Self-powered intracardiac implant devices show great promise for future clinical applications due to their extended operational lifespan and the potential to reduce the need for high-risk repeat surgeries. This study investigates the feasibility of harvesting energy from cardiac motion through in vivo testing of intracardiac devices. Comprehensive three-dimensional translational and rotational cardiac motions are captured in a porcine model using a miniaturized 9-degree-of-freedom motion sensor implanted at six strategic epicardial sites. Kinematic criteria are developed to evaluate the energy harvesting potential of each implant site based on the available kinetic energy, acceleration, and jerk factors. The recorded heart motion signals are analyzed and applied to a conceptual energy harvester proposed to identify the optimal implant site. The results reveal that the left ventricular apex emerges as a preferable site for energy harvesting, particularly at moderate heart rates. These findings offer valuable insights into optimizing self-powered intracardiac implants, reducing dependency on battery replacements, and enhancing long-term patient safety.

In traditional electrical steel production oxide inclusions are conventionally perceived as deleterious elements for the functional and structural properties. The present work describes the fabrication of a high silicon content electrical steel alloy (Fe-6.5wt%Si) using directed energy deposition (DED), coupled with oxide inclusions to mitigate core energy losses. Abnormal Grain Growth (ABG) was observed after thermal post-processing at 1000 degrees C for 24 h (1000-24), together with the creation of oxide inclusions mainly around the grain boundaries. Magnetic properties were assessed through dynamic and quasi-static measurements for both as-printed (AP) and 1000-24 samples. The quasi-static analysis revealed hysteresis losses of 206.9 J/m3 for the AP and 19.02 J/m3 for the 1000-24, with maximum flux densities of 1.295 T and 1.031 T, at the magnetic field of 3000 A/m. Dynamic magnetic analysis demonstrated an improvement of 39.2% in the total core losses of the 1000-24 sample (2088.8 J/m3), compared to the AP sample (3436.9 J/m3). The microstructure of the 1000-24 sample revealed the formation of Goss texture via ABG, ultimately decreasing the static hysteresis loss. Furthermore, an improved electrical resistivity compare to conventional electrical steel alloys was demonstrated at 119 mu Scm for the 1000-24 sample, and 105 mu Scm for the AP sample. This work introduces a promising avenue to minimize core energy losses by incorporating oxide inclusions and ABG Goss texture in additively manufactured soft magneitc components after thermal post-processing.

This paper is concerned with a contact problem which is geometrically two dimensional, but of finite extent in a third dimension. Two different contact models (common edge contact and incomplete contact) are analyzed, using a finite element model to investigate the 3D end effects. The object is to take the 2D plane strain solution in each model as a reference, and to show how it must be modified to allow for the 3D finite extent contact problem with free end faces. It is shown that, for a sufficiently long prismatic contact, the in-plane stress distribution at the mid-plane matches the solution to the 2D plane strain problem. Additionally, the end effect is evaluated using the finite element results to show how it decays with distance from the free end. The decay is exponential and governed by a dominant length-scale of the problem. For a common edge contact, this length-scale is the contact width. However, for a Hertzian contact, the contact width varies in the third dimension and the governing length scale is the radius of curvature, typically much larger than the contact width.

A Mori - Tanaka model of piezoelectric composites is used to study the effect of property contrast between the components of a two-component composite. The composite comprises a piezoelectric matrix and piezoelectric inclusions whose property values are scaled from those of the matrix. The scaling method allows a wide range of material combinations to be approximated without using explicit properties of specific materials. Additionally, the aspect ratio and volume fraction of inclusions is varied to seek optimum values of the piezoelectric coefficients in the composite. It was found that scaling the properties in the electroelastic moduli reveals significant results for the piezoelectric performance coefficients dhgh, κ33, g33 and kt. By varying the material scaling factors alongside the inclusion aspect ratio it is demonstrated that giant enhancements of the transducer figure of merit dhgh could potentially be achieved through composite design. This approach identifies some novel opportunities for optimised piezoelectric composites.

Mechanical energy harvesters show great potential as clean and sustainable energy sources to replace or supplement currently used chemical batteries. Conventional piezoelectric energy harvesting is constrained by low power density, which cannot generate sufficient electrical power for some electronics, particularly in space-sensitive applications. This review systematically examines the existing literature on piezoelectric energy harvesting, with an emphasis on the improvement of energy density by using different energy harvesting strategies. Then, attempts to use the non-linear electromechanical properties of ferroelectric/ferroelastic switching for energy harvesting are reviewed. Critical aspects of mechanical energy harvesting are covered: principles of energy conversion, operational modes, structure design, material properties, energy output, and applications. Comparing the piezoelectric effect to ferroelectric/ferroelastic switching, orders of magnitude increase in power density can be achieved by controlling polarization and residual stress. This review indicates that ferroelectric/ferroelastic switching could be a promising alternative to piezoelectrics for mechanical energy harvesting and identifies opportunities and future directions for practical applications.

Frequency limit and applicable frequency range of planar piezoelectric metamaterials connected to external circuits have not been well defined in estimating the sound transmission loss. This article extends the classical transfer matrix method for use in evaluating the sound transmission of thin-plate piezoelectric metamaterials in oblique incidence. Using the Kirchhoff thin plate theory, a modified transfer matrix method that takes factors of external circuits into consideration is developed for attenuation and control of acoustic waves. Several vibro-acoustic analytical models are compared, including the Kirchhoff thin plate theory, the Reissner-Mindlin thick plate theory and the theory of wave propagation in elastic solids. These theories are used to determine the dispersion relation, coincidence and transition frequency of thin and thick plate theories in analysing piezoelectric acoustic metamaterials, alongside a validation using the finite element method. Then acoustic properties of piezoelectric plates connected to passive external circuits are studied parametrically with both dimensional and dimensionless variables based on an equivalent Kirchhoff plate approximation. The findings show that external electrical impedance alone can be used to adjust the resonance frequency over a broad range and thereby control sound transmission loss. This provides considerable flexibility in modifying the acoustic properties of the piezoelectric metamaterial in comparison to traditional, fixed-structure metamaterials. The study indicates a straightforward and powerful analytical approach for the optimization of acoustic insulation using thin-plate piezoelectric metamaterials.

Improving the energy conversion efficiency of piezoelectric energy harvesters is of great importance, and one approach is to make more uniform use of the working material by ensuring a uniform strain state. To achieve better performance, this paper presents a four-point bending piezoelectric energy harvester with extensive investigation and modeling to identify the influential parameters. An electromechanical analytical model is presented and verified by experimental data. The frequency-domain method extracts the solutions for a general time-variable force and impact. Four-point bending is compared with the standard cantilever harvesters regarding voltage generation, mechanical strain, and figure of merit. Strain contours are analyzed and interpreted for this innovative approach, and the power generation by the optimal resistance load is studied. Dimensionless parameters are introduced and investigated to find the optimal operating conditions for the four-point bending harvester. Finally, the four-point bending performance and the best figure of merit are discussed with a view to the long-term fatigue life of the harvester. The results show that in the best four-point bending energy conversion conditions; the energy conversion coefficient is more than three times higher than that of typical cantilever energy harvesters. The results also illustrate that the axial strain experienced in a standard cantilever harvester is more than three times higher than that of the four-point bending harvester, suggesting the latter device may have favorable fatigue performance. Overall, the presented piezoelectric harvester has improved energy conversion efficiency and experiences a reduced and uniform surface strain, making it appropriate for high-efficiency energy harvesting systems.

Piezoelectric transducers have been widely employed for energy harvesting from vibration or kinetic energy sources. These systems, however, suffer from low energy density and consequently low power density at frequencies corresponding to common ambient vibrations. An alternative approach, using ferroelectric and ferroelastic switching offers potentially much greater energy density, at the cost of loss of linearity. Using a simple model of switching, a working cycle that could generate electrical energy from a harmonically varying source of stress is explored. The cycle uses depolarization by stress, followed by repolarization with combined electromechanical loading. A harvesting electric field and bias electric field are imposed to ensure a stable repeatable working cycle during the depolarization process and repolarization process, respectively. The bias electric field affects ferroelectric/ferroelastic switching, leading to a preferred direction of repolarization. By contrast, without bias electric field, stress alone would not trigger repolarization because of mechanically equivalent states with opposite polarization. The results illustrate that the bias electric field can be much lower than the harvesting electric field, requiring only a small electrical energy input during the cycle. Finally, the conversion efficiency of this cycle is estimated and improvements to the cycle are explored by adjusting the electrical and mechanical field amplitudes.

Acoustic energy is difficult to capture and utilise in general. The current work proposes a novel nanofibrous membrane-based (NFM) triboelectric nanogenerator (TENG) that can harvest acoustic energy from the environment. The device is ultra-thin, lightweight, and compact. The electrospun NFM used in the TENG contains three nanocomponents: polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), and multi-walled carbon nanotubes (MWCNTs). The optimal concentration ratio of the three nanocomponents has been identified for the first time, resulting in higher electric output than a single-component NFM TENG. For an incident sound pressure level of 116 dB at 200 Hz, the optimised NFM TENG can output a maximum open-circuit voltage of over 120 V and a short-circuit current of 30 μA, corresponding to a maximum areal power density of 2.25 W/m2. The specific power density reached 410 μW/g. The ability to power digital devices is illustrated by lighting up 53 light-emitting diodes in series and powering other devices. The findings may inspire the design of acoustic NFM TENGs comprising multiple nanocomponents, and show that the NFM TENG can promote the utilization of acoustic energy for many applications, such as microelectronic devices and the Internet of Things.

In rods and beams, piezoelectric patches with external circuits have been extensively studied to dampen structural vibrations at the sound source. This work uses a large flat-layer type of piezoelectric acoustic metamaterial (AM) model for noise attenuation in the sound transmission stage rather than at the sound source. This could be directly implemented as a large space sound transmission barrier at the interface of diverse media including gas, liquid, and solid materials. The general analytical model to derive acoustic properties of the piezoelectric acoustic metamaterial is established by the equivalent transfer matrix approach for normal incidence waves. This has been validated numerically using the finite element method and experimentally in the solid medium propagation for the first time. Moreover, a parametric study of sound transmission properties in air, water, and steel is conducted by adjusting external circuit parameters, flat-layer structures, and piezoelectric materials. The findings demonstrate the ability to control sound resonance frequency and bandwidth through the propagation process over a wide range using external circuit parameters alone. This endows the piezoelectric acoustic metamaterial with great versatility relative to conventional, fixed structure, metamaterials used as sound barriers at the interface of diverse media. In addition, the size of the piezoelectric AM can reach a deeply sub-wavelength level, less than 10−3 of the resonance wavelength in both water and solid media, which goes far beyond the wavelength-to-thickness ratio of classical acoustic metamaterials. The layer-type piezoelectric AM thus shows excellent performance in tunability and compactness for space-sensitive applications as well as great potential in combining metamaterials with electronic control.

The shape and strain field of a needle domain in a barium titanate single crystal are modelled using a distribution of dislocations and line charges. The arrangement of these dislocations and charges is a result of the balance of modified Peach–Koehler forces acting among the dislocations and a lattice friction assumed to act at each dislocation site. Based on measurements of needle shape by synchrotron X-ray diffraction, dislocation pile-up theory is used to compute the distribution of discrete dislocations along the needle and hence estimate the lattice friction. It is found that the lattice friction in this model is proportional to the opening angle of a wedge-shape needle domain and consistent with the observed magnitude of stress required to mobilize needle domains. The microstrain distribution around an a-a needle domain tip, obtained from X-ray diffraction measurement, is further used to test the dislocation model, with a similar pattern and magnitude of strains identified in the model and the experiment.

This article presents a comprehensive investigation into the homogenization and analysis of planar piezoelectric metamaterials. The classical transfer matrix method is extended by using homogenization methods to evaluate the sound transmission of piezoelectric metamaterials in both normal and oblique incidences. This has been validated numerically using the finite element method and experimentally in the solid medium propagation in normal incidence. Several vibro-acoustic analytical models are compared in oblique incidence, including the Kirchhoff thin plate theory, the Reissner-Mindlin thick plate theory, and the theory of wave propagation in elastic solids. These theories are used to determine the dispersion relation, coincidence, and transition frequency of thin and thick plate theories in analyzing piezoelectric metamaterials. Additionally, acoustic properties of piezoelectric layers connected to external circuits are parametrically studied, exploring both dimensional and dimensionless variables. Results indicate that significant control over the resonance frequency and sound transmission can be enabled by adjusting the external electrical impedance, flat-layer structures, and piezoelectric materials. This demonstrates excellent tunability and compactness of planar piezoelectric metamaterials for space-sensitive applications. The study indicates a straightforward and powerful analytical approach for the optimization of acoustic insulation using planar piezoelectric metamaterials.

Aiming toward improved energy conversion in piezoelectric energy harvesters, this study investigates four-point bending (FPB) energy harvesters (FPB-EH) to explore their prominent features and characteristics. The FPB configuration innovatively extends energy harvesting capabilities relative to conventional cantilever beams. The FPB-EH comprises a composite piezoelectric beam that rests on two supports of a fixed clamp, excited by contact force applied at two contact lines on a moving clamp. A comprehensive analytical electromechanical model for the vibrating energy harvester is presented with unique modeling features, including multi-beam sections and multi-mode-shape functions. Solutions of the analytical model are presented for a wide range of contact force types, including steady-state solutions for harmonic forces, impact forces, periodic and non-periodic arbitrary forces. This comprehensive model progresses the state-of-the-art piezoelectric modeling knowledge and is readily applicable to various energy harvesting configurations. The model is validated against experimental results and finite element analysis. Next, a parametric study was performed to evaluate the effects of various FPB characteristics, including the fixed and moving clamp spans, the waveform, and the period-time of contact force. The results indicate that the FPB configuration can enhance energy conversion efficiency and normalized output energy by factors of over 3 and 6, respectively. Finally, guidance is given for selecting between cantilever and four-point bending configurations.

Ferroelectric/ferroelastic switching, which can generate greater charge flows than piezoelectricity for the conversion of mechanical energy into electrical energy, has great potential for novel transducers. In this work, a stress-driven ferroelectric/ferroelastic energy harvester, exploiting internal bias fields in a partially poled ferroelectric, is explored. The harvester is tested and optimized for low-frequency applications, and the effects of electrical load impedance and operating frequency are studied. The device has a simple configuration and offers power density up to about 20 mW/cm3 of active material in the 1-20 Hz frequency range, which is a significant advance over piezoelectric transducers. Additionally, the results show that the energy output at a specific frequency can be optimized through appropriate choice of load impedance, and the optimized cycle works for over 107 cycles at 20 Hz with only slight fatigue degradation, where the peak voltage decreases by 13% and an accompanying 24% drop in average power output. This provides a new perspective for energy harvesting to maximize energy conversion based on ferroelectric/ferroelastic switching with controllable performance.

Piezoelectric energy harvesters have been widely developed in last decade due to their simplicity and practicality, but they suffer from low energy density. To increase the energy density, ferroelectric/ferroelastic switching could be an effective alternative energy harvesting approach. However, the nonlinearity and irreversibility of ferroelectric switching produces difficulty in establishing a stable working cycle. In this work, novel, practical and stable energy harvesting cycles using ferroelectric/ferroelastic switching are established and explored under quasi-static experimental conditions. A prototype device with a simple ‘sandwich’ configuration is tested. The results show that the cycle energy density can reach 11 mJ/cm3 under tensile loading and 3.2 mJ/cm3 under compression, demonstrating great potential for practical applications.

Acoustic metamaterials, structured to produce anomalous reflection and refraction indices that are not found in conventional materials, are gaining prominence in engineering applications. These artificial structures have enabled novel functionalities, such as negative effective properties, extraordinary wave manipulation, enhanced sound absorption and insulation, cloaking, acoustic wave focusing, and efficient energy harvesting. To evaluate the research progress in the field of acoustic metamaterials, we take a novel viewpoint, tracing the development from passive acoustic metamaterials to active piezoelectric acoustic metamaterials. The article summarizes recent research progress in acoustic metamaterials, with the first part describing passive acoustic metamaterials and the second part moving on to active piezoelectric acoustic metamaterials and metasurfaces. The topics covered include their general definition, mechanisms, classification, structure, and potential applications. Finally, we survey the current technical challenges from a practical engineering standpoint and discuss the future outlook in this field. (c) 2021 Elsevier Ltd. All rights reserved.

Polycrystalline ferroelectrics constitute the basis of many advanced technologies, including sensors and actuators. Their intricate domain patterns, and switching, drive the macroscopic electrical and mechanical properties of the material, where the domain switching behaviour is largely influenced by the grain-grain interaction of the domain walls. Domain wall continuity across grain boundaries is speculated to affect the domain wall – grain boundary interaction, although the true impact of this phenomenon on the ferroelectric properties, and the conditions under which continuity occurs, are not yet well understood. Whilst there are some theoretical reports, the link to experimental evidence is limited, greatly hindering the applicability and fundamental understanding of current polycrystalline based devices. In this work, we close this gap by studying several grain junctions in free-standing BaTiO3 thin films using microscopy techniques and rationalising the domain configurations with reference to martensite theory. A pleasing agreement of minimal strain and polarisation mismatch for a pair of domain variants were found in cases where domain wall continuity across grain boundaries was observed, confirming that domain continuity is related to the compatibility conditions at the grain boundary. Following this experimental validation, the mismatches for various combinations of Euler angles in bi-grain junctions were theoretically explored, offering valuable insights into specific cases where domain continuity can be expected. These results offer an advancement in the understanding of grain-grain-domain interactions and provides a template for the prediction and control of domain wall continuity in polycrystalline ferroelectrics, appealing to those working in polycrystal design and domain engineering.

In a simulated in-situ experiment annular contacts of 6082-T6 aluminium alloy were first exposed to various degrees of fretting wear, before synchrotron X-ray CT and diffraction were applied to examine the extent and development of wear damage. The wear volumes measured and development of the wear rate were consistent with the mathematical wear model of Fillot, Iordanoff & Berthier. Thickness and porosity of the worn zone were measured and the contact area between wearing elements estimated. Developments of residual strain and tribologically transformed structure were investigated through X-ray diffraction. This study demonstrates, for the first time, the value and viability of observing and quantifying wear through combination of X-ray CT and diffraction opening a path towards in-situ observations of wear.

Although piezoelectric energy harvesting is well established, ferroelectric/ferroelastic switching has not been widely used for energy harvesting. The main disadvantage of piezoelectric energy harvesters is their limited power density. In this respect, ferroelectric/ferroelastic switching is attractive because of the greater energies and charge flows involved. However, the associated nonlinearities and the difficulty of establishing a stable working cycle have prevented significant progress. In this work, a robust ferroelectric energy harvester based on partial ferroelectric switching is explored. The device is of simple construction and achieves a per-cycle energy density of about 1 mJ cm(-3), orders of magnitude greater than that of typical piezoelectrics. It is shown that only periodic compressive stress is needed to induce the energy harvesting cycles, yielding promising mechanical attributes that limit fatigue or fracture during cyclic loading. The results show this prototype device operating stably over 0.5 3 106 cycles at 20-Hz frequency, demonstrating promise for practical applications.