Flexible materials with high electromechanical coupling performance are highly demanded for wide applications for electromechanical sensors and transducers, including mechanical energy harvesters. ...Here, outstanding electromechanical performance is obtained in electrospun‐aligned polyvinylidene fluoride (PVDF) fiber film. A theoretical model is developed from systematic theoretical analyses to clarify the underlying constructive piezoelectric‐triboelectric mechanism in the polarized PVDF fiber films that explains the experimental observations well. The electrospinning process induces polarization alignment and thus tunes the electron affinity for PVDF fibers with different polarization terminals, which results in the constructive piezoelectric and triboelectric responses in the obtained PVDF fiber films. Extremely large effective piezoelectric performance properties are achieved in the direct piezoelectric measurements, reaching the maximum effective piezoelectric strain and voltage coefficients of −1065 pm V−1 and −9178 V mm N−1, respectively, at 100 Hz. In the converse piezoelectric measurements without a significant contribution from reversible triboelectric effect, the maximum effective piezoelectric strain and voltage coefficients are −166 pm V−1 and −1499 V mm N−1, respectively. The theoretical analyses and experimental results show the great potential of the electrospun aligned polar PVDF fiber material for various electromechanical device applications, particularly for mechanical energy harvesting.
Outstanding electromechanical conversion performance is achieved through constructive piezoelectric and triboelectric effects in aligned electrospun polyvinylidene fluoride (PVDF) fibers. A theoretical model is developed from systematic theoretical analyses to clarify the constructive piezoelectric‐triboelectric mechanism and explain the giant electric output in response to vibration in the polarized PVDF fiber material. Showing great potential for mechanical energy harvesting applications.
Shear mode guided waves are highly demanded for underwater structural health monitoring (SHM) applications due to their simplified non‐dispersive feature and minimal acoustic energy loss in the ...presence of liquid. Excitation and detection of pure shear wave are challenging using conventional piezoelectric materials used in the current ultrasonic transducers because they have complex piezoelectric responses mixed with multiple longitudinal, transverse, and shear modes. They also suffer from aging issue due to depoling. Here, conformable shear mode ultrasonic transducers are designed and made of flexible piezoelectric poly (L‐lactic acid) (PLLA) fibers on both flat and tubular structures. The electromechanical responses over a macroscopic area of the transducers are evaluated in a wide frequency range up to 500 kHz. The PLLA fiber‐based shear mode ultrasonic transducers exhibit a consistent sensitivity of detecting defects in liquid and air. In addition, the only shear mode in PLLA fibers originates from crystal structure without requiring electrical poling to render piezoelectricity, thus does not depole due to aging. The theoretical analyses including ab initio calculations and experimental results on both flat and tubular structures show the great potential of PLLA material and significant advantage of PLLA fiber‐based shear mode ultrasonic transducers for underwater SHM applications.
Pure shear mode and conformable ultrasonic transducers are designed and produced from flexible piezoelectric poly (L‐lactic acid) (PLLA) fibers with molecular chain orientation. The PLLA‐fiber transducers exhibit unique directivity for non‐dispersive shear wave, and no substantial change in the ultrasonic signals for operation in water. The theoretical analysis and experimental demonstration show great value for underwater ultrasonic structural health monitoring applications.
Background
The recently developed Caries Impacts and Experiences Questionnaire for Children (CARIES‐QC) is originally an English questionnaire targeting the assessment of caries‐related quality of ...life from a child's point of view.
Aim
This study aimed to translate and adapt the CARIES‐QC into the Arabic language and to test its reliability and validity on Arabic‐speaking children.
Design
A total of 234 children aged 5–16 years answered the translated questionnaire. Internal consistency was measured using Cronbach's alpha; 62 children answered the questionnaire again to evaluate the test‐retest reliability by calculating the intraclass correlation coefficient (ICC). Convergent validity was evaluated by correlating question scores with global question scores. Confirmatory factor analysis (CFA) was conducted to evaluate cross‐cultural validity.
Results
Cronbach's alpha of the CARIES‐QC/A was 0.905. The inter‐item correlation coefficients of the CARIES‐QC/A ranged from 0.240 to 0.850. The total ICC score was 0.960. CFA demonstrated acceptable fit to the data in the one‐factor model. Convergent validity indicated moderate correlation with the global question (rs = .740).
Conclusion
The CARIES‐QC/A is a valid and reliable tool that could be used to evaluate oral health–related quality of life in Arabic‐speaking children.
During the novel COVID-19 pandemic, many universities adopted distance and hybrid learning as a modification to their teaching methods to ensure continuity of education, abiding by the worldwide ...recommendations of social distancing.
To compare learning environments created through hybrid learning versus distance learning, to deliver paediatric dentistry course, and to assess the correlation between the created learning environment and students' satisfaction.
In this cross-sectional study, students enrolled in a hybrid paediatric dentistry course were asked to participate in an electronic survey. The learning environment was assessed using Distance Educational Learning Environment Survey (DELES), students' satisfaction was assessed using Satisfaction Scale (SS). Retrospective data for distance learning course was used for comparison. Ordinal data were compared using Mann-Whitney U test. Spearman's rank order correlation coefficient was used to correlate students' satisfaction with DELES. Multiple regression analysis was used to predict satisfaction.
A total of 376 students' data were considered in the study. Hybrid learning had significantly higher scores than distance learning in 3 DELES scales. There was a statistically significant weak positive correlation between satisfaction and DELES. Multiple regression analysis model was statistically significant and accounted for (22.8%) of the variance in students' satisfaction. Only "Instructor support" (p = 0.001) and "Student autonomy" (p < 0.001) had a significant effect on satisfaction.
This study supports the superiority of a hybrid learning environment over a complete distance learning environment, it also shows that satisfaction is correlated and can be predicted by the created learning environment.
This study has been registered on clinicaltrials.gov on 21 May 2020 with an identifier: NCT04401371 .
Two-dimensional (2D) organic-inorganic hybrid perovskites have attracted intense interests due to their quantum well structure and tunable excitonic properties. As an alternative to the well-studied ...divalent metal hybrid perovskite based on Pb
, Sn
and Cu
, the trivalent metal-based (eg. Sb
with ns2 outer-shell electronic configuration) hybrid perovskite with the A
M
X
formula (A = monovalent cations, M = trivalent metal, X = halide) offer intriguing possibilities for engineering ferroic properties. Here, we synthesized 2D ferroelectric hybrid perovskite (TMA)
Sb
Cl
with measurable in-plane and out-of-plane polarization. Interestingly, (TMA)
Sb
Cl
can be intercalated with FeCl
ions to form a ferroelastic and piezoelectric single crystal, (TMA)
-Fe(iii)Cl
-Sb
Cl
. Density functional theory calculations were carried out to investigate the unusual mechanism of ferroelectric-ferroelastic crossover in these crystals.
Distributed intelligence involving a large number of smart sensors and edge computing are highly demanded under the backdrop of increasing cyber‐physical interactive applications including internet ...of things. Here, the progresses on ferroelectric materials and their enabled devices promising energy autonomous sensors and smart systems are reviewed, starting with an analysis on the basic characteristics of ferroelectrics, including high dielectric permittivity, switchable spontaneous polarization, piezoelectric, pyroelectric, and bulk photovoltaic effects. As sensors, ferroelectrics can directly convert the stimuli to signals without requiring external power supply in principle. As energy transducers, ferroelectrics can harvest multiple forms of energy with high reliability and durability. As capacitors, ferroelectrics can directly store electrical charges with high power and ability of pulse‐mode signal generation. Nonvolatile memories derived from ferroelectrics are able to realize digital processors and systems with ultralow power consumption, sustainable operation with intermittent power supply, and neuromorphic computing. An emphasis is made on the utilization of the multiple extraordinary functionalities of ferroelectrics to enable material‐critical device innovations. The ferroelectric characteristics and synergistic functionality combinations are invaluable for realizing distributed sensors and smart systems with energy autonomy.
Ferroelectric materials possess extraordinary multiple signal or energy conversion and storage functions, including high dielectric permittivity, switchable spontaneous polarization, piezoelectric, pyroelectric, and bulk photovoltaic effects. The characteristics of ferroelectrics, and the synergized combinations of their multiple functionalities are invaluable for realizing distributed wireless sensors and smart systems with energy autonomy.
Shear mode‐guided ultrasonic waves are highly regarded for submerged or subterranean structural health monitoring (SHM), owing to their non‐dispersive feature and minimized acoustic energy loss when ...in contact with liquid or solid. High‐performance shear mode ceramic ultrasonic transducers with robustness and cost‐effectiveness are highly demanded for underwater or underground SHM applications, especially in harsh environments. However, the implementation of discrete shear mode piezoelectric ceramic ultrasonic transducers is hindered by the inconsistency with manual installation, lack of conformability on curved surfaces, and unreliable acoustic coupling between the transducers and the structure. Here, direct‐write conformable shear mode ultrasonic transducers made from piezoelectric lead‐free ceramic coatings, which are in situ produced on steel structures by a scalable thermal spray process, are proposed. The obtained lead‐free lithium‐doped potassium sodium niobate (KNN‐LN) ceramic coatings exhibit a high effective shear piezoelectric strain coefficient (d24, f) above 60 pm V−1 in a broad frequency range from 100 Hz to 200 kHz. The resulting conformable shear mode KNN‐LN ceramic coating transducers successfully showcase the functions of exciting and detecting stable shear mode ultrasonic wave signals with operation temperature exceeding 200 °C and demonstrate reliable capability in defect detection in both air and liquid environments.
Direct‐write conformable shear mode ultrasonic transducers are designed and produced from lead‐free piezoelectric potassium sodium niobate (KNN) ceramic coatings. These coating transducers ensure consistent, non‐dispersive shear wave transmission and stable ultrasonic signals across various temperatures and underwater conditions. Such reliability and robustness highlight their potential for monitoring the health of submerged or subterranean structures, especially in harsh environments.
Flexible and lightweight pressure sensors have attracted tremendous attention as a promising component of wearable biological motion sensors and artificial electronic skins. Here, the ...electromechanical response of as‐electrospun fiber mats composed of a commodity polymer, atactic polystyrene, which can be applied in low‐cost/large‐area, flexible, and lightweight pressure sensors is demonstrated. The fiber mat demonstrates a significantly high apparent converse piezoelectric constant of >30 000 pm V−1 under static measurement and ≈13 000 pm V−1 even at a high frequency of 1 kHz. The first theoretical model to explain the unique electromechanical response is constructed, which reveals that the softness and moderate charge of the fiber mat are the reasons for the significantly high electromechanical response. Further, apparent piezoelectric constants obtained by direct measurement are lower than those obtained by the converse measurement, which is attributed to the densification and hardening of the fiber mat due to prepressure applied in direct measurement. These findings are likely to serve as a milestone for the development of large‐area, flexible, and lightweight pressure sensors at low cost, as well as highly movable actuators like optical modulators without a substantial mechanical load.
A large electromechanical response of as‐electrospun fiber mats composed of a commodity polymer, atactic polystyrene, is demonstrated. The fiber mat apparently shows a high effective converse piezoelectric constant of >30 000 pm V−1 under static measurement conditions and ≈13 000 pm V−1 at 1 kHz. A theoretical model is constructed to explain the significant effective electromechanical response.
Hybrid organo-metal halide perovskites (OMHPs) have been extensively explored for photo or photo-enhanced applications, which are time, location or light-limited. Unlike in other works, herein, ...methylammonium lead iodide (MAPbI
3
) perovskite was employed as a small area (<1 cm
2
) stress-driven energy converter. Briefly, MAPbI
3
was infiltrated into a net-like composite scaffold, having three constituents; polyvinylidene fluoride (PVDF), polylactic acid (PLA) and tin dioxide (SnO
2
) electrospun nanofibres. A systematic vertical ultrasonic vibration was optimized and applied to each sample, followed by ice quenching. Addition of MAPbI
3
and vertical vibration altered the morphotropic phase nature of the composite towards desirable electroactive forms, without further poling, revealed by XRD, FTIR, and Raman studies. When the device was subjected to bending/compression-release forces, high output voltage of 4.82 V and current of 29.7 nA were obtained over an area of 0.0625 cm
2
. The champion device also registered high piezoelectric strain coefficients (
d
33
) of 123.93 pC N
−1
and 118.85 pC N
−1
(with and without a SnO
2
nanoparticle underlayer, respectively). We further elucidate the mechano-electrical outputs of MAPbI
3
devices grown on other distinctive underlayers. This work advances the drive towards all-day-all-night energy harvesting using OMHPs, the force being applied from ubiquitous motions or artificial movements.
Huge mechano-electrical performance obtained from net-like PVDF composites infiltrated with methylammonium lead iodide under vertical ultrasonic vibration, without additional poling.
This paper presents a method for measuring surface cracks based on the analysis of Rayleigh waves in the frequency domain. The Rayleigh waves were detected by a Rayleigh wave receiver array made of a ...piezoelectric polyvinylidene fluoride (PVDF) film and enhanced by a delay-and-sum algorithm. This method employs the determined reflection factors of Rayleigh waves scattered at a surface fatigue crack to calculate the crack depth. In the frequency domain, the inverse scattering problem is solved by comparing the reflection factor of the Rayleigh waves between the measured and the theoretical curves. The experimental measurement results quantitatively matched the simulated surface crack depths. The advantages of using the low-profile Rayleigh wave receiver array made of a PVDF film for detecting the incident and reflected Rayleigh waves were analyzed in contrast with those of a Rayleigh wave receiver using a laser vibrometer and a conventional lead zirconate titanate (PZT) array. It was found that the Rayleigh waves propagating across the Rayleigh wave receiver array made of the PVDF film had a lower attenuation rate of 0.15 dB/mm compared to that of 0.30 dB/mm of the PZT array. Multiple Rayleigh wave receiver arrays made of the PVDF film were applied for monitoring surface fatigue crack initiation and propagation at welded joints under cyclic mechanical loading. Cracks with a depth range of 0.36-0.94 mm were successfully monitored.
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