Fully Stretchable Thermoacoustic Electronic Skin Enabled by Geometrically Aligned Carbon Nanotube Bundles

A loudspeaker is an essential component in interactive electronics; however, conventional sound devices rely on electromechanical systems with inherently rigid moving parts, limiting their integration into emerging soft electronics. This work demonstrates a soft and stretchable thermoacoustic (TA) loudspeaker utilizing geometrically aligned carbon nanotubes (CNTs) partially embedded in an elastomeric substrate. When an electrical sound input is applied, the geometrically unique features of the aligned CNTs, which have a large surface‐to‐volume ratio with a high aspect ratio, enable Joule heating to effectively excite the surrounding air, generating audible sound without moving parts. These geometrical features remain stable even under 100% tensile strain, with only a 1.81 dB variation in sound pressure level (SPL). The TA loudspeaker is composed entirely of stretchable materials, including the sound‐emitting layer, substrate, and electrical pads, and produces acoustic waves with a 65.7 dB SPL across human‐audible frequencies (<20 kHz), even under 100% strain. Owing to its acoustic performance and mechanical compliance, the loudspeaker is demonstrated as acoustic electronic skin on various body parts, such as the finger and wrist, for future soft audio systems.