MIT engineers have developed a paper-thin speaker that can turn any surface into an active audio source.
This thin film speaker Produces a sound with minimal distortion while using some of the energy required for traditional speakers. The team’s hand-sized speakers weigh as much as a dime and can produce high-quality sound no matter what surface the film is glued to.
To achieve these characteristics, researchers have pioneered seemingly simple manufacturing techniques. It requires only three basic steps and can be scaled up to produce an ultra-thin speaker large enough to cover the interior of a car or create a room wallpaper.
When used in this way, thin-film speakers can provide active noise canceling in unpleasant environments, such as the cockpit of an airplane, by producing anti-phase sound with the same amplitude. The two sounds cancel each other out. Flexible devices can also be used for immersive entertainment, perhaps by providing 3D audio in theater and theme park rides. It is also lightweight and requires less power to operate, making it ideal for smart device applications with limited battery life.
“It’s amazing to take something that looks like a piece of paper, attach two clips to it, plug it into your computer’s headphone port, and you’ll start hearing the sound coming from it. You can use it anywhere. One is smidgeon. You need the power to do that. “
Bulović wrote the dissertation with lead author Jinchi Han, a postdoctoral fellow at ONE Lab, and co-author Jeffrey Lang, a professor of electrical engineering Vitesse. Research today IEEE transactions for industrial electronics..
Typical speakers found in headphones and audio systems use a current input to pass through a coil of wire to generate a magnetic field. This will move the speaker membrane, and the air will move over it and you will hear the sound. In contrast, new speakers use a thin film of molded piezoelectric material that moves when a voltage is applied, simplifying speaker design and moving air over it to produce sound.
Most thin-film speakers are designed to be self-contained because the film needs to be bent freely to produce sound. Mounting these speakers on the surface interferes with vibration and the ability to produce sound.
To overcome this problem, the MIT team rethought the design of thin film speakers. Their design relies on a small dome on a thin layer of piezoelectric material, each vibrating individually, rather than vibrating the entire material. Each of these domes, with a width of just a few hairs, is surrounded by spacer layers at the top and bottom of the film, allowing them to vibrate freely while protecting the domes from the mounting surface. The same spacer layer protects the dome from wear and shock during routine handling and increases the durability of the speaker.
To make a speaker, researchers used a laser to make a small hole in a thin sheet of PET, a type of lightweight plastic.They laminated the underside of the perforated PET layer with a very thin film (8 micron thin). Piezoelectric material, Called PVDF. Next, a vacuum was applied on top of the glued sheet, and a heat source of 80 degrees Celsius was applied underneath.
Because the PVDF layer is very thin Pressure difference What was created by the vacuum and heat source inflated it. Since PVDF cannot be forced through the PET layer, a small dome protrudes into the area not blocked by PET. These protrusions self-align with the holes in the PET layer. Researchers then laminate the other side of the PVDF with another PET layer to act as a spacer between the dome and the bonding surface.
“This is a very simple and straightforward process. In the future, when integrated with the roll-to-roll system, these speakers will be able to be manufactured at high throughput, which means they can be manufactured in large quantities. Walls, cars. It’s like a wallpaper that covers the interior of an aircraft, “says Han.
High quality, low power
The height of the dome is 15 microns, about one-sixth the thickness of human hair, and when vibrated it moves up and down only about 0.5 microns. Since each dome is a single sound-generating unit, thousands of these small domes need to vibrate together to produce audible sound.
An additional advantage of the team’s simple manufacturing process is its tunability. Researchers can resize the holes in the PET to control the size of the dome. A dome with a larger radius pushes more air away and produces more sound, but the larger the dome, the lower it is. Resonance frequency.. The resonant frequency is the frequency at which the device operates most efficiently, and low resonant frequencies cause audio distortion.
Once the researchers completed the manufacturing technique, they tested several different dome sizes and piezoelectric layer thicknesses to reach the optimum combination.
They tested thin-film speakers by mounting them on a wall 30 centimeters from the microphone and measuring sound pressure levels recorded in decibels. When 25 volts of electricity passed through the device at 1 kilohertz (1,000 cycles per second), the speaker produced high quality sound at a conversation level of 66 decibels. At 10 kHz, the sound pressure level increased to 86 decibels. This is about the same volume level as urban traffic.
Energy efficient devices require only about 100 milliwatts of power per square meter of speaker area. In contrast, the average home speaker can consume more than a watt to produce similar sound pressure at comparable distances.
The speaker’s resonant frequency is high enough that it can be effectively used in ultrasonic applications such as imaging because the small dome is vibrating rather than the entire film, Han explains. Ultrasound imaging uses very high frequency sound waves to generate an image, and the higher the frequency, the better the resolution of the image.
The device uses ultrasound to detect where a human is standing in a room, much like a bat uses echolocation. sound Bulović says they make waves to chase people as they move. If the vibrating domes of the thin film are covered with reflective surfaces, they can be used to create patterns of light for future display technologies. When immersed in a liquid, the vibrating membrane provides a new way to agitate chemicals, enabling chemical treatment techniques that use less energy than large batch processing methods.
“By activating a scalable physical surface, we have the ability to accurately generate the mechanical motion of air. The options for using this technology are endless,” says Bulović.
“I think this is a very creative approach to creating this class of ultra-thin speakers,” said Ioannis (John) Kymissis, a professor of electrical engineering at Columbia University and chair of the Department of Electrical Engineering. increase. This study. “The strategy of dome-forming film stacks using photolithographic patterned templates is very unique and can lead to a variety of new applications for speakers and microphones.”
Jinchi Han et al, Ultra-thin Flexible Loudspeaker Based on Piezoelectric Microdome Array, IEEE transactions for industrial electronics (2022). DOI: 10.1109 / TIE.2022.3150082
Massachusetts Institute of Technology
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