Shape-Configurable MXene-Based Thermoacoustic Loudspeakers with Tunable Sound Directivity

Film-type shape-configurable speakers with tunable sound directivity are in high demand for wearable electronics. Flexible, thin thermoacoustic (TA) loudspeakers-which are free from bulky vibrating diaphragms-show promise in this regard. However, configuring thin TA loudspeakers into arbitrary shapes is challenging because of their low sound pressure level (SPL) under mechanical deformations and low conformability to other surfaces. By carefully controlling the heat capacity per unit area and thermal effusivity of an MXene conductor and substrates, respectively, it fabricates an ultrathin MXene-based TA loudspeaker exhibiting high SPL output (74.5 dB at 15 kHz) and stable sound performance for 14 days. Loudspeakers with the parylene substrate, whose thickness is less than the thermal penetration depth, generated bidirectional and deformation-independent sound in bent, twisted, cylindrical, and stretched-kirigami configurations. Furthermore, it constructs parabolic and spherical versions of ultrathin, large-area (20 cm × 20 cm) MXene-based TA loudspeakers, which display sound-focusing and 3D omnidirectional-sound-generating attributes, respectively.