Displacement Current Of Triboelectric Nanogenerator

With the rapid development of the Internet of Things,sensors in the network show a trend of miniaturization,mobility,large numbers,and wide distribution,whereas energy supply for these wide-distributed sensors in large quantities has been encumbered by the traditional energy supply methods.Developing a feasible,sustainable,and distributed carbon-free green energy supply method has become increasingly pressing.Triboelectric nanogenerators(TENGs)based on the conjunction effect of contact electrification and electrostatic induction have attracted significant research efforts due to the potential advantages of low cost,high efficiency,simple structure,diverse material options and potential applications in energy supply.To convert mechanical energy into electrical energy in TENG,displacement current is the key point and clarification of its excitation mechanism and its characterization are critical to further expanding the TENG applications.In this work,the displacement current excited by a vertical contact-separate TENG is theoretically elucidated based on the scalar/vector potential,and a displacement current collecting method using metal collectors is developed according to the Gauss theorem.Using this method,the displacement current excited by PA6-PVDF TENG was successfully collected by a cooper collector and it is converted to electricity with an open-circuit voltage of 0.86 V and a short-circuit current of 20.25 n A.Moreover,the synchronized test indicates that the frequencies and waveforms of the collected displacement current are identical to the output of TENG,and the amplitude of displacement current shows a decrease.Using a ring-shaped cooper collector,the electrical output can be further improved to 2.14 V and 56.6 n A,and a green LED can be lighted wirelessly.In addition,the output of displacement current is related to the energy harvesting distance d and would diffuse in the air space,and the largest transmission distance of the displacement current is only 17.45 cm.To improve the transmission distance of displacement current,a dielectric plate is implemented to concentrate the electric field and a further increase of the polarization current density is required.Using a granite board as the transmission medium,the open-circuit voltage of the displacement current will firstly decrease from 1.11 V to 0.05 V and then increase to 0.52 V during a gradual increase of the energy harvesting distanced d from 0.2 cm to 26 cm.Using this setup,the furthest transmission distance can be improved to 5 m,and a liquid crystal display(LCD)can be wirelessly powered at 3.6m away.Based on this experiment,the transmission model of displacement current is modified accordingly,where the first item in the displacement current?_r?E/?t shows a three-dimensional diffusion in air,while the second item?P/?t shows a two-dimensional diffusion in the dielectric board,and the energy collected by the collector is the difference between these items.To further apply displacement current as the wireless power source for portable electronic devices,energy generation,collection and transmission based on human body are studied and the human skin is treated as the dielectric board in TENG.When the human body steps on the TENG with a frequency of 6.7 Hz,the collector stuck on the body skin can generate electricity with an open-circuit voltage of 726 V and a short-circuit current of 21.9?A.A 100?F capacitor can be charged from 0 V to 0.6 V within36 s,and 883 LEDs can be wirelessly lighted by a pedestrian on a 2.5 m road laid with TENG.Besides its application on human skin,the displacement current can also be used in-vivo as a wireless power source.In theory,a displacement current density of 71n A/m~2 can be collected wirelessly by an in-vivo implanted collector,accompanied by a TENG stuck on the body surface and driven at a 3.43 Hz frequency.This is further elucidated by the in-vivo simulation:the collector can output an open-circuit voltage of3.66 V and a short-circuit current of 185.28 n A with a 20 cm implantation depth.The output is actually regardless of the implantation depth.Besides,when the area of the collector S_C reduces from 5 cm~2 to 0.02 cm~2 and the thickness of the insulating layer of the collector increases from 0 mm to 1 mm,the output of the displacement current remains at 2.76 V and 99.72 n A.The output voltage and current can be further enhanced to 7.33 V and 358.88 n A,respectively by a 7.2 Hz driving frequency.In this way,an implantable oximeter is successfully powered in-vivo,and the wireless power supply of implantable electronics is realized.This in-vivo application of the displacement current is experimentally verified when the collector is stuck on the body surface and the TENG is implanted into the body,and the organic motility can be converted to displacement current and wirelessly transmitted output.In experiments,a mechanically asymmetric TENG is designed and implanted in-vivo to detect the duodenal peristalsis wirelessly.After converting the gastrointestinal peristalsis signal into displacement current,the duodenal peristalsis signal with an amplitude of 0.5 p A and frequency of 0.35 Hz is wirelessly collected in-vitro.This signal can be used to monitor the different physiological states before and after 50%glucose intragastric administration in real-time.