Recently, engineers at the Massachusetts Institute of technology have developed a paper thin speaker that can turn any surface into an audio source. This thin-film speaker produces the least audio distortion and consumes only a small part of the energy of traditional speakers. The research team demonstrated a palm sized speaker that weighs about a dime. No matter what surface the film is stuck to, it can play high-quality audio.
Thin film speakers produce the least audio distortion and consume only a small part of the energy of traditional speakers. The research team demonstrated a palm sized speaker that weighs about a dime. No matter what surface the film is stuck to, it can play high-quality audio.
In order to realize these characteristics, researchers have created a seemingly simple manufacturing process, which requires only three basic steps, and can be scaled up to produce ultra-thin speakers that can cover the interior of the car or be covered with room wallpaper. In this way, the thin-film loudspeaker can produce sound with the same amplitude and opposite phase in a noisy environment (such as the cockpit of an aircraft), and the two sounds can cancel each other. Thin film speakers can be used for immersive entertainment, such as providing three-dimensional space audio when riding in a theater or theme park. Due to its light weight and low power consumption, it is very suitable for intelligent device applications with limited battery life.
Vladimir bulovic, head of the one lab at MIT, said: "The thin-film speaker looks like a piece of thin paper. Connect two clips to power on, plug the relevant ports into the computer headphone connector, and then you can hear the sound it makes. This experience is very magical. It is very portable and can be used anywhere. People only need to provide a small amount of power to run."
Brovici and his colleagues Jinchi Han and Jeffrey Lang published the study in the IEEE Transactions of industrial electronics.
New scheme
The traditional loudspeaker in the earphone or audio system uses current input. The current generates a magnetic field through the coil. The magnetic field vibrates the loudspeaker membrane and moves the air above the loudspeaker membrane to produce the sound we hear. In contrast, the new speaker simplifies the speaker design by using a thin film made of piezoelectric material. When voltage is applied to the film, the film vibrates, moving the air above it and generating sound.
Most thin-film speakers are designed independently, because the thin-film must be bent freely to make sound. Installing it on the surface of an object will hinder its vibration and affect its ability to produce sound. In order to overcome this problem, the MIT research team redesigned the thin-film loudspeaker. After improvement, instead of making the whole thin-film vibrate, it relies on the micro dome structure on the thin piezoelectric material. Each dome structure vibrates independently, and its diameter is only several times that of human hair. The top and bottom of the thin-film are wrapped by spacer layers to protect them from the influence of the mounting surface and make them vibrate freely, In daily operation, the same spacer layer protects the dome from wear and impact, thus improving the durability of the loudspeaker.
In order to achieve the best effect of thin-film speakers, the researchers used a laser to cut small holes in pet (polyethylene terephthalate) sheet. Pet is a light plastic. They laid a very thin layer of PVDF material (a piezoelectric material) on the bottom of the perforated PET sheet. Then they applied a vacuum above the adhesive sheet and a heat source of 80 ° C below the adhesive sheet.
Because PVDF material is very thin, it expands due to the pressure difference generated by vacuum and heat source. PVDF material cannot forcibly penetrate PET sheet, so dome protrusion is generated at the small hole of PET sheet. Then the researchers laid a layer of PET sheet on the other side of the PVDF material as the spacing layer between the dome protrusion and the bonding surface.
Jinchi Han said: "this is a very simple and direct process. If we can combine the reel process in the future, we can produce these speakers in a high-throughput way, which means that it can be manufactured in batch and cover the interior of walls, cars or aircraft like wallpaper."
Most thin-film speakers are designed independently, because the thin-film must be bent freely to make sound. Installing it on the surface of an object will hinder its vibration and affect its ability to produce sound.
High quality, low power consumption
The height of the dome structure is only 15 microns, about one sixth of the diameter of human hair. When vibrating, they are only polarized up and down by 0.5 microns. Each dome is a separate sound source, so thousands of dome structures need to vibrate together to produce the sound heard by humans.
Another advantage of thin-film loudspeaker is its tunability - researchers can change the diameter of pet thin-film holes to control the size of the dome structure. The dome structure with larger radius produces greater sound, but it has lower resonance frequency. The resonance frequency is the most effective frequency for equipment operation, and lower resonance frequency will lead to audio distortion.
After completing the design of thin-film loudspeaker, the researchers tested several different dome sizes and piezoelectric layer thickness to achieve the best combination effect. They installed the thin-film speaker on the wall 30 cm away from the microphone and tested its sound pressure level (in decibels). When 25 Volts CURRENT passes through the device at 1000 Hz (1000 cycles per second), the speaker will produce 66 dB of high-quality sound. When it reaches 10 kHz, the sound pressure level will increase to 86 dB, which is about the same as the volume level of urban traffic.
The energy-saving device only needs about 100 MW of electric power per square meter. In contrast, an ordinary household speaker may consume more than 1 watt to produce similar sound pressure at a considerable distance. Jinchi Han explained that because the small dome structure vibrates constantly, rather than the whole film, the speaker can produce a high enough resonance frequency to be effectively used in the field of ultrasound. For example, ultrasound imaging uses very high-frequency sound waves to generate images, and higher frequencies will produce higher resolution images.
The device can also use ultrasound to detect people's position in the room, just like bat echolocation, and then shape sound waves to track human movement. Brovici said that if the thin-film vibrating dome structure is covered with a reflective surface, it can be used to create futuristic light display technology. If the film is immersed in liquid, the vibrating film can provide a new method of stirring chemical substances, so that the chemical treatment technology consumes less energy than the mass treatment method.
Brovici pointed out that we have the ability to accurately generate aeromechanical motion by activating retractable physical surfaces, and the application field of this technology is unlimited.
Ioannis kymisis, director of the Department of electrical engineering at Columbia University, said, "I think this is a very creative method. The strategy of stacking films into arches using lithographic pattern templates is very unique, which may lead to a series of new applications in speakers and microphones.".