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Flexible high-performance piezoelectric nanogenerator (PENG) excel in converting mechanical energy into electrical energy and exhibit remarkable sensitivity, a feature that is paramount for the development of self-driven piezoelectric sensors. In this study, electrospinning technology was used to prepare poly (vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] based piezoelectric nanofiber composite films containing potassium-sodium niobate nano particles (KNN NPs) and Nb 2 CT x co-doping, as well as single-component doping. The co-doped composite film attained an optimal β-phase content of 91.33%. Owing to the enhanced dipole alignment and interface charge polarization, the piezoelectric performance of the co-doped composite film was significantly enhanced compared to that of single-component doping. The co-doped piezoelectric composite film displayed a stable maximum output voltage of 20 V and an output current of 1.46 μA. The peak instantaneous power output was measured at 9.9 μW under the optimal resistive load of 10 MΩ. Durability testing over 2000 cycles affirmed the excellent mechanical stability of the piezoelectric composite film. Moreover, the fabricated piezoelectric composite film showed considerable potential in applications such as monitoring human activities and serving as an early warning system for natural disasters such as landslides, as indicated by the test results. [ABSTRACT FROM AUTHOR]

Ballistocardiography (BCG) studies ballistic forces on the body generated during a heartbeat. As it is an unobtrusive detection method, that requires sensors measuring small dynamic forces. Piezoelectric sensors are ideal, but improvements in sensitivity are needed. Here, a universal method is demonstrated to obtain enhanced effective transverse charge constants by utilizing thin and long sensors fabricated upon compliant substrates. This approach is validated using the uniquely printable and patternable piezoelectric polymer, poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE). Discrete sensors detect displacements of less than 1 µm, dynamic forces of ∼mN, and accelerations of ≈1 mm−1 s2. Since the sensor is screen‐printable, it is upscaled to a human‐sized array (60 × 90 cm, 255 sensors). High quality spatially resolved BCG measurements of a person is demonstrated in seated and supine positions. The obtained heart rate is verified using photoplethysmography. This development opens the door to ever‐more sensitive piezoelectric sensors, crucial for applications including and beyond healthcare. [ABSTRACT FROM AUTHOR]

In marine scientific research, ocean monitoring is crucial where the batterypowered sensor devices are placed under the water to collect different information like temperature, pressure, and turbidity in underwater sensor networks (UWSNs). Thus, keeping these devices active for longer periods is challenging. In the last decades, the piezoelectric transducer (PZT) material has been used widely for constructing more environmentally friendly energy harvesting systems. The PZT harvester offers a promising solution by eliminating the need for batteries for running devices in the future with less maintenance. The PZT harvester allows the system to generate higher voltage to run low-power devices. This paper designed and developed a new renewable energy harvester system using PZT transducers for running different types of underwater sensor devices like temperature, turbidity, and obstacle sensors. The proposed PZT-based energy harvester employs a twostage amplification model for generating higher voltage and current to run multiple devices. The sensing information collected from these sensors is transmitted to the cloud which is later utilized for analysis and decisionmaking. Experiment results show the proposed PZT-based energy harvester can generate a voltage of 13 volts (V) and a current of 43.3 milliampere (mA) equivalent to 562 milliwatt (mW) which is very good to run multiple low-power underwater sensor devices. [ABSTRACT FROM AUTHOR]

Assessing the vibration signature produced by a rotating component of the wind turbine enables the identification of operational conditions and the detection of potential faults at an early stage. The main purpose is to enhance the sustainability of wind turbines while increasing the lifespan and uptime of their operational systems. This vibration analysis is based on the processing of the signal provided by sensors, which often incorporates piezoelectric transducers. This paper evaluates the consequences of employing piezoelectric sensors used for vibration measurement on electrical machines integrated into wind turbines by conducting a life cycle assessment (LCA). The widespread use of piezoelectric materials is due to their high sensitivity to vibrations, although their selection is also influenced by regulatory restrictions. This research focuses on the environmental impact of piezoelectric accelerometers used commonly in condition monitoring systems. The collected literature data on the manufacturing processes are inputted into the LCA model which is powered by the Ecoinvent 3 database. The impact assessment is carried out using the European ILCD 2011 Midpoint+ method by calculating the unique scores of the selected impact categories. The results are presented and discussed in terms of environmental indicators, as well as ecological recommendations on the design. [ABSTRACT FROM AUTHOR]

Ensuring the safety of infants around swimming pools or hazardous areas can be tasking for caregivers and their parents. Providing safety devices that can keep track of infants and prevent them from going to unauthorized locations is very necessary. The study aims to design and implement an infant safety system that uses a Piezoelectric sensor. The paper constructed a system to alert parents of an infant's attempted entry into a dangerous area, such as balconies and swimming pools, and it also incorporated an automatic door-locking system around the location. The Piezoelectric Sensor Infant Monitoring System was designed to enhance infant safety at home. The system utilized piezoelectric transducers and pressure sensors, incorporating an automatic door to secure unauthorized zones. Components like Arduino Nano, an LCD, and a buzzer were used to create the prototype. The device was designed to harvest energy by converting mechanical energy from ambient vibrations into electrical energy that will send signals to the GSM module, alerting the homeowner by sending a call. The model adopts the technology of pressure control, and when the pressure reaches a set value and the dial of the scale reaches a specific value simultaneously, the automatic door will open. The device is designed to harvest energy by converting mechanical energy from ambient vibrations into electrical energy that will power the motor of the automatic door of the safety system. The test proved the system's effectiveness in accurately detecting and blocking an infant, but it only grants access to authorized individuals while alerting caregivers. The results demonstrated improved child safety, responsible parenting, and a secure environment. The Piezoelectric sensor safety system offers a practical solution for enhancing infant monitoring for safety and preventing avoidable mishaps, thereby reducing infant mortality and morbidity in present times. The system can serve as a protection device for very busy mothers. [ABSTRACT FROM AUTHOR]

It is demonstrated that the application of piezoelectric sensors to metallic bars and strands can enable determining the status of the integrity of these elements through the spectrum of their acoustic excitations. The voltage output of the piezo, secured to metal bars or strands, is fed to the input of a Fast Fourier Transform analyzer, which allows displaying the spectrum of the excitations from which information on the length, overall quality of the metal, and the presence of defects can be obtained. We show that the analysis, performed on several materials and strands of different lengths, could be useful for cases in which visible inspection and/or direct access to the entire body of the metallic elements is not possible. Applications of our study for testing metallic structures embedded in concrete foundations are reported for construction sites. [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]

Flexible piezoelectric sensors combine advantages including low‐cost, flexibility, multi‐functions, present a huge market prospect. In this research, multiwalled carbon nanotubes (MWCNT)/MXene/polyacrylonitrile (PAN) piezoelectric composites films for flexible piezoelectric sensors are fabricated by electrospinning technology, the planar zigzag conformation content of 97.98% in PAN composite fibers is achieved owing to the synergistic effect of MWCNT and MXene, the synergistic effect of MWCNT and MXene nanoparticles can also efficiently promote the mechanical performance and piezoelectric output. The piezoelectric sensor exhibits fast response time (10.21 ms), a possible mechanism is proposed to explain the improvement of piezoelectric effect. The sensor can measure human pulse, distinguish human movements, the fabricated sensor has broad practical value in the field of healthcare, its' use can contribute to stable and accurate measurements of physiological parameters, enabling applications in various healthcare and fitness monitoring scenarios. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to monitoring ultrasonic systems using structurally integrated piezoceramics. These are integrated into the sonotrode at different points and with different orientations. The procedure for integrating the piezoceramics into the sonotrode and their performance is experimentally investigated. We examine whether the measured signal can be used to determine the optimal operating frequency of the ultrasonic system, if integrating several piezoceramics enables discernment of the current vibration shape, and if the piezoceramics can withstand the high strains caused by the vibrations in a frequency range of approximately 20–25 kHz. The signals from the piezoceramic sensors are compared to the real-time displacement at different points of the sonotrode using a 3D laser scanning vibrometer. To evaluate the performance of the sensors, different kinds of excitation of the ultrasonic system are chosen. [ABSTRACT FROM AUTHOR]

The successful fabrication and application of 3D‐printed piezoelectric sensors, made from polyvinylidene fluoride‐barium titanate nanocomposites, for continuous blood pressure (BP) monitoring, is presented. The sensors are fabricated using direct‐ink write 3D printing technique possessing excellent flexibility, rendering them ideal for wearable applications. Key printing parameters, such as nozzle size and pressure, are optimized to achieve a β‐phase of 70% and an overall crystallinity of 48.3%. The sensors are characterized under dynamic pressures and show excellent linearity with a coefficient of determination (R2) of 0.99 and a pressure sensitivity of 0.024 V kPa−1, and demonstrate durability over 3600 cycles. The performance of our piezoelectric sensors is compared with a standard BP monitoring device for a subject, and a strong correlation with a standard deviation of 3.87 and 0.63 mmHg for sytolic BP and diastolic BP, respectively, is found. The development of sensors through 3D printing, as demonstrated in this study, represents a significant scientific advancement in the field of personalized healthcare. This novel approach enables the creation of customized wearable devices tailored for real‐time health monitoring of BP and heart rate. [ABSTRACT FROM AUTHOR]

Herein, the density functional theory is used to study the structural, mechanical, electrical, optical, and hydrogen evolution reaction (HER) properties of monolayer structures (α,β)–S2C2N2$\left(\right. \alpha , \beta \left.\right) – \left(\text{S}\right)_{2} \left(\text{C}\right)_{2} \left(\text{N}\right)_{2}$ and (α,β)–SCN/CN$\left(\right. \alpha , \beta \left.\right) – \text{SCN} / \text{CN}$. They are claimed to be stable monolayer structures by phonon dispersion and ab initio molecular dynamics (AIMD). Compared to graphene (≈340 N m−1), the (α,β)–SCN/CN$\left(\right. \alpha , \beta \left.\right) – \text{SCN} / \text{CN}$ shows a higher Young's modulus (≈429, 414 N m−1). Moreover, the piezoelectric stress coefficient of α‐SCN/CN$\text{SCN} / \text{CN}$ (d11$d_{11}$=2.65 pm V−1) is comparable with bulk piezoelectric α‐quartz (d11$d_{11}$=2.3 pm V−1). Exciton effect at M point causes redshift and enhancement of light absorption of α‐SCN/CN$\text{SCN} / \text{CN}$ and β–SCN/CN$\beta – \text{SCN} / \text{CN}$. The overpotential of β–SCN/CN$\beta – \text{SCN} / \text{CN}$ is only –0.072 V. Besides, the (α,β)–SCN/CN$\left(\right. \alpha , \beta \left.\right) – \text{SCN} / \text{CN}$ gives a small effective electron mass of about 0.2(m0). It is worth mentioning that the monolayer structures (α,β)–S2C2N2$\left(\right. \alpha , \beta \left.\right) – \left(\text{S}\right)_{2} \left(\text{C}\right)_{2} \left(\text{N}\right)_{2}$ show the semimetal phases. Due to the unique semimetal phase, the absorption of β–S2C2N2$\beta – \left(\text{S}\right)_{2} \left(\text{C}\right)_{2} \left(\text{N}\right)_{2}$ has an excellent performance in the near‐infrared (NIR) region. It can be enhanced at the NIR region and extended to the middle infrared region when applying tensile stress. These results provide more choices for 2D materials in electrocatalysis, piezoelectric sensors, visible light devices, and infrared photodetectors. [ABSTRACT FROM AUTHOR]

With the advent of the intelligence era, flexible piezoelectric tactile sensors are the key components for sensing information and sending signals. The performance parameters of piezoelectric sensors are closely related to the selection of piezoelectric materials. Compared with conventional piezoelectric materials, polyvinylidene fluoride (PVDF) has significant advantages in flexibility, stretchability, chemical stability, electromechanical conversion, ease of use, and acoustic propagation impedance. As a result, PVDF has become a popular topic of research. This paper introduces the working principle of piezoelectric materials and flexible piezoelectric sensors based on PVDF materials and details the research progress of different materials based on PVDF for the preparation of flexible piezoelectric tactile sensors, such as: PVDF and its copolymers for the preparation of flexible piezoelectric sensors and PVDF doped with other functional materials for the preparation of flexible piezoelectric sensors. In this paper, the advantages and disadvantages of different materials and the development prospects of PVDF flexible piezoelectric sensors are summarized to provide some insights for high‐performance flexible PVDF piezoelectric sensors. [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]

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]

According to the 2018 National Immunization Survey conducted by the Center for Disease Control and Prevention (CDC), 83.9% of the breastfeeding mothers in the United States have used a breast pump at least once. However, the majority of existing products use a vacuum-only mechanism to extract milk. This causes common breast injuries such as nipple soreness, breast-tissue damage, and lactation complications after pumping. The objective of this work was to develop a bio-inspired breast pump prototype, named as SmartLac8, that can mimic infant suckling patterns. The input vacuum pressure pattern and compression forces are inspired from term infants' natural oral suckling dynamics captured in prior clinical experiments. Open-loop input–output data are used to perform system identification for two different pumping stages that facilitates controller design for closed-loop stability and control. A physical breast pump prototype with soft pneumatic actuators and custom piezoelectric sensors was successfully developed, calibrated, and tested in dry lab experiments. Compression and vacuum pressure dynamics were successfully coordinated to mimic the infant's feeding mechanism. Experimental data on sucking frequency and pressure on the breast phantom were consistent with clinical findings. [ABSTRACT FROM AUTHOR]

Extreme environments are often faced in energy, transportation, aerospace, and defense applications and pose a technical challenge in sensing. Piezoelectric sensor based on single‐crystalline AlN transducers is developed to address this challenge. The pressure sensor shows high sensitivities of 0.4–0.5 mV per psi up to 900 °C and output voltages from 73.3 to 143.2 mV for input gas pressure range of 50 to 200 psi at 800 °C. The sensitivity and output voltage also exhibit the dependence on temperature due to two origins. A decrease in elastic modulus (Young's modulus) of the diaphragm slightly enhances the sensitivity and the generation of free carriers degrades the voltage output beyond 800 °C, which also matches with theoretical estimation. The performance characteristics of the sensor are also compared with polycrystalline AlN and single‐crystalline GaN thin films to investigate the importance of single crystallinity on the piezoelectric effect and bandgap energy‐related free carrier generation in piezoelectric devices for high‐temperature operation. The operation of the sensor at 900 °C is amongst the highest for pressure sensors and the inherent properties of AlN including chemical and thermal stability and radiation resistance indicate this approach offers a new solution for sensing in extreme environments. [ABSTRACT FROM AUTHOR]

This study looks at the synthesis of innovative PEO/PVA/SrTiO3/NiO nanocomposites for piezoelectric sensors and gamma shielding applications that are low weight, elastic, affordable and have good gamma ray attenuation coefficients. The impact of SrTiO3/NiO on the structural characteristics of the PEO/PVA mixture is investigated. The polymer mixture PEO/PVA received additions of SrTiO3/NiO at concentrations of (0, 1, 2, 3 and 4) weight percent by the casting method. On the top surface of the films PEO/PVA/SrTiO3/NiO NCs, scanning electron microscopy reveals several randomly distributed aggregates or fragments that are consistent and coherent. An optical microscope image collection reveals that the blend's additive distribution of NPs was homogenous. Gamma ray shielding application results show that the attenuation coefficient of PVA/PEO/SrTiO3/NiO NCs is increased by increasing concentration of SrTiO3/NiO nanoparticles. Radiation protection is another application for it. The pressure sensor application findings of NCs show that, when the applied pressure rises, electrical capacitance (Cp) increase. [ABSTRACT FROM AUTHOR]

Sensors are of great importance in different aspects of research and industry. Future sensors will require high‐efficient and low‐cost manufacturing, as well as high‐performance functionality in areas, such as mechanical sensing, biomedical, and optical applications. Recent advances in 3D printing open a new paradigm for sensors fabrication as a precision, customizable, and seamless process. In this article, the state‐of‐the‐art 3D printing methods in sensors manufacturing is reviewed and the performance of the 3D printed sensing materials and devices is summarized. Special attention is paid to emerging multimaterial printing and 4D printing technologies, which will benefit the fabrication of a new generation of structures with multifunctionalities. The content on 3D printed sensors covers piezoelectric sensors, medical, and optical sensing devices. The performance of 3D printed sensors in comparison with the sensors made by traditional manufacturing is also covered. Finally, section 4 provides the viewpoints on the future development of 3D printed sensors. [ABSTRACT FROM AUTHOR]

Conical shell structures are frequently submitted to severe static and dynamic mechanical loads that can result in situations that affect the service of the systems that are part of, or even cause catastrophic failures. For this reason, a common solution is to design an active deformation control system, usually using piezoelectric patches strategically distributed along the surface of the shell structure. Moreover, these elements may be part of an energy recovery system. This paper details the methodology to topologically optimize the placement of piezoelectric elements through a characteristic function, analysing static and free vibration loading cases by means of the finite element method. Then, the optimal arrangement of the electrode with different polarization profiles is distributed throughout the entire structure. The nature of the loading cases studied corresponds to a general situation where static loads and dynamics vibration are considered. The objective function of the problem only depends linearly on the displacement fields, and therefore, the optimal electrode profile can be obtained for any combination of loads. As a consequence, this technique allows for maximising the electric charge obtained, which results in a greater capacity for monitoring, actuation and/or energy harvesting. [ABSTRACT FROM AUTHOR]

The application of Polyvinylidene Fluoride or Polyvinylidene Difluoride (PVDF) in harvesting energy from tire deformation was investigated in this study. An instrumented tire with different sizes of PVDF-based piezoelectric patches and a tri-axial accelerometer attached to its inner liner was used for this purpose and was tested under different conditions on asphalt and concrete surfaces. The results demonstrated that on both pavement types, the generated voltage was directly proportional to the size of the harvester patches, the longitudinal velocity, and the normal load. Additionally, the generated voltage was inversely proportional to the tire inflation pressure. Moreover, the range of generated voltages was slightly higher on asphalt compared to the same testing conditions on the concrete surface. Based on the results, it was concluded that in addition to the potential role of the PVDF-based piezoelectric film in harvesting energy from tire deformation, they demonstrate great potential to be used as self-powered sensors to estimate the tire-road contact parameters. [ABSTRACT FROM AUTHOR]

Tactile sensing is increasingly attractive in various real-life applications, mainly driven by significant progress in semiconductor, sensing, and material science technologies. Different sensing techniques were suggested for specific design goals, as none of them can simultaneously feature all the properties of human skin: high spatial–temporal resolution and repeatability, ease of stretch and bend, insensitivity to environmental conditions such as electromagnetic Interference (EMI) noise and temperature variations, portability, and determining the intensity of both normal and shear stresses. This has driven researchers to suggest multimodality tactile sensors to enhance their capabilities. However, the sensing techniques focus mainly on five types: resistive, piezo-resistive, piezoelectric, capacitance, optical fiber, and visible-light cameras. This paper will reveal the most recent research on tactile sensors, including the sensor, front-end electronics, algorithms, and associated hardware accelerators. It also suggests potential design solutions that can enhance their overall performance. Thus, it can be a valuable tool for researchers and engineers involved in related research activities, as tactile sensing is essential for a wide range of applications, from robotics to medical fields and virtual/augmented reality. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to the structural integration of piezoceramics into thin-walled steel components for condition-monitoring applications. The procedure for integrating the sensors into metal components is described, and their functionality is experimentally examined with a 2 mm-thick steel sheet. The signal quality of the produced sensors is investigated in a frequency range from 100 Hz to 50,000 Hz and is compared with the results of piezo patches and strain gauges under the same conditions. The results show that due to a higher signal-to-noise ratio and a better coherence, the structurally integrated piezoceramics and the piezo patches are more qualified sensors for vibration measurement in the examined frequency range than the strain gauges. The measurements also indicate that the patches provide higher amplitudes for the frequency range up to 20 kHz. Beyond that, up to 40 kHz, the integrated sensors supplied higher amplitudes. The better signal quality in different frequency ranges as well as the different manufacturing and application methods can be interpreted as an advantage or disadvantage depending on the boundary conditions of the condition-monitoring system. In summary, structural integrated piezoceramics extend the options of monitoring technology. [ABSTRACT FROM AUTHOR]

Screen printed piezoelectric polyvinylidene fluoride–trifluoro ethylene (PVDF–TrFE)‐based sensors laminated between glass panes in the temperature range 80–110 °C are presented. No degradation of the piezoelectric signals is observed for the sensors laminated at 110 °C, despite approaching the Curie temperature of the piezoelectric material. The piezoelectric sensors, here monitoring force impact in smart glass applications, are characterized by using a calibrated impact hammer system and standardized impact situations. Stand‐alone piezoelectric sensors and piezoelectric sensors integrated on poly(methyl methacrylate) are also evaluated. The piezoelectric constants obtained from the measurements of the nonintegrated piezoelectric sensors are in good agreement with the literature. The piezoelectric sensor response is measured by using either physical electrical contacts between the piezoelectric sensors and the readout electronics, or wirelessly via both noncontact capacitive coupling and Bluetooth low‐energy radio link. The developed sensor concept is finally demonstrated in smart window prototypes, in which integrated piezoelectric sensors are used to detect break‐in attempts. Additionally, each prototype includes an electrochromic film to control the light transmittance of the window, a screen printed electrochromic display for status indications and wireless communication with an external server, and a holistic approach of hybrid printed electronic systems targeting smart multifunctional glass applications. [ABSTRACT FROM AUTHOR]

Personalised healthcare has seen significant improvements due to the introduction of health monitoring technologies that allow wearable devices to unintrusively monitor physiological parameters such as heart health, blood pressure, sleep patterns, and blood glucose levels, among others. Additionally, utilising advanced sensing technologies based on flexible and innovative biocompatible materials in wearable devices allows high accuracy and precision measurement of biological signals. Furthermore, applying real-time Machine Learning algorithms to highly accurate physiological parameters allows precise identification of unusual patterns in the data to provide health event predictions and warnings for timely intervention. However, in the predominantly adopted architectures, health event predictions based on Machine Learning are typically obtained by leveraging Cloud infrastructures characterised by shortcomings such as delayed response times and privacy issues. Fortunately, recent works highlight that a new paradigm based on Edge Computing technologies and on-device Artificial Intelligence significantly improve the latency and privacy issues. Applying this new paradigm to personalised healthcare architectures can significantly improve their efficiency and efficacy. Therefore, this paper reviews existing IoT healthcare architectures that utilise wearable devices and subsequently presents a scalable and modular system architecture to leverage emerging technologies to solve identified shortcomings. The defined architecture includes ultrathin, skin-compatible, flexible, high precision piezoelectric sensors, low-cost communication technologies, on-device intelligence, Edge Intelligence, and Edge Computing technologies. To provide development guidelines and define a consistent reference architecture for improved scalable wearable IoT-based critical healthcare architectures, this manuscript outlines the essential functional and non-functional requirements based on deductions from existing architectures and emerging technology trends. The presented system architecture can be applied to many scenarios, including ambient assisted living, where continuous surveillance and issuance of timely warnings can afford independence to the elderly and chronically ill. We conclude that the distribution and modularity of architecture layers, local AI-based elaboration, and data packaging consistency are the more essential functional requirements for critical healthcare application use cases. We also identify fast response time, utility, comfort, and low cost as the essential non-functional requirements for the defined system architecture. [ABSTRACT FROM AUTHOR]

Data glove devices, apart from being widely used in industry and entertainment, can also serve as a means for communication with the environment. This is possible thanks to the advancement in electronic technology and machine learning algorithms. In this paper, the results of the study using a designed data glove equipped with 10 piezoelectric sensors are reported, and the designed glove is validated on a recognition task of hand gestures based on 16 static signs of the Polish Sign Language (PSL) alphabet. The main result of the study is that recognition of 16 PSL static gestures is possible with a reduced number of piezoelectric sensors. This result has been achieved by applying the decision tree classifier that can rank the importance of the sensors for the recognition performance. Other machine learning algorithms were also tested, and it was showed that for the Support Vector Machines, k-NN and Bagged Trees classifiers, a recognition rate of the signs exceeding 90% can be achieved just for three preselected sensors. Such a result is important for a reduction in design complexity and costs of such a data glove with sustained reliability of the device. [ABSTRACT FROM AUTHOR]

With the fast growth of wireless communications between nodes and sensor units and the increase of devices installed in remote places, and the development of IIoT applications, new requirements for power energy supply are needed to assure device functionality and data communication capabilities during extended periods of time. For these applications, energy harvesting takes place as a good solution to increase the autonomy of remote measuring solutions, since the usage of conventional power supply solutions has clear limitations in terms of equipment access and increased maintenance costs. In this context, regenerative energy sources such as thermoelectric, magnetic and piezoelectric based, as well as renewable energy sources, such as photovoltaic and wind based, among others, make the development of different powering solutions for remote sensing units possible. The main purpose of this paper is to present a flexible testing platform to characterize piezoelectric devices and to evaluate their performance in terms of harvesting energy. The power harvesting solutions are focused on converting the energy from mechanical vibrations, provided by different types of equipment and mechanical structures, to electrical energy. This study is carried out taking into account the power supply capabilities of piezoelectric devices as a function of the amplitude, frequency and spectral contents of the vibration stimulus. Several experimental results using, as an example, a specific piezoelectric module, are included in the paper. [ABSTRACT FROM AUTHOR]

• Piezo sensors effectively capture the dynamic strain response under simulated pedestrian motions. • Strain modal parameters are obtained with a good correlation to acceleration-based modal parameters. • Lower-frequency strain modes are obtained with higher stability than the higher-frequency strain modes. • Piezo sensors effectively capture the strain modes of pedestrian footover bridge under pedestrian traffic with excellent repeatability. This study evaluates piezo sensors for modal identification of a scaled-down prototype of a pedestrian foot-over bridge under pedestrian motions and further extends the application in real-life structures. The piezo sensors-based results are compared with the accelerometers-based displacement modal parameters. Pedestrian motions are adopted to simulate the operational conditions of a pedestrian footover bridge with different patterns of pedestrian motions. Piezo sensors are found to effectively capture the low amplitude dynamic strain response under pedestrian motions. Strain modal testing captures the modal parameters positively correlated with conventional acceleration modal testing. Staggered pedestrian motions are best suited for actuating the structure uniformly at all instrumented nodes. Piezo sensor-based modal testing is extended to modal testing of real-life footover bridges under low amplitude ambient pedestrian traffic. Piezo sensors successfully capture the bending and torsion modes with good correlation with accelerometers-based modes. The strain-based modal parameters are obtained with excellent repeatability and negligible deviation. [ABSTRACT FROM AUTHOR]

Lumbar degenerative disease (LDD) refers to the nerve compression syndrome such as neurogenic intermittent claudication and lower limb pain, which disturbs people's daily life, and its incidence increases with age. Traditional diagnosis often employs magnetic response imaging or other imaging examinations. But the radiological data have uncertain clinical correlation and often be overemphasized in clinical decision making. Here, an active‐matrix sensing array (AMSA) is proposed to measure plantar pressure during walking, in order to improve LDD diagnostic processes. An array of piezoelectric sensors with high robustness are assembled. Combined with a support vector machine (SVM) supervised learning algorithm, the system can classify the common human motions of half‐squat, squat, jump, walk and jog with an accuracy up to 99.2%, demonstrating its capability of recognizing personal activities. More importantly, in 62 clinical samples of lumbar degenerative patients, the system can perform an artificial intelligence diagnosis, achieving an accuracy of 100% with an area under receiver operating characteristic curve of 0.998, and also gives out recovery assessments after surgery. Since the personal plantar pressure is also indicative of other diseases, such as diabetes and fasciitis, the system can be extended to other medical aspects, showing a broad impact in biomedical engineering. [ABSTRACT FROM AUTHOR]

Partial Discharge (PD) is one of the symptoms of an electrical insulation problem, and its permanence can lead to the complete deterioration of the electrical insulation in high-voltage equipment such as power transformers. The acoustic emission (AE) method is a well-known technique used to detect and localize PD activity inside oil-filled transformers. However, the commercially available monitoring systems based on acoustic sensors still have a high cost. This paper analyses the ability of low-cost piezoelectric sensors to identify PDs within oil-filled power transformers. To this end, two types of low-cost piezoelectric sensors were fully investigated using time-domain, frequency-domain, and time-frequency analysis, separately. Thereafter, the effectiveness of these sensors for PD detection and monitoring was studied. A three-phase distribution transformer filled with oil was examined. PDs were produced inside an oil-immersed transformer by applying a high voltage over two copper electrodes, and the AE sensors were coupled to the housing of the transformer. By extracting typical features from the AE signals, the PD signals were differentiated from on-site noise and interference. The AE signals were analyzed using acoustic signal metrics such as peak value, energy criterion, and other statistical parameters. The obtained results indicated that the used low-cost piezoelectric sensors have the capability of PD monitoring within power transformers. [ABSTRACT FROM AUTHOR]

At present, piezoelectric sensors are primarily applied in health monitoring areas. They may fall off owing to the adhesive's durability, and even damage the monitored equipment. In this paper, a piezoelectric film sensor (PFS) based on a positive piezoelectric effect (PPE) is presented and a ZnO film is deposited on a GH4169 superalloy steel (GSS) substrate using magnetron sputtering. The microstructure and micrograph of ZnO piezoelectric thin films were analyzed by an X-ray diffractometer (XRD), energy dispersive spectrometer (EDS), scanning electron microscope (SEM), and atomic force microscope (AFM). The results showed that the surface morphology was dense and uniform and had a good c-axis-preferred orientation. According to the test results of five piezoelectric sensors, the average value of the longitudinal piezoelectric coefficient was 1.36 pC/N, and the average value of the static calibration sensitivity was 19.77 mV/N. We selected the sensor whose parameters are closest to the average value for the dynamic test experiment and we drew the output voltage response curve of the piezoelectric film sensor under different loads. The measurement error was 4.03% when repeating the experiment six times. The research achievements reveal the excellent performance of the piezoelectric film sensor directly deposited on a GH4169 superalloy steel substrate. This method can reduce measurement error caused by the adhesive and reduce the risk of falling off caused by the aging of the adhesive, which provides a basis for the research of smart bolts and guarantees a better application in structural health monitoring (SHM). [ABSTRACT FROM AUTHOR]

Viscous dampers are a type of seismic damping equipment widely used in high-rise buildings and bridges. However, the viscosity of the damping fluid inside the viscous damper will change over time during its use, which significantly reduces the seismic performance of the viscous damper. Hence, it is necessary to monitor the viscosity of the fluid inside the damper over its service life. In this paper, a damping fluid viscosity monitoring method based on wireless impedance measurement technology is proposed. A piezoelectric sensor is installed in a damper cylinder specimen, and the viscosity of the damping fluid is determined by measuring the piezoelectric impedance value of the sensor. In this study, 10 samples of damping fluids with different viscosities are tested. In order to quantitatively correlate damping fluid viscosity and electrical impedance, a viscosity index (VI) based on the root mean square deviation (RMSD) is proposed. The experimental results show that the variation of the real part in the impedance signal can qualitatively determine the damping fluid viscosity while the proposed VI can effectively and quantitatively identify the damping fluid viscosity. [ABSTRACT FROM AUTHOR]

The interruption of a three-phase induction motor (TIM) on production lines represents a high financial and operational cost. However, these machines are often exposed to mechanical and electrical failures that can cause unexpected stoppages. Among these failures, the voltage unbalance (VU) is a supply fault that can lead to winding wear, torque losses, overheating, and other side effects. In this context, the acoustic emission (AE) analysis stands out as a promising nondestructive technique (NDT) in TIM monitoring. However, the AE method was not previously completely validated for VU diagnosis, and several research gaps need to be filled. Therefore, this work proposes a novel AE approach for detection, phase identification, and magnitude classification of VU. For this purpose, an electrical machine monitored by piezoelectric sensors was subjected to different levels of unbalanced voltages. The AE signals were processed using the novel zero-cross-weighted energy (ZE) index. This metric was based on the energy of the wavelet transform (WT) coefficients weighted by zero-crossing rate values. Experimental results revealed that the proposed index proved to be effective for detecting the VU occurrence. Besides, ZE-based data separation was proposed and achieved VU phase identification. Finally, the magnitude of the unbalanced voltages was classified by linear regression. The accuracy parameters for detection, phase identification, and magnitude classification stated the reliability of the new approach. Finally, the efforts of this work provide new functionalities to traditional AE systems. [ABSTRACT FROM AUTHOR]

• A novel piezoelectric sensor is designed for dynamic deformation monitoring of cantilever beams. • A theoretical method is proposed for reconstructing dynamic deformation from sensor signals. • A simple calibration method is presented to eliminate the need for precise sensors installation. • Dynamic deformation of a cantilever beam is effectively monitored in wind tunnel experiments. This paper proposes an effective analytical method for dynamic deformation monitoring of cantilever beams by combining piezoelectric ceramic sensors and modal analysis theory. The dynamic equation of beam with piezoelectric sensors is established using the assumed mode method, and the dynamic responses of the system are obtained. By analyzing the computational process inversely, the conversion matrix between sensor response and structural deformation is derived. The reconstruction equation for dynamic strain distribution of structure is obtained. The correctness and effectiveness of the proposed method are confirmed by comparing with the finite element method. Experiments based on this reconstruction method are designed to monitor dynamic deformation of a cantilever beam in bluff body wake in real-time. The obtained experimental results demonstrate high monitoring precision of the proposed method. This technological approach has the advantages of minimal sensor usage, cost-effectiveness, online monitoring, and potential for application in dynamic deformation monitoring of engineering structures. [ABSTRACT FROM AUTHOR]

The work presents a structural health monitoring (SHM) electronic system with real-time acquisition and processing for the determination of impact location in laminate. The novelty of this work is the quantitative evaluation of impact location errors using the Lamb wave guided mode S0, captured and processed in real-time by up to eight piezoelectric sensors. The differential time of arrival is used to minimize an error function for the position estimation. The impact energy is correlated to the amplitudes of the antisymmetric (A0) mode and the electronic design is described to avoid saturation for signal acquisition. The same electronic system is designed to acquire symmetric (S0) low level signals by adequate gain, bandwidth, and signal-to-noise ratio. Such signals propagate into a 1.4 mm thick aluminum laminate at the group velocity of 5150 m/s with frequency components above 270 kHz, and can be discriminated from the A0 mode to calculate accurately the differential arrival time. The results show that the localization error stabilizes at a value comparable with the wavelength of the S0 mode by increasing the number of sensors up to six, and then remains constant at up to eight sensors. This suggests that a compromise can be found between sensor density and localization error. [ABSTRACT FROM AUTHOR]

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Vacuum assisted resin infusion (VARI) has attracted more and more attentions in the aerospace field and the monitoring of the process variables has been one of the milestones for most aerospace companies. This study focuses on monitoring the flow front and curing degree of the resin in‐suit using a piezoelectric (PZT) sensor network. In the resin transfer stage, the propagation characteristics of Lamb waves were extracted from different paths to characterize the resin flow front, and the quadratic regression models of three variables were established. In the resin cure stage, the leaky Lamb waves and electromechanical impedance based on PZT sensors were simultaneously adopted to monitor the degree of cure of the resin globally and locally, respectively. The differential scanning calorimeter analysis was carried to see the compatibility among different methods for the curing degree. Experimental results demonstrated that it was feasible to monitor the flow front and curing degree of resin in VARI process using Lamb waves and electromechanical impedance based on a multifunctional piezoelectric sensor network. [ABSTRACT FROM AUTHOR]

This work presents the introduction and experimental investigation of an active-sensing acousto-ultrasound structural health monitoring approach for damage size quantification based on piezoelectric sensors/actuators mounted on multiple seemingly identical structural components. The objective of this work is to determine how reliable the damage diagnostics can be from one component to another similar (nominally identical) component using surface-mounted PZT (lead zirconate titanate) sensors/actuators, and also to evaluate how sensitive a sensor network configuration in terms of the number of sensors/actuators is with respect to its detection reliability. Extensive crack growth experiments on multiple identical coupons outfitted with the same sensor network configuration under cyclic loads were conducted to assess the damage quantification reliability from one coupon to another using the same diagnostic algorithm. The results of the study indicate that the crack size estimates obtained from the active-sensing structural health monitoring system can vary within the population of identical structural components (coupons), but the difference in quantifying damage among coupons decreases with the increase in the number of sensors and actuators used, that is, wave propagation paths. Furthermore, it is shown that the diagnostic results in terms of damage quantification converge with the increase in the number of sensors. The results of the study indicate that the diagnostic approach using a multi-path sensor network can reduce the damage quantification error from one component to another within a "hotspot" configuration (damage location is known or suspected a priori). Finally, the results of this study indicate that the more wave propagation paths used in the diagnostic active-sensing algorithm, the more reliable the damage quantification results are, provided that the same sensor network is used and installed at nominally identical locations for all coupons. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) is recognized as an efficient tool to interpret the reliability of a wide variety of infrastructures. To identify the structural abnormality by utilizing the electromechanical coupling property of piezoelectric transducers, the electromechanical impedance (EMI) approach is preferred. However, in real-time SHM applications, the monitored structure is exposed to several varying environmental and operating conditions (EOCs). The previous study has recognized the temperature variations as one of the serious EOCs that affect the optimal performance of the damage inspection process. In this framework, an experimental setup is developed in current research to identify the presence of fatigue crack in stainless steel (304) beam using EMI approach and estimate the effect of temperature variations on the electrical impedance of the piezoelectric sensors. A regular series of experiments are executed in a controlled temperature environment (25°C-160°C) using 202 V1 Constant Temperature Drying Oven Chamber (Q/TBXR20-2005). It has been observed that the dielectric constant (σ33T) which is recognized as the temperature-dependent constant of PZT sensor has sufficiently influenced the electrical impedance signature. Moreover, the effective frequency shift (EFS) approach is optimized in term of significant temperature compensation for the current impedance signature of PZT sensor relative to the reference signature at the extended frequency bandwidth of the developed measurement system with better outcomes as compared to the previous literature work. Hence, the current study also deals efficiently with the critical issue of the width of the frequency band for temperature compensation based on the frequency shift in SHM. The results of the experimental study demonstrate that the proposed methodology is qualified for the damage inspection in real-time monitoring applications under the temperature variations. It is capable to exclude one of the major reasons of false fault diagnosis by compensating the consequence of elevated temperature at extended frequency bandwidth in SHM. [ABSTRACT FROM AUTHOR]

The direction of arrival (DoA) estimation of Lamb waves is a fundamental task to locate acoustic events, such as those caused by impacts in plates or shells. To perform this task, a novel cluster of piezoelectric sensors is presented in this work. The designed cluster is composed by three irregularly shaped patch transducers (P1, P2 e P3). This is in contrast with the approaches that are typically presented in literature which are based on isotropic piezo-disks. In our approach, the transducers are shaped with a procedure based on the Radon Transform, so that the difference in time of arrival (DToA) of the Lamb waves at patches P1 and P2 is linearly related to the DoA, while P3 is designed so that it is possible to perform the estimation of DoA without knowing the actual wave velocity. The numerical validation shows that the performance in the DoA estimation achieved by means of the proposed cluster compares favorably with respect to clusters of conventional sensors, even in the case of noise-affected measurements. [ABSTRACT FROM AUTHOR]

This paper reports a novel method for fabrication of diaphragm along with microtunnels for various applications. Micromasking, grass formation, uniformity over the process wafer, notching, growth of thick silicon oxide masking layer, protection of microtunnel during diaphragm fabrication etc. are the major challenges in deep reactive ion etching (DRIE) of the existing silicon bulk micromachining process. The proposed fabrication technique solves these issues by proper selection of a stack of Al/SiO2 masking layers. Scanning Electron Microscopy (SEM) employed at intermediate fabrication stages shows that the microtunnel formed is smooth and pin hole free. The fabricated structures can be used in variety of applications such as pressure compensation in acoustic sensors, temperature compensation in integrated chips, liquid transportation in biological and chemical applications. In order to evaluate the device performance and practical applicability, investigations have been done on the device behavior as an acoustic sensor. Further, the deep cavity sealed with Pyrex glass and a sandwich structure on the front side with Al/ZnO/Al has been developed. This fabricated structure exhibits resonance frequency of 84kHz with high sensitivity of 58 $\mu V/Pa$. [ABSTRACT FROM AUTHOR]

The selection and application of an array of piezoelectric sensors for assessing the state of respiratory organs in calves by the composition of the headspace of the exhaled condensate are discussed. We considered the relationship between the output recorded data, calculated data of the sensor array, and the state of the respiratory system of an animal, determined by the results of clinical and laboratory studies. The features of chemical composition of the headspace of samples of the exhaled breath condensate in the norm and with inflammation are described. The results enable recommendations on an array of piezoelectric sensors with selected modifiers and the recorded and calculated parameters of the "electronic nose" to develop a method for the rapid diagnosis of inflammatory diseases of the respiratory system in calves by the composition of the volatile fraction of the exhaled breath condensate. [ABSTRACT FROM AUTHOR]

The paper describes the study carried out to determine the relationships between the amount of vibrations that happen inside the rock at the time of failure under tensile loading and different rock properties such as uniaxial compressive strength, uniaxial tensile strength, Young's modulus, cohesion, angle of internal friction and density. It is then tried to interpret what are the factors that affect the vibrations and the time to failure. To capture the vibrations piezoelectric sensors are used which capture the acoustic signals and convert them into electric signals. With the help of Picoscope, it was then possible to recover the acoustic signals. At the time of failure, the peak voltage (h) was recorded along with the span of time the rock took to fail (w). The h/w ratio was then obtained and used to relate it with different rock properties. h/w ratio is the measure of how much vibrations happen inside the rock and for what amount of time. It was observed to be highly related to uniaxial tensile strength, angle of internal friction and rock density. [ABSTRACT FROM AUTHOR]

Self‐powered wearable devices have attracted significantly increased attention in human motion monitoring. These flexible physical sensors conformally attach to the surface of the skin to provide new applications in human‐activity monitoring. Herein, a highly flexible and self‐powered piezoelectric pressure sensor for real‐time human motion detecting using a piezoelectric thin film with high filling ratio of lead zirconate titanate (PZT) nanofibers (NFs) in polydimethylsiloxane (PDMS) is reported. Due to the large dielectric constant of PZT and elastic properties of PDMS, the sensor performs in a wide linear region (1.25–250 kPa) with great linearity (pressure–voltage 0.9909) and good reproducibility over 2000 cycles. Using the sensor, various human body motions are detected, including joint bending, subtle/large wrist deformations, wrist and some common sporting movements. In addition, a sensor array is successfully developed to realize motion tracking, showing strong potential for application in personal recognition. [ABSTRACT FROM AUTHOR]

The measurement of cutting forces using highly sensitive piezoelectric force sensors is significant in the optimization of the machining process. In this study, the modelling and optimization of the cutting forces during the milling process of Ti6Al4V was carried out using the Response Surface Methodology (RSM) and the dynamometer. The ranges of the process parameters are: cutting speed (250-280 mm/min), feed per tooth (0.06-0.24 mm) and axial depth of cut (0.30-3.0 mm) are varied over four levels while cutting force serves as the response of the designed experiment. The physical experiments were carried out using a DMU80monoBLOCK Deckel Maho 5-axis CNC milling. Three sets of 2- flute, 10 mm corner radius mills was used for the machining operation. A solid rectangular work piece of Ti6Al4V was screwed to the stationary dynamometer (KISTLER 9257A 8-Channel Summation of Type 5001A Multichannel Amplifier) mounted directly to the machine table. Milling operations were performed using different cutting parameters of cutting speed, feed per tooth and depth of cut and data were collected through Data Acquisition (DAQ) connected to the computer. The numerical experiment produced a mathematical model for predicting the values of the cutting forces as a function of the independent process parameters while the physical experiment revealed that the piezoelectric sensor is highly sensitive to variations in the values of the cutting force. [ABSTRACT FROM AUTHOR]

Abstract A research procedure involving the fabrication of deformation sensors integrated into a FRP (fiber reinforced polymer) laminate structure is presented in this manuscript. The sensors were made from a nanocomposite based on epoxy resin and antimony sulfur iodide (SbSI) nanowires. The nanocomposite was applied as an active layer, locally placed in the laminate structure. The piezoelectric performance of the sensors was evaluated by non-destructive bending tests. The obtained electrical characteristics showed that the sensor response allows us to determine both the deformation rate and the strain of the material. This gives a potential use for these types of sensors in structure monitoring systems. The presence of a sensor in the laminate's structure does not cause a significant decrease in the mechanical performance of the material. [ABSTRACT FROM AUTHOR]

In this work, three carbon/glass hybrid composite tubes are instrumented with eight piezoelectric wafer active sensors (PWAS), used as passive receivers of acoustic emission (AE) signals. A three point bending quasi-static loading is conducted, either in a single cycle until failure or incrementally through multiple loading/unloading cycles. In the first instance, AE signal features such as maximum amplitude, peak frequency, signal duration, and energy are used to distinguish between different damage mechanisms such as matrix cracks, delamination, and fibre breakage. The group velocity of the longitudinal modes - L(0,1) and L(0,2) - is obtained experimentally in a pitch-catch configuration between the PWAS network using the time of flight (ToF). The time of arrival (ToA) method is then used to calculate damage source locations from the received AE signals. To involve more signal features for data classification, an unsupervised clustering algorithm is applied to the datasets. Optimisation of the number of clusters is completed by maximising the robustness and minimising the uncertainty of the final result. It is found that the temporal evolution of clusters indicate the ability to distinguish between the initiation and growth of damage, as well as identifying non-damage related signals caused by extraneous noise or related to the test set-up. [ABSTRACT FROM AUTHOR]

In this study, piezoelectric sensors design adhesively bonded on truss elements is treated in the framework of mathematical programming. A numerical formulation based on the strength capacity of set structure, adhesive and piezoelectric sensor is proposed. Inside the formulations maximum strength capacity of the adhesive is considered as a limit value in the design. Two formulations are established to obtain the maximum strength of the set; the first one is built on the basis of finite differences and the other one on a formulation of finite elements both based on an admissible static field. The lower bound method applied to limit analysis is extended in this research to analyze trusses with sensors including the adhesive interface. Four examples are designed to assess the numerical methodologies in which the results are compared with other known data. The main contribution of this work is focused on finding the maximum coupling load that a piezoelectric sensor can read before being debonded based on the minimum size constraint of the sensor. [ABSTRACT FROM AUTHOR]

This paper reviews recent progress on the wearable devices based on piezoelectric sensors. In recent years, many researches have turned eyes to the studies of wearable devices based on piezoelectric sensors because of the sensors' high sensitivity and efficiency. In addition, on account of their numerous advantages, the piezoelectric sensors have made great progress in medical monitoring domain. In this paper, the latest development for the use of piezoelectric sensors in medical devices will be reviewed briefly. The working principle of the piezoelectric sensors will be given. And then, the body parts that can be used for medical monitoring will be illustrated. After that, wearable medical devices made of different materials will be discussed, and their strengths and weaknesses will be analyzed. Finally, all the work listed in this article will be summarized and the future of piezoelectric sensors in the field of medical equipment will be expected. [ABSTRACT FROM AUTHOR]

This paper presents the design and experimental characterization of large-area active matrixes on foil for pressure-sensing applications. Front-end circuits based on organic thin-film transistors on a flexible substrate are laminated with a foil hosting screen-printed PDVF-TrFE piezo sensors to create the complete flexible sensing systems with $6 \times 10$ sensing elements on a $16.5~\text {cm} \times 27.5$ cm area. After defining the specifications based on the application scenarios, and designing two different front-end matrixes (A and B), the performance of the sensing surface B has been investigated in simulation. Numerical results show a readout speed of 5 kframe/s and 78.6 dB maximum signal-to-noise ratio with impact forces up to 50 kN. Experiments made with a prototype based on front end A confirm that the system can correctly reconstruct the impact profile of forces up to 50 kN obtained in a drop tower setup. Measurements of the front end circuit B show an input equivalent noise of 451 $\mu \text{V}_{\mathrm {rms}}$ and a 5% settling time of 13.8 $\mu \text{s}$ , both adequate for the specified applications. [ABSTRACT FROM AUTHOR]

The original noninvasive method for measuring the flow rate of liquids proposed in this work relies on the ability of the piezoelectric sensors embedded into pipes or pipe bends to detect the pressure fluctuations of turbulent flow. As the pressure fluctuation is directly related to the flow velocity, the electric responses of the piezoelectric sensors are correlated to the flow rate. Plastic pipes and pipe bends of different curvature radius with embedded piezoelectric ceramics of lead zirconate titanate (PZT) were used for measuring the flow rate of water. The piezoelectric sensors are placed close to the inner surface of pipe to increase their sensitivity to the pressure fluctuations of turbulent flow. Measurements of pipe vibration with accelerometers were also performed for comparison purposes. Frequency domain analyses demonstrate that the response of the piezoelectric sensors is mainly related to the pressure fluctuation of turbulent flow. Preliminary results of tests with straight acrylic pipes and 90° pipe bends made of polyvinyl chloride (PVC) demonstrate the effectiveness of the proposed technique. An interesting sensing performance to flow was observed for the PZT sensors installed in bends of small curvature radius. The disturbances to flow generate high pressure fluctuations in short radius bends, consequently improving the sensitivity to flow rate of the PZT sensors. Volumetric flow rates lower than 0.1 l/s were detected using a 90° bend of r/d = 0.5, with inside diameter d = 21 mm and integrated PZT sensors. As the pressure fluctuation is responsible for the pipe bend vibration, the sensitivity to flow rate of the accelerometers was also significantly improved. [ABSTRACT FROM AUTHOR]