• Energy Research

In this paper, we present a nonlinear energy harvester that is based on a "soft-mode" nonlinearity and is able to work in presence of a truly random excitations. The proposed harvester is configured with a cantilever beam structure, and, at the tip is a cylindrical container filled with freely moving iron balls. The nonlinearity is implemented through the container, as a piecewise function. This structure, in presence of noise, can be assumed as a second order (mass-spring-damper) nonlinear system where the length of the spring changes as a function of external vibration. As will be demonstrated, this nonlinearity will improve the performance of the energy harvester under random excitation. In comparison, the conventional approach based on resonant oscillators is able to collect energy only around its mechanical natural frequency, while the solution pursued here will present a wide spectrum of response. Furthermore, the implemented nonlinearity here does not possess any barrier of potential or mechanical threshold. Because of this, it is able to work at weak signal levels and without mixture of periodic signals. A piezoelectric element has been used to convert the mechanical vibrations into an electrical signal. The system has been modeled and simulated. Experimental validations have been carried out, demonstrating the suitability of the proposed solution.

Single‐source energy harvesters that convert solar, thermal, or kinetic energy into electricity for small‐scale smart electronic devices and wireless sensor networks have been under development for decades. When an individual energy source is insufficient for the required electricity generation, multi‐source energy harvesting is indicated. Current technology usually combines different individual harvesters to achieve the capability of harvesting multiple energy sources simultaneously. However, this increases the overall size of the multi‐source harvester, but in microelectronics miniaturization is a critical consideration. Herein, an advanced approach is demonstrated to solve this issue. A single‐material energy harvesting/sensing device is fabricated using a (K0.5Na0.5)NbO3‐Ba(Ni0.5Nb0.5)O3–Δ (KNBNNO) ceramic as the sole energy‐conversion component. This single‐material component is able simultaneously to harvest or sense solar (visible light), thermal (temperature fluctuation), and kinetic (vibration) energy sources by incorporating its photovoltaic, pyroelectric, and piezoelectric effects, respectively. The interactions between different energy conversion effects, e.g., the influence of dynamic behavior on the photovoltaic effect and alternating current–direct current (AC–DC) signal trade‐offs, are assessed and discussed. This research is expected to stimulate energy‐efficient design of electronic devices by integrating both harvesting and sensing functions in the same material/component.

AbstractPiezoelectric materials are widely used in electromechanical coupling components including actuators, kinetic sensors, and transducers, as well as in kinetic energy harvesters that convert mechanical energy into electricity and thus can power wireless sensing networks and the Internet of Things (IoT). Because the number of deployed energy harvesting powered systems is projected to explode, the supply of piezoelectric energy harvesters is also expected to be boosted. However, despite being able to produce green electricity from the ambient environment, high‐performance piezoelectrics (i.e., piezoelectric ceramics) are energy intensive in research and manufacturing. For instance, the design of new piezoceramics relies on experimental trials, which need high process temperatures and thus cause high consumption and waste of energy. Also, the dominant element in high‐performance piezoceramics is hazardous Pb, but substituting Pb with other nonhazardous elements may lead to a compromise of performance, extending the energy payback time and imposing a question of trade‐offs between energy and environmental benefits. Meanwhile, piezoceramics are not well recycled, raising even more issues in terms of energy saving and environmental protection. This paper discusses these issues and then proposes solutions and provides perspectives to the future development of different aspects of piezoceramic research and industry.

AbstractAmbient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere.

The concept of multisource energy harvesting (of light, kinetic, and thermal energy) using a single material has recently been proposed. Herein, the realization of this novel concept is discussed and insight into the electric field‐assisted modulation of photocurrent and pyroelectric current in a bandgap‐engineered ferroelectric KNBNNO ((K0.5Na0.5)NbO3‐2 mol% Ba(Ni0.5Nb0.5)O3−δ) is provided. Thereafter, direct current (DC) electrical modulation under the simultaneous inputs of light and thermal changes for photovoltaic and pyroelectric effects, respectively, is utilized to achieve several orders of increase in the output current density. This is attributed to a light‐assisted increase in the material's electrical conductivity and ferroelectric photovoltaic effect. The phenomena of electro–optic and thermo–electro–optic DC modulations are further used to propose two novel energy‐conversion cycles. The performance of both the proposed energy conversion cycles is compared with that of the Olsen cycle. The electro–optic and thermo–electro–optic cycles are found to harvest 7–10 times more energy than the Olsen cycle alone, respectively. Moreover, both energy‐conversion cycles offer broader flexibility and ease in operating conditions, thus paving a way toward the practical applications of multisource energy harvesting with a single material for enhanced energy‐conversion capability and device/system compactness.

AbstractEnergy harvesting technology may be considered an ultimate solution to replace batteries and provide a long‐term power supply for wireless sensor networks. Looking back into its research history, individual energy harvesters for the conversion of single energy sources into electricity are developed first, followed by hybrid counterparts designed for use with multiple energy sources. Very recently, the concept of a truly multisource energy harvester built from only a single piece of material as the energy conversion component is proposed. This review, from the aspect of materials and device configurations, explains in detail a wide scope to give an overview of energy harvesting research. It covers single‐source devices including solar, thermal, kinetic and other types of energy harvesters, hybrid energy harvesting configurations for both single and multiple energy sources and single material, and multisource energy harvesters. It also includes the energy conversion principles of photovoltaic, electromagnetic, piezoelectric, triboelectric, electrostatic, electrostrictive, thermoelectric, pyroelectric, magnetostrictive, and dielectric devices. This is one of the most comprehensive reviews conducted to date, focusing on the entire energy harvesting research scene and providing a guide to seeking deeper and more specific research references and resources from every corner of the scientific community.