High Signal-to-Noise Ratio Event-Driven MEMS Motion Sensing

Two solutions for improving MEMS triboelectric vibration sensors performance in contact-separation mode are reported experimentally and analytically. Triboelectric sensors have mostly been studied in the mesoscale. The gap variation between the electrodes induces a potential difference that represents the external vibration. Miniaturizing the device limits the sensor output because of the limited gap. This work offers a warped MEMS diaphragm constrained on its edges. The dome-shaped structure provides one order of magnitude larger displacement after contact-separation than standard designs resulting in one order of magnitude greater voltage and signal-to-noise-ratio. Second, micro triboelectric sensors do not operate unless the external vibration is sufficiently forceful to initiate contact between layers. The proposed constraints on the edge of the diaphragm provide friction during periodic motion and generate charges. The combination of the warped diaphragm and boundary constraints instead of serpentine springs increases the charge density and voltage generation. The mechanical properties and electrical output are thoroughly investigated including nonlinearity, sensitivity, and signal-to-noise ratio. A sensitivity of 250 mV g-1 and signal-to-noise-ratio of 32 dB is provided by the presented device at resonance, which is very promising for event-driven motion sensors because it does not require signal conditioning and therefore simplifies the sensing circuitry.

Biohybrid generators based on living plants and artificial leaves: influence of leaf motion and real wind outdoor energy harvesting

Plants translate wind energy into leaf fluttering and branch motion by reversible tissue deformation. Simultaneously, the outermost structure of the plant, i.e. the dielectric cuticula, and the inner ion-conductive tissue can be used to convert mechanical vibration energy, such as that produced during fluttering in the wind, into electricity by surface contact electrification and electrostatic induction. Constraining a tailored artificial leaf to a plant leaf can enhance oscillations and transient mechanical contacts and thereby increase the electricity outcome. We have studied the effects of wind-induced mechanical interactions between the leaf of a plant (Rhododendron) and a flexible silicone elastomer-based artificial leaf fixed at the petiole on power output and whether performance can be further tuned by altering the vibrational behavior of the artificial leaf. The latter is achieved by modifying a concentrated mass at the tip of the artificial leaf and observing plant-generated current and voltage signals under air flow. In this configuration, the plant-hybrid wind-energy converters can directly power light-emitting diodes and a temperature sensor. Detailed output analysis has revealed that, under all conditions, an increase in wind speed leads to nearly linearly increased voltages and currents. Accordingly, the cumulative sum energy reaches its highest values at the highest wind speed and resulting oscillations of the plant-artificial leaf system. The mass at the tip can, in most cases, be used to increase the voltage amplitude and frequency. Nevertheless, this behavior was found to depend on the individual configuration of the system, such as the leaf morphology. Analysis of these factors under controlled conditions is crucial for optimizing systems meant to operate in unstructured outdoor scenarios. We have established, in a first approach, that the artificial leaf-plant hybrid generator is capable of autonomously generating electricity outdoors under real outdoor wind conditions, even at a low average wind speed of only 1.9 m s^-1.

Large-Area Direct Laser-Shock Imprinting of a 3D Biomimic Hierarchical Metal Surface for Triboelectric Nanogenerators

Ongoing efforts in triboelectric nanogenerators (TENGs) focus on enhancing power generation, but obstacles concerning the economical and cost-effective production of TENGs continue to prevail. Micro-/nanostructure engineering of polymer surfaces has been dominantly utilized for boosting the contact triboelectrification, with deposited metal electrodes for collecting the scavenged energy. Nevertheless, this state-of-the-art approach is limited by the vague potential for producing 3D hierarchical surface structures with conformable coverage of high-quality metal. Laser-shock imprinting (LSI) is emerging as a potentially scalable approach for directly surface patterning of a wide range of metals with 3D nanoscale structures by design, benefiting from the ultrahigh-strain-rate forming process. Here, a TENG device is demonstrated with LSI-processed biomimetic hierarchically structured metal electrodes for efficient harvesting of water-drop energy in the environment. Mimicking and transferring hierarchical microstructures from natural templates, such as leaves, into these water-TENG devices is effective regarding repelling water drops from the device surface, since surface hydrophobicity from these biomicrostructures maximizes the TENG output. Among various leaves' microstructures, hierarchical microstructures from dried bamboo leaves are preferable regarding maximizing power output, which is attributed to their unique structures, containing both dense nanostructures and microscale features, compared with other types of leaves. Also, the triboelectric output is significantly improved by closely mimicking the hydrophobic nature of the leaves in the LSI-processed metal surface after functionalizing it with low-surface-energy self-assembled-monolayers. The approach opens doors to new manufacturable TENG technologies for economically feasible and ecologically friendly production of functional devices with directly patterned 3D biomimic metallic surfaces in energy, electronics, and sensor applications.

A Facile Method and Novel Mechanism Using Microneedle-Structured PDMS for Triboelectric Generator Applications

The triboelectric generator (TEG) is a cost-effective, multi-fabricated, friendly mechanical-energy-harvesting device. The traditional TEG, generally formed by two triboelectric materials in multilayers or a simple pattern, generated triboelectricity as it worked in the cycling contact-separation operation. This paper demonstrates a novel, high-aspect-ratio, microneedle (MN)-structured polydimethylsiloxane (PDMS)-based triboelectric generator (MN-TEG) by means of a low-cost, simple fabrication using CO₂ laser ablation on the polymethyl methacrylate substrate and a molding process. The MN-TEG, consisting of an aluminum foil and a microneedle-structured PDMS (MN-PDMS) film, generates an output performance with an open-circuit voltage up to 102.8 V, and a short-circuit current of 43.1 µA, corresponding to the current density of 1.5 µA cm^-2 . With introducing MN-PDMS into the MN-TEG, a great increase of randomly closed bending-friction-deformation (BFD) behavior of MNs leads to highly enhanced triboelectric performance of the MN-TEG. The BFD keeps increasingly on in-contact between MN with Al that results in enhancement of electrical capacitance of PDMS. The effect of aspect ratio and density of MN morphology on the output performance of MN-PDMS TEG is studied further. The MN-TEG can rapidly charge electric energy on a 0.1 µF capacitor up to 2.1 V in about 0.56 s. The MN-TEG source under tapping can light up 53 light-emitting diodes with different colors, connected in series.

Formation of Triboelectric Series via Atomic-Level Surface Functionalization for Triboelectric Energy Harvesting

Triboelectric charging involves frictional contact of two different materials, and their contact electrification usually relies on polarity difference in the triboelectric series. This limits the choices of materials for triboelectric contact pairs, hindering research and development of energy harvest devices utilizing triboelectric effect. A progressive approach to resolve this issue involves modification of chemical structures of materials for effectively engineering their triboelectric properties. Here, we describe a facile method to change triboelectric property of a polymeric surface via atomic-level chemical functionalizations using a series of halogens and amines, which allows a wide spectrum of triboelectric series over single material. Using this method, tunable triboelectric output power density is demonstrated in triboelectric generators. Furthermore, molecular-scale calculation using density functional theory unveils that electrons transferred through electrification are occupying the PET group rather than the surface functional group. The work introduced here would open the ability to tune triboelectric property of materials by chemical modification of surface and facilitate the development of energy harvesting devices and sensors exploiting triboelectric effect.

Magnetic-Assisted Noncontact Triboelectric Nanogenerator Converting Mechanical Energy into Electricity and Light Emissions

A magnetic-assisted noncontact triboelectric nanogenerator (TENG) is developed by combining a magnetic responsive layer with a TENG. The novel TENG device is applied to harvest mechanical energy which can be converted into electricity and light emissions. This work has potential for energy harvesting, magnetic sensors, self-powered electronics and optoelectronics applications.

Lawn Structured Triboelectric Nanogenerators for Scavenging Sweeping Wind Energy on Rooftops

A novel triboelectric nanogenerator (TENG) is designed, based on flexible and transparent vertical-strip arrays, for environmental wind-energy harvesting. Given the low cost, simple structure, and wide applicability, the TENGs present a green alternative to traditional methods used for large-scale wind-energy harvesting.

PEDOT as a Flexible Organic Electrode for a Thin Film Acoustic Energy Harvester

An efficient thin film acoustic energy harvester was explored using flexible poly(3,4-ethylene dioxythiophene) (PEDOT) films as electrodes in an all-organic triboelectric generator (AO-TEG). A thin film AO-TEG structured as PEDOT/Kapton//PET/PEDOT was prepared by the solution casting polymerization(SCP) on the dielectric polymer films. As-prepared AO-TEG showed high flexibility and durability due to the strong adhesion between the electrodes and the dielectric polymer. The short-circuit current density (Jsc), open-circuit voltage (Voc), and maximum power density (Pw) reached 50 mA/m(2), 700 V, and 12.9 W/m(2) respectively. The output current density decreased with the increase in the electrode resistance (Re), but the energy loss in the organic electrodes was negligible. The AO-TEG could light up 180 LEDs instantaneously upon touching of the AO-TEG with a palm (∼120 N). With the flexible structure, the AO-TEG was worn as clothes and generated electricity to light LEDs upon regular human movement. Furthermore, the AO-TEG was applicable as a thin film acoustic energy harvester, which used music to generate electricity enough for powering of 5 LEDs. An AO-TEG with a PEDOT electrode (Re = 200 Ω) showed instantaneous peak-to-peak voltage generation of 11 V under a sound pressure level (SPL) of 90-100 dB. The harvested acoustic energy through the AO-TEG was 350 μJ from the 4 min playing of the same single song. This is the first demonstration of a flexible triboelectric generator (TEG) using an organic electrode for harvesting acoustic energy from ambient environment.