This review offers a critical overview of recent developments in lead-free piezoelectric materials and flexible device architectures for self-powered wearable and Internet of Things systems. It examines the scientific and technological rationale for replacing conventional battery-dependent power sources with ambient mechanical energy harvesters, and it evaluates the relative merits of inorganic ceramics, organic polymers, and composite systems in achieving efficient electromechanical conversion under practical operating conditions. The discussion further considers compositional tuning, phase boundary engineering, microstructural optimization, and device-level integration as key strategies for improving piezoelectric output, mechanical compliance, durability, and manufacturability. By connecting fundamental materials design with application-driven device requirements, the review identifies the principal challenges and emerging directions necessary for the realization of reliable, scalable, and sustainable electronic platforms.

Renewable energy harvesting technologies, which convert ambient resources such as wind into electrical energy, have attracted significant attention as sustainable power sources for self-powered systems. However, the long-term applicability of wind energy harvesters in remote or extreme environments has not yet been fully discussed, particularly in terms of structural robustness and environmental adaptability. In this study, we designed a double-clamped flutter-type triboelectric generator (DFTEG) for efficient wind energy harvesting and evaluated its output performance under various simulated outdoor conditions. The DFTEG features a modular acrylic frame with a magnet-based assembly for easy maintenance and film replacement, utilizing PTFE films and aluminum electrodes to maximize the charge density difference according to the triboelectric series. Structural optimization revealed that a single-film configuration with a length of 110 mm produced the most stable flutter vibration and a large effective contact area, achieving a maximum open-circuit voltage of 42.28 V and a short-circuit current of 2.89 μA. Furthermore, performance evaluations under various environmental variables, including relative humidity, temperature, and sand particles interference, confirmed consistent electrical output across diverse environmental conditions. These results demonstrate the potential of the proposed DFTEG as an environmentadaptive independent power source capable of stable operation under complex environmental factors.

With the rapid expansion of electric vehicles (EVs) and energy storage systems (ESS), ensuring the operational safety of lithium-ion batteries has become a critical technical challenge. Conventional battery management systems (BMS) primarily rely on threshold-based rule logic, which is limited in detecting coupled anomalies and early-stage degradation patterns. In this study, a deep learning-based framework for multivariate anomaly detection is proposed using BMS sensor data, including voltage, current, temperature, state of charge (SOC), and state of health (SOH). Five representative fault scenarios were defined, including thermal runaway precursors, cell voltage imbalance, SOC inconsistency, internal resistance increase, and communication delay. The proposed CNN-LSTM model was compared with conventional Rule-based methods and machine learning models, including Isolation Forest, Autoencoder, and LSTM. Experimental results show that the proposed model achieved the highest performance, with an F1-score of 0.885, an AUC of 0.94, and a detection delay of 8.1 s. In contrast, the Rule-based method exhibited a significantly higher false negative rate of 42.0%, indicating limitations in detecting complex anomaly patterns. These results demonstrate that the proposed spatiotemporal deep learning approach can significantly improve the accuracy and responsiveness of battery anomaly detection. Furthermore, the proposed method is expected to contribute to enhancing safety, reliability, and predictive diagnostics in next-generation intelligent BMS platforms.

The expansion of smart healthcare and wearable electronics has intensified the need for fabric-based sensors that integrate conformally with the human body for continuous bio signal monitoring. However, the heavy reliance of conventional devices on external batteries remains a major obstacle to commercialization, necessitating the development of flexible piezoelectric energy harvesters that convert biomechanical energy into sustainable power. Here, we present a highly flexible and wearable piezoelectric energy harvester (PEH) fabricated by a screen-printing of BaTiO₃ nanoparticlePDMS composites onto a fabric substrate. An optimized piezo-ceramic filler concentration of 70 wt% yielded a peak output voltage of 0.52 V and a current of 40 nA under the mechanical bending deformations. The fabricated PEH demonstrated exceptional mechanical and electrical stability, showing no performance degradation of over 5,000 repetitive bending cycles. These results indicate that a PEH can function as a stable self-powered source within complex clothing environments, offering a promising pathway for next-generation autonomous wearable sensor systems.

Metamaterials, as artificially engineered structures with unconventional mechanical and acoustic properties, have recently emerged as a transformative platform for enhancing the capabilities of triboelectric nanogenerator (TENG) systems. Since the invention of TENG devices, extensive efforts have been devoted to improving charge density, output stability, and overall performance. Conventional performance optimization strategies mainly rely on device-level improvements such as surface chemistry modification, microstructuring, and nanopatterning. However, limited emphasis has been given to system-level development of smart self-powered intelligent systems. The integration of metamaterials into TENG devices opens a new era by enabling frequency-selective localization, mechanical impedance matching, and controllable deformation pathways. These engineered mechanical structures not only improve energy harvesting efficiency but also introduce new functionalities into the system. This review systematically summarizes recent advances in metamaterial-integrated TENG systems across four major application domains: (i) energy harvesting, (ii) acoustic telecommunication and acoustic-to-electric conversion, (iii) self-powered sensing, and (iv) vibration suppression and monitoring. Overall, the integration of metamaterials into TENG systems will pave the way for next-generation sustainable, intelligent, self-powered devices with diverse functionalities.

The increasing global demand for renewable energy has accelerated the deployment of offshore wind farms, thereby highlighting the need for advanced development and performance assessment techniques for dynamic submarine cables used in floating offshore wind systems. These cables are continuously subjected to combined thermal, electrical, and mechanical stresses, with mechanical loading playing a particularly dominant role. As a result, dynamic submarine cables exhibit degradation behaviors that differ significantly from those of conventional fixed submarine cables. This paper presents the design and implementation of a comprehensive evaluation system capable of applying combined thermal, electrical, and mechanical stresses to dynamic submarine cables. The system was validated using a 66 kV wet type submarine cable through commissioning tests and insulation performance measurements. Electrical stress of 72 kV, thermal stress exceeding 95°C, and mechanical stress corresponding to a bending radius of 20 times the cable diameter over 20 cycles were applied to verify system reliability. The subsequent insulation assessments quantitatively confirmed performance variations induced by the combined stresses. The results demonstrate that the proposed platform is the first system capable of simultaneously applying thermal, electrical, and mechanical stresses to dynamic submarine cables, and its operational performance has been successfully validated. This platform enables realistic reliability evaluation of dynamic cables used in floating offshore wind farms and is expected to improve the overall operational reliability of offshore wind power systems.

As electric vehicles (EVs) are rapidly adopted worldwide, large numbers are now transported by sea on dedicated car carriers. With this trend, concerns are increasing about fires and explosions caused by battery thermal runaway during marine transport, while existing SOC limits before loading remain largely empirical. This study experimentally investigates gas generation and explosion characteristics of EV lithium-ion cells under thermal runaway conditions representative of enclosed vehicle decks. We identify and quantify the main off-gas components and clarify the flammability behavior and explosion limits of key combustible species. The results provide basic data for assessing EV battery accidents at sea and support the development of safer ventilation and gas-management strategies for ships.

The rapid proliferation of artificial intelligence (AI) servers and high-performance computing systems has significantly elevated the technical and reliability requirements for multilayer ceramic capacitors (MLCCs). In such systems, MLCCs are critical passive components that must deliver high capacitance, fast transient response, and robust insulation performance under high temperature, voltage, and current density. This review examines the material, structural, and process innovations that underpin MLCC performance in AI applications. Key topics include the development of ultrathin dielectric layers (<0.5 μm), rare-earth doped BaTiO₃-based dielectrics with enhanced DC bias stability, and core-shell microstructures designed for temperature and field resilience. The paper also explores insulation degradation mechanisms―such as vacancydriven conduction and demixing―and advanced reliability assessment methodologies, including HALT, TSDC, and the tipping point framework. Comparisons with automotive-grade MLCCs highlight the unique requirements of AI systems, such as ultraminiaturization, high volumetric efficiency, and ppm-level field failure rates. Finally, the review discusses emerging trends in MLCC technology, including particle engineering, interface stabilization, and advanced lamination techniques, and provides insight into the future direction of capacitor development tailored to AI data center environments.

Humidity monitoring of exhaled breath has emerged as a vital approach for noninvasive respiratory health assessment, underscoring the need for sensitive and reliable humidity sensors. Despite its high conductivity and hydrophilic functional groups, reduced graphene oxide (rGO) often undergoes irreversible moisture adsorption and gradual oxidation by residual water, resulting in sensitivity degradation and long-term instability during cycling. In this study, a montmorillonite/reduced graphene oxide (MMT/rGO) composite is developed as a room-temperature humidity-sensing material, exhibiting an optimized response of 115%, more than 14 times higher than that of pristine rGO. This superior performance originates from the synergistic interaction between the reversible MMT swelling and the conductive rGO network near the electrical percolation transition, which ensures excellent stability and repeatability under repeated humidity cycles. These findings suggest that the MMT/rGO composite provides a cost-effective and biocompatible platform for next-generation wearable humidity sensors capable of continuous respiratory monitoring.

(La_1-xBi_xSr_0.3)FeO₃ ceramics exhibiting excellent magnetoresistance were synthesized via the conventional solid-state reaction method. The structural and electrical properties were investigated as a function of Bi³⁺ content to evaluate their potential application as temperature sensors. And the sintering temperature and time were 1,200℃ and 4 h, respectively. The structural and electrical properties were investigated as a function of Bi content. With increasing Bi substitution, a slight enhancement in both average grain size and relative sintered density was observed. In particular, the specimen with x = 0.3 exhibited an average grain size of approximately 0.82 μm. All samples demonstrated negative temperature coefficient of resistance (NTCR) behavior, and the electrical resistivity decreased with increasing Bi content. The resistivity of the (La_0.4Bi_0.3Sr_0.3)FeO₃ composition was 4.68 mΩ-cm at 25°C. Additionally, the temperature coefficient of resistance (TCR) and the B_25/75-value, which quantify the sensitivity of resistivity to temperature variations, were found to increase with Bi content. (La_0.4Bi_0.3Sr_0.3)FeO₃ sample exhibited a TCR of 0.43%/°C and a B_25/75-value of 1,096 K at room temperature. The electrical conduction mechanism of the (La_1-xBi_xSr_0.3)FeO₃ system was well described by the small polaron hopping model, wherein thermally activated charge carriers hop between localized Fe-O-Fe sites via electron-phonon interactions.

Thermal batteries are designed to activate at high temperatures (~500℃), therefore, the electrodes used in these systems are typically made into pellet form using compression molding techniques that do not involve polymer binders. However, the compression molding technique poses limitations in scaling up the electrode area without increasing thickness for high-power properties. Additionally, the tape casting method has been studied as a way to solve with, but too low a loading level is still an obstacle to practical use. This study fabricated a film cathode of high loading level (35.79 mAh·cm^-2) using the tape casting method for these problem. As utilized fabricated cathode, it investigated the influence of electrode thickness and density on electrochemical performance. Furthermore, a film cathode with a larger area but the same amount of active material as the pellet was fabricated, enabling the design of high-power cells with the same energy density. We expect that the fabricated film cathode with a high loading level and scalable area will enable the development of various thermal battery designs.

The rapid evolution of wearable technology has driven a surge in demand for sustainable, self-powered electronic devices. Flexible thermoelectric materials, capable of converting body heat into electricity, have emerged as a promising solution for powering next-generation wearables. This review comprehensively examines recent progress in organic (polymer-based) and hybrid thermoelectric materials, focusing on their design, fabrication, and integration into flexible architectures suitable for conformal contact with human skin. Key developments include advanced doping strategies, post-treatment techniques, and composite engineering, particularly in conductive polymers such as PEDOT: PSS and P3HT, which have significantly enhanced power factors and mechanical flexibility. Additionally, the integration of high-performance inorganic materials into stretchable systems has further elevated device efficiency and durability. The review highlights breakthroughs, ongoing challenges, and future opportunities in realizing practical, scalable, and high-efficiency wearable thermoelectric generators for sustainable energy harvesting applications.

Abstract In this study, to develop composition ceramics for energy harvesting devices, Pb(Ni_1/3Nb_2/3)O₃-Pb(Zr Ti)O₃ system ceramics substituted with Pb(Mg_1/2W_1/2)O₃ were manufactured by conventional mixed oxide method using Li₂CO₃ and Na₂CO₃ (LNCO) as sintering aids. Their microstructure and piezoelectric properties were also investigated. At the specimen sintered at 930℃, high values of piezoelectric properties appeared: the dielectric constant (εr) of 2,522 planar electromechanical coupling factor kp of 0.602, and k₃₁ of 0.385, d31 = 229 [pC/N], g₃₁ = 10.13 [mV.m/N], Qm of 70, respectively. These values were suitable for the application of devices such as energy harvesting devices and ultrasonic devices.

With the rapid development of digital technologies such as IoT, AI, and big data, electrical energy consumption is rapidly increasing. Electrical facilities that supply electrical energy are operated with high reliability and stability for end-of-life time. In addition, depending on the type of electrical load that consumes electrical energy in various forms, electrical insulation systems deteriorate due to electrical and thermal stress, which reduces electrical and mechanical insulation strength. Due to such continuous stress and electrical transient phenomena, electrical facilities may experience electrical accidents due to electrical insulation breakdown before the expected design lifetime. In addition, periodic inspections according to related regulations must be conducted to prevent unexpected electrical accidents, but this leads to problems in which the electrical facilities cannot be turned off. Therefore, it is believed that an uninterruptible diagnostic judgment technique that determines compliance with related regulations such as electrical facility technology standards, internal wiring regulations, and inspection regulations without turning off the electrical facilities and at the same time detects abnormal conditions of the facilities early, it is possible to prevent electrical accidents and improve the efficiency of electrical facilities. In this paper, we propose an uninterruptible power diagnosis judgment technique that can prevent or reduce electrical accidents in cast-iron transformers by applying judgment criteria of diagnostic sensors for various types of measurement parameters that can diagnose and evaluate the presence or absence of abnormalities in electrical equipment, including partial discharge, and AI algorithms learned from data of diagnostic sensors.

This study developed a dielectric composition for high-capacitance MLCCs with C0G and U2J temperature compensation characteristics (Class I) under reducing conditions. The potential application of this composition in highpermittivity class I MLCCs was examined. Using (Ba₀.₂₄Ca₀.₁₆Sr₀.₆)(TiₓZr₁₋ₓ)O₃. XRD analysis showed that secondary phases like Sr₂TiO₄ and TiO₂ formed at higher Ti content, affecting the stoichiometric balance. Adjusting the Ti/Zr molar ratio resulted in a dielectric constant of 41.2 ~ 105, a dielectric loss of 0.082 ~ 0.174%, and insulation resistance above 1.6 × 10¹³ ohms at 25℃. The TCC shifted from C0G to U2J as the Ti/Zr ratio increased, but the composition enabled the design of high-capacitance and high-voltage MLCCs with favorable dielectric and electrical properties.

The composite specimens of (1-x)(La_0.7Sr_0.3)MnO₃-xBaTiO₃ (x = 0.05 ~ 0.3) were synthesized using the conventional solid-state reaction method, and the sintering temperature and time were 1,300℃ and 3 hours, respectively. As a result of observing the structural characteristics, the crystal structure of LSMO-BT solid solution was shown in which the rhombohedral LSMO phase and the tetragonal BT phase were separated and distributed, respectively. And fine grains having relatively small and uniformly distributed grains with sizes ranging from approximately 0.4 to 0.5 μm and pores within the specimens were observed. Notably, variations in the BT content did not significantly affect the grain size or porosity distribution, and a relative density of about 90% or more was shown. The resistivity, temperature coefficient of resistance (TCR), and B_25/65-value of the 0.7LSMO-0.3BT specimen at room temperature showed the highest values of 1.94 Ω-cm, 0.292 %/℃, and 464 K, respectively. The resistivity behavior of the LSMO-BT composites matched well with the small polaron hopping conduction model.

This review examines the principles, limitations, and recent advancements in elastic modulus measurement using nanoindentation. The importance of accurate contact area prediction is discussed, along with the Oliver-Pharr method and its limitations. The Continuous Stiffness Measurement (CSM) technique is presented as a significant improvement, allowing continuous measurement of mechanical properties throughout the indentation process. For ultra-thin films, the Li and Vlassak method, which incorporates Yu's solution and the concept of effective thickness, is highlighted as a means to correct for substrate effects. Recent developments in artificial neural network-based models for elastic modulus prediction are also explored. These advancements have greatly expanded the applicability of nanoindentation in semiconductor and MEMS device reliability assessment.

With the extensive industrial growth driven by the Fourth Industrial Revolution and the excessive use of fossil fuels, greenhouse gas emissions have accelerated global warming. Energy harvesting technologies have garnered significant attention as a potential solution to this issue. Among them, triboelectric nanogenerators (TENGs) have emerged as promising candidates for energy collection and conversion. However, TENGs typically face limitations in providing an efficient energy supply due to their high output voltage and low output current. To overcome these challenges, numerous studies have explored various methods to enhance the output performance by increasing the surface area of the triboelectric materials. Herein, we report a high-output TENG fabricated through a simple scratch process. By utilizing sandpaper, typically used for abrasion or polishing, the surface roughness of the triboelectric material PFA was increased through surface scratching. The surface-engineered TENG, prepared through this simple and rapid process, demonstrated enhanced output characteristics with a voltage of 276 V and a current of 72 μA, showing a 21% increase in voltage and a 41% increase in current compared to the non-engineered counterpart, providing sufficient energy to power an LED. These results indicate that the scratch-based surface modification process using sandpaper offers an effective solution for improving triboelectric output performance, establishing TENGs as a key contributor to sustainable energy supply.

Al-Mo thin films were fabricated using combinatorial sputtering system to realize highly sensitive surface acoustic wave (SAW) devices. The Al-Mo sample library was grown with various chemical compositions and electrical resistivities, which provided important information for selecting the most suitable materials for SAW devices. As the SAWs generated from piezoelectric materials are significantly affected by the resistivity and density of the interdigital transducer (IDT) electrodes, three types of Al-Mo thin films with different Al contents were fabricated. The thickness of the Al-Mo thin film used in the SAW-IDT electrode was fixed at 150 nm. As the Al content of the Al-Mo thin film decreased from 81.2 to 30.3 at%, the resistivity decreased slightly from 5.43±0.15 to 4.87±0.1×10^-5 Ω-cm, whereas the calculated density increased significantly from 4.1 to 7.9 g/㎤. The SAW device composed of Al-Mo IDT electrodes resonated at 143 MHz without frequency shifts; however, the selectivity of the resonant frequency and insertion loss deteriorated as the Al content decreased. This suggest that the resonant characteristics of the SAW devices fabricated with Al-Mo thin films were more strongly influenced by the material density rather than the electrical properties of the IDT electrodes.

This paper presents a comparative analysis of the fire detection characteristics between conventional fire detector sensors and an Si-based color sensor. With the rapid industrial development in modern society, the concentration of urban populations and the expansion of building sizes have accelerated, leading to an increased frequency of large-scale fires. As a result, the importance of fire detection technologies has been emphasized. However, conventional detectors continue to experience issues such as false alarms and malfunctions. To address these challenges, a novel fire detection technology utilizing an Si-based color sensor, which is effective for fire detection, is proposed. To evaluate the fire detection performance of each sensor, a fire detection test apparatus was developed, and experiments were conducted separately under smoke and flame conditions to analyze the fire detection capabilities of the Si-based color sensor, temperature sensor, and flame detection sensor. The experimental results demonstrated that detection speed and sensor values varied depending on the type of combustible material. Specifically, in the smoke and flame tests, the Si-based color sensor detected fires 26.7 and 43.7 seconds faster than the temperature sensor, and 26.6 and 15.4 seconds faster than the flame detection sensor, respectively. Therefore, it was confirmed that the Si-based color sensor proposed in this study is an effective detection technology that is expected to provide improved performance compared to conventional fire detectors.

Energy harvesting technology offers an innovative solution for providing self-sustaining power to wearable and implantable electronic devices. However, traditional energy harvesters face limitations in operating within electrolytic environments or at low motion speeds. To overcome these challenges, a mechano-electrochemical energy harvester using carbon nanotubes has been developed. This technology relies on electrochemical ion movement to induce changes in electrochemical double-layer capacitance, enabling operation within electrolytes and optimizing performance at low deformation speeds. This environmentally friendly and sustainable energy solution is expected to play a crucial role in the advancement of future smart systems and wearable technologies.

The Internet of Things (IoT) device is a key component for Industry 4.0, which is the network in homes, factories, buildings, and infrastructures to monitor and control the systems. To demonstrate the IoT network, batteries are widely utilized as power sources, and the batteries inevitably require repeated replacement due to their limited capacity. Magneto-mechanoelectric (MME) generators are one of the candidate to develop self-powered IoT systems since MME generators can harvest electricity from stray alternating current (AC) magnetic fields arising from electric power cables. Herein, we report a magnetomechano- triboelectric generator enabled by a ferromagnetic-ferroelectric composite. In the triboelectric nylon matrix, a ferromagnetic carbonyl iron powder (CIP) was introduced to induce magnetic force near the AC magnetic field for MME harvesting. Additionally, a ferroelectric ceramic powder was also added to the MME composite material to enhance the chargetrapping capability during triboelectric harvesting. The final ferromagnetic-ferroelectric composite-based MME triboelectric harvester can generate an open-circuit voltage and a short-circuit current of 110 V and 8 μA, respectively, which were enough to turn on a light emitting diode (LED) and charge a capacitor. These results verify the feasibility of the MME triboelectric generator for not only harvesting electricity from an AC magnetic field but also for various self-powered IoT applications.

The advantage of OTFT technology is that large-area circuits can be manufactured on flexible substrates using a lowcost solution process such as inkjet printing. Compared to silicon-based inorganic semiconductor processes, the process temperature is lower and the process time is shorter, so it can be widely applied to fields that do not require high electron mobility. Materials that have utility as electrode materials include carbon that can be solution-processed, transparent carbon thin films, and metallic nanoparticles, etc. are being studied. Recently, a technology has been developed to facilitate charge injection by coating the surface of the Al electrode with solution-processable titanium oxide (TiOx), which can greatly improve the performance of OTFT. In order to commercialize OTFT technology, an appropriate method is to use a complementary circuit with excellent reliability and stability. For this, insulators and channel semiconductors using organic materials must have stability in the air. In this study, carbon-doped Mo (MoC) thin films were fabricated with different graphite target power densities via unbalanced magnetron sputtering (UBM). The influence of graphite target power density on the structural, surface area, physical, and electrical properties of MoC films was investigated. MoC thin films deposited by the unbalanced magnetron sputtering method exhibited a smooth and uniform surface. However, as the graphite target power density increased, the rms surface roughness of the MoC film increased, and the hardness and elastic modulus of the MoC thin film increased. Additionally, as the graphite target power density increased, the resistivity value of the MoC film increased. In the performance of an organic thin film transistor using a MoC gate electrode, the carrier mobility, threshold voltage, and drain current on/off ratio (I_on/I_off) showed 0.15 cm²/V·s, -5.6 V, and 7.5×10⁴, respectively.

Energy harvesting technology, which converts wasted energy sources in everyday life into usable electric energy, is gaining attention as a solution to the challenges of charging and managing batteries for the driving of IoT sensors, which are one of the key technologies in the era of the fourth industrial revolution. Hybrid energy harvesting technology involves integrating two or more energy harvesting technologies to generate electric energy from multiple energy conversion mechanisms. In this study, a hybrid energy harvesting device called TMPPEG (thermo-magneto-piezoelectric-pyroelectric energy generator), which utilizes low-grade waste heat, was developed by incorporating PVDF polymer piezoelectric components and optimizing the system. The variations in piezoelectric output and thermoelectric output were examined based on the spacing of the clamps, and it was found that the device exhibited the highest energy output when the clamp spacing was 2 mm. The voltage and energy output characteristics of the TMPPEG were evaluated, demonstrating its potential as an efficient hybrid energy harvesting component that effectively harnesses low-grade waste heat.

The fault current limiting characteristics of three-phase transformer type superconducting fault current limiter (SFCL), which consisted of three-phase primary and secondary windings wound on E-I iron core, one high-TC superconducting (HTSC) element connected with the secondary winding of one phase and another HTSC element connected in parallel with other two secondary windings of two phases, were analyzed. Unlike other three-phase transformer type SFCLs with three HTSC elements, three-phase transformer type SFCL using double quench has the merit to perform fault current limiting operation for three-phase ground faults with two HTSC elements. To verify its proper three-phase ground fault current limiting operation, three-phase ground faults such as single-line ground, double-line ground and triple-line ground faults were generated in three-phase simulated power system installed with three-phase transformer type SFCL using double quench. From analysis of its fault current limiting characteristics based on tested results, three-phase transformer type SFCL using double quench was shown to be effectively operated for all three-phase ground faults.

Stretchable piezoelectric energy harvester (S-PEHs) based on composite materials are considered one of the potential candidates for realizing wearable self-powered devices for smart clothing and electronic skin. However, low energy conversion performance and expensive stretchable electrodes are major bottlenecks hindering the development and application of S-PEHs. Here, we fabricated the S-PEH by adopting the piezoelectric composites with enhanced stress transfer properties and kirigamipatterned textile electrodes. The optimum contents of piezoelectric BaTiO₃ nanoparticles inside the carbon nanotube/ecoflex composite were selected as 30 wt% considering the trade-off between stretchability and energy harvesting performance of the device. The final S-PEH shows an output voltage and mechanical stability of ~5 V and ~3,000 cycles under repeated 150% of tensile strain, respectively. This work presents a cost-effective and scalable way to fabricate stretchable piezoelectric devices for self-powered wearable electronic systems.

The templated grain growth (TGG) method has gained significant attention for its ability to produce highly textured piezoelectric ceramics with significantly enhanced performance, making it a promising method for transducer and actuator applications. However, the texturing process using the TGG method requires the optimization of multiple steps, which can be challenging for beginners in this field. Therefore, in this tutorial, we provide an overview of the TGG method mainly based on our previous published works, including its various processing steps such as synthesizing anisotropic-shaped templates with size and size distribution control using the molten salt synthesis technique, tape casting, and identifying key factors for proper alignment of the templates in the target matrix system. Our goal is to provide a resource that can serve as a basic reference for researchers and engineers looking to improve their understanding and utilization of the TGG method for producing textured piezoelectric ceramics.

La_0.7-xCe_xSr_0.3MnO₃ specimens were fabricated by a solid state reaction method and structural and electrical properties with variation of Ce4+ contents were measured. All specimens exhibited a polycrystalline rhombohedral crystal structure, and the (110) peaks were shifted to low angle side with increasing the amount of Ce⁴⁺ contents. As Ce⁴⁺ ions with different ion radii and charges are substituted with La³⁺ ions, electrical properties are thought to be affected by changes in the double exchange interaction between Mn³⁺-Mn⁴⁺ ions due to distortion of the unit lattice, a decrease in oxygen vacancy concentration, and an increase in lattice defects. Resistivity gradually decrease as the amount of Ce⁴⁺ added increased, and negative temperature coefficient of resistance (NTCR) properties were shown in all specimens. In the La_0.5Ce_0.2Sr_0.3MnO₃ specimens, electrical resistivity, TCR and B-value were 31.8 Ω-cm, 0.55%/℃ and 605 K, respectively.

Triboelectric devices are attracting attention from researchers as self-powered electronic systems that can instantly convert mechanical input into electrical energy output. To improve triboelectric energy harvesting performance, increasing the number of contacts as well as the contact area has been carried out by numerous researchers. In this study, we design a shaker-type energy harvester which is called as maracas triboelectric generator (M-TEG), inspired by the structure of maracas, one of the musical percussion instruments. A tripod frame is inserted to the inside of a cylindrical case, which is a device with the electrodes of aluminum and copper. Then, the triboelectric energy harvesting characteristics between polypropylene (PP) balls and the electrodes are measured. The M-TEG with the frame generates the energy harvesting signals up to ~100 V and ~2.5 μA due to larger contact area and numbers, which enhances the voltage and current output by 250% and 610% compared to that without the frame, respectively. This study presents the feasibility of self-powered sensors and toys using improved triboelectric energy performance with a low-cost and simple manufacturing process in the interesting structure.

Integrating dielectric materials into LTCC is a convenient method to increase the integration density in electronic circuits. To enable co-firing of the high-k and low-k dielectric LTCC materials in a multi-material hetero-laminate, the shrinkage characteristics of both materials should be similar. Moreover, thermal expansion mismatch between materials during co-firing should be minimized. The alternating stacking of an LTCC with silica filler and that with calcium-zirconate filler was observed to examine the use of the same glass in different LTCCs to minimize the difference in shrinkage and thermal expansion coefficient. For the LTCC of silica filler with a low dielectric constant and that of calcium zirconate filler with a high dielectric constant, the amount of shrinkage was examined through a thermomechanical analysis, and the predicted appropriate fraction of each filler was applied to green sheets by tape casting. The green sheets of different fillers were alternatingly laminated to the thickness of 500 ㎛. As a result of examining the junction, it was observed through SEM that a complete bonding was achieved by constrained sintering in the structure of ‘calcium zirconate 50 vol%-silica 30 vol%-calcium zirconate 50 vol%’.