Scientists at MIT have created a loudspeaker as thin as paper, which can cover the whole house. This kind of thin-film speaker only needs a small part of the energy required by traditional speakers, but it can produce high-quality sound with minimal distortion. Scientists at MIT have created a loudspeaker as thin as paper, which can cover the whole house.
Scientists at the Massachusetts Institute of Technology have made paper-thin speakers that can cover the whole house. 1 MIT engineers have developed a paper-thin loudspeaker that can turn any surface into a sound source.
Its weight is equivalent to a coin of 10 cent, and it can emit high-quality sound no matter what surface it is attached to.
This kind of thin film speaker produces the least sound distortion and consumes much less energy than traditional speakers.
In order to realize these characteristics, researchers have created a seemingly simple manufacturing technology, which only needs three basic steps. With this technology, they can make an ultra-thin speaker large enough to cover the interior of a car or the whole room.
In addition, this kind of thin film loudspeaker can actively reduce noise in noisy environment (such as aircraft cockpit) by producing sound with the same amplitude but opposite phase. This flexible device can also be used for immersive entertainment, such as providing three-dimensional audio in theaters or theme parks. Because of its light weight and low power consumption, it is very suitable for smart devices with limited battery life.
This research result was recently published in IEEE Transactions on Industrial Electronics.
Paper link: https://ieeexplore.ieee.org/document/9714188.
"It's great to pick up a piece of paper that looks very thin, clamp it with two clips, insert it into the headphone jack of the computer, and then start to hear the sound it makes. It can be used anywhere, and it only needs a little electricity to run, "said Vladimir Bulovi, director of MIT.nano and author of the paper.
How is this film speaker made?
Typical speakers commonly used in headphones or audio systems use current input. The current passes through the coil to generate a magnetic field, which moves the loudspeaker diaphragm and drives the air above the diaphragm, thus generating the sound we hear. In contrast, the new speaker designed by MIT engineers simplifies the traditional design and uses a molded piezoelectric material film. When a voltage is applied to it, the film will move, thus driving the air above it and generating sound.
Most membrane speakers are designed to be independent (unsupported) because the membrane must be able to bend freely to produce sound. Mounting these speakers on the surface will hinder the ability of vibration and sound generation.
In order to overcome this problem, the MIT team reconsidered the design of thin-film speakers. The scheme they gave is that the whole material is not allowed to vibrate, but the sound is generated by the vibration of tiny domes on the thin layer of piezoelectric material, and each dome vibrates independently.
These domes, each as wide as a few hairs, are surrounded by gaskets at the top and bottom of the membrane to protect them from the installation surface while still allowing them to vibrate freely. In daily operation, the same spacer layer protects the dome from wear and impact, which improves the durability of the speaker.
To make loudspeakers, researchers use lasers to cut tiny holes in lightweight plastic PET boards. They placed a very thin (8 micron) piezoelectric film called PVDF under the perforated PET layer. Then, they vacuum the top of the adhesive board and apply a heat source of 80 degrees Celsius under the board.
Because the PVDF layer is very thin, the pressure difference between vacuum and heat source causes it to expand. PVDF can't force through the PET layer, so there will be a tiny dome where it is not blocked by PET. These protrusions are self-aligned with the holes in the PET layer. Then, the researchers laminated the other side of PVDF with another layer of PET as a spacer between the dome and the bonding surface.
"This is a very simple and clear process. If we combine it with the roll-to-roll process, we can mass-produce these speakers and then cover them on walls, cars or planes in a way similar to wallpaper. Han said in his first paper.
High quality and low power consumption
The small dome in the thin film speaker is 15 micron high, which is about one sixth of the thickness of human hair. They can only move up and down about half a micron when vibrating. Each dome is an independent sound generating unit, so thousands of such small domes need to vibrate together to produce audible sound.
Another advantage of the simple manufacturing process is that it is adjustable-researchers can change the size of the holes in PET to control the size of the dome. The dome with larger radius can drive more air to vibrate and produce louder sound, but the dome with larger radius also has lower vibration frequency, which will lead to audio distortion.
After perfecting the manufacturing technology, the researchers tested several different dome sizes and piezoelectric layer thicknesses to achieve the best combination.
They installed the thin-film speaker on the wall 30 cm away from the microphone and tested its sound pressure level (in decibels). When a voltage of 25 volts passes through the equipment at a frequency of 1 kHz, the speaker produces a high-quality sound of 66 decibels. At 10 kHz, the sound pressure level increases to 86 dB, which is approximately equivalent to the urban traffic volume.
This energy-saving device only needs about 100 MW per square meter of speaker area. In contrast, if a similar sound pressure is generated at a similar distance, an ordinary household speaker may consume more than 1 watt.
Han explained that because the micro dome vibrates, not the whole membrane, the speaker has a high enough vibration frequency to be effectively used in ultrasonic applications, such as imaging. Ultrasonic imaging uses extremely high frequency sound waves to produce images, and higher frequencies can produce higher resolution images.
Brovey said that the device can also detect the position of human standing in a room by using ultrasonic waves, just like bats use echolocation, and then follow human movements to form sound waves. If the vibrating domes of thin films are covered with reflective surfaces, they can be used to provide ideas for the light-emitting modes of future display technologies. If immersed in liquid, vibrating membrane can provide a new method to stir chemicals, so that chemical treatment technology can use less energy than quality treatment method.
"We have the ability to accurately generate the mechanical movement of air by activating the retractable physical surface. The imagination brought by this technology is infinite. Brovey said.
Scientists at MIT have made speakers as thin as paper, which can be spread all over the house. Recently, engineers from Massachusetts Institute of Technology have developed a new type of ultra-thin speaker, which is a flexible thin film device that may turn any object surface into a low-power and high-quality audio source.
This kind of thin-film speaker only needs a small part of the energy required by traditional speakers, but it can produce high-quality sound with minimal distortion. According to the demonstration of the research team, this palm-sized speaker weighs only a dime, and it can emit high-quality sound no matter what surface the film is bonded to.
In order to realize these characteristics, the researchers also created a seemingly simple manufacturing technology, which can be scaled up to produce an ultra-thin speaker large enough to cover the wallpaper in a car or room. In this way, the thin-film speaker can provide active noise reduction (that is, the two sounds cancel each other out) by generating sounds with the same amplitude but opposite phases in a noisy environment (such as the cockpit of an airplane).
In addition, this new device can also be used for immersive entertainment, such as providing 3D audio in theaters or theme parks. And because of its light weight, it needs very little power, which is very suitable for smart devices with limited endurance.
"It looks like a thin piece of paper. Stick two clips on it, plug in the earphone port of the computer, and then start listening to the sound it makes. It feels great. It can be used anywhere and only needs a power supply to run it. Vladimir Bolovi, correspondent of the research paper, director of MIT.nano and head of the Electronic Laboratory for Organic and Nanostructures (ONE Lab), said.
Brovey co-authored this paper with the first author, Jin Chi Han, a postdoctoral fellow in a laboratory, and Jeffrey Lang, a professor of electrical engineering. This study was published in IEEE Journal of Industrial Electronics.
Brand new ultra-thin speaker
As we all know, traditional speakers in headphones or audio systems use current input. When the ever-changing current is input through a coil that can generate a magnetic field to push the speaker diaphragm to vibrate, the air above it will vibrate, thus producing the sound we hear.
In contrast, this new loudspeaker device simplifies the loudspeaker design by using piezoelectric thin films. When a voltage is applied to it, the film will move, so the air above it will vibrate and produce sound.
Because the thin film speaker is designed independently, the thin film material must be bent freely to produce sound. But installing these speakers on the surface of objects will hinder vibration and their ability to produce sound.
In order to overcome this problem, MIT team reconsidered the design of thin film speakers. Their design does not make the whole material vibrate, but relies on tiny domes on a thin layer of piezoelectric material to make each dome vibrate separately.
These small domes, which are only a few hairs wide, are surrounded by gaskets at the top and bottom of the membrane, protecting them from the installation surface while still allowing them to vibrate freely. The same spacer layer can protect the dome from wear and impact in daily operation, thus improving the durability of the speaker.
The production process also looks very simple. First, the researchers used a laser to punch holes in a PET (a light plastic) sheet, and laminated a very thin piezoelectric material (as thin as 8 microns) on the lower side of the punched PET, called PVDF. Then they apply a vacuum on the bonded sheet and a heat source of 80 degrees Celsius below.
Because the PVDF layer is very thin, the pressure difference between vacuum and heat source causes it to expand. However, PVDF can't force through the PET layer, so the tiny dome will protrude in the area not covered by PET. And these protrusions are respectively aligned with the holes in the PET layer. Then, the researchers laminated another layer of PET on the other side of PVDF as a spacer between the dome and the bonding surface.
"This is a very simple and direct process. If we integrate it with the roll-to-roll process in the future, it will enable us to produce these speakers in Qualcomm. This means that it can be mass-produced, just as wallpaper can cover walls, cars or planes. " Han said:
High quality, low power consumption and unlimited application potential.
Each dome is an independent sound generating unit. Because the height of the dome is 15 micron, which is about one sixth of the thickness of human hair, it can only move up and down about half a micron when vibrating, so it takes thousands of such small domes to vibrate together to produce audible sound.
In addition, the manufacture of this ultra-thin sound device has another advantage, that is, it is adjustable, because researchers can change the size of the holes in PET to control the size of the dome. A dome with a larger radius will push more air and produce more sound, but its resonant frequency is also lower. The resonant frequency is the most effective frequency for equipment operation, and a lower resonant frequency will lead to audio distortion.
(Source: Massachusetts Institute of Technology)
After many tests, the researchers found the best combination of different dome sizes and piezoelectric layer thickness. Then, they installed the thin-film speaker on the wall 30 cm away from the microphone and tested it.
When a current of 25 volts passes through the device at 1 kHz (at the rate of 1 000 cycles per second), the speaker will produce high-quality sound of 66 decibels. At 10 kHz, the sound pressure level increases to 86 dB, which is roughly equivalent to the volume level of urban traffic.
This energy-saving speaker device only needs about 100 MW per square meter area. In contrast, an ordinary household speaker may consume more than 1 watt to generate similar sound pressure at a considerable distance.
The researchers explained that because only the tiny dome of the device vibrates, not the whole membrane, the speaker has a high enough resonance frequency, so it can also be effectively used in ultrasonic applications, such as ultrasonic imaging. Ultrasonic imaging uses very high frequency sound waves to produce images, and higher frequencies can produce better image resolution.
For example, the device can detect the standing position of a person in a room using ultrasonic waves and track the position, just like bats use echo positioning. If the vibrating domes of thin films are covered with reflective surfaces, they can be used to create light patterns for future imaging technology. If immersed in liquid, the vibrating membrane can also provide a new way to stir chemicals, so that the chemical treatment technology uses less energy than the quality treatment method.
"We have the ability to accurately generate the mechanical movement of air by activating the extensible physical surface. The options for how to use this technology are endless, "Brovey said.
Scientists at the Massachusetts Institute of Technology have made a paper-thin loudspeaker that can spread throughout the house. According to recent media reports, engineers at MIT have developed a paper-thin loudspeaker, which can turn any surface into an active sound source.
The sound distortion produced by this kind of thin film speaker is very small, and the energy used is only a small part of the energy required by traditional speakers.
The palm-sized speaker displayed by the team weighs about a dime. No matter what surface the film is bonded to, it can produce high-quality sound. In order to realize these extraordinary characteristics, researchers have created a seemingly simple manufacturing technology, which involves only three basic steps to manufacture ultra-thin speakers, and the area can be large enough to cover the interior of a car or paste wallpaper in a room.
Thin film speakers can provide active noise cancellation in noisy environments such as aircraft cockpit by producing sounds with the same amplitude but opposite phase. This flexible device can also be used for immersive entertainment, perhaps providing three-dimensional audio in entertainment facilities in theaters or theme parks. In addition, because it is light and requires little power to run, it is very suitable for smart devices with limited battery life.
It is understood that in headphones or audio systems, typical speakers use current input, and the current generates a magnetic field through the coil, which can move the speaker diaphragm and make the air above it move, thus generating sound. In contrast, the design of this new loudspeaker is simplified by using molded piezoelectric thin film materials. When a voltage is applied to the film, the film will move, thereby moving the air above it and generating sound.
Specifically, in order to make this kind of speaker, the researchers used a laser to punch holes in the PET sheet, which is a lightweight plastic. They laid a very thin piezoelectric PVDF film (only 8 microns thick) on the bottom of the perforated PET layer. Then they applied a vacuum on the bonded sheet and a heat source of 80 degrees Celsius under the sheet.
Because the PVDF layer is too thin, the pressure difference between vacuum and heat source causes it to expand. PVDF can't force through the PET layer, so the tiny dome protrudes where it is not blocked by PET. These protrusions can be self-aligned with holes in the PET layer. Then, the researchers laid another layer of PET on the other side of PVDF as a spacer between the dome and the bonding surface.
Their design is not to make the whole material vibrate, but to rely on tiny domes on a thin layer of piezoelectric material, and each dome vibrates separately. These domes, each only a few hairs wide, are surrounded by gaskets at the top and bottom of the membrane, protecting them from the installation surface while still allowing them to vibrate freely. The same spacer layer protects the dome from wear and impact in daily operation, thus enhancing the durability of the speaker.
The researcher said, "This is a very simple and direct process. If we can combine it with reel-to-reel processing technology in the future, we can produce these speakers in Qualcomm. This means that it can be manufactured in large quantities, covering walls, cars or planes like wallpaper. "