Hierarchically Constructed Liquid Metals for Sensitive Detection of High-Frequency Subtle Vibrations.

Strain sensors are widely used in wearable devices for monitoring physical activity. However, wearable sensors typically face complex dynamic environments. Measurement of subtle vibrations in these scenarios remains challenging, given the coupled output signals from diverse time-varying strains with distinct frequencies and amplitudes. In this work, a fibrous strain sensor with hierarchically constructed liquid metals (LMs) is reported for the sensitive detection of high-frequency subtle vibrations under intense dynamic strains. The structural design includes a thin continuous LM (CLM) layer on the exterior surface, a densely packed LM particle (LMP) layer in the middle, and LMP nodules in the inner core. The strain-sensing fiber exhibits an ultralow detection limit of 0.01% (5 μm strain) and response time of only 50 ms, and maintains a linearity approximated 0.999 over a strain range of up to 250%. We show that it is capable of recording both intense body movements and microstrains, such as damping and acoustic vibrations. We also show that the fiber strain sensor can precisely detect and discriminate subtle vibrations in dynamic environments, such as the body's high-frequency tremors during walking.