MIT's thin plastic speakers fall flat. And that's by design
- Reference: 1651215489
- News link: https://www.theregister.co.uk/2022/04/29/mit_flat_speakers/
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These sheet speakers could potentially be applied to any surface for sound output or input: think surround sound or noise cancellation in aircraft. The technology also has potential for ultrasound imaging and echolocation, among other possibilities.
The work is described in [1]a paper published recently in the journal IEEE Transactions on Industrial Electronics, "An Ultra-Thin Flexible Loudspeaker Based on a Piezoelectric Micro-Dome Array."
[2]
"It feels remarkable to take what looks like a slender sheet of paper, attach two clips to it, plug it into the headphone port of your computer, and start hearing sounds emanating from it," Vladimir Bulović, leader of the Organic and Nanostructured Electronics Laboratory (ONE Lab), director of MIT.nano, and senior author of the paper, [3]told the MIT News Office.
[4]
[5]
The other two co-authors of the paper are Jinchi Han, a ONE Lab postdoc, and Jeffrey Lang, professor of electrical engineering at MIT.
The boffins have produced a short YouTube video that demonstrates the technology:
[6]
[7]Youtube Video
Traditional speakers translate electrical signals into a magnetic field that moves a speaker membrane to create audible vibrations. The MIT academics got rid of the coiled wire that generates the membrane-moving magnetic field by using piezoelectric material – which converts electrical energy to mechanical energy (and vice versa) – to move a microarray of domes that generate sound.
Their design relies on a sheet of plastic known as PET (polyethylene terephthalate) that's perforated and layered with a thin film of piezoelectric material, called PVDF (polyvinylidene fluoride).
[8]
When these sheets are heat bonded to create a vacuum, the result is a flat array of tiny domes that move when voltage is applied. The design creates enough separation of materials to allow the domes to vibrate without interference when the plastic film has been mounted to a surface.
At a distance of 30cm (12 inches), it's claimed, these thin-film speakers can generate high-quality sound equivalent to the volume of a typical conversation (66 decibels) through the application of 25 volts of electricity at 1 kilohertz. At 10 kilohertz, sound output reached the level of city traffic (86 decibels).
The sheet-speakers supposedly require only 100 milliwatts of power per square meter of speaker area, significantly less than home speakers that use more than 1 watt of power for comparable sound pressure at the same distance.
Jinchi Han told The Register in an email that the speakers have been tested between 100 Hz to 100 kHz.
"They are able to produce sound at low frequencies, but sensitivities (acoustic pressure generated under unit voltage) are usually higher at high frequencies than those at low frequencies," said Han.
[9]Amazon Alexa can be hijacked via commands from own speaker
[10]Climate model code is so outdated, MIT starts from scratch
[11]MIT, Amazon, TSMC, ASML and friends to work on non-planet-killing AI hardware
[12]'Boombox' function sparks Tesla recall
According to the MIT News Office, the technology is simple to fabricate and can be scaled up to cover the interior of a room or vehicle – the research was funded in part by Ford Motor Company. This would allow covered surfaces to emit sound for listening or for noise cancellation.
Ioannis (John) Kymissis, professor of electrical engineering and Chair of the department of electrical engineering at Columbia University, told the MIT News Office that the technology could also be used to record sound – the domes, acting as tiny microphones, would capture vibrations.
MIT professor Jeffrey Lang confirmed as much in an email to The Register .
"The same device can work as a microphone," said Lang. "It can be mounted on the surface of any object and used for sound recording. The device itself is passive and generates voltage signal under incident acoustic waves. But we apply a small transimpedance amplifier in order to obtain a large signal-to-noise ratio."
"We actually have an upcoming paper that reports the microphonic performance of the same device. The amplifier is the only part that consumes power. If a standalone design is needed, usually the signal storage/processing and wireless transmission consume much more power than the amplifier itself."
"But we can either use a battery or integrate energy harvesting components to make it standalone without wiring to external power. For instance, our group is also developing thin-film solar cells and it's possible to integrate that with the acoustic thin film to provide the energy."
Han said the technology has potential for ultrasound applications because it can generate the high resonance frequency necessary for ultrasound imaging. Echolocation is another possible application, according to Bulović, who also suggested the micro-speaker array combined with a reflective surface could be used as a display technology by creating patterns of light. ®
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[1] https://ieeexplore.ieee.org/document/9714188
[2] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_offbeat/science&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=2&c=2Ymu3Sy@YpTsgAKY6YJ5BSQAAAMo&t=ct%3Dns%26unitnum%3D2%26raptor%3Dcondor%26pos%3Dtop%26test%3D0
[3] https://news.mit.edu/2022/low-power-thin-loudspeaker-0426
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[7] https://www.youtube.com/watch?v=pABxdxTuAY8
[8] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_offbeat/science&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=3&c=33Ymu3Sy@YpTsgAKY6YJ5BSQAAAMo&t=ct%3Dns%26unitnum%3D3%26raptor%3Deagle%26pos%3Dmid%26test%3D0
[9] https://www.theregister.com/2022/03/03/amazon_alexa_speaker_vuln/
[10] https://www.theregister.com/2022/04/13/climate_mit_fortran/
[11] https://www.theregister.com/2022/03/30/mit_ai_chips/
[12] https://www.theregister.com/2022/02/11/tesla/
[13] https://whitepapers.theregister.com/
PET indeed
Having moved with pets and having them travel in air carriers in loud aircraft or sitting on even louder tarmacs, I've long wished for some technology that can add noise-cancelling to the already compact, nay, crammed pet carriers/cages. These could be ideal as they wouldn't take up space on the inside.
Provided they can produce the required frequency range of whatever sounds need to be cancelled.
Re: PET indeed
they only go down to 100hz, so it can't cancel out a lot of the low end noise that you hear on a plane
Presumably a part of a hemisphere
could be used to focus the sound.
Not that I'd want to wander around with what might look like an exploded bra while boogieing down the street.
How long .....
..... before they make a transparent version that they then apply to your TV to give decent speakers without the need for a soundbar?
Re: How long ..... to give decent speakers
Ridiculous. They'll instead use the technology to make even worse speakers for your TV, but ones that save them a tiny amount of money per device.
Interesting tech!
Re noise-cancelling - in cars and aeroplanes the sounds tend to be lower frequencies. 100Hz to 100kHz range means they're not covering the 20-100Hz bracket where a lot of mechanical background noise lies. Also, human hearing tops out around 16kHz (higher for kids, lower for adults), that's why audio headphones / speakers have audio ranges of typically 20Hz-20kHz. (at really low frequencies, vibrations are no longer 'sounds' heard in the ear but rather vibrations felt in the whole body ).
Another interesting application might also be short distance radio-wave-free low-power communications in the inaudible range.
Although I do foresee a dystopian future where every surface that isn't an ad-screen is a speaker surface spouting inane muzak.
updated cliche
as well as the eyes in the picture following you around the room, its listening too
Needs work
Promising but it won't sound any good until there's an audiophile version. I'm thinking incorporate some gold leaf for a warmer, more rounded signal and fill those domes with argon for a really expansive soundstage.
What a pity...
> At a distance of 30cm (12 inches), it's claimed, these thin-film speakers can generate high-quality sound equivalent to the volume of a typical conversation
What a pity that they chose not to demonstrate that in the linked video, then. Only when I read the video title did I understand that I ought to have been able to hear a Queen track (God bless you, Ma'am) but I can still only barely pick it out of the noise. Reminds me of the quality of LW radio from a 6-transitor receiver, I'm afraid.
It can be mounted on the surface of any object and used for sound recording
Great. So inevitably somebody's going to market "smart wallpaper", which will talk to you and listen to everything you do or say.
Bass response...
Given how the perceived sound changes as the sheet is manipulated, I suspect the frequency response issues are mechanical in nature.
Maybe if a large sheet was tensioned in a frame you could get some good low frequency response.
I'm thinking of a solid state version of the legendary Quad electrostatic speakers...
It sounds an awful lot like NXT.
Having a quick google indicates that the NXT technology has (possibly is) in use in noise cancelling fighter aircraft cockpits (wind noise)
It has been used in hifi products but does not seem to work well below 100hz, so you need a sub
It seems to compete well with electrostatics in good implementations
Currently it seems to be used in https://symphonova.com/technology/
So, when they present their findings in a paper to those gathered at the annual conference of the society for audiological innovation . . . they won't actually need a speaker.