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The mechanic-electro coupling overlapping finite element method (OFEM) is proposed to improve the accuracy in solving the mechanical characteristics of piezoelectric structures. Based on the basic equations and boundary conditions of piezoelectric materials, overlapping triangle elements are used to discretize the solution domain of piezoelectric structures, and the displacement function and potential function of the mechanic-electro coupling OFEM are constructed through local interpolation. The control equation of the mechanic-electro coupling OFEM is derived using the variation principle. The accuracy and validity of this method are verified by comparing with the reference solution and analytical solution in patch test and piezoelectric patch bending test. The static characteristics of the cantilever-typed piezoelectric sensor model, the rectangular plate with one-sided piezoelectric patch configuration, and the hole-containing piezoelectric energy harvester model are analyzed. The mechanic-electro coupling OFEM has high engineering value and broad application prospects in analyzing the structural mechanical properties of intelligent piezoelectric components. [ABSTRACT FROM AUTHOR]

To facilitate unobtrusive and continuous sleep monitoring and promote intelligent sleep quality assessment, we present a dataset that includes multiple nights of continuous ballistocardiogram (BCG) data collected using piezoelectric film sensors from 32 subjects in their regular sleep environments. Besides, the referenced heart rate and respiratory data are also recorded by reference sensors to validate the accuracy of the cardiac and respiratory components extracted from the BCG signals. The dataset serves as a foundation for research on unobtrusive vital sign monitoring based on BCG signals, offering data support for the evaluation and optimization of sleep quality. [ABSTRACT FROM AUTHOR]

Curved shells are increasingly utilized in applied engineering due to their shared characteristics with other sandwich structures, flexibility, and attractive appearance. However, the inability of controlling and regulating vibrations and destroying them afterward is a challenge to scientists. In this paper, the curve shell equations and a linear quadratic regulator are adopted for the state feedback design to manage the structure vibrations in state space forms. A five-layer sandwich doubly curved micro-composite shell, comprising two piezoelectric layers for the sensor and actuator, is modeled by the fourth-order shear deformation theory. The core (honeycomb, truss, and corrugated) is analyzed for the bearing of transverse shear forces. The results show that the honeycomb core has a greater effect on the vibrations. When the parameters related to the core and the weight percentage of graphene increase, the frequency increases. The uniform distribution of graphene platelets results in the lowest natural frequency while the natural frequency increases. Furthermore, without taking into account the piezoelectric layers, the third-order shear deformation theory (TSDT) and fourth-order shear deformation theory (FOSDT) align closely. However, when the piezoelectric layers are incorporated, these two theories diverge significantly, with the frequencies in the FOSDT being lower than those in the TSDT. [ABSTRACT FROM AUTHOR]

In this work, the sound transmission loss (STL) of a simply supported doubly curved shallow aluminum shell covered by two layers of piezoelectric material, PZT-5H is presented. The study takes into account the presence of uncertain ambient temperature which is shown to significantly affect piezoelectric control of sound transmission. To derive the equations of motion, the assumed mode method combined with the first-order shear deformation theory and Hamilton's principles are employed. The modeling process incorporates the ambient temperature and thoroughly investigates its effects on STL, vibrational displacement, and piezoelectric voltage in terms of thermal strain, piezoelectric constants, and the pyroelectric coefficient uncertainties. Results show that uncertainty in environmental temperature significantly affects STL uncertainty up to 10% and vibrational displacement of the shell to the 15 times of its lowest value. The piezoelectric voltage also fluctuates with the variation in the temperature in a maximum range of 0.12–5.2 Volt. Further, the piezoelectric sensing voltage which accounts for the piezoelectric sensor thickness is observed to be highly sensitive to the temperature uncertainty with a maximum range of 0.65–7.6 Volt, causing depolarization and hysteresis nonlinearity. Thus, environmental temperature variation is considered as one of the main uncertain aspects for robust sound transmission controller. The proposed study provides an insightful investigation for robust piezoelectric control of STL in the presence of thermal uncertainty. [ABSTRACT FROM AUTHOR]

This paper addresses the traveling wave vibration control of rotating functionally graded material (FGM) conical shells via piezoelectric actuator and sensor pairs. Considering the circumferential initial stresses and Coriolis forces induced by rotation, as well as arbitrary boundary conditions, the electromechanically coupled governing equations of the rotating FGM conical shell with piezoelectric patches are established using the Lagrange equation. The model validation is carried out through a comparative analysis with existing literature. Base on the model, the linear–quadratic regulator controller is designed to suppress the traveling wave vibrations of rotating FGM conical shells considering the participation of multi-vibration modes in the dynamic responses. To evaluate the performance of the controller, free and forced vibrations of rotating FGM conical shells with different rotational speeds, material compositions and excitation positions are investigated in detail. Additionally, five typical piezoelectric sensors/actuators distributions are presented and the effects of piezoelectric patch layout on the control efficiency are discussed. [ABSTRACT FROM AUTHOR]

Manganese Mercury Thiocyanate Glycol MonoMethyl Ether (MMTCGMME) crystal is grown at room temperature by slow evaporation technique. The sample grown is confirmed by single crystal XRD and CHNSO analysis for elements. The single crystalline XRD of MMTCGMME crystal are 16.2052 Å, 7.2981 Å, and 13.5099 Å for a, b, c. The crystalline system is orthorhombic with space group as Pca21 which is the non-centrosymmetric type. The cut-off wavelength of MMTCGMME crystal is 206 nm is confirmed by absorbance spectrum. The bandgap value as 6 eV is confirmed by Tauc's plot for photonic use. The SEM morphological representation shows that there is no flaws and no defects in MMTCGMME. Phase matching provisioning of the MMTCGMME crystal material for particle size is observed that compared to KDP 1.845 times having higher second-order NLO coefficients than KDP. The MMTCGMME crystal has very low value of dielectric constant at higher frequencies and it is having higher dielectric constant value at lower frequency range is important for material and device fabrication The fluorescence analysis is reported with the emission at 489 nm for the excitation value of 250 nm of bluish green fluorescence emission. The piezoelectric coefficient is 5.2 pC/N for MMTCGMME. The red LED-based sensitivity is 8% at the room temperature of 28.9 °C. [ABSTRACT FROM AUTHOR]

The locked segment is critical for determining the stability of locked segment-type landslides. Research indicates that the volume expansion point marks the transition from the secondary creep stage to the tertiary creep stage in a landslide's evolution, and also separates the stable crack growth stage from the unstable crack growth stage in the locked segment. Identifying the volume expansion point is essential for early warning and predicting locked segment-type landslides. A series of instruments (resistance strain gauges, acoustic emission system, piezoelectric acceleration sensors, etc.) were used to conduct physical model tests of the landslide with retaining-wall-like locked segment under external load on the landslide's trailing edge. The evolution process of this landslide was analyzed through changes in slope shape and stress response characteristics. The experimental results reveal the failure mechanism of the landslide with retaining-wall-like locked segment: the upper part of the landslide thrusts and slides, the middle part squeezes and uplifts, the retaining-wall-like locked segment produces a locking effect, and compression-shear fracture of the retaining-wall-like locked segment leads to landslide failure. Based on the deformation and acoustic emission characteristics of the locked segment, a method for identifying the volume expansion point was established. This point was used as the onset of acceleration point in the inverse velocity method to predict the failure time of the locked segment-type landslides, incorporating the three-stage creep model and Fukumoto's theory. [ABSTRACT FROM AUTHOR]

Manganese mercury thiocyanate (MMTC), a nonlinear optical organometallic single-crystal material, was successfully grown by the Sankaranarayanan-Ramasamy (SR) method. The as-grown MMTC crystals were subjected to 50 shock pulses and designated as MMTC50S. The lattice parameters were measured by single-crystal x-ray diffraction (XRD) with values of a, b, and c of 11.3150 Å, 11.3150 Å, and 4.2720 Å with a tetragonal system for the pure MMTC, and values of 11.3180 Å, 11.3180 Å, and 4.2737 Å for MMTC50S, respectively. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups present in the MMTC50S crystal. Scanning electron microscopy (SEM) was used to assess the surface morphology, which revealed a pattern of minor defects and minor dislocations in the MMTC50S crystal in contrast to the pure form because of the shock pulses on the MMTC crystal to create the MMTC50S specimen. The UV-visible spectrum showed increased absorption for the MMTC50S crystal. Fluorescence (FL) studies revealed blue fluorescence emission for MMTC50S. Dielectric measurements were carried out and the dielectric constant was calculated for the grown sample. The piezoelectric coefficients and sensor response at room temperature were also determined for MMTC and MMTC50S. The maximum sensitivity for the MMTC50S with a red light-emitting diode (LED) was 8.88%, whereas the blue LED achieved 9% sensitivity. [ABSTRACT FROM AUTHOR]

Fabric-based composites with superior mechanical properties and excellent perceptive function are highly desirable. However, it remains a huge challenge to attain structure-function integration, especially for hybrid fabric composites. Herein, a skin-inspired interface modification strategy is proposed toward this target by constructing a hybrid smart fabric system consisting of two types of smart fabrics: carbon nanotube (CNT)/MXene-modified aramid fabrics and zinc oxide nanorod (ZnO NR)-modified carbon fabrics. Based on that, flexible piezoelectric pressure sensors with skin-like hierarchical perception interfaces are fabricated, which demonstrate superb sensitivity of 2.39 V·kPa-1 and are capable of various wearable monitoring tasks. Besides, the interface-modified hybrid fabric reinforced plastics can also be fabricated, which are proven to possess 13.6% higher tensile strength, 10.1% elastic modulus. More impressively, their average energy absorption can be improved by 111.9%, accompanied with inherent damage alert capability. This offers a paradigm to fabricate structure-function integrated hybrid smart fabric composites for the smart clothing and intelligent aerial vehicles. [ABSTRACT FROM AUTHOR]

The principal objective of this study is to apply the response surface methodology (RSM) to modeling and optimize the cutting-edge quality of three distinct types of PBs (Standard M60, Eucalyptus Bark EU, and fine-urea FU) under modified sawing conditions. The experimental work was conducted using a multi-function sawing machine equipped with a circular saw that was instrumented with a pair of piezo-electric sensors, a high-performance vector AC drive, and a current transducer. The edge-profile quality was assessed by an artificial innovative vision system able to extract a virtual profile, and from this, delamination criteria were developed by applying a fast Fourier transform (FFT). RSM was used to optimize the delamination criterion (Tw), specific cutting energy (Es), and feed per tooth (fz) as response variables when influenced by the factors feed speed (Vf) and frequency (N). The optimization process showed that PBs with fine-urea (FU) yielded the best edge-quality performing results with lower Tw delamination factor, however, with higher specific cutting energy (Es) when compared to particleboards composed of 60% recycled wood (M60) and Eucalyptus-based composition (EU). It can be explained by the fact that the special FU composition contributes to a greater blinding contact zone of particles resulting in better aggregation and superior cutting-edge quality. Correspondingly, the numerical optimization indicates that the delamination factor (Tw) is lower for FU (representing only 9.3% higher than the desirable value, DV) when compared with the desirable values of the particleboard M60 and EU. In addition to this aspect of the FU composition, the physical–mechanical properties also influence the edge quality; these aspects are considered the ones that most affect the Tw response parameter. The lowest Tw value was obtained for N = 50 Hz combined with a Vf = 9 m/min, indicating these particular machining conditions positively affect this response parameter. In conclusion, this study demonstrated that both the experimental and prediction results correlated well and highlighted that the use of the RSM is appropriate for edge quality analysis of the specific type of PB machining conditions and response parameters considered in this study. In addition, the suggested system based on an artificial vision technique for evaluating edge quality exhibited good capabilities for implementation in an industrial environment. [ABSTRACT FROM AUTHOR]

The multilayer composite film system was designed in this study. The multilayer composite film was constructed by alternating electrospinning of MXene doped with polyacrylonitrile (PAN) nanofilm and thermoplastic polyurethane (TPU) nanofilm as piezoelectric functional layer. After utilizing nanofilm material, the piezoelectric sensor was prepared and subsequently examined for its piezoelectric sensitivity, piezoelectric output, and mechanical characteristics. MXene/PAN/TPU multilayer composite films showed good piezoelectric output performance. The final experimental data showed that the piezoelectric sensor of the MXene/PAN/TPU-based system achieved 0.16 kPa−1 piezoelectric sensitivity, 150ms/140ms response time and recovery time, good output voltage and output current, and good output stability. In human biological motion detection, the generator produced a maximum output voltage of 30 V when pressed by the palm. Tests such as palm pressing, finger tapping, and footstomping demonstrated the potential of piezoelectric sensors in human energy harvesting and motion monitoring. Multilayer composite films had flexible mechanical properties and sensitive piezoelectric response and had broad application prospects in piezoelectric sensors and piezoelectric nanogenerators. [ABSTRACT FROM AUTHOR]

The goal of this research article is to investigate the effects of using two-dimensional functionally graded materials on the performance of piezoelectric sensors/actuators when subjected to simultaneous complex loading conditions. The considered disc-shaped sensors/actuators have nonuniform thicknesses and undergo asymmetric hygro-thermo-electro-mechanical loading. A power-law model is used to grade the materials radially, whereas the cosine function, which includes two independent parameters, describes the pattern along the circumferential direction. Comparing the results obtained by using the finite element method with those of one-dimensional graded structures leads to promising outcomes. For example, the radial displacement exhibits vital changes that varied between - 13 and 31 % . This is beneficial for such structures in terms of enhancing their sensing/actuating abilities. Also, the tangential stress can be reduced substantially by about 39.5 % through the proper selection of the corresponding material parameters. In addition, this reduction of the tangential stress has a positive effect on the von Mises stress that can be decreased by nearly 33 % . Accordingly, the structure would have improved durability and sustain higher loads. These findings would revolutionize the manufacturing of smart structures and enhance their behaviors under severe conditions. [ABSTRACT FROM AUTHOR]

The majority of the cell wall of a plant is composed of cellulose. Cellulose is an outstanding abundant, fibrous, and water-insoluble polymer on earth. The excellent hierarchical structure and semicrystalline nature of plant cellulose permit the easy isolation of nanofibers and nanocrystals through mechanically and chemically applied top-down destruction strategies. The cellulose molecules in nanocomposites can be separated into types such as bacterial nanocellulose (BNC), crystalline nanocellulose (CNC), and cellulose nanofibrils (CNF), which are biodegradable, environmentally friendly, and possess remarkably improved properties compared to conventional materials. Generally, they are deliberated as second-generation renewable resources, which assist as a superior replacement for petroleum-based materials. Research studies on nanocellulose are extensively accelerating due to petroleum-based materials issues like CO2 emissions, plastic based-pollution, and the absence of renewable energy. Research studies regarding these materials are interestingly increasing due to their outstanding properties such as biocompatibility, renewability, higher mechanical and lower density values, while sustainable production still associated with various challenges. Here, we comprehensively review the recent developments in nanocellulose production structural dimensions, properties, and applications, dedicated to drug delivery system, food industry, piezoelectric sensors, actuators, energy generators biosensing and bioimaging electronic devices. [ABSTRACT FROM AUTHOR]

Composite pressure vessels are seeing increasing demand in the oil and gas sector due to their excellent corrosion resistance. However, the assessment of the fatigue state of those structures still an open question. The goal of this work is use elastic wave data to access the fatigue damage (exudation). The Dynamic Time Warping method is proposed as a means of extracting features from guided wave ultrasound data that can describe the on-going fatigue induced damage of glass-fibre reinforced plastic pipes under fatigue-cycle loading. To test its efficiency, three pipe samples were fatigue tested to failure under internal pressure cycles with maximum values of 45 bar, 55 bar and 65 bar, and minimum pressures equal to 10% of the maximum, at a frequency of 0.8 Hz. A Guided Wave monitoring system consisting of a set of permanently attached piezoelectric sensors produced signals which were processed to obtain the Dynamic Time Warping distance, that was then used to obtain a Damage Index that expresses the cumulative fatigue damage suffered by the samples for each loading level. These results were comparable to data obtained from surface-mounted strain-gauges, even though temperature variations of up to 20 °C occurred during the tests and no direct temperature compensation was applied to the GW signals. The Dynamic Time Warping distance presents smaller influence of temperature and was able to better access the exudation of the samples. [ABSTRACT FROM AUTHOR]

With the increasing demand for flexible piezoelectric sensor components, research on polyvinylidene fluoride (PVDF) based piezoelectric polymers is mounting up. However, the low dipole polarization and disordered polarization direction presented in PVDF hinder further improvement of piezoelectric properties. Here, we constructed an oriented tertiary structure, consisting of molecular chains, crystalline region, and MXene sheets, in MXene/PVDF nanocomposite via a temperature-pressure dual-field regulation method. The highly oriented PVDF molecular chains form approximately 90% of the β phase. In addition, the crystalline region structure with long-range orientation achieves out of plane polarization orientation. The parallel orientation arrangement of MXene effectively enhances the piezoelectric performances of the nanocomposite, and the current output of the device increases by nearly 23 times. This high output device is used to monitor exercise action, exploring the potential applications in wearable electronics. [ABSTRACT FROM AUTHOR]

Piezoelectric accelerometers excel in vibration sensing. In the emerging trend of fully organic electronic microsystems, polymeric piezoelectric accelerometers can be used as vital front-end components to capture dynamic signals, such as vocal vibrations in wearable speaking assistants for those with speaking difficulties. However, high-performance polymeric piezoelectric accelerometers suitable for such applications are rare. Piezoelectric organic compounds such as PVDF have inferior properties to their inorganic counterparts such as PZT. Consequently, most existing polymeric piezoelectric accelerometers have very unbalanced performance metrics. They often sacrifice resonance frequency and bandwidth for a flat-band sensitivity comparable to those of PZT-based accelerometers, leading to increased noise density and limited application potentials. In this study, a new polymeric piezoelectric accelerometer design to overcome the material limitations of PVDF is introduced. This new design aims to simultaneously achieve high sensitivity, broad bandwidth, and low noise. Five samples were manufactured and characterized, demonstrating an average sensitivity of 29.45 pC/g within a ± 10 g input range, a 5% flat band of 160 Hz, and an in-band noise density of 1.4 µg/ Hz . These results surpass those of many PZT-based piezoelectric accelerometers, showing the feasibility of achieving comprehensively high performance in polymeric piezoelectric accelerometers to increase their potential in novel applications such as organic microsystems. [ABSTRACT FROM AUTHOR]

A signal is primarily generated when two objects collide, with one falling from a specific height and the other disrupting its balance. This signal contains an important component that aids in the diagnosis of material damage. In this work, a piezoelectric thin film sensor made of polyvinylidene fluoride (PVDF) was employed to monitor the impact signal and process the recorded signal. By stacking a left and right piezoelectric film sensor, drop impact experiments were performed on rubber sheet material. The data-acquisition system captured the impact signal, and a signal processing tool was used to assess its performance. To determine the time-frequency domain visibility of the impact signal, the short-time Fourier transform (STFT) and continuous wavelet transform (CWT) were used. The detection of the elastic signal and impact force on the material is suitable for piezoelectric film. A steel impactor strikes a silicon rubber sheet at a speed of 3.43 m/s and exerts an average impact force of 72.6 kN. To make the impact signal more visible, the noise signal can be denoised using a bandpass filter. The continuous wavelet transform has a high time-frequency resolution compared to the short-time Fourier transform. Additionally, the analysis of non-stationary signals is improved by using STFT and CWT approaches. Thus, the elastic signal detection in the material may be recognized using the average total of the signals identified by the sensor. [ABSTRACT FROM AUTHOR]

Nanotubes with multi-walled structures have the ability of changing the characterization of poly (Silicone Rubber) nanocomposites. In this way, silicone rubber/multiwalled carbon nanotubes (SR/MWCNTs) nanocomposite is achieved by reaction with multifunctional. A new design of SR/MWCNT nanocomposites was developed as a result of experiments to clarify the advantages of filling the MWCNTs with different patterns within the dielectrics. As part of this work, silicone rubber/multiwalled carbon nanotube nanocomposites and room temperature vulcanization (RTV) methods were used to fabricate piezoelectric sensors. The analysis of the frequency response of SR/MWCNT nanocomposites has been conducted under variable thermal conditions (20–40°C). This study succeeded in applying poly (Silicon Rubber) nanocomposites as piezoelectric sensors by exhibiting new electrical characteristics (resistance, capacitance, real and imaginary impedance) under various thermal conditions based on certain types and concentrations of MWCNTs. [ABSTRACT FROM AUTHOR]

A vital sign of the human body is respiration rate defined by the number of breaths a person takes per minute. In Bangladesh, respiratory diseases are very common. To find the respiration rate of patients, doctors use a traditional manual counting method. Sometimes this method is not accurate enough and is troublesome for them and it is time-consuming. Critical patients have very low breathing rates which makes it difficult to be counted and detected manually. That is why we developed a non-contact ultrasonic sensor-based method as well as a contact piezoelectric sensor-based method for obtaining respiration rate, and a comparison between them was demonstrated. The piezoelectric sensor was found to be more efficient and accurate and that is why we selected this sensor for the final design. We placed the sensor onto the subject's body and collected data from three positions: chest, upper and lower abdomen. We got two best positions based on body mass index (BMI). For low-BMI subjects, the best position was the chest and upper abdomen; for high-BMI subjects, it was the upper and lower abdomen. The accuracy of the device was 96.58%. Respiratory rate, heart rate, oxygen saturation, and BMI data were collected from 49 normal and respiratory disease patients of Chittagong Medical College Hospital and some volunteers to detect respiratory diseases. A logistic regression model was used for binary classification of this dataset to check whether the patient has respiratory diseases or not and found 88% accuracy for this model after five-fold cross-validation. [ABSTRACT FROM AUTHOR]

Piezoelectric sensors whose sensing performances can be flexibly regulated hold significant promise for efficient signal-acquisition applications in the healthcare field. The existing methods for regulating the properties of polyvinylidene fluoride (PVDF) films mainly include material modification and structural design. Compared to material modification, which has a long test period and an unstable preparation process, structural design is a more efficient method. The irigami structure combined with compressive buckling can endow the flexible film with rich macrostructural features. Here, a method is fabricated to modulate the sensing performance by employing distinct 3D structures and encapsulation materials with varying Young's moduli. The relationship among the aspect ratio (α), pattern factor (η), elastic modulus of encapsulation materials, and equivalent stiffness is obtained by finite element simulation, which provides theoretical guidance for the design of the 2D precursor and the selection of encapsulation materials. In the demonstration applications, the sensor accurately captures pulse waveforms in multiple parts of the human body and is employed for the pressure monitoring of different parts of the sole under various posture states. This method of structure design is efficient, and the preparation process is convenient, providing a strategy for the performance control of piezoelectric pressure sensors. [ABSTRACT FROM AUTHOR]

Purpose: Due to the remarkable physical properties of the graphene, the graphene-reinforced composite structures can be applied generally in the aerospace and other engineering fields. However, for the vibration amplitude attenuation of the graphene-reinforced structures, this is a challenging problem for researchers. The integrated piezoelectric sensors and actuators have many advantages as active intelligent materials in many mechatronic and vibration control systems. Therefore, the integrated piezoelectric actuator and sensor are designed by sticking piezoelectric patches on the surface of the FG–GRLCC rectangular plate to study the vibration amplitude attenuation. Methods: Based on the extended Halpin–Tsai micromechanical model, the elastic coefficients of the graphene-reinforced plate are formulated. Considering the classical laminated plate theory, the Hamilton principle, and the piezoelectric coupling effect, the dynamic equations of the piezoelectric FG–GRLCC rectangular plate are derived. The ordinary differential control equations of motion for the plate are obtained by applying the Galerkin method. To reduce vibration amplitude, the parameters of the positive position feedback (PPF) controller are designed using the Routh–Hurwitz stability criterion and the H ∞ optimal strategy. Results: The vibration characteristics for the piezoelectric FG–GRLCC rectangular plate with four different graphene distributions are studied. Numerical simulations are given to study the vibration amplitude attenuation via the proposed PPF control algorithm. In addition, the PPF control algorithm and the velocity feedback controller are compared. Conclusion: The designed PPF control algorithm can reduce the vibration amplitude for the four different graphene distribution for the FG–GRLCC rectangular plate subjected to the transverse excitation. In addition, the key of the vibration suppression is that the frequency of the PPF controller is same with the frequency of the structure. [ABSTRACT FROM AUTHOR]

Humans are distinguished by their walking patterns; many approaches, including using various types of sensors, have been used to establish walking patterns as biometrics. By studying the distinguishing features of a person's footsteps, footstep recognition may be utilized in numerous security applications, such as managing access in protected locations or giving an additional layer of biometric verification for secure admittance into restricted regions. We proposed biometric systems for verifying and identifying a person by acquiring spatial foot pressure images from the values obtained from the piezoelectric sensors using the Swansea Foot Biometric Database, which contains 19,980 footstep signals from 127 users and is the most prominent open-source gait database available for footstep recognition. The images acquired are fed into the ConvNeXt model, which was trained using the transfer learning technique, using 16 stride footstep signals in each batch with an Adam optimizer and a learning rate of 0.0001, and using sparse categorical cross-entropy as the loss function. The proposed ConvNeXt model has been adjusted to acquire 512 feature vectors per image, and these feature vectors are used to train the logistic regression models. We propose two biometric systems. The first biometric system is based on training one logistic regression model as a classifier to identify 40 different users using 1600 signals for training, 6697 signals for validation, and 200 signals for evaluation. The second biometric system is based on training 40 logistic regression models, one for each user, to validate the user's authenticity, with a total number of 2363 training signals, 7077 validation signals, and 500 evaluation signals. Each of the 40 models has a 40-training signal per client and a different number of signals per imposter, a different number of signals for the validation that ranges between 8 and 650 signals, a 5-signal for an authenticated client, and a different number of signals per imposter for evaluation. Independent validation and evaluation sets are used to evaluate our systems. In the biometric identification system, we obtained an equal error rate of 15.30% and 21.72% for the validation and evaluation sets, while in the biometric verification system, we obtained an equal error rate of 6.97% and 10.25% for the validation and evaluation sets. [ABSTRACT FROM AUTHOR]

This study focuses on the effect of temperature and preload force on capacitance and electromechanical impedance of lead zirconate titanate piezoelectric wafer active sensors for structural health monitoring of bolts. We explain the influence of temperature on the basis of the phenomenological thermodynamic theory of ferroelectricity by Landau, Ginsburg and Devonshire. The article illustrates the effect of damping the radial deformation of piezoelectric sensors on the capacitance and electromechanical impedance spectra in structural health monitoring of bolts. We also explains the similarities between the effects of temperature and preload force on the electromechanical impedance spectra. We establish a clear correlation between the mechanical strain in the region of the sensor (here due to a preload force), the capacitance and the electromechanical impedance spectra and thus show that piezoelectric sensors made of lead–zirconate–titanate can be used excellently in areas of variable mechanical strain. The article enhances the understanding of the measurement method and facilitates the transfer of the measurement method to other problems in structural health monitoring. Furthermore, the acquired knowledge serves as a solid basis for verifying the plausibility of data sets containing electromechanical impedance spectra. [ABSTRACT FROM AUTHOR]

Purpose: Energy-harvesting technology is based on the idea that devices can harvest the energy present in their ambient environment in real time and use it immediately, with or without the need for storage. This investigation focuses on the design, development, and analysis of an energy-harvesting system using commonly available piezo transducers. Methods: The prototype developed converts the energy from the mechanical vibration, due to footsteps, into electrical energy using piezoelectric sensors. Both simulations and experiments are carried out to validate the design and analyze the single and array piezoelectric energy harvester. The simulation results for single piezoelectric sensor have been obtained using LTspice tool. Results: On experimentation, it was observed that, the parallel combination of the array of piezoelectric sensors gives better energy-harvesting capability. Conclusion: The developed prototype demonstrates a low-cost energy-harvesting system that can be used in low-power applications. [ABSTRACT FROM AUTHOR]

Experimental and numerical approaches are used to quantify electrostatic and adhesive forces between a 250-µm long platinum microwire of 0.625-µm diameter and a tungsten microprobe of 5.0-µm diameter. The deformations of the microwire observed in the experiment are used as boundary conditions for the numerical analysis. The numerical analysis evaluates the respective elastic restoring forces required for the particular deformation. The microwire, with one end attached to a piezo-stage and another end free, is brought into the proximity of the microprobe by the piezo-stage. The microwire-free end is deflected instantly due to the electrostatic force and contacts the microprobe. Then, the microwire is pushed axially against the microprobe by the piezo-stage. It is deflected gradually in the lateral direction before sliding off the microprobe. The deflections are recorded and measured by an ultra-high accuracy optical microscope and verified by piezoelectric displacement sensors. The adhesive force is the reaction force at the microprobe contact surface during lateral deflection of the microwire since it is deflected without sliding off and maintains contact without normal contact force. The electrostatic and adhesive forces acting between the microwire and microprobe are balanced by the microwire elastic deformations and structural restoring forces. These two forces are quantified as 0.01007 µN and 0.059017 µN, respectively, using the FEA tool ANSYS Workbench to solve nonlinear contact problems. The method presented in this study could be used to measure electrostatic and adhesive forces in other microstructures, such as microrods, microbeams, diaphragms, microplates, etc., without force sensors. [ABSTRACT FROM AUTHOR]

The inculcation of bioinspiration in sensing and human-machine interface (HMI) technologies can lead to distinctive characteristics such as conformability, low power consumption, high sensitivity, and unique properties like self-healing, self-cleaning, and adaptability. Both sensing and HMI are fields rife with opportunities for the application of bioinspired nanomaterials, particularly when it comes to wearable sensory systems where biocompatibility is an additional requirement. This review discusses recent development in bioinspired nanomaterials for wearable sensing and HMIs, with a specific focus on state-of-the-art bioinspired capacitive sensors, piezoresistive sensors, piezoelectric sensors, triboelectric sensors, magnetoelastic sensors, and electrochemical sensors. We also present a comprehensive overview of the challenges that have hindered the scientific advancement in academia and commercialization in the industry. [ABSTRACT FROM AUTHOR]

High-temperature stable eco-friendly energy-harvesting technologies are in high demand for industrial applications wherein piezoelectric energy harvesting is gaining interest. The present work describes a high-temperature stable electrospun nanofiber-based flexible piezoelectric nanogenerator (PENG). A lead-free piezoelectric filler potassium sodium niobate (KNN) is incorporated in polyetherimide (PEI) matrix through an electrospinning process. A polymeric solution of PEI in 1-methyl-2-pyrrolidone (NMP) solvent is prepared at a fixed concentration of 25 wt% and filler loading varied from 1 to 3%. Among the various percentages of KNN NRs, 2% KNN NRs @ PEI nanocomposite demonstrates the most promising results (voltage of 6.3 V and current of 0.60 μA). In addition, the flexible nanogenerator holds its piezoelectric performance even at very high temperatures (studied up to 250 ºC) without any significant deterioration in properties. Finally, the optimized piezoelectric nanogenerator (PENG) is used to charge capacitor and glow LED. Therefore, the flexible nanogenerator prepared with 2% KNN NRs @PEI has huge potential to be explored as piezoelectric sensors or energy harvesters in high-temperature stable applications wherein the conventional piezoelectric polymers like PVDF and other thermoplastics fail to sustain their piezoelectric response. [ABSTRACT FROM AUTHOR]

The piezoelectric sensors modified with a molecularly imprinted polymer (MIP) with potassium sorbate (MIP-E202) and sodium benzoate (MIP-E211) imprints are tested and implemented in the determination of preservatives in soft drinks. Molecularly imprinted polymers were synthesized by noncovalent imprinting on the base of copolymer of 1,2,4,5-benzene tetracarboxylic acid dianhydride and 4,4'-diaminodiphenyl oxide in N,N-dimethylformamide (DMF) in the presence of templates. Piezoelectric sensors based on MIP and non-imprinted polymer (polyimide) were compared. High values of the imprinting factor (IF) and selectivity coefficient (k) obtained for MIP-E202 (IF = 5.4) and MIP-E211 (IF = 6.0) sensors indicated better selectivity and ability of MIP-based sensors to recognize target molecules than piezoelectric sensors modified with a reference polymer. The detectable concentrations range within 5–500 mg/L; the detection limits for potassium sorbate and sodium benzoate are 1.6 and 2.0 mg/L, respectively. The correctness of the determination of preservatives in model solutions was verified using the spike test. MIP-based sensors appeared sensitive to the determination of preservatives and insensitive to interfering substances. The matrix composition of the nonalcoholic drinks did not affect the value of the analytical signal of the piezoelectric sensor. High performance liquid chromatography (HPLC) was used as a reference method. The results of potassium sorbate and sodium benzoate determination in nonalcoholic drinks using piezoelectric sensors match the HPLC data rather well, their content in the studied soft drinks being 130–176 and 129–146 mg/L, respectively. [ABSTRACT FROM AUTHOR]

In this paper, active vibration control of a composite beam bonded with piezoelectric layers on the top and bottom surfaces as actuators/sensors rested on a Winkler-Pasternak elastic foundation and subjected to an axial load on the beams' both ends and also under the lateral excitation load is studied using the first-order shear deformation theory (FSDT). When a constant electric charge is imposed, the governing equations of motion have been derived based on the FSDT in conjunction with the classical laminated beam theory applying the Hamilton's principle. The governing coupled partial differential equations are converted to the coupled ordinary differential equations using the harmonic series solution and then are solved by the fourth-order Runge–Kutta method. The effect of changes different parameters including geometric ratio of the beam's length to its height, the composite lay-up angle, number of vibrational modes, density of the composite beam, boundary conditions and feedback control gain on the natural frequency of vibration and transverse displacement of the beam are investigated. The obtained results show that the natural frequency of the beam decreases with increasing the length of the beam. Moreover, it is noticed that by increasing the feedback control gain the frequency of vibration reduces which leads to a better control of the beam's vibration. [ABSTRACT FROM AUTHOR]

Machining of complex components with high added value requires the development and implementation of technologies for monitoring the processes outputs and to ensure the performance and reliability of the manufactured part. Cutting tool wear is one of the most relevant variables in machining due to its effect on both the machining cost and quality of the manufactured component. Although tool wear has been extensively investigated for more than a century, the advent of Industry 4.0 has required more accurate and reliable monitoring systems. This work investigates the feasibility of using a low-cost vibration sensor, based on a micro-electromechanical system (MEMS), connected to a wireless data transmission system attached to a rotary tool (milling cutter) for tool wear monitoring when milling annealed AISI H13 hot work die with coated tungsten carbide inserts. A microcontroller with an integrated internet connection connected to a local server through the Wi-Fi network was employed. In order to validate the proposed system, tests were performed comparing its behavior with a conventional piezoelectric sensor in terms of sensitivity to changes in the cutting conditions and tool wear evolution. The results indicated that the proposed system responds satisfactorily to changes in the cutting conditions, with approximately a four-fold increase in the acceleration amplitude when either cutting speed or axial depth of cut were doubled. Although neither the MEMS nor the piezoelectric accelerometer was capable to detect tool wear evolution (considering a tool life criterion VBB = 0.3 mm), the RMS value of the signal generated by the vibration sensor based on MEMS is approximately four times higher than that provided by the piezoelectric accelerometer, thus indicating a better representation of the vibration phenomenon resulting from fixing the MEMS on the tool (in contrast to the piezoelectric accelerometer attached to the workpiece). [ABSTRACT FROM AUTHOR]

Continuous health monitoring in private spaces such as the car is not yet fully exploited to detect diseases in an early stage. Therefore, we develop a redundant health monitoring sensor system and signal fusion approaches to determine the respiratory rate during driving. To recognise the breathing movements, we use a piezoelectric sensor, two accelerometers attached to the seat and the seat belt, and a camera behind the windscreen. We record data from 15 subjects during three driving scenarios (15 min each) city, highway, and countryside. An additional chest belt provides the ground truth. We compare the four convolutional neural network (CNN)-based fusion approaches: early, sensor-based late, signal-based late, and hybrid fusion. We evaluate the performance of fusing for all four signals to determine the portion of driving time and the signal combination. The hybrid algorithm fusing all four signals is most effective in detecting respiratory rates in the city ( P = 62.42 ), highway ( P = 62.67 ), and countryside ( P = 60.94 ). In summary, 60% of the total driving time can be used to measure the respiratory rate. The number of signals used in the multi-signal fusion improves reliability and enables continuous health monitoring in a driving vehicle. [ABSTRACT FROM AUTHOR]

In this study, we propose a piezoelectric ceramic sensor-based health monitoring method to monitor the stress state of diagonally braced H-shaped steel structures. Loading experiments were carried out on diagonally braced H-shaped steel under different working conditions. Subsequently, the amplitude and energy of piezoelectric signals under these two working conditions were compared and analyzed, and finite element analysis was performed using ABAQUS software to verify the results. The experimental results showed that with an increase in the web height or load, the time-domain waveform energy index of the H-shaped steel increased. Under different working conditions, such as a diagonally braced H-shaped steel member with a web height of 10 cm, when the pressure value was less than 10 N/mm2, the energy index increased by approximately 15.98% for every 1 N/mm2 increase in the pressure. When the pressure value was greater than 10 N/mm2 and less than 15 N/mm2, the energy index increased by approximately 1% for every 1 N/mm2 increase in pressure. Further, the energy index increased by approximately 8.4% for every 1 cm increase in the height of the web. Simultaneously, it can be seen from the results of the finite element analysis that the stress and strain at the induction position of the piezoelectric ceramic sensor increased with an increase in the external pressure. The study of structural health monitoring for diagonally braced H-shaped steel structures holds significant importance in ensuring the safety and reliability of these structures, achieving predictive maintenance, evaluating structural performance and energy efficiency, and optimizing structural maintenance. [ABSTRACT FROM AUTHOR]

A piezoelectric sensor with a recognition layer based on magnetic carbon nanocomposites, including multi-walled carbon nanotubes, magnetic Fe3O4 nanoparticles, and polymer nanospheres with molecular imprints of erythromycin and azithromycin, obtained by the "core–shell" method, is developed. Silicon dioxide particles are used as cores, on the surface of which a shell molecularly imprinted with macrolides is synthesized by free radical polymerization or the sol–gel method. SiO2 particles are obtained by the Stober method by varying the ratio of reagents during the synthesis. The size of the cores and nanoparticles of molecularly imprinted polymers (MIP) is determined by atomic force microscopy, and the density and uniformity of the layer on the surface of magnetic carbon nanocomposites (MCNC) are determined by the piezoelectric quartz crystal microbalance method. The optimal ratio of the reagents (template : functional monomer : cross-monomer) is established by a spectrophotometric method during the synthesis of "core–shell" nanostructures by free radical polymerization. A thin shell of SiO2 with imprints of an antibiotic based on organosilicon compounds used in the synthesis of the core is formed by the sol–gel method on the surface of the silicon dioxide core. The sensor recognition layer is formed under the action of an external magnetic field. The dependence of the analytical signal of the sensor based on MIP@SiO2/MCNC on concentration is linear in the range 5–160 µg/mL for azithromycin and 10–160 µg/mL for erythromycin, and with a recognition layer based on SiO2@SiO2/MCNC, in the concentration range 20–400 µg/mL for erythromycin. [ABSTRACT FROM AUTHOR]

Although there has been rapid advancement in piezoelectric sensors, challenges still remain in developing wearable piezoelectric sensors by a one-step, continuous and environmentally friendly method. In this work, a 1D flexible coaxial piezoelectric fiber was directly fabricated by melt extrusion molding, whose core and sheath layer are respectively slender steel wire (i.e., electrode) and PVDF (i.e., piezoelectric layer). Moreover, such 1D flexible coaxial piezoelectric fiber possesses short response time and high sensitivity, which can be used as a self-powered sensor for bending and vibration sensing. More interestingly, such 1D flexible coaxial piezoelectric fiber (1D-PFs) can be further endowed with 3D helical structure. Moreover, a wearable and washable motion monitoring system can be constructed via braiding such 3D helical piezoelectric fiber (3D-PF) into commercial textiles. This work paves a new way for developing 1D and 3D piezoelectric fibers through a one-step, continuous and environmentally friendly method, showing potential applications in the field of sensing and wearable electronics. [ABSTRACT FROM AUTHOR]

Water jet is an extensively used method for materials processing due to the possibility of operating in different environments (air, water), its safety during working with hazardous materials, and efficiency while cutting hard and brittle rock blocks. In this article, we have presented results of the research on processing aerated concrete by means of pulsating water jest. The discontinuity in water flow through the nozzle was achieved using an own-construction self-excited head. The intermittent flow had the greatest effect during operating in water environment. Machining efficiency for continuous and pulsating water jest was indicated by measuring erosive effects on processed materials. The occurrences of pulsations were confirmed while measurement of water jet thrust forces acting on piezoelectric sensor. It was concluded that pulsating water jet had greater processing effectiveness in a certain circumstances compared to the continuous flow, during the surface processing of concrete blocks. [ABSTRACT FROM AUTHOR]

Developing highly sensitive flexible piezoelectric sensor for wearable electronic devices have received considerable attention due to their promising application in physiological monitoring. Therefore, many research studies are conducted to enhance the piezoelectric response of poly(vinylidene fluoride) (PVDF)-based membrane. In this work, we present a novel flexible piezoelectric PVDF-based sensor with high-pressure sensitivity induced by the incorporation of microporous metal–organic framework (MOF) particles. Scanning electron microscopy images indicated the formation of uniform and bead-free PVDF/MOF nanofibrous composite with an average diameter of 173–241 nm. In this design, the microporous MOF crystals extremely enhanced the polar β-phase content of PVDF nanofibers by 20% without significant loss in its flexibility and synergistically promoted the piezoelectric performance of PVDF-based sensor. The PVDF nanofibers containing 1 wt% MOF crystals showed a peak-to-peak voltage of 3.84 V under an applied force of 2.5 N, which was superior to that of pristine PVDF nanofibers by 32%. Furthermore, the practical application of the developed PVDF/MOF nanofiber-based piezoelectric sensor was demonstrated for detecting human activities, showing a maximum output voltage of 2.08 V (for finger tapping), 5.92 V (for hand punching), and 20.66 V (for heel strike). The self-powered and highly sensitive PVDF/MOF nanofiber-based piezoelectric sensor also exhibits excellent long-term working stability with no obvious responsivity attenuation. The results of this work provide new insights for the development of next-generation piezoelectric sensors and energy harvesting systems. A novel flexible piezoelectric PVDF-based nanogenerator with high-pressure sensitivity induced by the incorporation of microporous MOF particles. The piezoelectric response of the developed PVDF/MOF nanogenerator indicated superior output voltage and sensitivity than most of the reported PVDF-based nanogenerators. [ABSTRACT FROM AUTHOR]

Moment tensor inversion (MTI) can be utilized in Acoustic Emission (AE) monitoring to determine source mechanisms of AE events and hence provide critical information on failure mechanisms of microcracks in laboratory rock tests. However, true amplitudes of motion may not be extracted from AE recordings due to several sensor unknowns, including the extent of sensor-specimen coupling, the transfer function of the sensor, and the uncertain effects of non-vertical incidence at piezoelectric sensors. Hence, amplitude or waveform-based moment-tensor inversion methods may not be practical for many AE monitoring of laboratory tests, and MTI will have to resort to methods based solely on first-P polarity which may have significant non-uniqueness, and hence uncertainty, due to the sparse coverage of first-P motion data on the focal sphere by typical AE sensor arrays. In this study, we explore the uncertainty of MTI based on P polarity as a result of the sparse coverage of the sensor array in laboratory AE monitoring through a set of synthetic examples. In a unit 3D homogeneous isotropic cubic rock sample, 18 selected moment tensors are placed at each of 6 arbitrarily selected source locations to represent typical tensile, shearing and compressional source types. The corresponding first P motion polarity data for 8 different designs of sensor arrays with varying number of sensors and coverage of the focal sphere are computed. Then, for each case, a grid search method is applied to determine the moment tensor solutions that can exactly match the recorded synthetic polarity data and estimate their non-uniqueness and uncertainty. Our synthetic examples show that with a limited number of first P motion data utilized (e.g., 6 and 8), a large number of moment-tensor solutions can generate polarities that exactly fit with the observations, making it difficult to separate different source types. On the other hand, with reliable first motion polarities recorded on at least 18 sensors evenly distributed on the sample, the non-uniqueness in moment-tensor solutions can be significantly reduced. The cumulative probability for uncertainty ≤ 5% increases from 0.4492 and 0.5358 for 6 and 8 first P motion polarities to 0.8960 for 18 polarity data according to our examples. This estimation of moment-tensor uncertainties helps improve sensor array designs, and for practical AE tests, it can be also used to provide the lower bound estimate of MTI uncertainty due to sensor array distribution. [ABSTRACT FROM AUTHOR]

Bio-mechanoreceptors capable of micro-motion sensing have inspired mechanics-guided designs of micro-motion sensors in various fields. However, it remains a major challenge for mechanics-guided designs to simultaneously achieve high sensitivity and broadband sensing due to the nature of resonance effect. By mimicking rat vibrissae, here we report a metamaterial mechanoreceptor (MMR) comprised of piezoelectric resonators with distributed zero effective masses featuring a broad range of local resonances, leading to near-infinite sensitivity for micro-motion sensing within a broad bandwidth. We developed a mechanical frequency-division multiplexing mechanism for MMR, in which the measured micro-motion signal is mechanically modulated in non-overlapping frequency bands and reconstructed by a computational multi-channel demodulation approach. The maximum sensitivity of MMR is improved by two orders of magnitude compared to conventional mechanics-guided mechanoreceptors, and its bandwidth with high sensitivity is extendable towards both low-frequency and high-frequency ranges in 0–12 kHz through tuning the local resonance of each individual sensing cell. The MMR is a promising candidate for highly sensitive and broadband micro-motion sensing that was previously inaccessible for mechanics-guided mechanoreceptors, opening pathways towards spatio-temporal sensing, remote-vibration monitoring and smart-driving assistance. There's a trade-off between the sensitivity and bandwidth for mechanics guided sensor designs. Here, authors report a mechanical sensor comprised of piezoelectric resonators with near infinite effective piezoelectric coefficients, leading to highly sensitive and broadband micromotion sensing. [ABSTRACT FROM AUTHOR]

Zinc oxide nanoparticles, especially those with a high aspect ratio (i. e., nanorods and nanowires), are of great interest for many applications as they are piezoelectric, photocatalytic and antimicrobial. In the present study, a plasma flight-thru synthesis method was developed that allows controlling the particle size and shape of the zinc oxide nanoparticles. In a direct current thermal plasma reactor operated at atmospheric pressure, zinc powder injected into the plasma jet was molten, vaporized and oxidized, which allowed growing zinc oxide nanoparticles. The particle spectrum ranged from small nanospheres to nanorods, nanowires and multipodic nanoparticles such as tetrapods. The influence of the oxygen rate and the plasma power (correlated to the discharge current) on the particle morphology was studied, and the feasibility of the nanowire-like particles as piezoelectric sensor material was investigated. Piezoelectric test sensors, equipped with the plasma-synthesized zinc oxide nanowires, successfully responded to mechanical stimulation after poling. [ABSTRACT FROM AUTHOR]

Background: Structural damage can be caused by various factors such as aging, environmental conditions, and unexpected events like earthquakes. Early detection of damage is crucial to prevent further deterioration, avoid catastrophic failure, and reduce maintenance costs. Damage detection methods that use piezoelectric sensors have gained popularity due to their non-destructive and non-invasive nature. Despite the progress made in the field of damage detection using piezoelectric sensors, there is still a need to improve the accuracy and reliability of those methods. Objective: This study aims to contribute to this by investigating the damage detection hybrid method, which uses the time-of-flight (ToF) criteria of acquired signals besides the energy loss damage index (DI) between damaged and intact states of a specimen, and exploring its possible improvements. The improvement potential in the investigated method regarding the signal processing details and the specification of the ToF used within the method, where the lack of information has been identified. Thus, the present study concentrates on those factors to get more benefit of the suggested method and extend its applicability. Results: The investigated factors play significant role in the accuracy and reliability of the method. By analyzing these criteria, this study contributes to the development of more advanced and reliable damage detection methods that can be applied to a wide range of structures, improving the ability to assess their structural health and safety. This study provides a better understanding of the hybrid method and contributes to the development of more accurate and reliable damage detection methods. The results of this study indicate that the proposed hybrid method effectively detects damage in the structural components under investigation with high accuracy and reliability. Methods: A 2D concrete plate is utilized to apply the proposed methodology. Hereby, various ToF criteria, truncation strategies of the signals, and the number of piezoelectric transducers used in the numerical experiment are examined to investigate their impact on the damage detection accuracy. Conclusion: Performance of the method was found to be significantly affected by selection of the investigated parameters, as well as of the number and placement of sensors. The findings suggest that a thorough analysis of these criteria can lead to further improvements in the accuracy and reliability of damage detection methods. [ABSTRACT FROM AUTHOR]

Continuous monitoring of arterial blood pressure (BP) outside of a clinical setting is crucial for preventing and diagnosing hypertension related diseases. However, current continuous BP monitoring instruments suffer from either bulky systems or poor user-device interfacial performance, hampering their applications in continuous BP monitoring. Here, we report a thin, soft, miniaturized system (TSMS) that combines a conformal piezoelectric sensor array, an active pressure adaptation unit, a signal processing module, and an advanced machine learning method, to allow real wearable, continuous wireless monitoring of ambulatory artery BP. By optimizing the materials selection, control/sampling strategy, and system integration, the TSMS exhibits improved interfacial performance while maintaining Grade A level measurement accuracy. Initial trials on 87 volunteers and clinical tracking of two hypertension individuals prove the capability of the TSMS as a reliable BP measurement product, and its feasibility and practical usability in precise BP control and personalized diagnosis schemes development. Continuous monitoring of arterial blood pressure is limited by bulky connecting systems and poor interfacial contact. Here, Li et al. report a wearable thin, soft, miniaturized system that integrates sensing, active pressure adaptation, and signal processing for improved performance and accuracy. [ABSTRACT FROM AUTHOR]

Most cracks do not grow straight due to the inhomogeneity of material properties. Furthermore, quantifying structural damage using Lamb waves is difficult due to uncertain crack shape. Here, we present a newly developed finite element model to simulate the propagation of Lamb waves in a cracked plate to quantify the influence of crack size and orientation on the characteristics of Lamb wave propagation. This model includes a piezoelectric actuator and sensor to generate and receive the tone-burst signals of Lamb wave. The damping coefficient of the finite element model was calibrated with the experimental data of plates without a crack. The Lamb wave propagation simulations were performed with various crack sizes, crack orientations, and distances between the actuator and sensor. Our model was utilized to investigate the influence of crack orientation on damage quantification based on the signal phase change and normalized amplitude. We successfully evaluated the effect of the incident angle of the crack, crack size, and distance between the sensors on the change of the plate wave signal characteristics. The signal characteristics obtained from our novel finite element model can be used to develop a quantification model to estimate the crack size, direction, and distance from the sensor. [ABSTRACT FROM AUTHOR]

Crack imaging is attractive in the community of nondestructive testing and structural health monitoring of plate-like structures. However, most existing research focuses on the imaging of single crack, while limited work has been reported for the imaging of multiple cracks. To this end, the application of the Lamb wave-based technique is presented in this paper to image the multiple cracks. The antisymmetric mode (A0) of Lamb wave propagation in the thin plate is simulated using the numerical finite element method, and a circular piezoelectric sensor array is considered to capture the Lamb wave signals. The damage index taking into account the attenuation of the reflected signal amplitude is proposed using the reflection signals from the cracks, and the Hilbert transform is used to extract the information of damage. The damage scanning map is constructed to show the damage location in the plate. The proposed damage identification algorithm based on Lamb wave propagation is also used to detect two cracks in the thin plates. The consideration of wave attenuation improves the identification of multiple cracks. The proposed damage identification algorithm using a phased piezoelectric sensor array shows its potential to locate the cracks in thin plates. [ABSTRACT FROM AUTHOR]

Monitoring the dressing operation of grinding wheels is crucial for optimizing the grinding process and ensuring quality outcomes. This study presents a novel data-driven method utilizing piezoelectric diaphragm signals, combined with the root mean square deviation index (RMSD) and power spectral density (PSD), to determine the optimal moment for interrupting the dressing operation of conventional aluminum oxide grinding wheels. By addressing the existing gaps in transition methods between dressed and undressed grinding wheels, as well as exploring untested metrics in digital signal processing, this research expands the use of alternative piezoelectric transducers for monitoring dressing. The proposed methodology utilizes a commercial acoustic emission (AE) sensor as a reference and employs experimental dressing tests to validate its effectiveness. The signals from both the AE sensor and the piezoelectric diaphragm are collected and subjected to digital processing to extract relevant features based on the proposed approach. Results demonstrate that the RMSD index successfully extracts information about the cutting surface conditions of the grinding wheel from signals obtained by both AE sensors and piezoelectric diaphragms. Furthermore, by selecting frequency bands that exhibit strong correlations with the grinding wheel's cutting surface conditions, a threshold is defined, enabling timely interruption of the dressing operation, thereby ensuring the restoration of the grinding wheel for continued use in grinding applications. Ultimately, this study showcases the feasibility of a non-invasive method for monitoring the dressing operation of conventional grinding wheels, contributing significantly to the optimization of the grinding process. [ABSTRACT FROM AUTHOR]

On the Earth, the human body is designed and adapted to function under uniform gravitational acceleration. However, exposure to microgravity or weightlessness as experienced by astronauts in space causes significant alterations in the functioning of the human cardiovascular system. Due to limitations in using real microgravity platforms, researchers opted for various ground-based microgravity analogs including head-down tilt (HDT) at fixed inclination. However, in the present study, an investigation of response of various cardiac parameters and their circulatory adaptation in 18 healthy male subjects was undertaken by using an indigenously developed 360° rotating platform. Cardiac pulse was recorded from 0° to 360° in steps of 30° inclination using piezoelectric pulse sensor (MLT1010) and associated cardiac parameters were analyzed. The results showed significant changes in the pulse shape while an interesting oscillating pattern was observed in associated cardiac parameters when rotated from 0° to 360°. The response of cardiac parameters became normal after returning to supine posture indicating the ability of the cardiovascular system to reversibly adapt to the postural changes. The observed changes in cardiac parameters at an inclination of 270°, in particular, were found to be comparable with spaceflight studies. Based on the obtained results and the proposed extended version of fluid redistribution mechanism, we herewith hypothesize that the rotation of a subject to head down tilt inclination (270°) along with other inclinations could represent a better microgravity analog for understanding the cumulative cardiac response of astronauts in space, particularly for short duration space missions. [ABSTRACT FROM AUTHOR]

Static break-down tests were carried out with samples made of carbon fiber plastics. Testing for defects was performed using acoustic emission and strain gaging methods. Four wire strain gages were glued to each sample in the aperture area, and four piezoelectric sensors were installed along aperture edges to form a working testing zone. Recording the signals associated with the failure of the composite material of the samples and their location were carried out by an acoustic emission system. During the tests, a strain gage system recorded loads and deformations that lead to the initiation of destruction process in carbon fiber plastics. The destruction type was determined based on analyzing the microsections made from the signal location zone in the sample. The main informative parameters of acoustic emission signals were associated with the destruction type of carbon fiber plastics. [ABSTRACT FROM AUTHOR]

The study of shape memory alloys (SMAs) is widely spread in academic and industrial circles due to a large number of applications. In this context, understanding their critical phase transformation temperatures to use as actuators or sensors requires analysis by consolidated techniques, such as Differential Scanning Calorimetry (DSC). In this work, an experimental testing platform was developed as an alternative, whose function is to determine these phase transformation temperatures of SMAs through the electromechanical impedance (EMI) using piezoelectric sensors attached to the surface of the SMA samples. This equipment submits the PZT + SMA heterostructures to controlled thermal cycling and presents the electromechanical impedance magnitude and phase angle curves as real-time responses. To validate and survey the operational limits of the equipment, tests were performed on NiTi, and NiTiNb SMA samples, whose transformation temperatures obtained by EMI were compared with those obtained by DSC. The results showed considerable similarity compared to those by DSC. This way, an infrastructure that allows for a deeper study of the process was obtained, also promoting the optimization of the test parameters for the most diverse materials. [ABSTRACT FROM AUTHOR]

Comparative experimental studies of the shock-induced particle ejection ("dusting") from the free rough (Rz20) surface of copper and lead liners exposed to one or two successive shock waves separated in time by 0.2 μs have been carried out for the first time. This situation usually occurs in cumulative systems for the compression of the plasma by cylindrical or spherical liners shock or quasi-isentropically accelerated by explosion products. Using pulsed X-ray diffraction, laser optical recording, piezoelectric pressure sensors, and heterodyne interferometry, a qualitative picture has been studied and the quantitative characteristics of particle ejection from the free surface such as the velocities of the free surface and the particle flux front and the density (mass) distribution of particle flux in the direction of its motion, which are necessary for more accurate determination of features and the development of more appropriate models of the effect, have been evaluated. [ABSTRACT FROM AUTHOR]

The problem of electrothermomechanical behavior and durability of inelastic shells of revolution with piezoelectric sensors and actuators under axisymmetric resonance vibrations is stated and a problem-solving method is presented. Numerical experiments for a round plate with a piezoelectric sensor were conducted to study the effect of geometric nonlinearity on the frequency dependences of deflection amplitudes, self-heating temperature, and electrical sensor index. The dependence of the service time of the system on extreme amplitudes of mechanical load and the thermal-transfer conditions on its surface is studied using a criterion of assessing local durability from the maximum self-heating temperature. [ABSTRACT FROM AUTHOR]

P(VDF-TrFE)-based nano-fiber reinforced piezoelectric sensors are extensively used for energy harvesting, structural health monitoring and medical applications. However, low efficiency and sensitivity have been major issues to address. The sensor efficiency can be improved by adding ZnO nanoparticles. The aim of the present research is to study and quantify the effect of ZnO nanoparticles (higher percentage) on P(VDF-TrFE)-based nanocomposites. Here, poly(vinylidene fluoride-trifluoroethylene) copolymer and zinc oxide nanoparticle-based nanocomposite are prepared using one-step electrospinning method. ZnO nanoparticles with 18% w/v and 18% w/w concentration are considered for preparing P(VDF-TrFE)/ZnO solution. These concentrations were taken relative to both of P(VDF-TrFE) polymer and dimethylformamide (DMF) solvent. The nanocomposite films were characterized using different techniques and their β phase enhanced with the addition of filler. The viscosity, storage and loss modulus increased with the addition of filler, while damping factor decreased. The piezoelectric nanogenerators (PENG) were fabricated, and their piezoelectric outputs were recorded in terms of voltage under various loading such as pressing, bending and tapping by human hand. The piezoelectric output of the PENGs is enhanced from 704 mV to 1.15 V and 4 to 5.2 µA. It is observed that the addition of ZnO nanoparticles into the P(VDF-TrFE) nanofiber made the composite film more active and sensitive. The findings of this study open the door for developing self-powered wearable electrical systems and devices. [ABSTRACT FROM AUTHOR]