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This paper aims to improve the performance of the piezoelectric buckled beam under low vibration environment using the noncontact magnetic modulation method. Based on the bi-stable buckling beam structure, the magnetic force is introduced to capture more energy. In order to investigate the influence of magnetic force in the process of vibration, the dynamic response of the harvester is analyzed under different magnetic force through numerical simulation and experiment. It is found that the magnetic force has a softening effect on the structure, namely, it could reduce the stiffness of the buckled beam. Therefore, the energy harvester could realize large-amplitude vibration under low-amplitude or low-frequency vibration with the help of magnetic force. The experimental results show that the harvester can realize inter-well vibration only when the vibration acceleration is 3.5 g and the frequency is 15 Hz without the magnetic force. The harvester only needs 2.5 g acceleration or 10 Hz vibration frequency to realize the large-amplitude vibration. While in the case of 12 mm magnetic gap. After the magnetic force is introduced in the harvester, the voltage output under 2.5 g acceleration is increased from 1 to 4 V, and the voltage output at 10 Hz vibration frequency is increased from 0.2 to 2 V. Therefore, the proposed magnetically tuned bi-stable energy harvester can better operate in low frequency and low amplitude environments. [ABSTRACT FROM AUTHOR]

With the development trend of miniaturization, lightweight and portability of electronic equipment, piezoelectric devices have been widely applied to transducers, sensors and energy harvesters. Piezoelectric polymers, like poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), possess the advantages of light weight, good flexibility, and simple preparation methods. However, P(VDF-TrFE) films is not entirely composed of piezoelectric phase (β phase), so increasing the content of β-phase is very important for the piezoelectric property of P(VDF-TrFE) films. Doping nanomaterials with unique properties has been proved to be a feasible way to increase the content of β-phase. In this paper, hexagonal boron nitride (h-BN) nanosheets, a kind of 2-dimensional van der Waals materials with wide bandgap, as filler were doping into poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) piezoelectric films by solution casting method. The composite films as designed, in which h-BN nanosheets were uniformly dispersed in P(VDF-TrFE), achieved higher contents of piezoelectric phase (β phase). Compared with pure P(VDF-TrFE) films, the optimal P(VDF-TrFE)/BN piezoelectric film achieved a much higher piezoelectric coefficient (d 33) (∼42 pC/N), also leading to a higher piezoelectric voltage output than that of pure P(VDF-TrFE). By laminating the P(VDF-TrFE)/BN films as designed with FeSiB Metglas, high magnetoelectric voltage coefficients under zero and low DC magnetic bias were achieved. In summary, this paper presents a feasible and potential method for improving PVDF piezoelectricity, which has been successfully applied in high performance magnetoelectric devices. [ABSTRACT FROM AUTHOR]

Tunnels for subways and railways are a vital part of urban transportation systems, where shield tunneling using assembled segmental linings is the predominant construction approach. With increasing operation time and varying geological conditions, shield tunnels usually develop defects that compromise both structural integrity and operational safety. One common issue is the separation of segment joints that may cause water/mud penetration and corrosion. Existing inspection strategies can only detect openings after their occurrence, which cannot provide early warnings for predictive maintenance. To address this issue, this work proposes a multi-point seam contact pressure monitoring method for joint opening identification. It first derived the theoretical correlation between contact pressure distribution and segment opening; then, a finite element model was established to explore the stress and deformation responses under combined axial and bending loads. Finally, multi-point piezoelectric film sensors were implemented on a scaled segment model to validate the theoretical and numerical analyses. Results indicate that the multi-point monitoring method can effectively identify opening amounts at the segment joints with an average error of 8.8%, confirming the method's feasibility. These findings support the use of this monitoring technique for early detection and assessment of joint openings in shield tunnels. [ABSTRACT FROM AUTHOR]

We introduce a micro-electromechanical system (MEMS) energy harvester, designed for capturing flow energy. Moving beyond traditional vibration-based energy harvesting, our approach incorporates a cylindrical oscillator mounted on an MEMS chip, effectively harnessing wind energy through flow-induced vibration (FIV). A highlight of our research is the development of a comprehensive fabrication process, utilizing a 5.00 µm thick cantilever beam and piezoelectric film, optimized through advanced micromachining techniques. This process ensures the harvester's alignment with theoretical predictions and enhances its operational efficiency. Our wind tunnel experiments confirmed the harvester's capability to generate a notable electrical output, with a peak voltage of 2.56 mV at an 8.00 m/s wind speed. Furthermore, we observed a strong correlation between the experimentally measured voltage frequencies and the lift force frequency observed by CFD analysis, with dominant frequencies identified in the range of 830 Hz to 867 Hz, demonstrating the potential application in actual flow environments. By demonstrating the feasibility of efficient energy conversion from ambient wind, our research contributes to the development of sustainable energy solutions and low-power wireless electron devices. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study presents a numerical simulation-based investigation of a MEMS (micro-electromechanical systems)technology-based deformable mirror employing a piezoelectric film for fundus examination in adaptive optics. Compared to the classical equal-area electrode arrangement model, we optimize the electrode array for higher-order aberrations. The optimized model centralizes electrodes around the mirror center, which realizes low-voltage driving with high-accuracy correction. The optimized models exhibited commendable correction abilities, achieving a unidirectional displacement of 5.74 μm with a driven voltage of 15 V. The voltage–displacement relationship demonstrated high linearity at 0.99. Furthermore, the deformable mirror's influence matrix was computed, aligning with the Zernike standard surface shape of the order 1–3. To quantify aberration correction capabilities, fitting residuals for both models were calculated. The results indicate an average removal of 96.8% of aberrations to the human eye. This underscores that the optimized model outperforms the classical model in correcting high-order aberrations. [ABSTRACT FROM AUTHOR]

Tunnels for subways and railways are a vital part of urban transportation systems, where shield tunneling using assembled segmental linings is the predominant construction approach. With increasing operation time and varying geological conditions, shield tunnels usually develop defects that compromise both structural integrity and operational safety. One common issue is the separation of segment joints that may cause water/mud penetration and corrosion. Existing inspection strategies can only detect openings after their occurrence, which cannot provide early warnings for predictive maintenance. To address this issue, this work proposes a multi-point seam contact pressure monitoring method for joint opening identification. It first derived the theoretical correlation between contact pressure distribution and segment opening; then, a finite element model was established to explore the stress and deformation responses under combined axial and bending loads. Finally, multi-point piezoelectric film sensors were implemented on a scaled segment model to validate the theoretical and numerical analyses. Results indicate that the multi-point monitoring method can effectively identify opening amounts at the segment joints with an average error of 8.8%, confirming the method’s feasibility. These findings support the use of this monitoring technique for early detection and assessment of joint openings in shield tunnels.

Sleep apnea hypoventilation syndrome (SAHS) is a potentially dangerous and common disease that can affect the patient's health and even lead to sudden death during sleep, making it necessary to monitor changes in respiratory status in real time. Traditional medical devices are mainly concentrated in hospitals and are not conducive to widespread use, while wearable medical devices are well suited to this task. Occasional transient respiratory obstruction is common during sleep for normal people, but it is pathological if SAHS occurs very frequently and severe. In this paper, a respiration monitoring system based on piezoelectric film sensor was fabricated, which can make real-time monitoring, record and display the respiration rate, and automatically recognize it and sound a warning. The proposed system shows great potential for wearable SAHS monitoring instrument. [ABSTRACT FROM AUTHOR]

The acoustic waves of higher orders propagating in a layered structure consisting of a silicon plate coated with piezoelectric ZnO and/or AlN films were used for the development of a sensor with selective sensitivity to liquid viscosity η in the range of 1–1500 cP. In that range, this sensor possessed low sensitivity to liquid conductivity σ and temperature T in the ranges of 0–2 S/m and 0–55 °C, respectively. The amplitude responses insensitive to the temperature instead of the phase were used to provide the necessary selectivity. The sensor was based on a weak piezoactive acoustic wave of higher order. The volume of the probes sufficient for the measurements was about 100 μL. The characteristics of the sensors were optimized by varying the thicknesses of the structure layers, number of layers, wavelength, wave propagation direction, and the order of the acoustic waves. It was shown that in the case of the layered structure, it is possible to obtain practically the same selective sensitivity toward viscosity as for acoustic waves in pure ST, X quartz. The most appropriate waves for this purpose are quasi-longitudinal and Lamb waves of higher order with in-plane polarization. It was found that for various ranges of viscosity η = 1–20 cP, 20–100 cP, and 100–1500 cP, the maximum sensitivity of the appropriate wave is equal to 0.26 dB/cP, 0.087 dB/cP, and 0.013 dB/cP, respectively. The sensitivity of the waves under study toward the electric conductivity of the liquid is much less than the sensitivity to liquid viscosity. These two responses become comparable only for very small η < 2 cP. The waves investigated have shown no temperature responses in contact with air, but in the presence of liquid, they increase depending on liquid properties. The temperature dependence of liquid viscosity is measurable by the same sensors. The results obtained have shown the possibility of designing acoustic liquid viscosity sensors based on multilayered structures. The set of possible acoustic waves in layered structures possesses modified propagation characteristics (various polarization, phase velocities, electromechanical coupling coefficients, and attenuations). It allows choosing an optimal acoustic wave to detect liquid viscosity only. [ABSTRACT FROM AUTHOR]

We introduce a micro-electromechanical system (MEMS) energy harvester, designed for capturing flow energy. Moving beyond traditional vibration-based energy harvesting, our approach incorporates a cylindrical oscillator mounted on an MEMS chip, effectively harnessing wind energy through flow-induced vibration (FIV). A highlight of our research is the development of a comprehensive fabrication process, utilizing a 5.00 µm thick cantilever beam and piezoelectric film, optimized through advanced micromachining techniques. This process ensures the harvester’s alignment with theoretical predictions and enhances its operational efficiency. Our wind tunnel experiments confirmed the harvester’s capability to generate a notable electrical output, with a peak voltage of 2.56 mV at an 8.00 m/s wind speed. Furthermore, we observed a strong correlation between the experimentally measured voltage frequencies and the lift force frequency observed by CFD analysis, with dominant frequencies identified in the range of 830 Hz to 867 Hz, demonstrating the potential application in actual flow environments. By demonstrating the feasibility of efficient energy conversion from ambient wind, our research contributes to the development of sustainable energy solutions and low-power wireless electron devices.

This study presents a numerical simulation-based investigation of a MEMS (micro-electromechanical systems)technology-based deformable mirror employing a piezoelectric film for fundus examination in adaptive optics. Compared to the classical equal-area electrode arrangement model, we optimize the electrode array for higher-order aberrations. The optimized model centralizes electrodes around the mirror center, which realizes low-voltage driving with high-accuracy correction. The optimized models exhibited commendable correction abilities, achieving a unidirectional displacement of 5.74 μm with a driven voltage of 15 V. The voltage–displacement relationship demonstrated high linearity at 0.99. Furthermore, the deformable mirror’s influence matrix was computed, aligning with the Zernike standard surface shape of the order 1–3. To quantify aberration correction capabilities, fitting residuals for both models were calculated. The results indicate an average removal of 96.8% of aberrations to the human eye. This underscores that the optimized model outperforms the classical model in correcting high-order aberrations.

In order to solve the problem of ineffective utilization of waste heat generated by energy consumption in industrial production and life, a low-frequency thermal energy conversion type piezoelectric energy trap is proposed, and relevant theoretical analysis and experimental research are conducted. The device utilizes a piezoelectric film (polyvinylidene fluoride) combined with a shape memory alloy and features a simple green structure that can supply energy to microelectronic devices. First, the structural design and working principle of the device are analyzed and the dynamics model is built. Second, COMSOL Multiphysics simulation software (Version 5.6) is used to analyze and calculate the output voltage of shape memory alloy shrinkage, piezoelectric film shape and parameters. Finally, the experimental prototype is machined and fabricated by the fine engraving machine, and the experimental platform is built for relevant performance tests. The experimental results show that when the temperature is 100 °C, the maximum strain of shape memory alloy with 1 mm diameter is 0.148 mm. When the shape of the piezoelectric film is triangular, the length of the bottom edge is equal to the height of the triangle and the thickness ratio is 0.5, the maximum output voltage is 2.12 V. The experimental results verify the feasibility of the designed device and provide new ideas for subsequent research on piezoelectric energy capture. [ABSTRACT FROM AUTHOR]

Copyright of Advanced Textile Technology is the property of Zhejiang Sci-Tech University Magazines and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Poly(l‐lactic acid) (PLLA) films have excellent piezoelectric properties, but the strong hydrophobicity of the surface makes it difficult for cells to attach there. PLLA nanofibers have good biocompatibility, but the weak piezoelectric coefficient limits the ability of the nanofibers to stimulate cell growth. Therefore, the PLLA piezoelectric film is combined with the PLLA nanofibers to make a multilayer film. In our tests, the piezoelectric output of the multilayer film ≈260 mV. In the biological experiments section, without piezoelectric stimulation, the cell length on the nanofibers is approximately twice that of the cells in the blank control group. The length of cells cultured on piezoelectric‐based stimulated nanofibers is more than twice that of cells cultured on nanofibers without piezoelectric stimulation. Therefore, it is confirmed that under the dual action of nanofiber guidance and piezoelectric stimulation, the growth rate of cells is four times faster than that in ordinary Petri dishes. Intracellular calcium imaging experiments confirmed that the concentration of Ca2+ in electrically stimulated cells is approximately twice that of ordinary cells. It is also confirmed that piezoelectric materials can complete electrical stimulation of cells in indirect contact with cells. [ABSTRACT FROM AUTHOR]

Pipeline leakage causes enormous safety and economic concerns; therefore, sensors which are high-performance and durable are in high demand for improving monitoring accuracy and for avoiding economic loss. In this work, mica-based flexible PZT sensors showed high sensitivity, with 140 mV N−1 and 467 mV N−1 for the output voltage, with regard to the tapping and bending modes, respectively. They can monitor airflow in normal conditions with high sensitivity and a linearity of 424 mV MPa−1 and 0.99, respectively. In the event of a pipeline leak, the mica-based sensors exhibited a rapid response time as short as 0.578 s. Furthermore, they generated distinct voltage levels at different distances from the leakage point, thus providing valuable information for accurately locating the source of the leakage. [ABSTRACT FROM AUTHOR]

Abstract Piezoelectric polymers have been widely used in a variety of applications, including tactile sensors, energy harvesting, polymer actuators, and biological devices. In this investigation, we fabricated the PLLA (poly(L‐lactic Acid)‐based bimorph structures for piezoelectric motor applications. First, a strain measurement setup was established to measure the strain of the PLLA and PDLA film at different temperatures. The effective piezoelectric constants d14 calculated for the PLLA and PDLA films were 10.2 pC/N and 9.4 pC/N, respectively. Furthermore, the PLLA films showed a strong thermostability of piezoelectricity at 130°C. The PLLA bimorph minimotor showed the maximum load of 1.2 g and the maximum torque of 0.019 cN·m. The minimotors were capable of rotating a plastic hemisphere container in the clockwise and counterclockwise directions at 65 V voltage. Due to the light weight, low driving voltage, and thermal stability, the PLLA/PDLA motors show a great promise in future Braille display, robots, and mini‐digital camera applications.

In order to solve the problem of conventional energy shortages, a non-resonant impact piezoelectric energy capture device using a (polyvinylidene fluoride) piezoelectric film at low frequency is proposed, and related theoretical analysis and experimental studies are conducted. The device has a simple internal structure, is green and easy to miniaturize, and is capable of harvesting energy at low frequencies to supply energy to micro and small electronic devices. First, to verify the feasibility of the device, the structure of the experimental device is modeled and dynamically analyzed. Then the modal, stress–strain, and output voltage of the piezoelectric film are simulated and analyzed using COMSOL Multiphysics simulation software. Finally, the experimental prototype is built according to the model, and the experimental platform is constructed to test the relevant performance. The experimental results show that the output power produced by the capturer varies within a certain range when the capturer is excited externally. With an external excitation force of 30 N, a piezoelectric film bending amplitude of 60°, and a piezoelectric film size of 45 × 80 mm, the resulting output power voltage is 21.69 V, the output current is 0.07 mA, and the output power is 1.5176 mW. This experiment verifies the feasibility of the energy capturer and provides a new idea for powering electronic components. [ABSTRACT FROM AUTHOR]

ZnO flower-like (ZFL) and needle (ZLN) structures were synthesized and embedded into UV-curable acrylic resin (EB), with the aim to study the effect of filler loading on the piezoelectric properties of the resulting composite films. The composites showed uniform dispersion of fillers within the polymer matrix. However, by increasing the filler amount, the number of aggregates increased, and ZnO fillers appeared not to be perfectly embedded in polymer film, indicating poor interaction with acrylic resin. The filler content increase caused an increase in glass transition temperature (Tg) and a decrease in storage modulus in the glassy state. In particular, compared with pure UV-cured EB (Tg = 50 °C), 10 wt.% ZFL and ZLN presented Tg values of 68 and 77 °C, respectively. The piezoelectric response generated by the polymer composites was good when measured at 19 Hz as a function of the acceleration; the RMS output voltages achieved at 5 g were 4.94 and 1.85 mV for the composite films containing ZFL and ZLN, respectively, at their maximum loading levels (i.e., 20 wt.%). Further, the RMS output voltage increase was not proportional to the filler loading; this finding was attributable to the decrease in the storage modulus of the composites at high ZnO loading rather than the dispersion of filler or the number of particles on the surface. [ABSTRACT FROM AUTHOR]

Abstract Poly(l‐lactic acid) (PLLA) films have excellent piezoelectric properties, but the strong hydrophobicity of the surface makes it difficult for cells to attach there. PLLA nanofibers have good biocompatibility, but the weak piezoelectric coefficient limits the ability of the nanofibers to stimulate cell growth. Therefore, the PLLA piezoelectric film is combined with the PLLA nanofibers to make a multilayer film. In our tests, the piezoelectric output of the multilayer film ≈260 mV. In the biological experiments section, without piezoelectric stimulation, the cell length on the nanofibers is approximately twice that of the cells in the blank control group. The length of cells cultured on piezoelectric‐based stimulated nanofibers is more than twice that of cells cultured on nanofibers without piezoelectric stimulation. Therefore, it is confirmed that under the dual action of nanofiber guidance and piezoelectric stimulation, the growth rate of cells is four times faster than that in ordinary Petri dishes. Intracellular calcium imaging experiments confirmed that the concentration of Ca2+ in electrically stimulated cells is approximately twice that of ordinary cells. It is also confirmed that piezoelectric materials can complete electrical stimulation of cells in indirect contact with cells.

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Poly(vinylidene fluoride) (PVDF) has been a kind of particularly attractive piezoelectric materials for its excellent piezoelectric property. Due to its light weight, impedance characteristic is very similar to water, and good mechanical flexibility, PVDF piezoelectric film is very suitable for the field of hydrophones. Although the piezoelectric ceramic hydrophone has been widely used, but due to the disadvantage of high inherent frequency and fragile characteristics of the piezoelectric ceramics slice, the development of the piezoelectric hydrophone is limited. The application of PVDF piezoelectric film has solved many problems encountered in the use of piezoelectric ceramics. In this article, the classification of hydrophone is briefly introduced at first, and then the current status of hydrophone research is involved. And then, by analyzing the electrical equivalent model of the PVDF piezoelectric sensitive unit, the signal conditioning circuit of the PVDF piezoelectric hydrophone is summarized as well. After that, the current status of PVDF hydrophone research is discussed. Finally, a summary of all the work listed in this article is given and an outlook of PVDF hydrophone is proposed. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, a piezoelectric micromachined ultrasonic transducer (PMUT) is integrated with a microliter-sized volume-tunable Helmholtz resonator. The passive Helmholtz resonator is constructed using an SU8 photolithography-defined square opening plate as the neck portion, a 3D-printed hollow structure with a threaded insert nut, and a precision set screw to form the volume-controllable cavity of the Helmholtz resonator. The fabricated piezoelectric films acted as ultrasonic actuators attached to the surface of the neck SU8 plate. Experimental results show that the sound pressure level (SPL) and operation bandwidth could be effectively tuned, and a 200% SPL increase and twofold bandwidth enhancement are achieved when setting the cavity length to 0.75 mm compared with the open-cavity case. A modified Helmholtz resonator model is proposed to explain the experimental results. The adjusting factors of the effective mass and viscous damper are created to modify the existing parameters in the conventional Helmholtz resonator model. The relationship between the adjusting factors and cavity length can be described well using a two-term power series curve. This modified Helmholtz resonator model not only provides insight into this active-type Helmholtz resonator operation but also provides a useful estimation for its optimal design and fabrication. [ABSTRACT FROM AUTHOR]

During people's normal movement, the sole of foot is the only part of human body that contacts with the ground. The pressure information of sole directly reflects the physiological health and movement posture of human. A plantar pressure measurement system was designed with an insole type for measuring plantar pressure during normal movement. The insole embedded five PVDF piezoelectric film sensors, and then places the insole in the measured sports shoes. In order to obtain better pressure response effect, two small raised blocks were pasted under each piezoelectric film sensor to increase the sensitivity of the sensor. The plantar pressure data was sent to PC by wireless serial port. An intuitive and easy-to-use GUI interface was designed by the MATLAB software. The interface can display the pressure distribution at each point of the sole of both feet. [ABSTRACT FROM AUTHOR]

This article presents a wearable breath-monitoring device integrated with humidity- and ammonia-sensing functions. The breath-monitoring device was constructed using a piezoelectric cantilever array and hollow flexible polydimethylsiloxane (PDMS) membrane. Important parameters of breath, such as the respiratory rate and tidal volume, can be detected without actuated energy. The Nafion-based capacitive humidity sensor and ZnO nanoparticle-based resistance ammonia sensor were compactly integrated into the housing ring of a breath monitoring device. The fabricated humidity sensor demonstrated a faster response in the sensing range below 75% compared with a commercial product. The sensitivity of the fabricated ammonia sensor reached 0.16 ppm/mV and the sensor exhibited an approximately fourfold shorter response time compared with the commercial product. Two applications were tested for the developed device prototype. One was monitoring the humidity and ammonia of the environmental air along with breath parameters while breathing. The other was to examine the amount of breath air exhaled from the body of the subject. The total power consumed by the developed prototype device was approximately 46 mW, which is significantly lower than that of existing commercial products. This compact and lightweight prototype device demonstrates significant potential for wearable applications. [ABSTRACT FROM AUTHOR]

The relatively low piezoelectric constant of aluminum nitride (AlN) piezoelectric film limits the development and application of the acoustic field performance of AlN-based micromachined ultrasonic transducers; thus, in this study we establish a mid- to low-frequency transducer unit model to address this problem. The transducer operates at 4.5 MHz, and the construction of a clamped structure is first investigated to ensure the feasibility of performance analysis. Secondly, the effectiveness of the optimized upper electrode distribution proposed in this paper in improving the acoustic field radiation of the array element is also compared with the original structure. Finally, the influence of the optimized electrode geometry parameters on the acoustic wave direction is analyzed. The finite element simulations are performed in the COMSOL Multiphysics (COMSOL) software and post-processing results are analyzed. Based on the simulation results, the proposed optimal distribution of the upper electrode makes the radiation beam uniform and symmetrical in the case of both the clamped model and the optimized structure model. In the case of the upper electrode radius of 28 µm, this electrode division operation makes the unit vibration mode switching in the frequency range more moderate. The sound field radiation improvement of the proposed optimized structure model is better than that of the clamped structure. [ABSTRACT FROM AUTHOR]

The acoustic waves of higher orders propagating in a layered structure consisting of a silicon plate coated with piezoelectric ZnO and/or AlN films were used for the development of a sensor with selective sensitivity to liquid viscosity η in the range of 1–1500 cP. In that range, this sensor possessed low sensitivity to liquid conductivity σ and temperature T in the ranges of 0–2 S/m and 0–55 °C, respectively. The amplitude responses insensitive to the temperature instead of the phase were used to provide the necessary selectivity. The sensor was based on a weak piezoactive acoustic wave of higher order. The volume of the probes sufficient for the measurements was about 100 μL. The characteristics of the sensors were optimized by varying the thicknesses of the structure layers, number of layers, wavelength, wave propagation direction, and the order of the acoustic waves. It was shown that in the case of the layered structure, it is possible to obtain practically the same selective sensitivity toward viscosity as for acoustic waves in pure ST, X quartz. The most appropriate waves for this purpose are quasi-longitudinal and Lamb waves of higher order with in-plane polarization. It was found that for various ranges of viscosity η = 1–20 cP, 20–100 cP, and 100–1500 cP, the maximum sensitivity of the appropriate wave is equal to 0.26 dB/cP, 0.087 dB/cP, and 0.013 dB/cP, respectively. The sensitivity of the waves under study toward the electric conductivity of the liquid is much less than the sensitivity to liquid viscosity. These two responses become comparable only for very small η < 2 cP. The waves investigated have shown no temperature responses in contact with air, but in the presence of liquid, they increase depending on liquid properties. The temperature dependence of liquid viscosity is measurable by the same sensors. The results obtained have shown the possibility of designing acoustic liquid viscosity sensors based on multilayered structures. The set of possible acoustic waves in layered structures possesses modified propagation characteristics (various polarization, phase velocities, electromechanical coupling coefficients, and attenuations). It allows choosing an optimal acoustic wave to detect liquid viscosity only.

In order to solve the problem of ineffective utilization of waste heat generated by energy consumption in industrial production and life, a low-frequency thermal energy conversion type piezoelectric energy trap is proposed, and relevant theoretical analysis and experimental research are conducted. The device utilizes a piezoelectric film (polyvinylidene fluoride) combined with a shape memory alloy and features a simple green structure that can supply energy to microelectronic devices. First, the structural design and working principle of the device are analyzed and the dynamics model is built. Second, COMSOL Multiphysics simulation software (Version 5.6) is used to analyze and calculate the output voltage of shape memory alloy shrinkage, piezoelectric film shape and parameters. Finally, the experimental prototype is machined and fabricated by the fine engraving machine, and the experimental platform is built for relevant performance tests. The experimental results show that when the temperature is 100 °C, the maximum strain of shape memory alloy with 1 mm diameter is 0.148 mm. When the shape of the piezoelectric film is triangular, the length of the bottom edge is equal to the height of the triangle and the thickness ratio is 0.5, the maximum output voltage is 2.12 V. The experimental results verify the feasibility of the designed device and provide new ideas for subsequent research on piezoelectric energy capture.

ScAlN films are currently being investigated for their potential use in surface acoustic wave (SAW) devices for next-generation mobile networks because of their high piezoelectricity. This paper describes the numerical simulation of SAW propagation in c -axis-tilted ScAlN films on silicon substrates and a fabrication technique for preparing c -axis-tilted ScAlN films on silicon substrates. The electromechanical coupling coefficient K 2 of SAW propagating in the ScAlN film/silicon substrate increased due to the c -axis tilt angle. The maximum K 2 value is approximately 3.90%. This value is 2.6 times the maximum K 2 value of the c -axis-oriented ScAlN film/silicon substrate structure. The c -axis-tilted ScAlN films with an Sc concentration of 40% were prepared on a silicon substrate via RF magnetron sputtering based on the self-shadowing effect, and the maximum c -axis tilt angle was 57.4°. These results indicate that this device structure has the potential for SAW device applications with well-established micromachining technology derived from silicon substrates. [ABSTRACT FROM AUTHOR]

In this paper, potassium sodium niobate lead-free piezoelectric thin films were prepared by sol-gel method. The electric domain structure and optical band gap of the thin films were regulated by doping Mn. It is found that Mn doping increases the grain size and density of KNNLT piezoelectric film surface. In addition, Mn doping can regulate the electric domain of thin films. Increasing Mn doping concentration can regulate the size and distribution of electric domain, and the ratio of 71° electric domain increases with the increase of doping concentration. The results show that the optical band gap decreases gradually with the increase of doping amount when the annealing temperature is 650 °C. The lowest optical band gap reaches 3.426 eV, and is lower than the undoped KNNLT films. [ABSTRACT FROM AUTHOR]

Influence of fabric electrode on polyvinylidene fluoride (PVDF) piezoelectric film property was studied. Sheet resistance of 3. 5 Ω·cm² silver paste screen printing polyester fabric was prepared by screen printing method. Silver-plated polyester fabric and copper screen fabric with same sheet resistance were selected. Three kinds of fabric were used as electrode together with PVDF piezoelectric film to encapsulate and prepare flexible piezoelectric sensor. Dielectric contact property, sensitivity and durability of the three fabric piezoelectric sensors were tested. The test results showed electrode dielectric impedance of silver-plated fabric and copper screen fabric were stable when the frequency was lower than 4 kHz. When the frequency was around 1x104 Hz, the fluctuation of relative dielectric constant for silver paste screen printing fabric electrode was obvious. It was obviously higher than those of the other two fabric electrodes under high frequency condition. The dielectric property of silver-plated fabric electrode was close to that of copper screen fabric electrode. The three kinds of electrode all had a certain piezoelectric susceptibility. The sensitivities of silver paste screen printing fabric electrode and copper screen fabric electrode were slightly higher. After 2 000 times of pressing, sawtooth square signals still could be output for silver-plated fabric electrode and copper screen fabric electrode. Obvious baseline drift phenomenon was appeared for silver paste screen printing fabric electrode. It is considered that the overall properties of flexible piezoelectric sensor packaged by copper screen fabric as electrode are better. Dielectric property and durability of silver-plated fabric are better. Sensitivity of silver paste screen printing fabric is better. The three kinds of fabric can be used as electrode material to produce sensor. However, problems like motion artifact and so on need to be further studied. [ABSTRACT FROM AUTHOR]

Pipeline leakage causes enormous safety and economic concerns; therefore, sensors which are high-performance and durable are in high demand for improving monitoring accuracy and for avoiding economic loss. In this work, mica-based flexible PZT sensors showed high sensitivity, with 140 mV N−1 and 467 mV N−1 for the output voltage, with regard to the tapping and bending modes, respectively. They can monitor airflow in normal conditions with high sensitivity and a linearity of 424 mV MPa−1 and 0.99, respectively. In the event of a pipeline leak, the mica-based sensors exhibited a rapid response time as short as 0.578 s. Furthermore, they generated distinct voltage levels at different distances from the leakage point, thus providing valuable information for accurately locating the source of the leakage.

In order to solve the problem of conventional energy shortages, a non-resonant impact piezoelectric energy capture device using a (polyvinylidene fluoride) piezoelectric film at low frequency is proposed, and related theoretical analysis and experimental studies are conducted. The device has a simple internal structure, is green and easy to miniaturize, and is capable of harvesting energy at low frequencies to supply energy to micro and small electronic devices. First, to verify the feasibility of the device, the structure of the experimental device is modeled and dynamically analyzed. Then the modal, stress–strain, and output voltage of the piezoelectric film are simulated and analyzed using COMSOL Multiphysics simulation software. Finally, the experimental prototype is built according to the model, and the experimental platform is constructed to test the relevant performance. The experimental results show that the output power produced by the capturer varies within a certain range when the capturer is excited externally. With an external excitation force of 30 N, a piezoelectric film bending amplitude of 60°, and a piezoelectric film size of 45 × 80 mm, the resulting output power voltage is 21.69 V, the output current is 0.07 mA, and the output power is 1.5176 mW. This experiment verifies the feasibility of the energy capturer and provides a new idea for powering electronic components.

Accurate and efficient measurements of the piezoelectric properties of AlN and AlScN films are very important for the design and simulation of micro-electro-mechanical system (MEMS) sensors and actuator devices. In this study, a process control monitor (PCM) structure compatible with the device manufacturing process is designed to achieve accurate determination of the piezoelectric coefficients of MEMS devices. Double-beam laser interferometry (DBLI) and laser Doppler vibrometry (LDV) measurements are applied and combined with finite element method (FEM) simulations, and values of the piezoelectric parameters d33 and d31 are simultaneously extracted. The accuracy of d31 is verified directly by using a cantilever structure, and the accuracy of d33 is verified by in situ synchrotron radiation X-ray diffraction; the comparisons confirm the viability of the results obtained by the novel combination of LDV, DBLI and FEM techniques in this study. [ABSTRACT FROM AUTHOR]

The ScxAl1-xN wurtzite structure has been shown theoretically and experimentally to exhibit significantly higher piezoelectric coupling compared to pure AlN. In this work, a plasma-assisted epitaxial growth method has been used to synthesize epitaxial (0002) ScxAl1-xN films on c-sapphire substrates from x = 0.07 to 0.30 by co-evaporating high-purity Sc and Al sources in the presence of a nitrogen plasma generated by an RF plasma source. Epitaxial ScxAl1-xN films with highly oriented (0002) grains and in-plane registry were produced on c-sapphire substrates that were pre-exposed to the nitrogen plasma to form an oxynitride seed layer. Growth of ScxAl1-xN films was carried out at 930°C under both metal-rich and N-rich conditions using precisely controlled Sc, Al, and N-plasma fluxes. Metal-rich depositions yielded non-(0002)-oriented ScxAl1-xN grains and intermetallic ScAl grains. Nitrogen-rich growth with a Sc/Al flux ratio of 1/3 produced the best (0002) epitaxy as determined by x-ray diffraction analysis. Surface acoustic wave resonator (SAWR) devices were fabricated from 500-nm-thick ScxAl1-xN and AlN films to extract their electromechanical coupling coefficients, k2. As the Sc concentration in the films increases, the degree of (0002) epitaxy is reduced, yet the value of k2 increases becasue there is more Sc in the wurzite lattice despite the decreased level of (0002) grain alignment. The use of a 10-nm-thick SixNy capping layer on top of the ScxAl1-xN films aids in preventing etching during SAWR device photolithography and also helps hinder film oxidation up to 800°C. [ABSTRACT FROM AUTHOR]

Purpose: To test the validity of a force-based detection system (ISFD: intra-splint force detector) to record sleep bruxism (SB) in comparison to portable polysomnography (PSG).Methods: Simultaneous portable PSG recordings with a masseter electromyography (EMG) channel and ISFD with a deformation-sensitive piezoelectric film were performed on six participants with definite SB. First, simulated bruxism behaviors (static clenching, grinding, tapping, and rhythmic clenching) were recorded using both EMG and ISFD. Using these data, interval and duration criteria for ISFD data conditioning were established. Then, portable PSG recordings were conducted with the ISFD during sleep. Using the above criteria, ISFD events were compared with EMG-based SB episodes (the gold standard), and the sensitivity and positive predictive value of ISFD events were calculated. Spearman's correlation coefficients between true-positive ISFD events and SB episodes were then calculated.Results: Among the tested conditioning criteria, a 3-s interval combined with a 1-s duration was selected. The median sensitivity and positive predictive value for the ISFD were 0.861 and 0.585, respectively. The duration of true-positive ISFD events was correlated with that of EMG-based SB episodes (rho = 0.658, P < 0.01).Conclusion: ISFD has validity for SB detection and could be an alternative to single-channel EMG-based recordings. [ABSTRACT FROM AUTHOR]

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ZnO flower-like (ZFL) and needle (ZLN) structures were synthesized and embedded into UV-curable acrylic resin (EB), with the aim to study the effect of filler loading on the piezoelectric properties of the resulting composite films. The composites showed uniform dispersion of fillers within the polymer matrix. However, by increasing the filler amount, the number of aggregates increased, and ZnO fillers appeared not to be perfectly embedded in polymer film, indicating poor interaction with acrylic resin. The filler content increase caused an increase in glass transition temperature (Tg) and a decrease in storage modulus in the glassy state. In particular, compared with pure UV-cured EB (Tg = 50 °C), 10 wt.% ZFL and ZLN presented Tg values of 68 and 77 °C, respectively. The piezoelectric response generated by the polymer composites was good when measured at 19 Hz as a function of the acceleration; the RMS output voltages achieved at 5 g were 4.94 and 1.85 mV for the composite films containing ZFL and ZLN, respectively, at their maximum loading levels (i.e., 20 wt.%). Further, the RMS output voltage increase was not proportional to the filler loading; this finding was attributable to the decrease in the storage modulus of the composites at high ZnO loading rather than the dispersion of filler or the number of particles on the surface.

Strain can modulate bandgap and carrier mobilities in two-dimensional (2D) materials. Conventional strain-application methodologies relying on flexible/patterned/nanoindented substrates are limited by low thermal tolerance, poor tunability, and/or scalability. Here, we leverage the converse piezoelectric effect to electrically generate and control strain transfer from a piezoelectric thin film to electromechanically coupled 2D MoS 2 . Electrical bias polarity change across the piezo film tunes the nature of strain transferred to MoS 2 from compressive (∼0.23%) to tensile (∼0.14%) as verified through Raman and photoluminescence spectroscopies and substantiated by density functional theory calculations. The device architecture, on silicon substrate, integrates an MoS 2 field-effect transistor on a metal-piezoelectric-metal stack enabling strain modulation of transistor drain current (130×), on/off ratio (150×), and mobility (1.19×) with high precision, reversibility, and resolution. Large, tunable tensile (1056) and compressive (-1498) strain gauge factors, electrical strain modulation, and high thermal tolerance promise facile integration with silicon-based CMOS and micro-electromechanical systems.

In this study, a piezoelectric micromachined ultrasonic transducer (PMUT) is integrated with a microliter-sized volume-tunable Helmholtz resonator. The passive Helmholtz resonator is constructed using an SU8 photolithography-defined square opening plate as the neck portion, a 3D-printed hollow structure with a threaded insert nut, and a precision set screw to form the volume-controllable cavity of the Helmholtz resonator. The fabricated piezoelectric films acted as ultrasonic actuators attached to the surface of the neck SU8 plate. Experimental results show that the sound pressure level (SPL) and operation bandwidth could be effectively tuned, and a 200% SPL increase and twofold bandwidth enhancement are achieved when setting the cavity length to 0.75 mm compared with the open-cavity case. A modified Helmholtz resonator model is proposed to explain the experimental results. The adjusting factors of the effective mass and viscous damper are created to modify the existing parameters in the conventional Helmholtz resonator model. The relationship between the adjusting factors and cavity length can be described well using a two-term power series curve. This modified Helmholtz resonator model not only provides insight into this active-type Helmholtz resonator operation but also provides a useful estimation for its optimal design and fabrication.

Accurate and efficient measurements of the piezoelectric properties of AlN and AlScN films are very important for the design and simulation of micro-electro-mechanical system (MEMS) sensors and actuator devices. In this study, a process control monitor (PCM) structure compatible with the device manufacturing process is designed to achieve accurate determination of the piezoelectric coefficients of MEMS devices. Double-beam laser interferometry (DBLI) and laser Doppler vibrometry (LDV) measurements are applied and combined with finite element method (FEM) simulations, and values of the piezoelectric parameters d33 and d31 are simultaneously extracted. The accuracy of d31 is verified directly by using a cantilever structure, and the accuracy of d33 is verified by in situ synchrotron radiation X-ray diffraction; the comparisons confirm the viability of the results obtained by the novel combination of LDV, DBLI and FEM techniques in this study.

Force touch function in interactive displays gains increasing interests due to its ability in detecting 3D information from customers, giving rise to plenty of novel and advanced services for users and therefore increasing the efficiency of human‐machine interactivity. In this article, piezoelectric based force touch architecture and machine learning algorithms are smoothly combined for implementation of user‐centered force level recognition and user identity authentication. [ABSTRACT FROM AUTHOR]