ENGINEERING TECHNOLOGY

Paper-thin speakers are out! The amazing invention of Dr. MIT


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Small domes in acoustic films form an array structure. Courtesy of respondents

As you sit on the couch, the room’s wallpapers let you play music, immersing you in real surround sound, and they also have a microphone function that lets you call the smart home.

It sounds sci-fi, but it can really become a reality. The most important thing is that to make such a magical film speaker, only low-cost piezoelectric film materials and simple processing technology are needed, which has the prospect of large-scale application compared with the previous technology.

Carrying this dream is a very cool new multifunctional acoustic film. Its inventor is Han Jinchi, a postdoctoral fellow in the Department of Electrical and Electronic Engineering and Computer Science at the Massachusetts Institute of Technology (MIT). Recently, the study was published in the international top journal IEEE Transactions on Industrial Electronics.

Clever “sandwich” design

Researchers can always make those seemingly fanciful ideas come true one by one, and better benefit mankind.

This is the case with Han Jinchi’s team’s research. Compared with the traditional speakers that are now on the market, they prefer to make a very thin, flexible, transparent and better acoustic alternative. These shining points also happen to be favored by some internationally renowned companies.

At first, they had a lot of ideas, and then sifted through three more suitable solutions, two of which were acoustic films based on electrostatic effects and one acoustic films based on piezoelectric technology. After modeling and simulation, after measuring the difficulty of processing, the piezoelectric solution won.

“It’s amazing to pick up something that looks like paper and clip an audio cable to it, and plug the other end of the audio cable into your computer’s headphone port to hear it.” The presentation video attached to the paper describes the new invention.

In fact, there have been membrane speakers before, but the membrane must be able to vibrate freely after the voltage is added to produce sound. This means that the film must be designed to be suspended so that the vibration is not hindered. However, without allowing it to touch any surface, it cannot be made into wallpaper to paste on the indoor wall, nor can it be embedded in the car interior, which greatly limits the scope of application.

Therefore, the hanging thin film structure is the key. Han Jinchi uses a clever “sandwich” design to solve this problem.

“It doesn’t have to make the whole film dangling and vibrating, I designed some suspended microstructures — many small bubble-like domes that vibrate freely and replace the overall vibration of the film to produce sound.” Han Jinchi, the first author of the paper, introduced it to China Science News.

These dome microstructures are processed on an ultra-thin polyvinylidene difluoroethylene piezoelectric film using a vacuum embossing process, which is sandwiched between two porous PET (polyethylene terephthalate) material, which is equivalent to creating a certain space for the dome, so that they are always suspended and can vibrate freely.

Both layers of PET perform their respective duties: the bottom layer is to allow the piezoelectric film to form a space with the surface of the installed object, so as not to affect the vibration of the dome, ensuring excellent performance in a variety of applications, and the top layer is to protect the fragile small dome from wear and impact during daily operation, improving durability. Because the ultra-thin piezoelectric film is directly touched by hand, it is easy to cause deformation or even depression in the upper dome.

Each small dome is about 15 microns high, less than the thickness of a single hair. The thickness of piezoelectric materials is only 8 to 12 microns. The thickness of PET is 50 microns. Although so many materials are superimposed, the entire acoustic film is still very thin, about 0.1 mm thick, equivalent to a piece of paper.

Han Jinchi said they can also make the membrane speaker thinner. Because the PET used in this study is readily available on the market, thinner PET materials can be processed in the future.

Everything seems to be very random, but in fact, the team is far-sighted.

“Our core idea is to be pragmatic and the aim is not to set records in performance, so the highlight is not in the material itself.” Han Jinchi said that the use of the most common materials, the lowest cost of processing methods, but also to ensure excellent performance, in order to make this technology go further.

Low power consumption, high performance, noise reduction

Common speakers are driven by current, require a large current input, and generate a magnetic field through the coil, driving the diaphragm to vibrate and produce sound. However, a large current can easily lead to serious heat generation and energy loss.

The thin-film speaker developed by the team, each tiny dome on its piezoelectric material is a separate sound unit, and when thousands of such small domes form an array structure and vibrate together, sound can be produced. “The whole process is driven by an electric field, there is no large current, there is no obvious heat generation phenomenon, and the power consumption is much lower than that of existing speakers.” Han Jinchi said.

It is worth mentioning that compared with the existing types of membrane speakers, the invention has higher sensitivity and bandwidth in generating sound, and can be applied to any object surface. Even on some curved or irregular surfaces, it still produces high-quality sound.

Don’t underestimate the ability of these small domes, they can not only produce sound waves, but also sense sound waves. That said, the acoustic film can also be used as a microphone to record audio with high fidelity.

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Acoustic film Courtesy of the interviewee

Its ability to actively reduce noise has attracted even more attention. “In the future, large-area thin-film speakers can actively reduce noise by producing sound of the same amplitude but with opposite phases in noisy environments, such as the cockpit of an airplane.” Han Jinchi said.

In the future, more requirements will be required for different applications, and the advantage of this technology is also the high adjustability.

“There is still a lot of room for improvement in performance now, and we can also do a lot of microstructure design to replace the dome, and even do some specific microstructure combinations to improve the characteristics of low frequency.” Han Jinchi said.

Next, they will continue to try and continue to improve, so that the technology can be used in the future in space active noise reduction and immersive audio, human-machine acoustic interface, smart home, flexible consumer electronic devices, ultrasonic ranging and imaging, biomedical engineering and other fields.

I do research entirely because of love

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Han Jinchi in MIT’s lab. Courtesy of respondents

Like many science and engineering students, Han Jinchi has also experienced a mental journey from confusion to determination.

In 2009, he was admitted to the Department of Electrical Engineering and Applied Electronics Technology of Tsinghua University, and the first two years of undergraduate were spent in classes, studies and examinations, and he almost “settled down” in the self-study room with serious efforts, just to stand out from many elites. But such a step-by-step life has always made him feel lacking in taste, and even a little confused.

Until his junior year, a chance allowed Han Jinchi to participate in a new wireless charging project, which happened to be the SRT Challenge Cup project that year. It was this opportunity that made him have a strong interest in scientific research, “I prefer to do research than to get a high score on the exam.” ”

When the “switch” is turned on, it is out of control. Later, Han Jinchi participated in some domestic and foreign scientific research competitions as an undergraduate and frequently won awards. One of the most impressive was that he participated in the IEEE PES GM (Annual Meeting of the Electric Power and Energy Association of the Institute of Electrical and Electronics Engineers) in the United States during the summer of his junior year.

The event was dedicated to students to open an academic poster competition, Han Jinchi took his scientific research results to compete with 190 undergraduate and graduate students from all over the world, and his demonstration of wireless charging was recognized by the judges and experts, and finally won the Best Poster Award with the second place, becoming the first Asian student to receive the award.

“At first, I went with the attitude of ‘seeing the world’, and I also wanted to take this opportunity to communicate with experts. Winning the award in the end was a great encouragement to me, and the whole process of research also made me feel very satisfied. Since then, I’ve wanted to devote more time to research. Han Jinchi said.

After the school, he continued to focus on scientific research in the field of electrical engineering in his original department, and his supervisor also gave him enough freedom to choose the research he liked. Later, Han Jinchi chose to continue his doctoral studies at MIT and engaged in postdoctoral research at MIT. His passion for micro-nanoelectronics and micro-nano processing has led him to pursue challenging and innovative research in the field of micro-nanoelectronic devices.

“MIT’s micro-nanoelectronics major is very famous, and it is of great significance to me to continue to engage in cross-disciplinary and cross-disciplinary research here. Professor Jeffrey Lang, one of my PhD and postdoctoral supervisors and corresponding author of this paper, is influential in the field of mechatronics and has imparted a lot of experience to me. “Han Jinchi enjoys the current research atmosphere.

Han Jinchi said that in the future, he will continue to do scientific research as always. “I hope to make some valuable and promising results that can contribute to improving people’s lives.” (Source: China Science Daily Zhang Qingdan)

Related paper information:https://doi.org/10.1109/TIE.2022.3150082



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