# Self-Powered, Hybrid, Multifunctional Sensor for a Human Biomechanical Monitoring Device
## 3 Results and Discussion
When both the PENG and the TENG are working simultaneously, the SPMS has a much better electrical performance than that of the individual energy harvesting units (PENG or TENG). The average voltage and current output were 103 V and 302 \(\upmu\)A, respectively. To accurately analyze the superimposed output of the SPMS, the mechanical motion frequency was operating at 1 Hz. Superposition can be completed piezoelectrically and triboelectrically for the hybrid system as illustrated in Supplementary Information Figure S4 with the results of the open-circuit voltage (OCV) and short-circuit current (SCC) of the SPMS operating under various working frequencies from 0.5 to 2 Hz. Indistinct differences appeared in the results. Furthermore, Supplementary Information Figure S5 shows the validated piezoelectric tests of polarity for both forward and reverse connections. Figure 3a presents #60 grit sandpaper, which was used to grind the PTFE surface as a triboelectric layer microstructure. The sandpaper had a coarse grit size with an average diameter of about 269 \(\upmu\)m and the voltage output was about 3.9 V. The surface of the #120 grit sandpaper is shown in Figure 3b. The average diameter of the grit on the sandpaper surface was 115 \(\upmu\)m. The data graph shows the voltage output was 3.8 V. As shown in Figure 3c, #600 grit sandpaper had an average grit diameter of 25.8 \(\upmu\)m. The measurement chart shows the voltage output was approximately 4.5 V. Micromorphology of the #1000 grit sandpaper is presented in Figure 3d; it had a uniform surface with a grit diameter of 18.3 \(\upmu\)m; it had the best voltage performance with a value of 6.6 V. The comparative test was set to measure the output of a single triboelectric layer. As shown in Figure 3e, the triboelectric output of the surface roughness test increased with smaller grit size. The reason is that the smaller the surface structure is, the larger is the total contact area compared to the surface with a larger-scale structure. The triboelectric layers' contact area will make the triboelectric voltage output perform better. Figure 2: (**a**) Working mechanism of the proposed SPMS whose piezoelectric and triboelectric charge generation and electricity generation processes can be described by the compression/deformation/touch/release processes. (**b**) The open-circuit voltage (OCV) and short-circuit current (SCC) of the triboelectric generators (TENG) with the PTFE film and Al film touch/release processes with an accumulated displacement \(\sim\)0.35 mm were \(\sim\)84 V and 300 \(\mu\)A, respectively. (**c**) The OCV and SCC of the piezoelectric device with an accumulated displacement \(\sim\)5 mm was \(\sim\)22 V and 285 nA, respectively. (**d**) The OCV and SCC of the superposition integrated SPMS were \(\sim\)103 V and 302 \(\mu\)A, respectively. The peak values of the voltage and current on different loads are displayed in Figure 4a, showing the trend of the signal when resistance increased. Figure 4b illustrates the instantaneous maximum power value. This discovery also indicated that if the load had a resistance of nearly 100 k\(\Omega\), the sensor ran most efficiently and the highest power output was about 38 mW. Figure 4c is the characterization of the sensor performance and the relationship between the applied force and electrical voltage, showing the promising potential of the self-powered pressure sensor. The human motion-induced testing mode was performed by pressing on top of the SPMS in a cyclic and reciprocating motion  
Figure 3: (**a**) Scanning electron microscope (SEM) image of 60 grit sandpaper and the voltage output test in the TENG. (**b**) 120 grit sandpaper SEM image. (**c**) Micomorphology of 600 grit sandpaper with the voltage output test. (**d**) 1000 grit sandpaper SEM image and the voltage output test. (**e**) Particle size comparison of the voltage output with different microstructures and surface roughness. at the frequency of \(1\) Hz.