Study in circular auxetic structures for efficiency enhancement in piezoelectric vibration energy harvesting

Technology-forcing to reduce environmental noise pollution: a prospectus

BACKGROUND

Environmental movements of the late 20th century resulted in sweeping legislation and regulatory actions to reduce the prevalence of diverse pollutants. Although the consequences of noise pollution to public health, environment, and the economy have been recognized over the same time period, noise has received far less policy attention. Correspondingly, even while evidence of the diverse and detrimental effects of noise pollution on human health has grown, solutions and actual reductions in environmental noise remain seemingly out of reach.

OBJECTIVE

To address this shortcoming, we developed a prospectus for environmental noise reduction through technology-forcing policies. Technology-forcing describes intent to encourage technological solutions for pollution control through policy and regulations, and has been a critical component of national and global progress in reducing environmental pollutants.

METHODS

We take advantage of the unique policy history for noise in the United States - which initially enacted, but then abandoned federal noise regulation. We compare this history against outcomes from contemporaneous environmental legislation for air, water, and occupational pollution control, to demonstrate the potential for technology-forcing to reduce noise pollution. Our review then identifies promising solutions, in the form of existing technologies suitable for innovation and diffusion through technology-forcing regulations and incentives.

RESULTS

Based on this review, we outline a program for noise policy development to support efforts to reduce environmental noise pollution worldwide. The proposed program consists of three steps, which are to (i) identify dominant sources of noise pollution, (ii) combine legislative or regulatory provisions with suitable systems of enforcement and incentives, and (iii) anticipate and prepare for stages of technological change.

IMPACT STATEMENT

Analysis of noise policy often focuses on justifying the need to reduce noise pollution. In this article, we demonstrate how technology-forcing regulations could also promote much-needed innovation and diffusion of technologies to reduce environmental noise pollution. We first establish the potential for technology-forcing by comparing technology outcomes from environmental legislation passed contemporaneously to the inactive US Noise Control Act. We next review promising innovations available for diffusion in multiple sectors to reduce environmental noise. Lastly, we recommend a program to support development of technology-forcing noise policies, to help ensure that the benefits of reduced noise pollution are distributed equitably.

Exploiting nonlinearities through geometric engineering to enhance the auxetic behaviour in re-entrant honeycomb metamaterials

Classical approaches to enhance auxeticity quite often involve exploring or designing newer architectures. In this work, simple geometrical features at the member level are engineered to exploit non-classical nonlinearities and improve the auxetic behaviour. The structural elements of the auxetic unit cell are here represented by thin strip-like beams, or thin-walled tubular beams. The resulting nonlinear stiffness enhances the auxeticity of the lattices, especially under large deformations. To quantify the influence of the proposed structural features on the resulting Poisson's ratio, we use here variational asymptotic method (VAM) and geometrically exact beam theory. The numerical examples reveal that 2D re-entrant type micro-structures made of thin strips exhibit an improvement in terms of auxetic behaviour under compression. For the auxetic unit cell with thin circular tubes as members, Brazier's effect associated with cross-sectional ovalisation improves the auxetic behaviour under tension; the enhancement is even more significant for the 3D re-entrant geometry. Thin strip-based auxetic unit cells were additively manufactured and tested under compression to verify the numerical observations. The experimentally measured values of the negative Poisson's ratio are in close agreement with the numerical results, revealing a 66% increase due to the nonlinearity. Simulation results showcase these alternative approaches to improve the auxetic behaviour through simple geometric engineering of the lattice ribs.

Engineering Ferroelectricity and Large Piezoelectricity in h-BN

Hexagonal boron nitride (h-BN) is a well-known layered van der Waals (vdW) material that exhibits no spontaneous electric polarization due to its centrosymmetric structure. Extensive density functional theory (DFT) calculations are used to demonstrate that doping through the substitution of B by isovalent Al and Ga breaks the inversion symmetry and induces local dipole moments along the c-axis, which promotes a ferroelectric (FE) alignment over antiferroelectric. For doping concentrations below 25%, a "protruded layered" structure in which the dopant atoms protrude out of the planar h-BN layers is energetically more stable than the flat layered structure of pristine h-BN or a wurtzite structure similar to w-AlN. The computed polarization, between 7.227 and 21.117 μC/cm2, depending on dopant concentration and the switching barrier (16.684 and 45.838 meV/atom) for the FE polarization reversal are comparable to that of other well-known FEs. Interestingly, doping of h-BN also induces a large negative piezoelectric response in otherwise nonpiezoelectric h-BN. For example, we compute d33 of -24.214 pC/N for Ga0.125B0.875N, which is about 5 times larger than that of pure w-AlN (5 pC/N), although the computed e33 (-1.164 C/m2) is about 1.6 times lower than that of pure w-AlN (1.462 C/m2). Because of the layered structure, the rather small elastic constant C33 provides the origin of the large d33. Moreover, doping makes h-BN an electric auxetic piezoelectric. We also show that ferroelectricity in doped h-BN may persist down to its trilayer, which indicates high potential for applications in FE nonvolatile memories.

Modeling of Shunted Piezoelectrics and Enhancement of Vibration Suppression through an Auxetic Interface

In this study, a new technique is presented for enhancing the vibration suppression of shunted piezoelectrics by using an auxetic composite layer. Finite element models have been created to simulate the dynamic behavior of the piezoelectric composite beam. In particular, 2D FE and 3D FE models have been created by simulating the shunt as a passive controller and their results are compared. Furthermore, a parametric analysis is presented of the circuit elements, i.e., the resistors, inductors, and capacitors and of the auxetic material, i.e., the thickness. It was found that the proposed modification by adding an auxetic layer of a considerable thickness enhances the electromechanical coupling and indirectly influences the vibration control of the whole structure. However, the use of 3D modeling is necessary to study this auxetic enhancement.

Modeling, Simulation and Analysis of Intermediate Fixed Piezoelectric Energy Harvester

To address the problem that piezoelectric energy harvesters are difficult to apply in certain environments, this paper establishes the theoretical study of the intermediate fixed disc piezoelectric energy harvester (IFDPEH) based on the unimorph under concentrated force. The reliability of the model was indirectly verified by numerical simulation and Computer-Aided Engineering (CAE) simulation. The effects of load, radius ratio (piezoelectric layer/intermediate support), thickness ratio (piezoelectric layer/total thickness), and elastic modulus ratio (substrate/piezoelectric layer) on electrical energy were studied. The results indicate that the radius/thickness ratios of the IFDPEH based on aluminum and beryllium bronze are 0.05/0.31 and 0.05/0.48, respectively. In addition, through parameter comparison, it is found that the most important parameters affecting IFDPEH power are radius ratio and large load. The results are demonstrated to be meaningful for broadening the application of piezoelectric energy harvesters by the derived closed-form equations for the electrical energy along the diameters of the piezoelectric discs in the z-direction.

On-Body Piezoelectric Energy Harvesters through Innovative Designs and Conformable Structures

Recent advancements in wearable technology have improved lifestyle and medical practices, enabling personalized care ranging from fitness tracking, to real-time health monitoring, to predictive sensing. Wearable devices serve as an interface between humans and technology; however, this integration is far from seamless. These devices face various limitations such as size, biocompatibility, and battery constraints wherein batteries are bulky, are expensive, and require regular replacement. On-body energy harvesting presents a promising alternative to battery power by utilizing the human body's continuous generation of energy. This review paper begins with an investigation of contemporary energy harvesting methods, with a deep focus on piezoelectricity. We then highlight the materials, configurations, and structures of such methods for self-powered devices. Here, we propose a novel combination of thin-film composites, kirigami patterns, and auxetic structures to lay the groundwork for an integrated piezoelectric system to monitor and sense. This approach has the potential to maximize energy output by amplifying the piezoelectric effect and manipulating the strain distribution. As a departure from bulky, rigid device design, we explore compositions and microfabrication processes for conformable energy harvesters. We conclude by discussing the limitations of these harvesters and future directions that expand upon current applications for wearable technology. Further exploration of materials, configurations, and structures introduce interdisciplinary applications for such integrated systems. Considering these factors can revolutionize the production and consumption of energy as wearable technology becomes increasingly prevalent in everyday life.