Imagine having your favorite music immerse you as it’s broadcast throughout your room by the wallpaper. That’s one potential application of a new material being developed by engineers at MIT.

Noisy siblings? Loud construction right outside your window? A flexible new loudspeaker could help you rest easy. It could someday turn your walls into noise-canceling systems. And when you’re ready to liven things up, use the same wallpaper — or the surfaces of other ordinary objects in your room — to play music.

The new loudspeaker is super thin ― about as thick as a few sheets of paper. It’s lightweight and flexible enough to stick to most surfaces. It also produces high quality sound. And you can make it big, as in wall-sized, notes Jinchi Han. He’s an electrical engineer at the Massachusetts Institute of Technology in Cambridge.

At the heart of most speakers are moving membranes. An electric current makes them vibrate quickly. That sends nearby air molecules moving — and generating sound waves. Those vibrating air molecules are “the working principle for sound generation,” explains Han.

The new speakers don’t use such membranes. Instead, lots of dome-shaped microstructures cover their surface. The researchers start with a thin, flat sheet of some material. Then they use pressure to pull that material through openings in a template. This creates the dome shapes.

When squeezed, the material they use creates an electric charge. Such materials are known as piezoelectric (PEE-zoh-ee-LEK-trik). But applying an electric field across the material will also cause the domes to expand and contract, Han explains. That can vibrate nearby air molecules, generating sound.

Because the design is so flexible and durable, companies could potentially integrate speakers into T-shirts or other personal items. Or users could make their own.

Han and his colleagues describe their innovation February 15 in IEEE Transactions on Industrial Electronics.

Other researchers have created piezoelectric speakers. But none are like these. What’s special here are those micro-domes.

Old-style piezoelectric speakers broadcast sound waves through the motion of the whole speaker. Mounting such speakers onto a solid surface, Han says, would hamper their sound by restricting that motion.

Han’s team sandwiches their new material between two plastic sheets (to protect the domes). Tiny holes punched through the sheets line up in such a way that the domes can expand into these holes as they vibrate.

“The bottom layer elevates the small domes so that they can vibrate freely even if the speaker is mounted on a surface,” Han reports. They can vibrate even if the surface is rough or curved. The upper protective layer “is thicker than the domes are high,” he explains. So he notes that if you touch the surface, “you don’t need to worry about damaging these small structures.”

Han points to another benefit of this tech. Large expanses of the new material could make controlling noise a whole lot easier.

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Noise-canceling systems already exist. Most detect sound waves in the environment and then generate new sound waves to “cancel” those out. But whether it works for a listener depends on where that listener’s ears are in relation to the approaching sound waves.

Trying to cancel noise this way everywhere inside a room would be tricky, Han points out. It would take lots of microphones and speakers, which can be bulky and expensive.

Here, each dome works as a tiny speaker. The domes can generate sound waves all together, in groups or individually. Wallpapering your bedroom with this material would create speakers all around you. Those same speakers also could dampen — or cancel — unwanted sound. When desired, you could turn any space into “a quiet zone where you could sleep or study without too much noise,” Han says. He also sees applications in cars, airplanes, apartments or anywhere unwanted noise is a problem.

Another plus? The new design costs far less and uses less energy than conventional speakers.

The researchers built a prototype — a sheet of the material that’s 10 centimeters by 10 centimeters (about 4 inches by 4 inches). The piece has more than 8,000 domes. Super-sizing the design would be straightforward, Han says. But first his lab needs to get some new tools.

Large versions could be the next step for immersive, or 3-D, sound experiences, says Lori Beckstead. She teaches audio and digital media at Toronto Metropolitan University in Ontario, Canada. She’s also a sound artist.

In an immersive sound experience, sounds seem to come from all directions. Such designs can help people fully engage in performances, virtual-reality scenarios, museum exhibits and other experiences. The new speakers are so thin and light they “could be placed in spaces where traditional loudspeakers might have been impractical,” Beckstead adds. 

And that doesn’t just apply to immersive sound. She notes that adding noise-canceling technology to loud spaces — from restaurants to noisy manufacturing plants — would be fantastic. “Poorly designed sound environments can be detrimental to anything from mental health to productivity to mood.”

3-D: Short for three-dimensional. This term is an adjective for something that has features that can be described in three dimensions — height, width and length. 

acoustic: Having to do with sound or hearing.

audio: Having to do with sound.

broadcast: To cast — or send out — something over a relatively large distance. A farmer may broadcast seeds by flinging them by hand over a large area. A loudspeaker may send sounds out over a great distance. An electronic transmitter may emit electromagnetic signals over the air to a distant radio, television or other receiving device. And a newscaster can broadcast details of events to listeners across a large area, even the world.

colleague: Someone who works with another; a co-worker or team member.

contract: To activate muscle by allowing filaments in the muscle cells to connect. The muscle becomes more rigid as a result.

digital: (in computer science and engineering)  An adjective indicating that something has been developed numerically on a computer or on some other electronic device, based on a binary system (where all numbers are displayed using a series of only zeros and ones).

electric charge: The physical property responsible for electric force; it can be negative or positive.

electric current: A flow of electric charge — electricity — usually from the movement of negatively charged particles, called electrons.

electronics: Devices that are powered by electricity but whose properties are controlled by the semiconductors or other circuitry that channel or gate the movement of electric charges.

engineer: A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need. (v.) To perform these tasks, or the name for a person who performs such tasks. An electrical engineer designs, builds or analyzes electrical equipment.

environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

field: (in physics) A region in space where certain physical effects operate, such as magnetism (created by a magnetic field), gravity (by a gravitational field), mass (by a Higgs field) or electricity (by an electrical field).

innovation: (v. to innovate; adj. innovative) An adaptation or improvement to an existing idea, process or product that is new, clever, more effective or more practical.

manufacturing: The making of things, usually on a large scale.

media: A term for the ways information is delivered and shared within a society. It encompasses not only the traditional media — newspapers, magazines, radio and television — but also digital outlets, such as Twitter, Facebook, Instagram, TikTok and WhatsApp. The newer, digital media are sometimes referred to as social media. The singular form of this term is medium.

membrane: A barrier which blocks the passage (or flow through) of some materials depending on their size or other features. Membranes are an integral part of filtration systems. Many serve that same function as the outer covering of cells or organs of a body.

mental health: A term for someone’s emotional, psychological and social well-being. It includes how people handle stress and manage fear or anxiety. Poor mental health can be triggered by disease or merely reflect a short-term response to life’s challenges.

physical: (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

piezoelectric: An adjective describing the ability of certain materials (such as crystals) to develop an electric voltage when deformed, or squeezed.

prototype: A first or early model of some device, system or product that still needs to be perfected.

scenario: A possible (or likely) sequence of events and how they might play out.

sibling: An offspring that shares the same parents (with its brother or sister).

sound wave: A wave that transmits sound. Sound waves have alternating swaths of high and low pressure.

system: A network of parts that together work to achieve some function. For instance, the blood, vessels and heart are primary components of the human body's circulatory system. Similarly, trains, platforms, tracks, roadway signals and overpasses are among the potential components of a nation's railway system. System can even be applied to the processes or ideas that are part of some method or ordered set of procedures for getting a task done.

technology: The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

unique: Something that is unlike anything else; the only one of its kind.

vibrate: To rhythmically shake or to move continuously and rapidly back and forth.

virtual reality: A three-dimensional simulation of the real world that seems very realistic and allows people to interact with it. To do so, people usually wear a special helmet or glasses with sensors.

wave: A disturbance or variation that travels through space and matter in a regular, oscillating fashion.

Journal: J. Han, J. Lang and V. Bulovic. An ultra-thin flexible loudspeaker based on a piezoelectric micro-dome array. IEEE Transactions on Industrial Electronics. Published online February 15, 2022. doi: 10.1109/TIE.2022.3150082.

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