Tech Briefs Magazine - May 2021 - 14

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Platform Converts Headphones from
" Dumb " to " Smart "
The difference between smart and dumb
headphones is that the
smart ones go beyond
playing music - they
can be physiological
monitors and virtual
touchscreens. Xiaoran Fan, while a doctoral candidate at Rutgers University, led
a team of researchers that developed a
method called HeadFi that uses ordinary headphones as sensors.

form a semi-sealed enclosure of space that
resonates and amplifies some frequency.
It's the same with headphones. When
you have the headphones on your ears, a
unique pattern of frequencies is amplified,
so by looking at the signal strength at various frequencies, we can detect whether
the headphones are on your head - if
they are, we start the sensing application.
Tech Briefs: What are some
applications of headphones being
used to measure something?

Tech Briefs: How did this project start?

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Xiaoran Fan: I'm an audiophile, so
I've been interested in headphones.
Although simple headphones are used
for applications like studio mixers and
home audio, recently we've been seeing
smart headphones from Apple, Samsung,
and Microsoft. We've always known that
the drivers in headphones, in principle,
work similarly to microphones. Since
microphones can sense signals, that
means headphones can, by default, also
do it. That was the initial incentive that
started me in this direction.
Tech Briefs:How are headphones
used as microphones?
Fan: Basically, drivers are just transducers that convert electrical signals
into mechanical signals. These transducers can be made to operate in reverse.
But the problem is that the headphones
are optimized for playing music - the
music signal is dominant. But the sound
signals in the left and right drivers are
balanced, so subtracting them will leave
only an unbalanced sensor signal.
We have a fully automated process of
two steps. The first step is to detect
whether your headphones are on your
head, then second, we run the application.
We use a trick based on the seashell effect
to check whether the headphones are on
your head. Holding a seashell to your ear,
you hear something like a sea noise. That's
because the seashell and your ear canal
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Fan: We've recognized four applications: gesture recognition, heart rate monitoring, user identification, and voice
communication. Take heart rate monitoring. When you're hurrying, your
heart is pumping - it makes a mechanical vibration through your body that the
headphones can capture. But the channels from your heart to the left headphone and to the right headphone are
different. By running the difference signal through our algorithm, we can find
the period of your heart rate.
I think the most interesting application
is user identification. The headphone
generates a swipe signal - swiping up a
frequency band and sending the signal
into your ear. The interesting part is that
everyone's ear canal has a different structure - it's like a fingerprint - so the
echo received by the headphones will be
different for everyone. And that difference is also different from person to person - even between identical twins.
Tech Briefs: When might this
become commercialized?
Fan: We are using the Rutgers commercialization center website to look for a
partner. We're exploring potential partners like Apple, Samsung, or Microsoft.
We are aiming to make the platform plugand-play and we're also writing Android
software to make it easy to demonstrate.
Read the full transcript of this Q&A at
www.techbriefs.com.
Tech Briefs, May 2021

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Tech Briefs Magazine - May 2021

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