Search Results (1,132)

In this study, a method for introducing titanium dioxide nanoparticles (TiO₂NPs) into the polymer matrix of a ferroelectric copolymer of vinylidene fluoride with tetrafluoroethylene P(VDF-TFE) is proposed and optimized. A comprehensive analysis showed that TiO₂NPs content has a significant effect on the structure formation processes in the polymer matrix, the degree of crystallinity, phase composition, and surface morphology of the composites. By optimizing the amount of doped nanoparticles, it is possible to increase the electrical strength and permittivity of the material, as well as enhance the piezoelectric response compared to a film without TiO₂NPs. The introduction of TiO₂NPs into the P(VDF/TFE) polymer matrix promotes efficient polarization of the composite film without preliminary high-temperature orientational drawing. The approaches presented in this study can simplify process operations in the manufacture of flexible sensors, wearable electronics, and other devices that require a combination of piezoelectric activity and high electrical strength. Full article

Acoustic emission (AE) monitoring has been widely employed for condition assessment of mechanical seals. However, the physical origin of high-frequency AE activity under elastohydrodynamic lubrication (EHL) conditions remains insufficiently understood. To address this, a physics-based forward-modelling framework is developed by integrating transient EHL analysis, dynamic interfacial load mapping, and piezoelectric signal transduction. The simulated AE responses are compared with experimental measurements acquired from a GM150 sensor under both normal and defect operating conditions. The results indicate that dynamic oil-film pressure fluctuations provide a physically plausible excitation mechanism for high-frequency AE activity under EHL conditions. The present study provides a mechanistic relationship between lubrication behavior and AE responses, providing a physics-based foundation for the interpretation of AE signals and condition monitoring of lubricated mechanical seal systems. Full article

Acoustic emission (AE) sensing is widely used for structural health monitoring, but conventional piezoelectric sensors can be constrained in high-temperature and radiation environments. This study evaluates whether an Idaho National Laboratory-developed magnetostrictive AE sensor retains sufficient information for automated impact-source classification under a controlled room-temperature configuration. A total of 334 synchronized acquisitions from six impact classes were recorded at 20 MHz using three fixed, non-coincident sensor channels. Because sensor type was not independently varied from position, mounting, coupling, bandwidth, or propagation path, comparisons represent complete sensor-channel responses rather than isolated transduction mechanisms. Each waveform was represented by 16 time-domain, spectral, and band-power features. Random forest classifiers were evaluated for individual channels, 48-feature fusion, and equal-vote decision fusion using 30 repeated stratified holdout runs and stratified 10-fold cross-validation. The magnetostrictive channel achieved 95.35 ± 2.45% mean holdout accuracy, compared with 92.37 ± 2.94% and 96.31 ± 1.98% for the two commercial channels. Feature-level fusion achieved 97.12 ± 2.19% and 97.91 ± 3.18% under holdout and 10-fold cross-validation, respectively. Because class-specific blocks were split at the event level, these accuracies are within-campaign and within-specimen, may be optimistic, and do not establish block-independent or operational generalization; validation using randomized or interleaved repeated blocks, multiple specimens, position-controlled comparisons with swapped, rotated, or co-located sensor placements, and harsh-environment testing remains necessary. Full article

By introducing BaTiO₃ into conventional hydroxyapatite (HA) bioactive ceramic coatings, a novel HA/BaTiO₃ piezoelectric-hydrophilic bioactive ceramic coating was developed. In this research, four groups of composite coatings with BaTiO₃ contents of 0, 10, 20, and 30 wt.% were comparatively fabricated and investigated, which in situ constructs a bioelectric microenvironment on the titanium surface. This strategy achieves the effective integration of electrical stimulation with bioactive ceramic coatings, resulting in a piezoelectric-hydrophilic bioactive ceramic layer that mimics biomineralization-driven osteogenesis. Experimental results demonstrate that, through laser cladding, BaTiO₃ particles can be embedded within the piezoelectric-hydrophilic bioactive ceramic coating, endowing the coating with mechano-electrical conversion functionality. Microdomain piezoelectric responses were successfully generated on the coating surface, and based on the maximum local piezoelectric response, the optimal BaTiO₃ content was determined to be 20 wt.%, yielding a microdomain piezoelectric coefficient of 712.6 pm/V. Furthermore, the piezoelectric-hydrophilic bioactive ceramic coating exhibits excellent bioactivity. Electrostatic interactions between piezoelectric charges and inorganic ions in physiological fluids facilitate the adsorption of calcium and phosphorus salts onto the coating surface, thereby enhancing surface hydrophilicity. This promotes the infiltration of inorganic ions and water molecules at the material interface, which in turn strengthens bioactivity, accelerates bone integration, and expedites the establishment of a robust osseointegration interface between joint prostheses and host bone. Full article

This study reports the development of an intelligent dual-layer wound dressing engineered to achieve active wound repair. The self-standing dressing integrates a polyvinylidene fluoride (PVDF) piezoelectric electrospun membrane with a multifunctional hydrogel based on interfacial fusion. The PVDF layer converted mechanical energy derived from human body movement into electrical stimulation, which dramatically motivated the controlled release of diclofenac sodium (DFs) encapsulated in the hydrogel. The relatively small diameter fibers and network caused strong connection with the hydrogel and smooth transfer of electricity. When a positive potential of 1.5 V was applied, up to a 55 μg mL⁻¹ cumulative amount of DFs was released, about five times higher than that only based on drug diffusion. This enhanced release rate resulted from the cooperation of accelerated drug migration under electrically driven and dynamic changes of the gel’s microstructure, which was the result of reversible behavior of borate bonds within the hydrogel. Consequently, the hydrogel exhibited self-healing properties and a tensile strain of up to 600%, much higher than that of conventional hydrogels. Under mechanical motivation, the dressing exhibited enhanced DFs release ability, confirming the piezoelectric transition and controlled drug release abilities. Therefore, the present work offers an innovative solution for the intelligent management of chronic wounds. Full article

Distal-less homeobox 1 (DLX1) has emerged as a promising urinary biomarker for prostate cancer. This study developed a label-free piezoelectric acoustic biosensor for selective DLX1 detection using a quartz crystal microbalance (QCM). The QCM gold electrode was sequentially functionalized with L-cysteine, graphene oxide (GO), and an amine-terminated DLX1 capture probe covalently immobilized through EDC–NHS-mediated amide bond formation. Stepwise surface functionalization was characterized by X-ray photoelectron spectroscopy (XPS), supported by contact angle measurements, X-ray diffraction, and field-emission scanning electron microscopy. XPS provided multi-element evidence for Au–S thiolate formation, GO deposition, amide coupling, probe immobilization, and Watson–Crick hybridization with the synthetic DLX1 target. Under optimized conditions, the biosensor exhibited a linear response to DLX1 concentrations and achieved a limit of detection of 81.19 nM. Non-complementary sequences, including PCA3 and SARS-CoV-2, produced frequency shifts below 9 Hz, confirming high selectivity. Comparative experiments showed that GO-mediated covalent immobilization was essential for reliable detection, whereas direct DNA attachment to bare Au generated anomalous positive frequency shifts, which were attributed to weak physisorption. The proposed platform offers a sensitive and selective strategy for quantitative DLX1 detection and may support future point-of-care nucleic acid diagnostics. Full article

Burns injuries present critical health and care challenges and remain one of the leading causes of preventable morbidity globally. The pathophysiology of burns injuries combines barrier disruption, dysregulated inflammation and biofilm-driven polymicrobial infection. Zinc oxide nanoparticles (ZnO NP) offer unique, multi-functional capabilities of broad-spectrum antimicrobial, pro-regenerative zinc (II) ion sources and an intrinsic transducer that is piezoelectric, photoresponsive and pH-responsive. This paper presents a comprehensive review of ZnO NP for the treatment of skin burns injuries with a focus on its multifunctional nanotherapeutic and sensor-integrated platforms. A structured literature search of PubMed, Scopus, Web of Science, Embase and IEEE Xplore covering the period 2015 to 2025 was conducted to identify and consolidate relevant pre-clinical and clinical evidence on ZnO-based and sensor-integrated burn wound platforms. From the survey across hydrogels, electrospun nanofibers, films, sprays, and three-dimensional bio-printed constructs, it is established that ZnO formulations achieve 60–95% wound closure by day 14 versus 30–55% for untreated controls, with 3–7 log10 colony-forming-unit reductions and minimum inhibitory concentrations of 8–256 micrograms per millilitre against multidrug-resistant pathogens. Wound healing is driven by sustained Zn²⁺ release, reactive-oxygen-species-mediated bactericidal action, matrix-metalloproteinase-9 modulation, vascular-endothelial-growth-factor and hypoxia-inducible-factor-1-alpha angiogenesis, and nuclear-factor-kappa-B suppressed inflammation. Emerging closed-loop sensor-integrated dressings deliver real-time wound pH, temperature, and matrix-metalloproteinase-9 readout coupled to near-field-communication actuated on-demand zinc release. Clinical translation is affected by several factors such as dose-dependent cytotoxicity associated with excessive ROS generation or dissolution, limited standardisation of green-synthesis methodologies, batch-to-batch variability in nanoparticle physicochemical properties and limited clinical trial data. ZnO-based theranostic platforms hold practical clinical translation potentials provided reproducible GMP-scale synthesis, long-term biocompatibility validation and comprehensive regulatory classification is systematically addressed. Full article

This work investigates the development of multifunctional bioceramic composites based on hydroxyapatite reinforced with the lead-free piezoelectric phase sodium potassium niobate, Na_0.5K_0.5NbO₃. Hydroxyapatite powder was synthesized by aqueous precipitation and combined with sodium potassium niobate synthesized by solid-state reaction to produce bulk ceramics containing 0, 10, 20, and 30 wt.% sodium potassium niobate, consolidated by conventional sintering. The materials were characterized in terms of density, linear shrinkage, phase composition, microstructure, elemental composition, flexural strength, and antibacterial response. X-ray diffraction analysis confirmed the coexistence of hydroxyapatite and orthorhombic sodium potassium niobate, with the intensity of sodium potassium niobate-related reflections increasing with its content, together with minor secondary phases. Scanning electron microscopy revealed the progressive incorporation of sodium potassium niobate grains into the hydroxyapatite matrix and showed a strong dependence of porosity on sodium potassium niobate content. Flexural tests showed that intermediate sodium potassium niobate additions improved strength compared with monolithic hydroxyapatite, whereas highly porous compositions exhibited reduced mechanical performance. Agar-diffusion tests against representative Gram-positive and Gram-negative strains showed measurable inhibition zones, although the differences between pure hydroxyapatite and composites containing sodium potassium niobate were limited and species-dependent. Slight increases were observed for P. aeruginosa and S. aureus, whereas no appreciable changes were detected for the other strains. Therefore, these findings should be regarded as preliminary evidence of antibacterial response rather than as confirmation of an intrinsic antibacterial effect of sodium potassium niobate. Overall, the structural and mechanical results indicate that hydroxyapatite/sodium potassium niobate composites are promising lead-free candidates for the development of multifunctional bioceramics, while their antibacterial response requires further validation. Full article

Two-dimensional (2D) organic–inorganic hybrid perovskites exhibit coupled ionic, electronic, and electromechanical responses that can strongly influence local charge transport. Here, solution-processed mixed-halide butylammonium lead perovskite crystals were mechanically exfoliated and investigated using X-ray diffraction, atomic force microscopy, piezoresponse force microscopy (PFM), and conductive atomic force microscopy (c-AFM). PFM measurements under −5, 0, and +5 V revealed clear bias-dependent changes in amplitude and phase, indicating an electric field-sensitive local electromechanical response. Local c-AFM measurements showed nonlinear bipolar hysteresis, with a pronounced increase in current near +7–8 V and a decrease near −7 to −6 V during the subsequent negative sweep. Because the crystals are mixed ionic–electronic conductors and the nanoscale tip–sample junction introduces substantial injection and contact barriers, the observed behavior is interpreted as resistive switching-like conductivity modulation, rather than definitive ferroelectric switching. The results are consistent with the combined contributions of charge injection, trap filling, possible ionic redistribution, and piezoelectricity-associated modulation of the local transport barrier. These findings provide nanoscale insight into electric field-dependent electromechanical and out-of-plane conductive behaviors in layered 2D hybrid perovskites. Full article

Piezoelectric unimorph actuators are promising candidates for precision actuation systems in small satellites, where their electromechanical performance must remain predictable under vacuum and temperature variations. However, actuator performance is determined not only by the piezoelectric material but also by the passive layer and bonding interface, whose combined influence under thermal-vacuum conditions requires systematic evaluation. This study presents a numerical and experimental investigation of the temperature-dependent electromechanical characteristics of piezoelectric unimorph actuators incorporating PIC 181 piezoceramic plates, passive layers made of 7075-T6 aluminum or Ti-6Al-4V titanium, and three different vacuum-compatible bonding materials. Numerical analyses were performed to determine modal, impedance–frequency, and displacement–frequency characteristics over the temperature range of 253.15–323.15 K, while experimental investigations under vacuum conditions quantified the additional influence of the bonding interface. Increasing temperature caused a decrease in resonance frequency for both passive-layer configurations. Actuators with Ti-6Al-4V passive layers generally exhibited higher resonance frequencies, lower impedance values, and larger displacement amplitudes than those with 7075-T6 aluminum passive layers. The maximum measured displacement amplitudes reached 23.11 µm for the aluminum-based actuator and 29.67 µm for the titanium-based actuator at 323.15 K. Among the investigated bonding materials, BM No. 3 consistently provided the lowest impedance and highest displacement response. The results demonstrate that passive-layer and bonding-material selection should be considered jointly and identify the Ti-6Al-4V/BM No. 3 combination as the most favorable among the investigated configurations for resonant piezoelectric unimorph actuation under the tested thermal-vacuum conditions. Full article

Harsh-environment pressure sensing requires piezoelectric materials that can simultaneously withstand elevated temperature, mechanical loading, and structural degradation. GaN is a promising lead-free piezoelectric semiconductor owing to its wide bandgap, high thermal stability, and non-centrosymmetric wurtzite structure. However, its piezoelectric output can be significantly affected by free-carrier compensation in unintentionally n-type GaN. Here, we report a flexible all-inorganic piezoelectric pressure sensor based on a directly grown h-BN/GaN heterostructure thin film. The h-BN layer was deposited on GaN/Si by plasma-enhanced chemical vapor deposition, followed by backside Si removal, electrode deposition, and transfer onto a flexible Cu foil substrate. Structural characterizations confirmed the formation of a compact h-BN/GaN interface with clear lattice fringes, preferential out-of-plane orientation, and characteristic Raman signatures of both h-BN and GaN. Compared with the flexible GaN/Cu reference, the h-BN/GaN device exhibits modified interfacial electrical transport behavior, enhanced voltage and current-density outputs, and prolonged transient voltage retention. Finite-element simulations reveal modified electrostatic potential distribution after h-BN integration, while electrical and interfacial characterizations suggest electronic structure modulation and reduced carrier compensation effects at the heterointerface. Raman optothermal analysis indicates an improved relative/local thermal response of the h-BN/GaN device under identical optical excitation conditions, supporting its enhanced thermal robustness. Under 200 psi at 400 °C, the h-BN/GaN sensor maintains an output voltage of approximately 27.65 mV, about 2.32 times that of the GaN reference. This work demonstrates an interfacial engineering strategy based on two-dimensional h-BN integration for constructing flexible, thermally robust, and high-output piezoelectric sensors for harsh-environment monitoring. Full article

Currently, acoustic sensing technology is widely applied in military defense, non-destructive testing (NDT), and biomedical imaging, and it is increasingly penetrating various aspects of daily life. However, traditional piezoelectric acoustic sensors are highly susceptible to performance degradation when operated in harsh environments. In contrast, optical microcavities-a class of optical resonant cavities with characteristic dimensions on the micrometer scale—offer distinct advantages, including compact footprints, immunity to electromagnetic interference (EMI), and ultra-high sensitivity. Leveraging these exceptional properties, researchers have extensively explored acoustic sensing technologies based on optical microcavity platforms. This paper reviews recent research progress in optical microcavity-based acoustic sensing, categorized by the structural configurations of the microcavities. First, we introduce the key performance specifications of different optical microcavities in acoustic sensing, such as sensitivity and frequency response bandwidth. Second, we categorically discuss the structural designs of various optical microcavities alongside corresponding optimization methods to improve sensing performance. Finally, we summarize the current applications of optical microcavity-based acoustic sensing across multiple fields and outline future development trends in this research area. Full article

Structural health monitoring (SHM) based on ultrasonic-guided waves has been widely investigated for aerospace, transportation, marine engineering, petrochemical equipment and large-scale civil infrastructure. As the core component for guided-wave excitation and signal reception, the transducer directly affects electromechanical conversion efficiency, modal selectivity and service stability. Interdigital transducers (IDTs) are characterized by a lightweight structure, designable wavelength, tunable operating frequency and good array compatibility, and therefore show considerable potential for curved structures, composite components and large-area online monitoring. The periodically repeated interdigital electrode pattern represents a basic form of structural symmetry in IDTs, providing the geometric basis for wavelength matching and frequency-selective response, while substrate properties govern the electromechanical conversion efficiency and stability of the device. This review focuses on the research progress of substrate materials for flexible IDTs. The material characteristics and application status of inorganic piezoelectric materials, piezoelectric polymers, piezoelectric composites and heterogeneous integrated substrates are summarized. The differences among typical substrate systems are compared in terms of electromechanical coupling, flexible conformability, thermal stability, acoustic loss and integration process. Recent applications of IDTs in guided-wave damage detection, flexible sensing, high-temperature monitoring and on-chip acoustic devices are also discussed. The main challenges and future directions of IDT substrate materials are analyzed to provide guidance for material selection, device design and SHM applications. Full article

The piezocatalytic activity of metal–organic frameworks (MOFs) is generally hampered by an insufficient intrinsic piezoelectric response, which largely restricts their application in energy catalytic conversion. Herein, MIL-125-NH₂(Ti) (denoted NM) was chosen as a prototypical model to demonstrate that defect engineering serves as an efficient strategy to simultaneously reinforce the piezoelectric characteristics and piezocatalytic hydrogen evolution performance of MOFs. Multiple comprehensive characterizations verify that thermally treated NM-250 (NM thermally treated at 250 °C under flowing N₂ atmosphere) contains abundant in situ-generated oxygen vacancies. These defects disrupt the high intrinsic structural symmetry of pristine NM and promote the establishment of polarized electric fields upon mechanical excitation. Electrochemical measurements further reveal that the introduced oxygen vacancies effectively suppress charge carrier recombination and accelerate interfacial charge transfer, thereby facilitating the piezocatalytic hydrogen evolution reaction. Benefiting from the optimized piezoelectric polarization and improved charge separation efficiency, NM-250 delivers a piezocatalytic H₂ production rate of 413.5 μmol g⁻¹ h⁻¹, exceeding the value of pristine NM (180.9 μmol g⁻¹ h⁻¹) by 2.28 times. This work elucidates the underlying mechanism by which oxygen vacancy defects modulate piezoelectric polarization and catalytic kinetics and validates defect engineering as a promising route to construct high-performance MOFs-based piezocatalysts. Full article

There is an increasing demand for ultrasound imaging technologies, particularly wearable and portable systems, for continuous physiological monitoring applications. Although some recent flexible ultrasound devices have adopted polymer encapsulations, typical rigid transducer designs still include metal housings and costly electrodes, contributing to increased device weight and fabrication cost. To address these limitations, we developed an aluminum-electrode/3D-printed polymer-housing ultrasound transducer (APUT) utilizing a polyvinylidene fluoride piezoelectric film. Compared to a gold-electrode/metal-housing ultrasound transducer, the APUT material costs and total weight were approximately 66% and 86% lower, respectively. Acoustic evaluation revealed a center frequency of 24.5 MHz and a fractional bandwidth of 60.9%, with axial and lateral resolutions of 51 and 152 μm, respectively. Furthermore, during a 3-h pulsed operation test, the APUT exhibited an initial increase in capacitance followed by a relatively stable response, with no progressive surface-temperature increase detected within the accuracy of the measurement method. Finally, successful ex vivo imaging of chicken breast tissue confirms the APUT’s biomedical applicability, highlighting its potential as a wearable, portable, and disposable ultrasound platform. Full article