Wearable PVDF transducer for biomechanical energy harvesting and gait cycle detection

Piezoelectric transducers can be used to both harvest biomechanical energy and to detect gait cycle events. Several designing factors influence the efficiency of the energy harvesting system, such as the location of the transducers, their mechanical/electrical parameters and the correct matching of the load resistor. In this research, a piezoelectric polyvinylidene fluoride (PVDF) film - LDT4-028k - is simultaneously used as energy harvester for recovering energy associated with human walking, and as an active sensor to detect stance and swing phases of human gait. The PVDF transducer was placed on the back of the knee through an elastic cotton leotard, which allowed obtaining an output power of 1.45 μW during walking. Moreover, we presented a patterns' comparison between the signals of the PVDF transducer with a gyroscope. By using the output signal of the PVDF transducer we were able to distinguish the two phases of gait cycle with a difference in time of about 15 ms as compared to the events estimated through a gyroscope placed on the shank.