Electric field-fabricated ultra-sensitive mechanoluminescent composites for self-powered force sensing

Flexible force sensors for wearable health monitoring and soft robotics increasingly demand high mechanical compliance and low-power operation. This study reports a stretchable, ultra-sensitive, and mechanically powered mechanoluminescent (ML) force-sensing composite fabricated with an electric field generated by a high voltage discharge. The resulting composite, namely ultra-sensitive ML composite (USMLC), possesses a dense, shallowly embedded ML particle sensing layer approximately 300 µm thick. The ultra-sensitivity is compared to conventional homogeneous ML composites of the same ML concentration, where the USMLCs exhibit a nearly 4000% enhancement in the measured ML intensity. In addition, the USMLCs maintain high stretchability ( > 85% ultimate strain) and demonstrate repeatable mechano-optical sensing response over 1000 cycles of loading with a high signal-to-noise ratio. Furthermore, USMLCs are integrated with miniaturized photodiodes for compact optical readout, enabling relative spatiotemporal ML intensity mapping in localized indentation tests and a proof-of-concept transtibial prosthetic socket phantom test. Collectively, electric field-fabricated ML composites provide a scalable route to highly sensitive, self-powered optical force sensors for wearable and robotic tactile sensing.