Inkjet-Printed, Paper-Based Thermoacoustic Loudspeakers with Mechanical Robustness and Versatile Form-Factor

This paper reports a foldable, paper-based, mechanically durable loudspeaker for human-audible flexible electronics without the restriction of form shapes. This loudspeaker emits acoustic waves without any moving part, as it converts an electrical signal into a thermally induced mechanical oscillation of air molecules, which is referred to as a thermoacoustic effect. Solution-based carbon nanotubes (CNTs), as sound-emitting materials, are patterned on designated areas via a commercial inkjet printer, facilitating large scalable and mass-producible fabrications. One-dimensional structures of CNTs allow them to be compatible with conventional inkjet printing processes without clogging of printing heads. Also, the CNT-dispersed ink is uniformly applied on a paper substrate with a controlled amount through inkjet printing, thus forming a conductive percolation network of CNTs with a lightweight. As a result, these loudspeakers show the enhancement of sound emission and thermal stability by reducing the total heat mass and suppressing the excessive localized heating, respectively. Furthermore, the loudspeakers exhibit outstanding mechanical durability under various stresses, including repeated bending, folding (over 1000 cycles), and continuous operation for 24 hours.