Mechanical Energy Harvesting Technology Research Articles

A Wireless Triboelectric Nanogenerator

AbstractA new “wireless” paradigm for harvesting mechanical energy via a 3D‐printed wireless triboelectric nanogenerator (W‐TENG) comprised of an ecofriendly graphene polylactic acid (gPLA) nanocomposite and Teflon is demonstrated. The W‐TENG generates very high output voltages >2 kV with a strong electric field that enables the wireless transmission of harvested energy over a distance of 3 m. The W‐TENG exhibited an instantaneous peak power up to 70 mW that could be wirelessly transmitted for storage into a capacitor obviating the need for hard‐wiring or additional circuitry. Furthermore, the use of W‐TENG for wireless and secure actuation of smart‐home applications such as smart tint windows, temperature sensors, liquid crystal displays, and security alarms either with a single or a specific user‐defined passcode of mechanical pulses (e.g., Fibonacci sequence) is demonstrated. The scalable additive manufacturing approach for gPLA‐based W‐TENGs, along with their high electrical output and unprecedented wireless applications, is poised for revolutionizing the present mechanical energy harvesting technologies.

Maximized Effective Energy Output of Contact‐Separation‐Triggered Triboelectric Nanogenerators as Limited by Air Breakdown

Recent progress in triboelectric nanogenerators (TENGs) has demonstrated their promising potential as a high‐efficiency mechanical energy harvesting technology, and plenty of effort has been devoted to improving the power output by maximizing the triboelectric surface charge density. However, due to high‐voltage air breakdown, most of the enhanced surface charge density brought by material/surface optimization or external ion injection is not retainable or usable for electricity generation during the operation of contact‐separation‐triggered TENGs. Here, the existence of the air breakdown effect in a contact‐separation mode TENG with a low threshold surface charge density of ≈40–50 µC m−2 is first validated under the high impedance external load, and then followed by the theoretical study of the maximized effective energy output as limited by air breakdown for contact‐separation‐triggered TENGs. The effects of air pressure and gas composition are also studied and propose promising solutions for reducing the air breakdown effect. This research provides a crucial fundamental study for TENG technology and its further development and applications.

Theoretical study on rotary-sliding disk triboelectric nanogenerators in contact and non-contact modes

The triboelectric nanogenerator (TENG) has emerged as a new and effective mechanical energy harvesting technology. In this work, a theoretical model for a rotary-sliding disk TENG with grating structure was constructed, including the dielectric-to-dielectric and conductor-to-dielectric cases. The finite element method (FEM) was utilized to characterize the fundamental physics of the rotarysliding disk TENG working in both contact and non-contact modes. The basic properties of disk TENG were found to be controlled by the structural parameters such as tribo-surface spacing, grating number, and geometric size. From the FEM calculations, an approximate V–Q–α relationship was built through the interpolation method, and then the TENG dynamic output characteristics with arbitrary load resistance were numerically calculated. Finally, the dependencies of output power and matched resistance on the structural parameters and rotation rate were revealed. The present work provides an in-depth understanding of the working principle of the rotary-sliding disk TENG and serves as important guidance for optimizing TENG output performance in specific applications.

Efficient Charging of Li-Ion Batteries with Pulsed Output Current of Triboelectric Nanogenerators.

The triboelectric nanogenerator (TENG) is a promising mechanical energy harvesting technology, but its pulsed output and the instability of input energy sources make associated energy‐storage devices necessary for real applications. In this work, feasible and efficient charging of Li‐ion batteries by a rotating TENG with pulsed output current is demonstrated. In‐depth discussions are made on how to maximize the power‐storage efficiency by achieving an impedance match between the TENG and a battery with appropriate design of transformers. With a transformer coil ratio of 36.7, ≈72.4% of the power generated by the TENG at 250 rpm can be stored in an LiFePO4–Li4Ti5O12 battery. Moreover, a 1 h charging of an LiCoO2–C battery by the TENG at 600 rpm delivers a discharge capacity of 130 mAh, capable of powering many smart electronics. Considering the readily scale‐up capability of the TENG, promising applications in personal electronics can be anticipated in the near future.

Optimization of Triboelectric Nanogenerator Charging Systems for Efficient Energy Harvesting and Storage

Triboelectric nanogenerator (TENG) technology has emerged as a new mechanical energy harvesting technology with numerous advantages. This paper analyzes its charging behavior together with a load capacitor. Through numerical and analytical modeling, the charging performance of a TENG with a bridge rectifier under periodic external mechanical motion is completely analogous to that of a dc voltage source in series with an internal resistance. An optimum load capacitance that matches the TENGs impedance is observed for the maximum stored energy. This optimum load capacitance is theoretically detected to be linearly proportional to the charging cycle numbers and the inherent TENG capacitance. Experiments were also performed to further validate our theoretical anticipation and show the potential application of this paper in guiding real experimental designs.

Recent progress in piezoelectric nanogenerators as a sustainable power source in self-powered systems and active sensors

Mechanical energy sources are abundant in our living environment, such as body motion, vehicle transportation, engine vibrations and breezy wind, which have been underestimated in many cases. They could be converted into electrical energy and utilized for many purposes, including driving small electronic devices or even constructing an integrated system operated without bulky batteries and power cables. Many progresses have been made recently in the mechanical energy harvesting technology based on piezoelectric nanogenerators (PENGs). By introducing a new sandwich structure design, high performance PENGs can be achieved through very simple fabrication process with good mechanical stability by utilizing ZnO nanowires (NWs). By further optimizing the nanomaterials׳ properties and device structure, the PENG׳s open circuit (OC) voltage can be elevated to over 37V. Two important applications of this technology are that the nanogenerator can be used as a sustainable power source for self-powered system and can worked as active sensors. Several demonstrations are reviewed here. Finally, perspectives of this mechanical energy harvesting technology are discussed. Co-operation with power management circuit, capability of integrating with a system, and low cost large-scale manufacturing processing are suggested to be the key points toward commercialization of PENGs.

Theoretical systems of triboelectric nanogenerators

Triboelectric nanogenerator (TENG) technology based on contact electrification and electrostatic induction is an emerging new mechanical energy harvesting technology with numerous advantages. The current area power density of TENGs has reached 313W/m2 and their volume energy density has reached 490kW/m3. In this review, we systematically analyzed the theoretical system of triboelectric nanogenerators. Starting from the physics of TENGs, we thoroughly discussed their fundamental working principle and simulation method. Then the intrinsic output characteristics, load characteristics, and optimization strategy is in-depth discussed. TENGs have inherent capacitive behavior and their governing equation is their V–Q–x relationship. There are two capacitance formed between the tribo-charged dielectric surface and the two metal electrodes, respectively. The ratio of these two capacitances changes with the position of this dielectric surface, inducing electrons to transfer between the metal electrodes under short circuit conditions. This is the core working mechanism of triboelectric generators and different TENG fundamental modes can be classified based on the changing behavior of these two capacitances. Their first-order lumped-parameter equivalent circuit model is a voltage source in series with a capacitor. Their resistive load characteristics have a “three-working-region” behavior because of the impedance match mechanism. Besides, when TENGs are utilized to charge a capacitor with a bridge rectifier in multiple motion cycles, it is equivalent to utilizing a constant DC voltage source with an internal resistance to charge. The optimization techniques for all TENG fundamental modes are also discussed in detail. The theoretical system reviewed in this work provides a theoretical basis of TENGs and can be utilized as a guideline for TENG designers to continue improving TENG output performance.

Mixed mode fatigue crack growth and the strain energy density factor: Lam, Y. C. Theor. Appl. Fract. Mech. Oct. 1989 12, (1), 67–72

Mechanical energy sources are abundant in our living environment, such as body motion, vehicle transportation, engine vibrations and breezy wind, which have been underestimated in many cases. They could be converted into electrical energy and utilized for many purposes, including driving small electronic devices or even constructing an integrated system operated without bulky batteries and power cables. Many progresses have been made recently in the mechanical energy harvesting technology based on piezoelectric nanogenerators (PENGs). By introducing a new sandwich structure design, high performance PENGs can be achieved through very simple fabrication process with good mechanical stability by utilizing ZnO nanowires (NWs). By further optimizing the nanomaterials׳ properties and device structure, the PENG׳s open circuit (OC) voltage can be elevated to over 37 V. Two important applications of this technology are that the nanogenerator can be used as a sustainable power source for self-powered system and can worked as active sensors. Several demonstrations are reviewed here. Finally, perspectives of this mechanical energy harvesting technology are discussed. Co-operation with power management circuit, capability of integrating with a system, and low cost large-scale manufacturing processing are suggested to be the key points toward commercialization of PENGs.