The membrane speaker produces the least amount of audio distortion and consumes a fraction of the energy of a conventional speaker. The team demonstrated a palm-sized speaker, weighing about a dime, that could play no matter what surface the membrane was stuck to High quality audio.
To achieve these properties, the researchers pioneered a deceptively simple fabrication process that, in just three basic steps, can be scaled up to create speakers that are thin enough to cover the interior of a car or wallpaper a room. In this way, membrane speakers can produce sounds of the same amplitude and opposite phase in a noisy environment (such as an airplane cockpit), which cancel each other out. Film speakers can be used for immersive entertainment, such as providing three-dimensional spatial audio while riding in theaters or theme parks. Because of their light weight and low power requirements, they are ideal for smart device applications with limited battery life.
Vladimir Bulovic, head of MIT’s Organic Nanostructure Electronics Laboratory (ONE Lab), said: “The thin-film speaker looks like a thin piece of paper, connecting two clips to energize, related to It’s an amazing experience to plug a port into a computer headphone jack and hear it make a sound, it’s so portable, it can be used anywhere, and people only need a small amount of power to run it.”
Brovici and research colleagues Jinchi Han and Jeffrey Lang report the study in the IEEE Transactions on Industrial Electronics.
New solution
Traditional speakers in headphones or audio systems use current input. The current is passed through a coil to generate a magnetic field. The magnetic field vibrates the speaker membrane, causing the air above the speaker membrane to move, thereby producing the sound we hear. In contrast, the new speaker simplifies speaker design by using a membrane made of a piezoelectric material that vibrates when voltage is applied to the membrane, moving the air above it and producing sound.
Most membrane speakers are self-contained because the membrane must bend freely to produce sound, and mounting it on a surface would block its vibration, affecting its ability to produce sound. To overcome this problem, the MIT team redesigned the thin-film speaker. Instead of making the entire membrane vibrate, the MIT team relied on tiny domes on thin piezoelectric materials, each vibrating individually, with a diameter of only Several times the size of a human hair, the top and bottom of the membranes are wrapped by a spacer layer that protects them from the mounting surface while still allowing them to vibrate freely. During daily operation, the same spacer layer protects the dome from abrasion and impact, thereby Improved speaker durability.
To get the best results from the thin-film speakers, the researchers used a laser to cut small holes in a sheet of PET (polyethylene terephthalate), a lightweight plastic, and they laid a layer on the bottom of the perforated PET sheet. Very thin PVDF material (a piezoelectric material), after which they applied a vacuum above the bonded sheet and a heat source of 80 degrees Celsius below the bonded sheet.
Since the PVDF material is very thin, the pressure difference generated by the vacuum and the heat source causes it to expand, and the PVDF material cannot forcibly penetrate the PET sheet, so a dome protrusion is generated at the small hole of the PET sheet. The researchers then placed a thin layer of PET on the other side of the PVDF material to act as a spacer between the dome protrusions and the bonding surface.
Jinchi Han said: “It’s a very simple and straightforward process, and if we can combine the roll-to-roll process in the future, we can produce these speakers in a high-throughput way, which means it can be mass-produced and covered like wallpaper on walls, Inside a car or an airplane.”
Most membrane speakers are self-contained because the membrane must bend freely to produce sound, and mounting it on a surface would block its vibration, affecting its ability to produce sound.
High quality, low power consumption
The domes are only 15 microns high, about one-sixth the diameter of a human hair, and they are only polarized up and down by 0.5 microns when they vibrate. Each dome is a separate source of sound, so it takes thousands of domes to vibrate together to generate The sound that humans hear.
Another benefit of the thin-film speaker is its tunability—the researchers can change the diameter of the holes in the PET flakes to control the size of the dome. Domes with larger radii produce louder sound, but have lower resonant frequencies. The frequency is the frequency at which the device operates most efficiently, and lower resonant frequencies can cause audio distortion.
After the researchers perfected the thin-film speaker design, they tested several different dome sizes and piezoelectric layer thicknesses to find the best combination. They mounted the membrane speaker on a wall 30 cm from the microphone and tested its sound pressure level (measured in decibels), which produced 66 decibels when a 25-volt current was passed through the device at 1,000 Hz (1,000 cycles per second). At 10 kHz, the sound pressure level will increase to 86 dB, about the same volume level as city traffic.
The energy-saving device requires only about 100 milliwatts of electrical power per square meter, compared to the over 1 watt that a typical home speaker might consume to generate a similar sound pressure over a considerable distance. Jinchi Han explained that because the small dome structure is constantly vibrating, rather than the entire membrane vibrating, the loudspeaker can generate a high enough resonant frequency to be effectively used in the field of ultrasound, for example: ultrasound imaging, which uses very high frequency sound waves produce images, higher frequencies produce higher resolution images.
The device can also use ultrasonic waves to detect a person’s position in a room, much like bat echolocation, and then shape the sound waves to track human movement, Brovici said. If a thin-film vibrating dome structure is covered with a reflective surface, it can be used for the creation of futuristic light display technology. If the membrane is immersed in liquid, the vibrating membrane could provide a new method of stirring the chemistry, making the chemical processing technique less energy-intensive than bulk processing methods.
With our ability to precisely generate aero-mechanical motion by activating stretchable physical surfaces, the fields of application of this technology are limitless, Brovisi points out.
“I think it’s a very creative approach,” said Ioannis Kymissis, chair of the department of electrical engineering at Columbia University. “The strategy of stacking film into arches using lithographic pattern templates is very unique and may A range of new applications are created in loudspeakers and microphones.
