Microphones can be used as sensors to detect much more than just sound waves. An Economist article titled "Teaching old microphones new tricks" reminds us of this fact, citing the use of microphones to track everything from lung function to heart health.
In particular, a growing number of players have decided to tap the power of the smartphone microphones for medical applications. Examples include AliveCor's heart monitor for the iPhone 4, 4S, and 5. The device consists of a case with electrodes positioned on the back that detect ECG data from the skin, converting them to ultrasonic FM sound signals that are sent to the smartphone's microphone.
John Stankovic, a professor at of the University of Virginia (Charlottesville) is using microphones more directly to track heart health. Stankovic is exploring the use of custom earphones used with accelerometers and extra microphones to monitor arterial pulse via the user's ears. Shahriar Nirjon, a graduate student at the university has developed an app called Musical Heart that measures a user's heart rate and recommends music based on a heart-rate objective. For instance, if a user is exercising, the app can help select a song to help ramp up the pulse. The device then will analyze how effective a given song is at energizing the user and use that data in the future. Similar technology could be used to accomplish the opposite: calming users facing stressful events. Stankovic is specifically targeting the technology's use in conjunction with anesthesiology.
|The Scanadu Scout is an example of a device that makes use of microphones to monitor health metrics.|
The microphone also plays an important role in Scanadu's Scout health monitor, a scanner packed with sensors that relays users' health metrics to their smartphone. The device is not commercially available at present but so far has attracted $551,411 at the time of writing on crowdfunding platform Indiegogo. Its funding goal was $100,000 and 19 days remain in the fundraising campaign.
A company known as SpiroSmart have developed an iPhone app that uses the phone's microphone to simulate a digital spirometer to monitor lung function. The software listens to the resonance of expelled air. In a clinical study, it was shown to be nearly as precise as a clinical spirometer. The app, along with AliveCor's heart monitor were recently featured in a TEDMED presentation titled "The Smartphone Physical."