• Researchers develop a paper-thin loudspe

    From ScienceDaily@1:317/3 to All on Tue Apr 26 22:30:46 2022
    Researchers develop a paper-thin loudspeaker
    The flexible, thin-film device has the potential to make any surface into
    a low-power, high-quality audio source

    Date:
    April 26, 2022
    Source:
    Massachusetts Institute of Technology
    Summary:
    Researchers created an ultrathin loudspeaker that can turn any rigid
    surface into a high-quality, active audio source. The fabrication
    process can enable the thin-film devices to be produced at scale.



    FULL STORY ==========================================================================
    MIT engineers have developed a paper-thin loudspeaker that can turn any
    surface into an active audio source.


    ==========================================================================
    This thin-film loudspeaker produces sound with minimal distortion while
    using a fraction of the energy required by a traditional loudspeaker. The hand-sized loudspeaker the team demonstrated, which weighs about as much
    as a dime, can generate high-quality sound no matter what surface the
    film is bonded to.

    To achieve these properties, the researchers pioneered a deceptively
    simple fabrication technique, which requires only three basic steps and
    can be scaled up to produce ultrathin loudspeakers large enough to cover
    the inside of an automobile or to wallpaper a room.

    Used this way, the thin-film loudspeaker could provide active noise cancellation in clamorous environments, such as an airplane cockpit,
    by generating sound of the same amplitude but opposite phase; the two
    sounds cancel each other out. The flexible device could also be used for immersive entertainment, perhaps by providing three-dimensional audio in
    a theater or theme park ride. And because it is lightweight and requires
    such a small amount of power to operate, the device is well-suited for applications on smart devices where battery life is limited.

    "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. It can be used anywhere. One
    just needs a smidgeon of electrical power to run it," says Vladimir Bulović, the Fariborz Maseeh Chair in Emerging Technology, leader
    of the Organic and Nanostructured Electronics Laboratory (ONE Lab),
    director of MIT.nano, and senior author of the paper.

    Bulović wrote the paper with lead author Jinchi Han, a ONE Lab
    postdoc, and co-senior author Jeffrey Lang, the Vitesse Professor
    of Electrical Engineering. The research is published today in IEEE
    Transactions of Industrial Electronics.



    ==========================================================================
    A new approach A typical loudspeaker found in headphones or an audio
    system uses electric current inputs that pass through a coil of wire
    that generates a magnetic field, which moves a speaker membrane, that
    moves the air above it, that makes the sound we hear. By contrast, the
    new loudspeaker simplifies the speaker design by using a thin film of a
    shaped piezoelectric material that moves when voltage is applied over it,
    which moves the air above it and generates sound.

    Most thin-film loudspeakers are designed to be freestanding because
    the film must bend freely to produce sound. Mounting these loudspeakers
    onto a surface would impede the vibration and hamper their ability to
    generate sound.

    To overcome this problem, the MIT team rethought the design of a thin-film loudspeaker. Rather than having the entire material vibrate, their design relies on tiny domes on a thin layer of piezoelectric material which each vibrate individually. These domes, each only a few hair-widths across,
    are surrounded by spacer layers on the top and bottom of the film that
    protect them from the mounting surface while still enabling them to
    vibrate freely. The same spacer layers protect the domes from abrasion and impact during day-to-day handling, enhancing the loudspeaker's durability.

    To build the loudspeaker, the researchers used a laser to cut tiny holes
    into a thin sheet of PET, which is a type of lightweight plastic. They laminated the underside of that perforated PET layer with a very thin film
    (as thin as 8 microns) of piezoelectric material, called PVDF. Then they applied vacuum above the bonded sheets and a heat source, at 80 degrees Celsius, underneath them.



    ========================================================================== Because the PVDF layer is so thin, the pressure difference created by
    the vacuum and heat source caused it to bulge. The PVDF can't force its
    way through the PET layer, so tiny domes protrude in areas where they
    aren't blocked by PET. These protrusions self-align with the holes in
    the PET layer. The researchers then laminate the other side of the PVDF
    with another PET layer to act as a spacer between the domes and the
    bonding surface.

    "This is a very simple, straightforward process. It would allow us to
    produce these loudspeakers in a high-throughput fashion if we integrate
    it with a roll- to-roll process in the future. That means it could be fabricated in large amounts, like wallpaper to cover walls, cars, or
    aircraft interiors," Han says.

    High quality, low power The domes are 15 microns in height, about
    one-sixth the thickness of a human hair, and they only move up and down
    about half a micron when they vibrate.

    Each dome is a single sound-generation unit, so it takes thousands of
    these tiny domes vibrating together to produce audible sound.

    An added benefit of the team's simple fabrication process is its
    tunability - - the researchers can change the size of the holes in
    the PET to control the size of the domes. Domes with a larger radius
    displace more air and produce more sound, but larger domes also have lower resonance frequency. Resonance frequency is the frequency at which the
    device operates most efficiently, and lower resonance frequency leads
    to audio distortion.

    Once the researchers perfected the fabrication technique, they tested
    several different dome sizes and piezoelectric layer thicknesses to
    arrive at an optimal combination.

    They tested their thin-film loudspeaker by mounting it to a wall 30
    centimeters from a microphone to measure the sound pressure level,
    recorded in decibels.

    When 25 volts of electricity were passed through the device at 1 kilohertz
    (a rate of 1,000 cycles per second), the speaker produced high-quality
    sound at conversational levels of 66 decibels. At 10 kilohertz, the sound pressure level increased to 86 decibels, about the same volume level as
    city traffic.

    The energy-efficient device only requires about 100 milliwatts of power
    per square meter of speaker area. By contrast, an average home speaker
    might consume more than 1 watt of power to generate similar sound pressure
    at a comparable distance.

    Because the tiny domes are vibrating, rather than the entire film,
    the loudspeaker has a high enough resonance frequency that it can
    be used effectively for ultrasound applications, like imaging, Han
    explains. Ultrasound imaging uses very high frequency sound waves to
    produce images, and higher frequencies yield better image resolution.

    The device could also use ultrasound to detect where a human is standing
    in a room, just like bats do using echolocation, and then shape the
    sound waves to follow the person as they move, Bulović says. If the vibrating domes of the thin film are covered with a reflective surface,
    they could be used to create patterns of light for future display
    technologies. If immersed in a liquid, the vibrating membranes could
    provide a novel method of stirring chemicals, enabling chemical processing techniques that could use less energy than large batch processing methods.

    "We have the ability to precisely generate mechanical motion of air by activating a physical surface that is scalable. The options of how to
    use this technology are limitless," Bulović says.

    This work is funded, in part, by the research grant from the Ford Motor
    Company and a gift from Lendlease, Inc.


    ========================================================================== Story Source: Materials provided by
    Massachusetts_Institute_of_Technology. Original written by Adam
    Zewe. Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Jinchi Han, Jeffrey Lang, Vladimir Bulovic. An Ultra-Thin Flexible
    Loudspeaker Based on a Piezoelectric Micro-Dome Array. IEEE
    Transactions on Industrial Electronics, 2022; 1 DOI:
    10.1109/TIE.2022.3150082 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220426153637.htm

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