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Abstract:We demonstrate a new paradigm for the wireless harvesting of mechanical energy via a 3D-printed triboelectric nanogenerator (TENG) which comprises a graphene polylactic acid (gPLA) nanocomposite and Teflon. The synergistic combination of eco-friendly PLA with graphene in our TENG exhibited an output voltage > 2 kV with an instantaneous peak power of 70 mW, which in turn generated a strong electric field to enable the wireless transmission of harvested energy over a distance of 3 m. Specifically, we demonstrate wireless and secure actuatation 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). Notably, such high electric output of a gPLA-based TENG enabled unprecedented wireless transmission of harvested mechanical energy into a capacitor, thus obviating the need for 2 additional electronics or energy sources. The scalable additive manufacturing approach for gPLA-based TENGs, along with their high electrical output can revolutionize the present method of harnessing the mechanical energy available in our environment.

Research into the development of triboelectric nanogenerators (TENGs) has exponentially expanded over the last 5 years with TENGs expected to be a prominent alternative energy-harvesting source in the near future. Notwithstanding the rapid progress in TENG development and their applications, the start-up cost of required research equipment and components remains high for new entrants into the field. A substantial portion of that cost is for the preamplifier, which is needed for measuring the output current of a TENG. Here, an ultra-low-cost device is presented that can measure the TENG output current, which is a crucial parameter in the characterization of TENG electrical performance. This alternative approach is expected to enable research groups in the future to partially offset the initial expense of instrumentation necessary for TENG research, and accelerate the development and applications of TENGs.

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Despite their wide spread applications, the mechanical behavior of helically coiled structures has evaded an accurate understanding at any length scale (nano to macro) mainly due to their geometrical complexity. The advent of helically coiled micro/nanoscale structures in nano-robotics, nano-inductors, and impact protection coatings has necessitated the development of new methodologies for determining their shear and tensile properties. Accordingly, we developed a synergistic protocol which (i) integrates analytical, numerical (i.e., finite element using COMSOL®) and experimental (harmonic detection of resonance; HDR) methods to obtain an empirically validated closed form expression for the shear modulus and resonance frequency of a singly clamped helically coiled carbon nanowire (HCNW), and (ii) circumvents the need for solving 12th order differential equations. From the experimental standpoint, a visual detection of resonances (using in situ scanning electron microscopy) combined with HDR revealed intriguing non-planar resonance modes at much lower driving forces relative to those needed for linear carbon nanotube cantilevers. Interestingly, despite the presence of mechanical and geometrical nonlinearities in the HCNW resonance behavior the ratio of the first two transverse modes f2/f1 was found to be similar to the ratio predicted by the Euler-Bernoulli theorem for linear cantilevers.

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We report a fully electrical microcantilever device that utilizes capacitance for both actuation and detection and show that it can characterize various gases with a bare silicon microcantilever. We find the motion of the cantilever as it rings down when the oscillating force is removed, by measuring the voltage induced by the oscillating capacitance in the microcantilever∕counterelectrode system. The ringdown waveform was analyzed using an iterative numerical algorithm to calculate the oscillator motion, modeling the cantilever∕electrode capacitance to calculate the electrostatic force. We find that nonlinearity in the motion of the cantilever is not necessarily a disadvantage. After calibration, we simultaneously measure viscosity and density of several gaseous mixtures, yielding viscosities within ±2% and densities within ±6% of NIST values.

As novel fibers with enhanced mechanical properties continue to be synthesized and developed, the ability to easily and accurately characterize these materials becomes increasingly important. Here we present a design for an inexpensive tabletop instrument to measure shear modulus (G) and other longitudinal shear properties of a micrometer-sized monofilament fiber sample, such as nonlinearities and hysteresis. This automated system applies twist to the sample and measures the resulting torque using a sensitive optical detector that tracks a torsion reference. The accuracy of the instrument was verified by measuring G for high purity copper and tungsten fibers, for which G is well known. Two industrially important fibers, IM7 carbon fiber and Kevlar(®) 119, were also characterized with this system and were found to have G = 16.5 ± 2.1 and 2.42 ± 0.32 GPa, respectively.