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  1. Abstract

    Contact electrification in a gas medium is usually followed by partial surface charge dissipation caused by dielectric breakdown of the gas triggered during separation of the surfaces. It is widely assumed that such discharge obeys the classical Paschen’s law, which describes the general dependence of the breakdown voltage on the product of gas pressure and gap distance. However, quantification of this relationship in contact electrification involving insulators is impeded by challenges in nondestructive in situ measurement of the gap voltage. The present work implements an electrode-free strategy for capturing discrete discharge events by monitoring the gap voltage via Coulomb force, providing experimental evidence of Paschen curves governing nitrogen breakdown in silicone-acrylic and copper-nylon contact electrification. It offers an alternative approach for characterizing either the ionization energies of gases or the secondary-electron-emission properties of surfaces without the requirement of a power supply, which can potentially benefit applications ranging from the design of insulative materials to the development of triboelectric sensors and generators.

     
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  2. Abstract

    This paper examines the effect of viscoelasticity on the dynamic behavior of a bistable dome-shaped structure represented as a lumped parameter viscoelastic von Mises truss. The viscoelastic system is governed by a third order jerk equation. The presence of viscoelasticity also introduces additional time scales and degrees of freedom into the problem when compared to their viscous counterparts, thus making the study of these systems in the presence of harmonic loading even more interesting. It is highly likely that the system would exhibit non-regular behavior for some combination of forcing frequency and forcing amplitude. With this motivation, we start by studying the dynamics of a harmonically forced von Mises truss in the presence of viscous damping only. This leads to a Duffing type equation with an additional quadratic non-linearity. We demonstrate some of the rich dynamic behavior that this system exhibits in some parameter ranges. This provides useful insight into the possible behavior of the viscoelastic system. The viscous damper is then replaced by a viscoelastic unit. We show that the system can exhibit both regular as well as chaotic behavior. The threshold limit for the chaotic motion has been determined using Melnikov’s criteria and verified through numerical simulations using the largest Lyapunov exponent.

     
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  3. In this article we propose a theoretical investigation of the nonlinear dynamical response of a class of planar resonators dubbed the V-Shaped resonator. The resonators are intended for energy harvesting purpose and are designed to exhibit two-to-one internal resonance. In particular, we navigate the design space for the generalized V-shaped resonator to investigate the influence of shape parameters on the performance of the Vibration Energy Harvester. Notably, we introduce two metrics that help elucidating the role of the shape parameter in dictating the behavior of the system in terms of peak voltage and operational bandwidth width. For simplicity, we consider that the system is subjected to harmonic excitations near its primary resonances. 
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  4. Abstract

    Kirigami is defined as the ancient Japanese art of cutting and folding paper to create three-dimensional structures, which is a subset of the larger term. Recent developments in kirigami-based structures have sparked interest in the engineering community for the development of mechanical metastructures with customized behavior such as negative Poisson’s ratio, out-of-plane buckling, and soft robot locomotion. In this manuscript, nonlinear springs based on kirigami are developed; the springs can be used to create customized nonlinear oscillators and vibration suppression systems. A Helmholtz-Duffing oscillator with nonlinear damping is created by attaching a mass to a smooth track with the kirigami springs attached to it.

    Kirigami springs were made by strategically cutting plastic sheets in predetermined patterns and arranging them in a ring. Identification of the unknown system parameters is accomplished through the use of a two-step procedure. To determine the quasi-static behavior of the spring, it was first subjected to tensile testing. These parameters serve as the foundation for developing a strategy for determining the unknown energy loss parameters in a system. In the second step, the Method of Multiple Scales is used to develop an approximate solution for the transient response, which is then tested. This solution is coupled with an optimization routine that, by modifying the unknown model parameters, seeks to reduce the error between the experimental free oscillations and the developed analytical solution as closely as possible.

     
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  5. Human–machine interactions (HMIs) describe how humans engage various systems, including those that are smart, autonomous, or both. Most HMIs either allow the human to control the machine (an instrument panel), allow the machine to obtain data (a heart monitor), or even both (a virtual reality setup). HMIs may be placed in three broad classes. In one class, the individual is active in the interaction—that is, the individual is the user or purchaser of a technology such as an automobile. In another class, the user is passive but consenting in the interaction—that is, the interaction occurs with their consent, such as the use of devices for medical diagnosis. There is also a class in which the user is passive and nonconsenting in the interaction, such as the use of facial recognition for law enforcement purposes. 
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  6. Abstract

    The flexibility of planar triboelectric nanogenerators (TENGs) enables them to be embedded into structures with complex geometries and to conform with any deformation of these structures. In return, the embedded TENGs function as either strain‐sensitive active sensors or energy harvesters while negligibly affecting the structure's original mechanical properties. This advantage inspires a new class of multifunctional materials where compliant TENGs are distributed into local operational units of mechanical metamaterial, dubbed TENG‐embedded mechanical metamaterials. This new class of metamaterial inherits the advantages of a traditional mechanical metamaterial, in that the deformation of the internal topology of material enables unusual mechanical properties. The concept is illustrated with experimental investigations and finite element simulations of prototypes based on two exemplar metamaterial geometries where functions of self‐powered sensing, energy harvesting, as well as the designated mechanical behavior are investigated. This work provides a new framework in producing multifunctional triboelectric devices.

     
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  7. Triboelectric energy harvesters or nanogenerators exploit both contact electri cation and electrostatic induction to scavenge excess energy from random motions of mechanical structures. This study focuses on the modeling of triboelectric energy harvesters in the con guration of contact-separation impact oscillators. While mechanical and electrostatic elements in such systems can be satisfactorily modeled based on existing theories, the underlying physics of contact electri cation is still under debate. The aim of this work is to introduce the surface charge density of dielectric layers as a variable into the macroscopic equations of motion of triboelectric impact oscillators by experimentally investigating the relation between the impact force and the charge transfer during contact electri cation. Specifi cally, specimens with selected pairs of materials are put under a solenoid-driven pressing tester which charges the specimens with a vertical force whose magnitude, frequency and duty cycle can be controlled. An electrometer is used to monitor the short circuit charge flow between the electrodes from which the charge accumulation on dielectric layers can be extracted. With results from parameter-sweep tests, the produced map from contact force to surface charge density can be integrated into equations of motion via curve fitting or interpolation. 
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  8. Electret based energy scavenging devices utilize electro-static induction to convert mechanical energy into electrical energy. Uses for these devices include harvesting ambient energy in the environment and acting as sensors for a range of applications. These types of devices have been used in MEMS applications for over a decade. However, recently there is an interest in triboelectric generators/harvesters, i.e., electret based harvesters that utilize triboelectrification as well as electrostatic induction. The literature is filled with a variety of designs for the latter devices, constructed from materials ranging from paper and thin films; rendering the generators lightweight, flexible and inexpensive. However, most of the design of these devices is ad-hoc and not based on exploiting the underlying physics that govern their behavior; the few models that exist neglect the coupled electromechanical behavior of the devices. Motivated by the lack of a comprehensive dynamic model of these devices this manuscript presents a generalized framework based on a Lagrangian formulation to derive electromechanical equation for a lumped parameter dynamic model of an electret-based harvester. The framework is robust, capturing the effects of traditional MEMS devices as well as triboelectric generators. Exploiting numerical simulations the predictions are used to examine the behavior of electret based devices for a variety of loading conditions simulating real-world applications such as power scavengers under simple harmonic forcing and in pedestrian walking. 
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