The Flexible Sound Source

Acoustic devices, as essential media for information transmission and interaction, are undergoing a paradigm shift from conventional rigid architectures toward flexible, integrated, and intelligent systems. With the rapid advancement of flexible electronics and electronic skins, the development of flexible sound sources (FSSs) capable of conformal integration with complex surfaces while maintaining high acoustic performance has become a key research focus. This review systematically summarizes recent progress in FSS technologies based on four primary electroacoustic transduction mechanisms: thermoacoustic, piezoelectric, electrostatic, and electromagnetic. For each mechanism, strategies for improving sound pressure level, frequency response, and energy conversion efficiency are fundamentally unlocked from the interdependent perspectives of material innovation and structural engineering. In addition, mainstream fabrication processes of FSSs are comprehensively evaluated. The broad applications of FSSs in wearable communication, medical health monitoring, and human-machine interaction are further highlighted. Finally, the grand challenges hindering the practical deployment of FSSs are critically elucidated, including the efficiency-flexibility paradox, the lack of unified performance evaluation standards, and the paradigms of system-level co-optimization and multifunctional integration, thereby providing a strategic roadmap for future research toward commercially viable flexible acoustic systems.