Microsoft has all but pulled out of the fitness tracker market, but its time there resulted in some interesting research. A patent filed on April 2nd, 2015 has recently come to light via the WIPO, and it reveals an interesting solution.
Heartbeat sensing is standard in wearables these days. The Microsoft Band had one, as does the Apple Watch and Fitbits. However, the data isn't particularly detailed. It gives heart rate, and that's about it. That's where Microsoft's technology comes in.
Non-Invasive Pulse Sensor
Microsoft's heartbeat sensor would sit between tendons on the wrist to deliver information on arterial blood pressure, pulse-wave velocity, and augmentation index. Here's how it works:
“The system includes a one-piece flexible cap configured to fit around a flexible piezo-resistive sensor that is configured to alter an internal resistance upon deflection. The flexible cap includes a deflection wall shaped to conform between a radius and a flexor carpi radialis tendon, and configured to deflect towards the flexible piezo-resistive sensor in proportion to pressure applied by a radial artery. A pressure-transducing medium is sealed between the one-piece flexible cap and the flexible piezo-resistive sensor, such that deflection of the deflection wall towards the flexible piezo-resistive sensor causes proportional deflection of the flexible piezo-resistive sensor.”
It's a very sciency explanation, and I don't pretend to understand half of it. Essentially, though, a piezo-resistive sensor uses a different method to optical ones. Optical sensors base heart rate on changes in light, which has a lot of noise and potential miscalculations.
A piezo-resistive sensor would sit on a single artery and has the advantage of less noise, better battery efficiency, and more detailed information. The downside is that the wearable would have to be lower on the arm. This could result in a less comfortable device and could restrict movement.
It's a nice idea and one that we would have liked to see Microsoft test. Though the Band 3 has been canceled, reports suggest that a company is making new sensors for Microsoft. It wouldn't surprise us if Microsoft is making a new wearable with this technology.
You can read the full patent yourself here.