## 4 Results and Discussion
The output voltage as a function of the mechanical vibration frequency was analysed for the PGANF (Figure 5A). It was found that after application of an external force with a low cyclic frequency of 2 Hz across the PGANF FENG resulted in a low piezoelectric potential, whereas the high cyclic frequency of 8 HZ induced a maximum piezoelectric potential. In a typical experiment, the PGANF FENG exhibited a piezoelectric voltage of 2.1 V when applied with a high mechanical frequency of 8 Hz, whereas it exhibited a lower piezoelectric voltage of 0.648 V for a small mechanical vibration with 2 Hz frequency (Figure S5 of SI). This is due to the particular orientation of the electric dipoles in the NF due to the stress-induced poling effect [47]. Figure 5B shows that the cyclic loading and unloading on the piezoelectric device with 12N force at a constant 8 Hz frequency generates a piezoelectric  
Figure 2: (**A**) XRD, (**B**) FTIR showing the \(\beta\) phase nucleation in the NF samples, (**C**) Raman spectra showing the characteristic peak of GO in the PGANF, (**D**) DSC thermograph of PGANF showing the melting temperature Tm. potential of 2V steadily for more than 2000 cycles (Figure 5B insert shows a detailed magnified plot of generated piezoelectric potential during cyclic loading). This result depicts the durability and mechanical stability of a fabricated low-cost piezoelectric device, which could be used for long term biomechanical piezoelectric sensor applications. This remarkable durability confirms the applicability of PGANF FENG. Figure 4: Electrical response of the nanogenerators under a constant mechanical vibration frequency of 8 Hz and a uniform force of 12 N. (**A**) PGANF, (**B**) PGRNF, (**C**) PNF, (**D**) Comparison of the maximum output voltage. Figure 3: Schematic illustration showing. (**A**) the experimental set up for piezoelectricity measurement, (**B**) schematic illustration showing the working mechanism of the PGANF ferroelectric nanogenerator (FENG). After confirming the direct piezoelectricity and durability of PGANF FENG, we set out to investigate its efficacy to recover biomechanical energy. Starting from a low frequency biomechanical motion of finger stretching and relaxation to high frequency locomotion, sensing was performed. As per the study for the finger movement, the PGANF FENG device generated a piezoelectric output voltage of 0.08V, confirming the efficacy of the proposed device for the real-time non-invasive monitoring of the human physiological signals (Figure 6). We also tested the efficacy of the PGANF FENG device to harness the energy from our movements while sitting in a chair called a smart chair. Here, we attached the prototype PGANF FENG device onto the handle of an office chair and the frequent hand pushes evoked a piezoelectric output potential of 1.9 V. Further application of the PGANF FENG device was extended to analyse as a locomotion detector. The output power obtained from the device attached on the sandal exhibited a very high mechanical strength as well as comparable piezoelectric output potential of 6 V.  
Figure 5: (**A**) The piezoelectric voltage generated from the PGANF FENG under different mechanical vibration frequency, (**B**) Mechanical durability test of the PGANF FENG under repeated pushing and no pushing conditions with frequency of 8 Hz at a uniform force of 12 N.