(Nanowerk Spotlight) Speakers have come a long way from the bulky boxes and paper cones of the early 20th century. Today’s high-tech versions are getting smaller and smarter, opening doors to exciting new applications. But even as modern speakers shrink, challenges remain in balancing portability, audio quality, and directional sound control.
Now researchers in South Korea may have brought us closer to having it all. They developed an ultra-thin thermoacoustic speaker with unique shape-changing abilities. Made with advanced nanomaterials, it can stretch, bend, and morph into different configurations while producing quality sound.
At the core of the new speaker is a conductive material called MXene that generates sound through heat oscillations. When alternating current passes through the MXene layer, it periodically heats and cools, creating pressure waves that we hear as sound. Key to performance is keeping the heating element thin. The MXene used here is only 78 nanometers thick, about a thousand times thinner than a human hair. This gives it a low heat capacity per area, enabling efficient sound generation with minimal input power.
The speaker also incorporates an ultrathin, 0.8 micron thick substrate made of parylene. With low thermal conductivity, the parylene substrate further improves efficiency by reducing heat loss and allowing rapid heating and cooling of the MXene.
Together, the thin MXene heating element and parylene substrate give the speaker surprising versatility. It can generate high volume, audiophile-quality sound up to 74.5 decibels while also stretching, bending, twisting, and morphing into different 3D configurations. Other nanomaterial speakers have shown good flexibility or volume, but few combine both strengths like this one does.
A shape-configurable MXene-based thermoacoustic (TA) loudspeaker with directivity-tunable sound generation. a) Schematic illustrating the working mechanism of the flexible MXene-based TA loudspeaker. b) Conceptual sound-pressure/distance plots and sound directivities of unidirectional thick (top) and bidirectional ultrathin substrates (middle), and schematics depicting 3D sound distributions of differently configured ultrathin TA loudspeakers (cylindrical, uniaxial kirigami, parabolic, and spherical) (bottom). c) Conceptual plots of intrinsic variables (HCPUA and thermal effusivity [top]) and extrinsic variables (input power and distance [bottom]). d) Photographs showing an MXene-based TA loudspeaker with an ultrathin (0.8-µm-thick) parylene substrate (left; scale bar, 2 cm); deformable and conformal contact with a fabric electrode having a line width of 150 µm (middle; scale bar, 500 µm); and a large-area (20 cm × 20 cm) specimen (right; scale bar, 5 cm). (Reprinted with permission from Wiley-VCH Verlag) (click on image to enlarge)
Other nanomaterial speakers primarily showcase either flexibility or sound quality. Carbon nanotube speakers adapt well to different environments, performing impressively both underwater and on land due to their thermo-acoustic properties. Another innovation utilized carbon nanotube assemblies to design a hybrid thermo-electromagnetic sound transducer with unique sound generation features. Using a carbon nanotube thin film, researchers created a flexible flag loudspeaker, emphasizing the flexibility of nanomaterials. On the other hand, by exploiting the electrical and mechanical properties of graphene, researchers developed electrostatic graphene loudspeakers that efficiently convert electrical signals to sound, performing comparably to or better than similar sized commercial counterparts, showcasing the potential for high sound quality.
While these examples demonstrate the individual strengths of nanomaterial speakers in terms of flexibility or sound quality, none have showcased the ability to excel in both aspects concurrently as the MXene speaker does.
What truly sets the new speaker apart is its shape-shifting abilities. The researchers demonstrated how it can stretch up to 50% of its length, bend to a 0.12 mm radius, and twist 180 degrees without audio degradation. This high deformability allows dynamically reconfiguring the speaker to steer sound precisely. For example, a parabolic dish shape just 8cm wide focuses sound into a tight beam. Making it cylindrical emits sound radially. Even crumpled into a ball, it generates omnidirectional sound without muffling. The shape change directly impacts functionality, essentially “shifting” the speaker between forms to control directionality. This capability to dramatically alter form and function surpasses conventional rigid speakers.
Besides changing directionality, the researchers found the thin construction produces sound from both sides. This is uncommon in speakers where substrate thickness exceeds the audio frequency’s thermal penetration depth. It allows rich acoustic effects, like surrounding listeners with immersive omnidirectional sound.
The study shows the potential of nanomaterials to keep pushing speakers forward. While audiophiles already enjoy ever-shrinking wireless earbuds, can we imagine a not-too-distant future with speakers seamlessly embedded into clothing or ephemeral objects? This research brings that vision closer.
If the speaker can be mass produced cheaply, applications abound. Its conformability and precision directional control opens options like adjustable spotlights for sound, flexible active displays, and lightweight immersive entertainment setups. For now, costs likely limit adoption to higher-end uses. But the fast pace of materials science suggests those barriers will eventually fall.
Of course, technical hurdles remain. The prototype’s longevity, maximum volume, and behavior at extreme deformations need further study. And MXene’s long-term environmental impacts require investigation. But the speaker’s unique versatility shows the vast potential in combining emerging materials sciences with creative structural designs.
So the next time you stream music or watch a movie, take a moment to appreciate the engineering that brings you such amazing audio experiences. Thanks to dedicated researchers exploring nanomaterials’ frontiers, speakers continue getting smaller, smarter, and ever more capable. We can look forward to the day they disappear into our clothing or environment—when sound becomes as customizable and omnipresent as light itself.
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