# Zinc Oxide-Based Rotational-Linear Triboelectric Nanogenerator
## 3 Results and Discussion
### Optimization of Performance Characteristics  
From the analysis of the results, we see that the electrical performance of the RL-TENG is inferior to what we would anticipate compared to the results that we obtained for the Kapton/ZnO layers in previous experiments. When the same triboelectric surfaces of area 2 \(\times\) 2 cm\({}^{2}\) were evaluated [18], the output voltage reached about 20 V, the short circuit current 12 uA, the open circuit voltage 105 V and the maximum output power 350 uW, which is much higher compared to the results obtained for a single triboelectric pair. To  
Figure 8: Energy stored in the capacitor as a function of time after charging for rotational velocities (**a**) 60 rpm and (**b**) 300 rpm.  
Figure 7: (**a**) Disk A for in-phase operation of triboelectric pairs, (**b**) output voltage of T1 and T3 for disk A, (**c**) disk B for out-of-phase operation of triboelectric pairs and (**d**) output voltage of T1 and T3 for disk B.  
some extent, this is expected since the surface area of the triboelectric areas T1, T2 and T3 is reduced compared to the previous ones by 2.4 times (1.67 cm\({}^{2}\) compared to 4 cm\({}^{2}\)).  
There are also other parameters that could influence the triboelectric performance that are related to the operational principle of the triboelectric generator. Being a transient phenomenon, the triboelectric signal will depend strongly on the relative velocity between the two surfaces. [PERSON] et al. [22] showed that the relative velocity of the triboelectric surfaces affects the instantaneous signal as well as the average power of TENGs. They also provided evidence that the separation phase of the two triboelectric surfaces could also impact the electrical performance of the tribogenerator. Another parameter that affects the triboelectric signal is the contact force that develops between the two triboelectric surfaces. [PERSON] et al. [23] studied theoretically and experimentally the influence of the contact force of the triboelectric signal TENG using a PDMS film with microdome patterns. As a reference electrode, a PET film was used. The triboelectric signal was measured against a PET reference surface. They demonstrated that, by changing the contact force from 4.4 N to 5.1 N, the triboelectric signal increased by 100%.  
To verify the influence of the above-mentioned parameters (surface area and transition time/force) on the triboelectric signal, we have fabricated a part of a more robust prototype tribogenerator. In this case, the surface area of the prototype was the same as that of the test triboelectric generators (Figure 9a). In addition, we have enhanced the mechanical stability of the structure and used a stronger return spring. Typical results are shown in Figure 9b. We see that the maximum voltage per tap is 12 V for a rotational velocity of 350 rpm. Moreover, the maximum power per tap is 10 times more compared to that of the triboelectric pairs used in the RL-TENG. Our results indicate that, with a more robust structure and with larger triboelectric contact areas, significantly enhanced performance can be obtained for the RL-TENG.