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a closed circuit, forming a freestanding TENG. Water inside the cylinder in turn contacts the top and bottom inner electrodes as vibration is applied. Because the PFA has a negative surface charge and water can undergo self-ionization, the water ions are aff ected by the electrical fi eld, causing charge separation and accumulation. When the charge-separated water touches the electrode, an electrical output is generated. T e MSW-TENG generates approximately 5mW when the device is shaken at 1.5Hz with a load resistance of 1MΩ. Figures 2b and 2c compare VOC


and ICC


of a conventional TENG


with our MSW-TENG. T e average peak voltage and current of the MSW-TENG are more than double that of the conventional TENG because water with accumulated charge is in direct contact with the conductive material. Figures 2d and 2e show the results of an experiment comparing


a single generator situated on top of the MSW-TENG and a dual generator on top and bottom of the tube. In the single-generator setup, the non-electrode end of the tube is covered with a lid – we used PTFE tape. T e peak output of the MSW-TENG with a single generator is higher than that of a dual generator; however, the dual generator produces more output peaks compared to the other. In Figure 3a, A1


and A2


and internal diameter of the cylinder respectively, with d1 the distance between the two electrodes, and d2


represent the area of the inner electrode being


the length of the


outer electrode. To compare the electrical output associated with diff erent design parameters, the root-mean-square (rms) values were calculated to evaluate the continuous power as the MSW- TENG generated a sharp peak output. T e voltage (VRMS current (IRMS


) and ) are calculated as follows:


Figure 3b shows the VRMS


and IRMS


values of the MSW-TENG


with diff erent ratio of water to PFA cylinder volume. T e total PFA cylinder size is about 50mL (0.23cm diameter and 12cm height). We used 5mL and 40mL of DI water, occupying 10% and 80% of the cylinder’s volume, respectively. As shown in Figure 3b, the water volume ratio of 10% generates


the highest output, which declines as the water volume increases, since the space in which it can move to build up its charge becomes limited. Figure 3c shows the VRMS


and IRMS for diff ering inner electrode


sizes. T e inner diameter of the PFA cylinder is 23mm, with the area 415.265mm2


and IRMS increase as the electrode area increases. . T e electrode area ratios of 5%, 25%, 50%, 75%


and 100% in Figure 3c correspond to inner electrode diameters of 5, 11, 16, 20 and 23mm, respectively. Both VRMS


When water collides with the top surface of the PFA cylinder, mechanical energy is lost and the water’s velocity signifi cantly decreases. In general, the charge separation and accumulation of water are closely related to its velocity. T erefore, the water that contacts the electrode aſt er having been in contact with the dielectric material is expected to have less accumulated positive charge.


Figure 1: Mobile stick water-type triboelectric nanogenerator (MSW-TENG): (a) construction; (b) VOC


and (c) ICC


outputs; (d) average peak voltage, current and (e) power, depending on the external load As the size of the inner electrode decreases, the probability of


water with high mechanical energy contacting the inner electrode also decreases, with less output being generated. Figure 3d shows the VRMS


and IRMS values of the MSW-TENG


for diff erent distances between the inner and outer electrodes. A 2cm-wide electrode is attached on the side of the PFA cylinder at distances of 2, 4, 6 and 8cm from the cylinder’s top surface. The MSW-TENG produces a higher electrical output when


the electrode is placed closer to the top surface of the cylinder. When mechanical vibration excites the water, the water inside the cylinder forms a shape akin to a triangle owing to gravity. Consequently, a larger area of the external electrode is covered by water since the outer electrode is close to the bottom of the cylinder. As the water blocks the electrical potential of the PFA, it produces less electricity. When the device has a wide outer electrode, additional space is available to increase the area covered by the water. Figure 3e shows


www.electronicsworld.co.uk April 2022 39


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