Paper-Thin Loudspeakers: The Possibilities Of Technology Are Limitless
MIT (Massachusetts Institute of Technology) engineers have developed a very thin loudspeaker. By placing this loudspeaker on any surface, that surface can become a source of sound.
Paper-Thin Loudspeakers: The Possibilities Of Technology Are Limitless
Sound quality from this paper-thin loudspeaker is pretty good. And the sound of the original audio is very little distorted or distorted in this loudspeaker. Compared to normal loudspeakers, this speaker also consumes less power.
The loudspeaker that the researchers demonstrated as their invention weighs only about a coin and is about the size of a palm. But this speaker can be placed on any surface and used as a loudspeaker.
Researchers have adopted excellent techniques to create such high-tech speakers. This speaker is made in 3 easy steps. And by following these steps it is possible to make loudspeakers several times larger. In this way, the entire interior of the car or the entire wall of a house can be covered with loudspeakers by making it on a large scale.
Speakers can also perform noise cancellation in very noisy places such as airplane cockpits. For this reason, a wave of the same amplitude as the sound wave of the surrounding environment will be generated from the loudspeaker. As a result, two identical sound waves of opposite types will cancel each other out. This way the external noise can be reduced with the help of this speaker.
This loudspeaker can also be used to create an immersive environment or a digital environment. 3D audio can be played with these speakers in places like theaters or theme parks. Again, the use of this speaker will be very useful in smart devices that cannot use very large batteries. Because the speaker is very light weight and requires very little power to run.
“It’s a wonderful thing. It looks like a thin sheet of paper. You attach two clips to it, and insert it into the computer’s headphone port. You will see what great sound is produced from this speaker. You can use this device everywhere. It takes very little electricity to run.” said lead researcher Vladimir Bulovich. He is currently appointed as the Fariborj Masih Chair in the Department of Emerging Technologies at MIT. At the same time, he is the head of this university’s ‘Organic and Nanostructured Electronics Laboratory’ (abbreviated ONE Lab) and director of ‘MIT Nano’.
The lead author of the paper on the loudspeaker was Jinchi Han, a postdoc in the One Lab. Another one of the authors is Jeffrey Lang, ‘Vites Professor’ of the University’s Department of Electrical Engineering. The research paper was published in the journal IEEE Transactions on Industrial Electronics.
New Method Of Making Thin Speakers
In loudspeakers of the type we see in typical headphones or audio systems, a magnetic field is created by current flowing through a coil of wire. This magnetic field causes the speaker screen to vibrate, causing the air adjacent to the screen to vibrate. And it is from those air waves that we hear sound.
On the other hand, this innovative loudspeaker is made with a thin membrane made of a type of material called piezoelectric. The properties of this material are such that when an electrical voltage is applied to it, it vibrates the surrounding air to produce sound. As a result, this newly invented device works in a much simpler way than the ordinary loudspeaker.
Most of the thin speakers that have been invented before cannot be mounted on any other surface. This is because they have to be flexed conveniently for the sound to come out of the loudspeakers. And these thin speakers can’t bend when attached to a surface. As a result, the sound quality deteriorates.
To eliminate this problem, MIT researchers have designed a new method of loudspeaker construction. The new speaker does not produce sound by vibrating the whole part as in earlier invented thin speakers. Rather, many small dome-shaped structures are made and placed on the speaker. These tiny domes, as wide as the width of a few human hairs, can generate vibrations on their own. Also, these domes are protected by a layer on both sides, so that vibrations can easily be generated even if attached to any other surface.
As a result, the quality of the sound coming from this speaker does not decrease even after being placed on any surface. Rather, the extra screen used to protect the domes makes the speakers last longer.
The researchers used a widely used lightweight plastic called ‘PET’ to make the loudspeaker. First, a very small hole is made on one side of this PET plastic sheet using a laser machine to make the loudspeaker. Now the other side of the perforated sheet is laminated or wrapped with a very thin piezoelectric material called ‘PVDF’. And laminate is made with only 8 micron thick layer. The entire speaker is then placed upside down in a vacuum and heat is applied below at 80°C.
And this film called ‘PVDF’ is so thin that when pressure changes due to air voids and heat, the film swells. But this ‘PVDF’ substance cannot penetrate plastic. As a result, a layer of ‘PVDF’ is formed in the form of domes only where there are small pores. This is how tiny domes of PVDF are formed.
The researchers then coated the other side of the ‘PVDF’ screen in the same manner, creating another layer between the dome and the speaker. This latter layer acts as a protective layer between the surface where the speaker will be mounted and the dome.
“It’s a very simple, common process,” says researcher Han. These speakers can be produced in large quantities if manufactured in the ‘roll to roll’ process. And in the future these speakers can be produced in such a large scale that it will be possible to install these speakers like wallpaper on walls, cars and even inside airplanes.”
Better Quality Sound With Less Power
The speaker’s domes are only 15 microns in height, which is about one-sixth the width of a human hair. Domes can only fluctuate by half a micron during vibration. And from each dome the sound is produced separately. So thousands of domes have to vibrate together to produce sound for our ears.
This simple method of loudspeaker invention has resulted in another significant benefit of increasing sound levels. Basically changing the size of the holes in the PET plastic also changes the shape of the dome. And because larger radius domes can move more air, more noise is generated. However, larger domes have a lower ‘resonance frequency’. Basically, the resonance frequency is the frequency at which the best quality sound is heard from the speaker. Distortion occurs when the resonant frequency is low.
When the researchers perfected the method of making the speakers, they worked with different sized domes and different thicknesses of piezoelectric screens to see which combination produced the best results.
They placed this thin loudspeaker on a wall 30 cm away from the microphone and tested how it sounded. A 25 volt current flowing through the device at 1 kHz (1000 cycles per second) produces a sound of 66 decibels from the speaker. Basically the volume we speak during a normal conversation is close to 66 decibels. And when the electricity is flowing at a rate of 10 kilohertz, the sound pressure level or sound pressure is 86 decibels, which is almost as intense as the sound of city vehicles.
And this super energy efficient speaker only consumes 100mW of power per square meter. On the other hand, a typical home speaker uses more than 1 watt of electricity to produce the same amount of sound pressure.
According to Han, this speaker does not vibrate as a whole, only its small domes vibrate separately, so the speaker has a considerable amount of resonance frequency. Sound at this frequency can be useful for a variety of ultrasound applications. For example, ‘ultrasound imaging’ can be done better with its help. In ultrasound imaging, images are created with very high frequency sound waves. The higher the frequency, the better the image resolution.
Just as bats use sound waves to navigate, Bulovich said, this device could also use ultrasound to detect the presence of people in a room. It can then generate sound waves in such a way that it can follow where the person is going.
In the future, a thin layer can be added on top of the speaker dome to reflect light. In this way, different light patterns can be created within the speaker. Thus this device may also contribute to future display technology.
New techniques for dissolving chemicals can also be developed using the vibrations generated by this device when immersed in water or another liquid. A new technique developed with this machine can work with less energy than the way chemicals are dissolved during mixing, currently done in ‘batch processing’.
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“We have the ability to very precisely create and control the mechanical movement of air by activating a surface of any size,” Bulovich said. The possibilities of how this technology can be used are limitless.”
Ioannis Kimisis, chairman of Columbia University’s Department of Electrical Engineering and Kenneth Breyer Professor of Electrical Engineering, said, “I think this new method of making very thin speakers is very creative.” He was not involved in this study. According to him, the technique of making miniature domes using photolithography pattern templates is quite new. He is optimistic that there will be a lot of work with this technology in speakers and microphones in the future.
Part of the funding for this research came from a research grant from Ford Motor Company. And the rest came as a gift from a company called ‘Lindley’s Inc.’
