man floating in a pool wearing headphones

Engineers give ‘dumb’ headphones IQ boost

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Engineers from Rutgers University, New Jersey, USA, have found a cheap, simple way to transform ordinary headphones into sensors which can be plugged into smartphones to identify users and monitor their heart rates, among other functions.

Headphones are among the most popular wearable devices in the world. In recent years, they have continued to expand their functions and become 'smart', adapting sound in response to external stimuli.

For example, both Apple Airpods and Samsung Galaxy Buds have microphones in or near the ear to enable active noise cancellation and audio personalisation, while Microsoft's Surface headphones have embedded sensors to enable on-ear gesture control. Some headphones can even be used to pick up vital signs, functioning as heart-rate monitors.

These functions rely on auxiliary sensors such as accelerometers, gyroscopes and microphones, which most ordinary headphones do not have. In 2019, over 99 per cent of consumer headphones were not equipped with embedded sensors.

The Rutgers engineers’ invention ('HeadFi') could allow users to enjoy sensing functionality without having to buy an expensive new pair of smart headphones with embedded sensors or to add sensors to their existing headphones.

The technique is based on a small low-power, low-cost plug-in headphone adaptor which connects the headphones to a pairing device (such as a smartphone) and turns them into a sensing device. It does not require the addition of sensors and avoids changes to headphone hardware or any other customisations which might increase their weight or bulk.

HeadFi leverages the coupling effect between the headphones and its surroundings; when a user wears a pair of headphones, the headphones, ear canal and eardrum form a semi-hermetic space which is extremely sensitive to pressure changes. A pressure change can be induced by a gentle touch to the headphones or the repetitive deformation of blood vessels in the ear canal associated with the wearer’s heart rate. As the voltage measured at the headphones is affected by these pressure changes, it is possible to use voltage to detect small physiological changes.

HeadFi turns the two drivers already inside all headphones into a versatile sensor to pick up these changes. This allows the headphones to perform sensing tasks and play music at the same time.

“HeadFi could turn hundreds of millions of existing, regular headphones worldwide into intelligent ones with a simple upgrade,” said Dr Xiaoran Fan, primary inventor of HeadFi. He completed the research during his final year at Rutgers and has since moved to the Samsung AI Center in New York. He plans to present his paper on HeadFi at MobiCom 2021 in October.

The engineers trialled their converted headphones with 53 participants, using 54 pairs of headphones with prices ranging from just $2.99 to $15,000. They found that HeadFi helped reach 97.2 per cent to 99.5 per cent accuracy on user identification; 96.8 per cent to 99.2 per cent on heart-rate monitoring, and 97.7 per cent to 99.3 per cent on gesture recognition.

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