Anisotropic Liesegang pattern for the nonlinear elastic biomineral-hydrogel complex.

The Liesegang pattern is a beautiful natural anisotropic patterning phenomenon observed in rocks and sandstones. This study reveals that the Liesegang pattern can induce nonlinear elasticity. Here, a Liesegang-patterned complex with biomineral-hydrogel repetitive layers is prepared. This Liesegang-patterned complex is obtained only when the biomineralization is performed under the supersaturated conditions. The Liesegang-patterned complex features a nonlinear elastic response, whereas a complex with a single biomineral shell shows a linear behavior, thus demonstrating that the Liesegang pattern is essential in achieving nonlinear elasticity. The stiff biomineral layers have buffered the concentrated energy on behalf of soft hydrogels, thereby exposing the hydrogel components to reduced stress and, in turn, enabling them to perform the elasticity continuously. Moreover, the nonlinear elastic Liesegang-patterned complex exhibits excellent stress relaxation to the external loading, which is the biomechanical characteristic of cartilage. This stress relaxation allows the bundle of fiber-type Liesegang-patterned complex to endure greater deformation.

Wireless Stand-Alone Trimodal Interactive Display Enabled by Direct Capacitive Coupling.

With recent advances in interactive displays, the development of a stand-alone interactive display with no electrical interconnection is of great interest. Here, a wireless stand-alone interactive display (WiSID), enabled by direct capacitive coupling, consisting of three layers: two in-plane metal electrodes separated by a gap, a composite layer for field-induced electroluminescence (EL) and inverse piezoelectric sound, and a stimuli-responsive layer, from bottom to top, is presented. Alternating current power necessary for field-induced EL and inverse piezoelectric sound is wirelessly transferred from a power unit, with two in-plane electrodes remotely separated from the WiSID. The unique in-plane power transfer through the stimuli-sensitive polar bridge allows stand-alone operation of the WiSID, making it suitable for the wireless dynamic monitoring of medical fluids. Moreover, a haptic wireless stand-alone trimodal interactive display mounted on a human finger is demonstrated, whereby touch is wirelessly displayed in various outputs of EL, inverse piezoelectric sound, and tactile vibration, making it suitable for a wireless three-mode smart braille display.

Versatile surface for solid-solid/liquid-solid triboelectric nanogenerator based on fluorocarbon liquid infused surfaces.

The triboelectric nanogenerator (TENG) is a recent mechanical energy harvesting technology that has been attracting significant attention. Its working principle involves the combination of triboelectrification and electrostatic induction. The TENG can harvest electrical energy from both solid-solid and liquid-solid contact TENGs. Due to their physical difference, triboelectric materials in the solid-solid TENG need to have high mechanical properties and the surface of the liquid-solid contact TENG should repel water. Therefore, the surface of the TENG must be versatile for applications in both solid-solid and liquid-solid contact environments. In this work, we develop a solid-solid/liquid-solid convertible TENG that has a slippery liquid-infused porous surface (SLIPS) at the top of the electrode. The SLIPS consists of a HDFS coated hierarchical Al(OH)3 structure and fluorocarbon liquid. The convertible TENG developed in this study is capable of harvesting electricity from both solid-solid and liquid-solid contacts due to the high mechanical property of Al(OH)3 and the water-based liquid repelling nature of the SLIPS. When the contact occurs in freestanding mode, electrical output was generated through solid-solid/liquid-solid sliding motions. The convertible TENG can harvest electricity from both solid-solid and liquid-solid contacts; thus, it can be a unified solution for TENG surface fabrication.

Hand-Driven Gyroscopic Hybrid Nanogenerator for Recharging Portable Devices.

With the rise of portable and wearable electronics, a fast-charging, long-lasting power solution is needed; thus, there are attempts to harvest energy from the ambient environment. Mechanical energy harvesting through piezoelectric and triboelectric nanogenerators (PENG and TENG) is a promising approach due to their light weight, low cost, and high-power density in comparison to other technologies. Both types of generators are capable of charging portable and smart devices on their own by converting mechanical energy into electricity. However, most previous methods have excessive input conditions, such as high rpm and input frequency, that can be only applied with other actuators. Here, a hand-held gyroscopic generator is presented that uses the gyroscopic principle to reach a rotation rate above 8000 rpm with only hand input. The generator comprises a rotating flywheel inside a casing. Both the flywheel and casing have a TENG, and with a hybrid generator, electrical power is produced from rotation, vibration, and centrifugal force during operation. The device shows a consistent open-circuit voltage (V OC) of 90 V and a closed-circuit current (I CC) of 11 µA with a frequency of 200 Hz. As a stand-alone device, this generator can power portable sensors and smartphones through hand rotation.

Energy-loss return gate via liquid dielectric polarization.

There has been much research on renewable energy-harvesting techniques. However, owing to increasing energy demands, significant energy-related issues remain to be solved. Efforts aimed at reducing the amount of energy loss in electric/electronic systems are essential for reducing energy consumption and protecting the environment. Here, we design an energy-loss return gate system that reduces energy loss from electric/electronic systems by utilizing the polarization of liquid dielectrics. The use of a liquid dielectric material in the energy-loss return gate generates electrostatic potential energy while reducing the dielectric loss of the electric/electronic system. Hence, an energy-loss return gate can make breakthrough impacts possible by amplifying energy-harvesting efficiency, lowering the power consumption of electronics, and storing the returned energy. Our study indicates the potential for enhancing energy-harvesting technologies for electric/electronics systems, while increasing the widespread development of these systems.

Highly reliable wind-rolling triboelectric nanogenerator operating in a wide wind speed range.

Triboelectric nanogenerators are aspiring energy harvesting methods that generate electricity from the triboelectric effect and electrostatic induction. This study demonstrates the harvesting of wind energy by a wind-rolling triboelectric nanogenerator (WR-TENG). The WR-TENG generates electricity from wind as a lightweight dielectric sphere rotates along the vortex whistle substrate. Increasing the kinetic energy of a dielectric converted from the wind energy is a key factor in fabricating an efficient WR-TENG. Computation fluid dynamics (CFD) analysis is introduced to estimate the precise movements of wind flow and to create a vortex flow by adjusting the parameters of the vortex whistle shape to optimize the design parameters to increase the kinetic energy conversion rate. WR-TENG can be utilized as both a self-powered wind velocity sensor and a wind energy harvester. A single unit of WR-TENG produces open-circuit voltage of 11.2 V and closed-circuit current of 1.86 µA. Additionally, findings reveal that the electrical power is enhanced through multiple electrode patterns in a single device and by increasing the number of dielectric spheres inside WR-TENG. The wind-rolling TENG is a novel approach for a sustainable wind-driven TENG that is sensitive and reliable to wind flows to harvest wasted wind energy in the near future.