# A Self-Powered Basketball Training Sensor Based on Triboelectric Nanogenerator
## 3 Tests  
The test equipment is shown in Figure 2a. During the tests, the output signal of the sensor is sequentially connected to the data acquisition card (USB5632, ART Technology Co., LTD., Beijing, China) and the electrometer (6514, Keithley Co., LTD., Solon, OL., America), and finally connected to the computer. The computer is installed with software written by LabVIEW language, so the sensor output signal can be processed in real-time. It can be seen from Figure 2b,c that the sensor can output two obvious voltage and current pulse signals when impacted by a basketball twice in succession, and the amplitude are respectively 52 V and 4 uA, so both voltage and current output signals can be selected as the sensor detection signal. But the anti-interference ability of the voltage signal is stronger because the voltage signal amplitude is much larger than the noise signal; this research selected the voltage pulse as the detection signal of the sensor. During the children's basketball training, the more times the basketball impacts the target area per unit time, the stronger the basic basketball ability of the children--that is, the working frequency of the sensor needs to meet the actual needs. Through experiments and investigations, it can be known that the frequency of slab basketball will not exceed 5 Hz, so we tested the output signal characteristics of the sensor in the frequency range of 0 to 5 Hz, and the results are shown in Figure 3. As shown in Figure 3a,b, the amount of transferred charge gradually decreases as the impact frequency increases, which results in a gradual decrease in the output voltage. The reason may be insufficient frictional contact during high-frequency impact, which further results in a reduction in the frictional contact area, and ultimately a reduction in output. But the output voltage amplitude of the sensor is still about 46 V at the working frequency of 5 Hz, and the amplitude is still much larger than the noise signal, so the sensor can work normally within the working frequency of 0 to 5 Hz. In addition, the output current gradually increases with the increase of the impact frequency, which can be seen in Figure 3c, and the reason may be that the number of impacts per unit time increases, resulting in an increase in the total amount of cumulative output current. Figure 3: The output signal characteristics of the sensor under different frequencies. (**a**) Transferred charge under different frequencies; (**b**) output voltage under different frequencies; (**c**) output current under different frequencies. Figure 2: The output signal of the sensor. (**a**) Pictures about the test devices and the sensor; (**b**) output voltage signal of the sensor; (**c**) output current signal of the sensor. Further, we tested the output signal characteristics of the sensor under different working conditions, and the results are shown in Figure 4. As shown in Figure 4a, the output voltage gradually increases with the increases of the impact pressure of the basketball on the sensor, but it will remain at the maximum value of about 52 V when the impact pressure is greater than 10 N. During actual basketball training, the impact pressure is much greater than 10 N, due to the combined effect of basketball gravity and slap force, which means that the sensor can output the maximum voltage in actual application. As shown in Figure 4b, the output voltage is inversely proportional to the temperature, and it will reduce to about 50 V when the temperature reaches 75 \({}^{\circ}\)C, but the value of 50 V is still much larger than the noise signal, which means that the sensor can work normally within the temperature range of less than 75 \({}^{\circ}\)C.  
Relative humidity will also affect the output of the sensor, so we conducted tests, and the results, shown in Figure 4c, show that the output of the sensor decreases by about 28% as the relative humidity increases to 95%.