Maxwell Displacement Current Research Articles

Positive impact of surface defects on Maxwell's displacement current-driven nano-LEDs: The application of TENG technology

As the core component of a nanopixel light-emitting display, the GaN-based nanoscale light-emitting diode (nLED) faces the problem of low electroluminescence efficiency resulting from the introduction of surface defects when its lateral size is reduced to the nanometer scale. Thus, reducing the surface defect density is an important direction in nLED-related research. This study, with the triboelectric nanogenerator-driven LED as its inspiration, reveals that surface defects have a positive impact on the performance of nLEDs driven by Maxwell’s displacement current, and we call the related driving mode the noncarrier injection mode. Through finite element simulations, we studied the dynamic variations of the carrier concentration, the energy band, and the light emission rate to analyze the impact of the behavior of surface defect excitation on device performance. We found that surface defects can act as electron pumps under the combined effect of the reverse electric field and the built-in electric field and can generate carriers through surface defect excitation to increase the intensity of noncarrier injection luminescence, which is completely different from the traditional understanding of surface defects. In addition, we propose a tapered structure to further increase the light emission rate by regulating the behaviors of radiation recombination and surface defect excitation. The results of this work open a new perspective on the impacts of surface defects on nLEDs and provide significant information for additional applications of Maxwell's displacement current.

The coupled-motion enhanced wireless signal transmission with long distance based on Maxwell’s displacement current

Wireless signal transmission plays an increasingly imperative role in numerous aspects of modern society, but it still remains challenging to achieve it with low-cost and efficient way. Herein, we demonstrate a long-distance wireless signal transmission system, which mainly includes an electrodeless triboelectric nanogenerator coupled with linear motion and rotational motion (LR-TENG) as a transmitter and a receiver located at a distance. Based on the varying electric field originated from Maxwell's displacement current, the maximum transmission distance of LR-TENG can reach 86 cm under the external excitation of 1 Hz, creating the highest record among the relevant researches. In addition, the influence of obstacle type, thickness, size and position on signal transmission has been systematically investigated for the first time, and the distribution of time-varying electric field in space is also analyzed qualitatively. Furthermore, a Labview interface is developed for accurate positioning in complex scenes relying on the received signals from multiple receivers at different positions. This work illustrates a simple and feasible design method for extending the distance of wireless signal transmission based on TENG, and promotes its application in the field of wireless communication.

Magnetic field assisted high performance triboelectric nanogenerators based on P(VDF–HFP)/NiFe2O4 nanofiber composite

Triboelectric nanogenerators (TENGs), which are powered by Maxwell's displacement current, have a wide range of applications, including energy harvesting and self-powered sensors. However, very little attention has been paid to the effect of the ferromagnetic medium on TENG displacement current. Herein, flexible ferrimagnetic poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF–HFP))/nickel ferrite (NiFe2O4) fiber composite film based TENGs were fabricated and their performances were analysed. Highly crystalline, ferrimagnetic NiFe2O4 nanofibers with high aspect ratio were prepared using electrospinning technique by systematic optimization of spinning parameters. Thereafter, the fibers were reinforced into the polymeric matrix to improve the β–phase and dielectric constant which in turn significantly enhanced the TENG performance. The β–phase enhancement in the composite films was confirmed by XRD and FTIR analysis; 77 % of the β–phase was achieved with the incorporation of NiFe2O4 fiber. Morphological features were examined using SEM and AFM, which revealed more β–phase spherulite formation in the composite films. A notable increase in the dielectric properties was evidenced with the addition of NiFe2O4 fibers and a maximum dielectric constant of∼26 was attained at 100 Hz. The TENG was developed using P(VDF-HFP)/NiFe2O4 and nylon which generated an output voltage (Vpp) and current (Ipp) values of 584 V and 25 μA, respectively. Furthermore, the performance of TENG under an external magnetic field was examined, and a notable improvement in performance was observed, paving the way for the application of NiFe2O4 fibers in hybrid energy harvesters and self-powered sensors.

Maxwell displacement current induced wireless self-powered gas sensor array

Maxwell displacement current induced by triboelectric nanogenerators (TENGs) endows an efficient route in wireless power transmission and self-powered sensing technique. Herein, we invented a Maxwell displacement current motivated wireless self-powered gas sensor array (WSA) for wireless and passive respiratory analysis and exhaust emission monitoring. The as-prepared WSA exhibited a maximum response value of 147% toward 100 ppm NH3 and 87% toward 0.5 ppm NO2, respectively. By combining experimental characterization and finite element analysis, the influence of induction distance and electrode arrangement on the transducing and sensing properties of WSA was systematically investigated. Meanwhile, the prepared WSA possessed good repeatability, selectivity, and long-term stability towards NH3 and NO2. Finally, triggered by the mechanical energy from human respiration and object rotation, the as-received WSA is capable of actively distinguishing trace-level ammonia and nitrogen dioxide, illustrating the feasibility in respiratory analysis and air quality monitoring. This work opens up a new paradigm for self-powered wireless gas detection with attribute of cost effectiveness, multivariable, easy fabrication, and environment friendliness.

Self-powered sensors driven by Maxwell's displacement current wirelessly provided by TENG

Electrodeless triboelectric nanogenerator (EL-TENG) is a kind of novel TENG that has no metal electrodes and the power is transmitted via Maxwell's displacement current. For a rotation EL-TENG, the power is collected by an induction coil at a vertical distance of 20 cm. A self-powered sensor is demonstrated based on Maxwell's displacement current supplied wirelessly by EL-TENG. Such a design can use one EL-TENG to drive multiple wireless senses for the purposes such as control switches for desk lamps and alarm system. This kind of wireless and self-powered sensor has broad applications in the fields of Internet of Things, big data and artificial intelligence.

Nonpolar Liquid Lubricant Submerged Triboelectric Nanogenerator for Current Amplification via Direct Electron Flow

AbstractTriboelectric nanogenerators (TENGs) can convert a mechanical energy input to an electric energy output through Maxwell's displacement current. By increasing the electrical output and overcoming the mechanical limitations of TENGs, such devices can be used as an auxiliary power source for portable electronics. Nevertheless, the generation mechanism and structure must be optimized to compensate for the electrical and mechanical limitations of TENGs. This paper reports on a nonpolar liquid lubricant submerged TENG (LLS‐TENG), which can overcome the existing electrical and mechanical limitations of the TENG. When a nonpolar liquid lubricant is filled in the LLS‐TENG, the air breakdown can be effectively blocked owing to the large Debye length of such lubricants. In addition, the rolling friction and lubrication present in the LLS‐TENG can significantly reduce the friction wear of the device. Consequently, the LLS‐TENG can charge a commercial capacitor and battery by generating a high voltage and current output of up to 200 V and 170 mA, respectively.

Homotopy and adomian semi-numerical solutions for oscillatory flow of partially ionized dielectric hydrogen gas in a rotating MHD energy generator duct

Hydrogen-based MHD power generators offer significant advantages over conventional designs. The optimization of these energy devices benefits from both laboratory scale testing and computational simulation. Motivated by this, in the current work, a mathematical model is developed for MHD pumping of partially ionized hydrogen in a rotating duct with oscillatory, Maxwell displacement and magnetic induction effects under an inclined static magnetic field. Perfectly electrically conducting duct walls are assumed. The non-dimensional conservation equations are solved using the power-series based Homotopy Analysis Method (HAM) with an appropriate embedding parameter. Detailed graphical visualization of the impact of emerging parameters on the non-dimensional primary and secondary velocity components (u,v) and magnetic induction components (bx,by) across the duct is presented. Average squared residual errors for all key variables εu,εv,εbx,εby with associated CPU times at various orders of the HAM iteration are also included. Validation with an Adomian Decomposition Method (ADM) is also conducted, and excellent agreement is obtained (tabulated). The computations have shown that with increasing inverse Ekman number strong damping is observed in the primary flow whereas the secondary flow is accelerated, in particular in the core region of the duct. With elevation in Maxwell displacement effect (for the case of a 45° inclined magnetic field i.e. θ=π/4 ) there is a strong decrease in primary magnetic induction at the lower wall of the duct and elevation in magnitudes at the upper duct wall; however, in the core region no tangible modification is computed. The opposite trend is observed for the secondary magnetic induction. With increasing magnetic Prandtl number (i.e. ratio of magnetic Reynolds number to ordinary Reynolds number) in the presence of strong Maxwell displacement current, strong magnetic field and high inverse Ekman number, the primary velocity is accelerated in both the left and right half space of the duct with a dip in magnitude at the centreline. However, the secondary velocity exhibits a much lower enhancement in both zones with only weak acceleration near the duct walls. Both velocity components achieve symmetrical distributions about the duct centreline. A significant depletion in primary magnetic induction is computed near the lower duct wall with enhancement near the upper duct wall; the contrary behaviour is exhibited by the secondary induced magnetic field. Applications of the study arise in hybrid rotating hydrogen based MHD energy generators and furthermore the computations provide a good basis for generalization to 3-dimensional flows with commercial multi-physical fluid dynamic codes e.g. ADINA-F, COMSOL, ANSYS FLUENT-Maxwell wherein further phenomena may be explored including Alfven wave effects and dielectric losses.

Designing Rules and Optimization of Triboelectric Nanogenerator Arrays

AbstractA triboelectric nanogenerator (TENG) is an effective means for the conversion of mechanical energy into electricity. Although Maxwell's displacement current is the underline mechanism of TENGs, the spatial and temporal variations of the electric field and electric displacement remain elusive, which prohibits an effective optimization of the energy conversion process. Here, the electric field distribution and energy dynamics of TENGs is determined using 3D mathematical modeling. The electrical energies stored in TENGs and extracted into the external circuit are calculated quantitatively whereby the ratio of the two, defined as the output efficiency, is obtained. Then, the power density and energy density of TENGs are defined. Utilizing the principle of virtual work, the minimum required external force–time relationship is evaluated. The influence of device parameters, geometry, and optimum conditions are discussed systematically so as to determine general optimization guidelines for TENGs. In addition, although the fringing electric field is practically inevitable, adjustments of the gap distance between neighboring TENG devices to assure that an optimized fringing electric field is “leaked”, is demonstrated to lead to improvement in a TENG array. Then, for the first time, this work presents universal design rules and holistic optimization strategies for the network structure of TENGs.

Magneto-optical measurements of Maxwell displacement current

The concept of Maxwell's displacement current is still not fully understood. In this paper, we measured the magnetic field between the plates of a charging capacitor using a magneto-optical method, which is generally explained to be produced by Maxwell's displacement current. We observed the asymmetric radial profile of the magnetic field between them, which could not be explained by using the displacement current. In contrast, it could be explained naturally, if we assumed that the magnetic field was produced by the practically existing conduction currents, which consist of the surface currents on the plates, the current in the charging wires connected to it and the return current connected to the electric power supply.

Novel wireless power transmission based on Maxwell displacement current

Abstract Wireless power transmission (WPT) is vitally important for portable electronics. Recently, wireless energy delivery via Maxwell displacement current from triboelectric nanogenerator may open new routes to develop novel technologies especially for implantable medical devices and sensor network due to its flexibility, adaption, convenience and safety. In this paper, the propagation characteristics of WPT are explored, which are based on displacement current from a spherical high frequency electric field. The results showed that the spherical surfaces with the same radius from the center have equal value of electric field intensity. When the receiver has a larger area or workload, the output has a higher value, which is subject to the electric field intensity. However, the current is almost unchanged with increasing output power below 15 kΩ of load resistance in series, which may have potential applications for sensors. Furthermore, the receiver circuit of wireless energy is in accordance with the traditional serial and parallel circuit regularity. Based on these, we are going to assume that the electric field source is a reservoir, and water flow is analogous to current. The assumption is suitable for studying propagation characteristics. This new discovery may also offer a new research direction for WPT based on Maxwell displacement electric field.

Three-dimensional modeling of alternating current triboelectric nanogenerator in the linear sliding mode

Energy harvesting from mechanical motions has immense applications such as self-powered sensors and renewable energy sources powered by ocean waves. In this context, the triboelectric nanogenerator is the cutting-edge technology that can effectively convert ambient mechanical energy into electricity through the Maxwell's displacement current. While further improvements of the energy conversion efficiency of triboelectric nanogenerators critically depend on theoretical modeling of the energy conversion process, to date only models based on single-relative-motion processes have been explored. Here, we analyze energy harvesting of triboelectric nanogenerators using a three-dimensional model in a linear-sliding mode and demonstrate a design of triboelectric nanogenerators that have a 77.5% enhancement in the average power in comparison with previous approaches. Moreover, our model shows the existence of a DC-like bias voltage contained in the basic AC output from the energy conversion, which makes the triboelectric nanogenerators an energy source more pliable than the traditional AC power generation systems. The present work provides a framework for systematic modeling of triboelectric nanogenerators and reveals the importance of obtaining direct analytical insight in understanding the current output characteristics of the triboelectric nanogenerators. Incorporating our model analysis in future designs of triboelectric nanogenerators is beneficial for increasing the energy conversion power and may provide insights that can be used in engineering the profile of the output current of the nanogenerators.

Dynamical charge transfer model for high surface charge density triboelectric nanogenerators

Triboelectric nanogenerators have made great progress and paved the way for green energy, self-powered implantable medical devices and a large number of sensors in the Internet of Things. Maxwell's displacement current is the fundamental theoretical framework of nanogenerators. Quantum model of charge transfer between atoms have been devoted to understanding the triboelectric effect. Increasing the output power of triboelectric nanogenerators is one of the most important subjects for practical application. Here, we study the charge transfer process in triboelectric materials and propose a triboelectric material charge transfer dynamic model. Dynamic charge transfer enables triboelectric nanogenerators to achieve high surface charge density and the superior device robustness, which can significantly improve the output power and life time of triboelectric nanogenerators. The charge transfer model provides not only deeply understanding for high performance of triboelectric nanogenerator, but also a useful guide for the optimization and design of high performance triboelectric materials.

Application of Displacement-Current-Governed Triboelectric Nanogenerator in an Electrostatic Discharge Protection System for the Next-Generation Green Tire

Electrostatic discharge (ESD), a universal phenomenon derived from tribocharging and electrostatic induction, has always been regarded as a negative effect because it may cause various types of damage, such as gas explosions, wildfires, failure of integrated circuits, and so on. Normally, ESD is avoided by conducting those harmful charges through the surface or the whole bulk, by means of improving the conductivity of dielectrics or directly using conductive materials. However, the first approach compromises other performances at the same time, whereas the second one can be applied in only a few circumstances. In this Article, we analyzed the working principle of the triboelectric nanogenerator from the perspective of the time variation of the surface-charge-introduced polarization density , the second term of Maxwell's displacement current. Then, we demonstrated an electrostatic protective system by implanting a conductive layer under the tribocharging surface to form a triboelectric nanogenerator (TENG). Theoretical derivation, finite element analysis, and experimental results prove that this system can efficiently prevent ESD without sacrificing any other performance. Finally, we applied it to the next generation of the green tire, which can save >10% of fuel but still cannot be commercialized due to the potential ESD risk. This research work reveals a way to prevent ESD and shows great potential in the field of engineering.

Quantifying the power output and structural figure-of-merits of triboelectric nanogenerators in a charging system starting from the Maxwell's displacement current

Conversion of mechanical energy into electricity using triboelectric nanogenerators (TENGs) is a rapidly expanding research area. Although the theoretical origin of TENGs has been proven using the Maxwell's displacement current (ID), a profound quantitative understanding of its generation is not available. Moreover, a comprehensive analysis of the fundamental charging behavior of TENGs and building a standard to evaluate each TENG's unique charging characteristic are critical to ensure efficient use of them in practice. We present a thorough analysis of TENG's charging behavior through which a more complete evaluation of TENG charging is proposed by introducing the structural figure of merit (FOMCs) in a charging system (powering capacitors). The analysis is based on Maxwell's displacement current and results are verified experimentally. To achieve this, according to the distance-dependent electric field model, we provide a systematic discussion on the generation of ID in TENGs, along with the derived analytical formula and numerical calculations. This work suggests a new way to deeply understand the nature of the ID generated within the TENGs; and the modified FOMCS can be used to predict the charging characteristics of TENGs in an energy storage system, allowing us to utilize the TENGs more efficiently towards different applications.

Efficient Delivery of Power Generated by a Rotating Triboelectric Nanogenerator by Conjunction of Wired and Wireless Transmissions Using Maxwell's Displacement Currents

AbstractEnergy harvesting and power delivery are key technologies for self‐powered systems toward the internet of things, and integration of the two should be prioritized. The dominant mechanism of a triboelectric nanogenerator (TENG) is Maxwell's displacement current, which exists both inside the media/device and in the space surrounding the device. The displacement current transmitted in media inside the device can be collected by wired transmission using two electrodes, while the component that is leaked in to the space surrounding the device can be partially collected wirelessly. Herein, simultaneous collection of power transmitted through wires and wirelessly by a rotating TENG, is demonstrated. The wired component gives an output of ≈2 mA and ≈110 V, and the wireless component using the finite size of the collector gives an output current and voltage of ≈3 µA and ≈17.5 V (power density of 21.8 mW m−2). Small mobile electronics and a digital camera can be charged. The study extends the application of TENGs for practical applications.

Harvest of ocean energy by triboelectric generator technology

Water wave energy widely distributed in the globe is one of the most promising renewable energy sources. However, it has not been effectively exploited by current energy harvesting technologies which primarily rely on electromagnetic generator (EMG). EMG's have various limitations, especially when operating in environment with irregular and/or low frequencies ( < 5 Hz) wave motions. Triboelectric nanogenerators (TENGs) exhibit obvious advantages over EMG in harvesting energy from low-frequency water wave motions. The networking of TENGs has been regarded as a potential method towards large-scale blue energy harvesting. In this review, recent progress of the TENG technology for blue energy harvesting is presented, including a comparison between TENG and EMG in physics and engineering design, and the fundamental mechanism of nanogenerator based on Maxwell's displacement currents is systematically introduced. The review of hydrodynamic TENG, liquid-solid contact electrification TENG, hybrid (dual-modes) TENG, fully enclosed TENG, and TENG network for blue energy harvesting is discussed. The TENG networks are expected to harvest large-scale blue energy from the ocean, which will be a feasible approach for realizing the blue energy dream. Moreover, the energy harvested by TENG from various sources, such as human motion and vibration, is not only new energy, but more importantly, energy using for the new era-the era of internet of things.At the request of the authors, this article is being retracted effective 15 May 2019.

Ultralight, self-powered and self-adaptive motion sensor based on triboelectric nanogenerator for perceptual layer application in Internet of things

In the Internet of things (IoT), motion sensor in the perceptual layer is at the forefront of the information collection, which plays a crucial role in the IoT. However, with a large number of commercial applications, several problems of motion sensor limit the development of IOT such as poor portability, poor environmental adaptability, and high energy consumption, etc. In this work, an ultralight, self-powered and self-adaptive motion sensor (UMS) is reported. Total mass of the UMS is less than 20 mg. Self-powered characteristic of the UMS is achieved based on the principle of triboelectric nanogenerator by using the coupling of triboelectrification and electrostatic induction as governed by the Maxwell's displacement current. Moreover, the UMS shows satisfactory self-adaptive performance of both temperature and humidity, less-sensitive to temperature in surroundings, from 15 ℃ to 60 ℃, and ambient humidity under 90% RH. Furthermore, sensing signals triggered by different motion behaviors, such as grasping, walking, stooping and so on, can be distinguished by the processor clearly, which can be applied to motion recognition and machine control. This work presents a novel UMS with characteristics of portability, energy conservation and environmental friendliness. The UMS shows broad prospect in perceptual layer application in IoT.

Some remarks on the charging capacitor problem

The charging capacitor is the standard textbook and classroom example for explaining the concept of the so-called Maxwell displacement current. A certain aspect of the problem, however, is often overlooked. It concerns the conditions for satisfaction of the Faraday-Henry law inside the capacitor. Expressions for the electromagnetic field are derived that properly satisfy all four of Maxwell’s equations in that region.

Three-dimensional ultraflexible triboelectric nanogenerator made by 3D printing

As the fast developments of wearable devices, artificial intelligences and Internet of Things, it is important to explore revolutionary approach and fabrication method for providing flexible and sustainable power sources. We report here a practical, ultraflexible and three-dimensional TENG (3D–TENG) that is capable of driving conventional electronics by harvesting biomechanical energy. Such TENG is made for the first time by the unique additive manufacturing technology—hybrid UV 3D printing. The TENG is made up of printed composite resin parts and ionic hydrogel as the electrification layer and electrode. A sustainable and decent output of 10.98W/m3 (Pv, peak power per unit volume) and 0.65mC/m3 (ρsc, transferred charge per unit volume) are produced under a low triggering frequency of ~ 1.3Hz, which is attributed to the Maxwell's displacement current. Meanwhile, a self-powered SOS flickering and buzzing distress signal system, and smart lighting shoes are successfully demonstrated, as well as self-powered portable systems of a temperature sensor or a smart watch. Our work provides new opportunities for constructing multifunctional self-powered systems toward the applications in realistic environments.

On Maxwell's displacement current for energy and sensors: the origin of nanogenerators

Self-powered system is a system that can sustainably operate without an external power supply for sensing, detection, data processing and data transmission. Nanogenerators were first developed for self-powered systems based on piezoelectric effect and triboelectrification effect for converting tiny mechanical energy into electricity, which have applications in internet of things, environmental/infrastructural monitoring, medical science and security. In this paper, we present the fundamental theory of the nanogenerators starting from the Maxwell equations. In the Maxwell's displacement current, the first term e 0 ∂ E ∂ t gives the birth of electromagnetic wave, which is the foundation of wireless communication, radar and later the information technology. Our study indicates that the second term ∂ P ∂ t in the Maxwell's displacement current is directly related to the output electric current of the nanogenerator, meaning that our nanogenerators are the applications of Maxwell's displacement current in energy and sensors. By contrast, electromagnetic generators are built based on Lorentz force driven flow of free electrons in a conductor. This study presents the similarity and differences between pieozoelectric nanogenerator and triboelectric nanogenerator, as well as the classical electromagnetic generator, so that the impact and uniqueness of the nanogenerators can be clearly understood. We also present the three major applications of nanogenerators as micro/nano-power source, self-powered sensors and blue energy.