work was named “APG: Audioplethysmography for Cardiac Monitoring in Hearables.”
Audioplethysmography, often known as APG, is a technique that enables ANC wearables to monitor physiological data such as heart rate and heart rate variability without the need for extra sensors or a reduction in battery life.
Google’s research has introduced an innovative technology known as APG, which stands for “arteria auricularis profunda photoplethysmogram.” APG offers several notable advantages, including its resilience to motion artifacts, adherence to stringent safety regulations with an 80 dB margin below the limit, resistance to seal conditions, and inclusivity across all skin tones.
The foundation of this breakthrough lies in the deep ear artery, scientifically referred to as the arteria auricularis profunda, responsible for supplying blood to the auditory canal. This artery intricately connects with a network of smaller vessels that permeate the canal extensively. What’s fascinating is that even subtle variations in the shape of these blood vessels, influenced by the heartbeat and blood pressure, can result in minute alterations in the volume and pressure of the ear canals. This unique physiological response makes the ear canal an ideal location for health sensing, as observed by Google’s research team.
While previous research has explored the use of wearables for health monitoring, typically involving the integration of an array of sensors like photoplethysmograph (PPG) and electrocardiogram (ECG) with a microcontroller, this approach comes with a set of challenges. It introduces additional costs, weight, power consumption, and complexity in acoustic design, thereby posing form factor constraints for wearables, all of which hinder their widespread adoption.
Google has identified that current Active Noise Cancellation (ANC) wearables utilize a combination of feedback and feedforward microphones. These microphones are capable of detecting and recording various biological signals both inside and outside the ear canal, thereby opening up opportunities for health monitoring. However, it’s important to note that consumer-grade ANC headphones are equipped with high-pass filters, primarily designed to mitigate issues stemming from body movements or strong wind noise. Unfortunately, these filters also present a challenge when trying to incorporate health features that rely on passive listening to low-frequency signals.
APG ingeniously overcomes these hardware limitations by emitting a low-intensity ultrasound probing signal through an ANC headphone’s speakers. This signal prompts the generation of echoes, which are subsequently received via on-board feedback microphones. The subtle displacements of the ear canal skin and the vibrations caused by the heartbeat modulate these echoes, enabling precise health monitoring without the hindrance of high-pass filters. This breakthrough not only promises more accurate and convenient health monitoring but also addresses the practical challenges associated with integrating health features into hearable devices.
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Multi-Tone Approach
APG, short for “arteria auricularis profunda photoplethysmogram,” boasts a remarkable advantage in its ability to simultaneously transmit multiple frequencies. This unique capability not only allows for a higher-quality signal but also enhances its resilience to motion artifacts. The multi-tone approach employed by APG opens up exciting possibilities for the development of advanced signal-processing techniques.
Google’s commitment to rigor and precision is evident in its extensive user experience studies involving 153 participants. These studies consistently demonstrated that APG delivers accurate heart rate and heart rate variability measurements. This level of reliability is a significant step forward in the field of health monitoring technology.
What sets APG apart from traditional PPG (photoplethysmogram) is its resilience to variations in skin tone, sub-optimal seal conditions, and differences in ear canal size. Traditional PPG has often struggled with delivering consistent performance across different skin tones, but APG manages to overcome this limitation. This resilience ensures that APG can provide dependable health monitoring for a wide range of users, regardless of their characteristics.
In a statement, Google underlined the accessibility and adaptability of APG, noting that it can transform any True Wireless Stereo (TWS) Active Noise Cancellation (ANC) headphones into smart sensing headphones with a simple software upgrade. This ease of integration allows users to harness the power of health sensing without the need for complex hardware modifications.
Google further emphasized the significance of APG in the realms of biomedical and mobile research. APG represents not only a technological advancement but also a groundbreaking shift in our understanding of health sensing. It unlocks new possibilities for low-cost, accessible health monitoring, potentially revolutionizing the way we engage with our health and well-being.
In summary, APG’s ability to transmit multiple frequencies, its proven accuracy in health monitoring, and its resilience to various user characteristics make it a game-changing technology. It has the potential to democratize health sensing and contribute to the advancement of biomedical and mobile research, bringing affordable and dependable health monitoring to a wide range of users.