Piezoelectric Film Sensor Research Articles

A ballistocardiogram dataset with reference sensor signals in long-term natural sleep environments

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

Longitudinal analysis of lower limb muscle activity and ankle tendon biosignals using structural equation modeling

We collected biosignals from 63 participants and extracted the features corresponding to each level of exerted muscle force. Data were classified into typical and atypical patterns. Data analysis was performed using the Linear Latent Curve Model (LCM) and the Conditional Linear LCM. The typical patterns demonstrated a high degree of fit. Factors, such as ankle circumference and muscle mass, influenced the model intercept. A larger ankle circumference indicated attenuation of signal transmission from the tendon to the skin surface, leading to lower biosignal values. These results indicate that biosignals from the tendons near the ankle can be captured using piezoelectric film sensors. There are studies that define biosignals originating from tendons as mechanotendography. It has been demonstrated that the relationship between biosignals originating from tendons and the exerted muscle force can be explained linearly. Insights from this study may facilitate individualized approaches in the fields of motion control and rehabilitation. Physiological studies to elucidate the mechanisms underlying biosignal generation are necessary.

Analysis of Vibration Electromechanical Response Behavior of Poly(Vinylidene Fluoride) Piezoelectric Films

Studying the electromechanical response behavior of piezoelectric thin films under different loading conditions is of great value for the development and optimization of piezoelectric sensors and flexible portable electronic devices. This paper establishes the theory of large deflection vibration of rectangular four-edge simply supported piezoelectric thin films using the energy method, and analyzes the electromechanical response characteristics of vibration force (including resonant frequency and nonlinear vibration). Meanwhile, the electromechanical response behavior of Poly(vinylidene fluoride) (PVDF) films under different loading conditions (static and harmonic vibration) is analyzed. The study investigates the nonlinear vibration characteristics and resonance frequency variations under different film sizes and thickness conditions in the case of various loading conditions. The developed model can predict the resonance frequency associated with the plate dimensions. This study is of great significance for the research and application of laminated piezoelectric film sensors.

Transient behavior of a plate partially immersed in the fluid subjected to impact loadings: Theoretical analysis and experimental measurements

This study aimed to investigate the transient behavior of a rectangular plate partially in contact with fluid subjected to a dynamic external force. To this purpose, a theoretical model was developed to analyze vibration characteristics and transient wave propagation. Based on superposition method, the dry mode shapes and natural frequencies of the plate under vacuum could be obtained. The dry mode shapes were treated as the fundamental function to construct the wet mode that describes the vibration behavior of the fluid-plate coupled system. The velocity potential and fluid pressure within a finite tank due to the plate deflection were derived using an equation governing the incompressible fluid. Based on the relationship between dry mode shape and wet mode shape, the fluid-plate coupled system's wet mode shape and resonant frequency could be determined from the frequency response function. Applying the normal mode method, the transient displacement of plate and fluid pressure can be obtained by solving a system of non-homogeneous differential equations. The theoretical predictions were verified by finite element method (FEM) and experimental measurements. Experiments were conducted using piezoelectric film sensors (polyvinylidene fluoride, PVDF) to measure the force history induced by a steel ball impact to quantitatively analyze the transient response. The comparison results proved that the theoretical predictions and experiments were in good agreement, including the transient responses of the displacement and in-plane strain of a plate partially submerged in the fluid. The results indicate that changes in water depth can induce resonance frequency shifts and wet mode shape distortions, which also illustrate that the vibrational properties of wet modes affect transient behavior. The proposed transient solution demonstrates an analytical approach that connects the physical significance of the dynamic behavior of the fluid-plate coupled system in time and frequency domains; it provides a connection between the transient behaviors and vibration characteristics.

Identification of Shield Tunnel Segment Joint Opening Based on Annular Seam Pressure Monitoring.

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.

High Signal to Noise Ratio Piezoelectric Thin Film Sensor Based on Elastomer Amplification for Ambulatory Blood Pressure Monitoring.

Continuous pulse wave detection can be used for monitoring and diagnosing cardiovascular diseases, and research on pulse sensing based on piezoelectric thin films is one of the hot spots. Usually, piezoelectric thin films do not come into direct contact with the skin and need to be connected through a layer of an elastic medium. Most views think that the main function of this layer of elastic medium is to increase the adhesion between the sensor component and the skin, but there is little discussion about the impact of the elastic medium on pulse vibration transmission. Here, we conducted a detailed study on the effects of Young's modulus and the thickness of elastic media on pulse sensing signals. The results show that the waveform amplitude of the piezoelectric sensing signal decreases with the increase of Young's modulus and thickness of the elastic medium. Then, we constructed a theoretical model of the influence of elastic media on pulse wave propagation. The amplitude of the pulse wave signal detected by the optimized sensor was increased to 480%. Our research shows that by regulating Young's modulus and thickness of elastic media, pulse wave signals can undergo a similar amplification effect, which has an important theoretical reference value for achieving ambulatory blood pressure monitoring based on high-quality pulse waves.

A biomimetic nociceptor system with tactile perception based on Ni-Al layered double hydroxides/gelatin heterojunction memristor

The sensations of touch and pain are fundamental components of our daily existence, serving as conduits for providing crucial insights into our environment and ensuring the safeguarding of our health. To date, the exploration of artificial systems that combine pain and touch perception has remained very limited. Moreover, memristor based visualization of pain degree is rarely reported. The electronic simulation of the from pressure stimuli to nociceptors was conducted in this work. For this purpose, a bionic sensory system has been developed to present tactile perception. In this system, the piezoelectric film sensor serves as an electronic skin to mimic artificial mechanoreceptors for sensing external pressure stimulation and generating signals. Meanwhile, the Ni-Al layered double hydroxides (LDHs)/gelatin heterojunction memristor emulates biological nociceptors to receive and process receptor signals, with luminous diode used as displays to indicate the degree of artificial contusion. The Ni-Al LDHs/gelatin heterojunction memristor demonstrates essential characteristics of nociceptors, including threshold, no adaptation, relaxation, and sensitization phenomena of allodynia and hyperalgesia. This biomimetic artificial tactile and pain perception system successfully simulates the perception threshold and sensitivity to pressure stimuli. The potential ability of humanoid robots could be demonstrated by utilizing the system as an artificial tactile alarm system.

Design and Experimental Evaluation of a Dual-Cantilever Piezoelectric Film Sensor with a Broadband Response and High Sensitivity.

Cantilever-beam-type PVDF (Polyvinylidene Fluoride) piezoelectric film sensors are commonly utilized for vibration signal detection due to their simple structures and ease of processing. Traditional cantilevered PVDF piezoelectric film sensors are susceptible to the influence of the second-order vibration mode and have a low lateral stress distribution at the free end, which limit their measurement bandwidth and sensitivity. This study is on the design of a dual-cantilever PVDF piezoelectric film sensor based on the principle of cantilevered piezoelectric film sensors. The results of the experiments indicate that, compared to a typical single-arm piezoelectric cantilever beam vibration sensor, the developed sensor has a longer second-order natural frequency that ranges from 112 Hz to 453 Hz, while the first-order natural frequency is maintained at around 12 Hz. This leads to a better ratio of the second-order natural frequency to the first-order natural frequency and a wider frequency response range. At the same time, the sensitivity is increased by a factor of 3.48.

A sleep respiratory monitoring system based on piezoelectric film sensors

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.

Repeatability and reproducibility of 2 digital occlusal analyzers for measuring the right- and left-side balance of occlusal contact forces: An in vitro study

Statement of problemAlthough different digital occlusal analyzers have been marketed, comparative studies are lacking. PurposeThe purpose of this in vitro study was to compare the repeatability and reproducibility of 2 different digital occlusal analyzers (T-Scan and OccluSense) for measuring the right- and left-side balance of occlusal contact forces. Material and methodsThe repeatability and reproducibility of the 2 digital occlusal analyzers for measuring the balance of occlusal contact forces were determined and compared by using the Gauge Repeatability and Reproducibility tests based on the International Organization for Standardization (ISO), ISO 5725-2 and ISO 5725-3 standards. Ten different dental casts were mounted in the maximum intercuspation position on a semi-adjustable articulator. Then, the balance of occlusal contact forces in each of the 10 articulated dental casts was measured 24 times with each of the 2 digital occlusal analyzers. In addition, as the OccluSense, unlike the T-Scan, does not have a centering support for the piezoelectric film sensor, measurements with it were performed without and with a custom-designed and manufactured centering support. Finally, the repeatability and reproducibility of both digital occlusal analyzers were determined and compared using the Gauge Repeatability and Reproducibility tests. ResultsThe repeatability and reproducibility tests revealed that only 0.8% of the variance of the measurements obtained with the T-Scan was due to repeatability and reproducibility (0.4% repeatability, 0.4% reproducibility). In contrast, 12% of the variance of the measurements obtained with the OccluSense was due to repeatability and reproducibility (2.2% repeatability, 9.8% reproducibility). However, when using OccluSense with the centering support, the variance decreased to 6.4% (2.8% repeatability, 3.6% reproducibility). According to the Automotive Industry Action Group classification, the repeatability and reproducibility of the T-Scan were good, those of the OccluSense poor, and those of the OccluSense with the centering support medium. ConclusionsThe repeatability and reproducibility of the T-Scan were significantly better than those of the OccluSense for measuring the balance of occlusal contact forces. Furthermore, the repeatability and reproducibility of the OccluSense were significantly improved when used with a device to center the piezoelectric film sensor between the incisors. Nevertheless, the repeatability and reproducibility of the T-Scan were better.

Improving the precision of recordings acquired with digital occlusal analyzers: A dental technique

A technique to improve the precision of recordings acquired with the 2 main digital occlusal analyzers on the market (T-Scan and OccluSense) is presented. This technique consists of using digital occlusal analyzers with a customizable centering tray. The virtual design of the centering tray is available online, together with that of the adapters required for both digital occlusal analyzers. The designs can be downloaded and additively manufactured for clinical use. These parts improve the positioning of the piezoelectric film sensors of the digital occlusal analyzers in the patient's mouth and thus the precision of their records. Improving the precision of the records of the digital occlusal analyzers is especially important for the comparison of records obtained at different stages of rehabilitation treatment.

Study of okra pectin prepared by sweeping frequency ultrasound/freeze-thaw pretreatment on corrosion inhibition of ANSI 304 stainless steel in acidic environment

Green and efficient metal corrosion inhibitors are very essential, and natural okra pectin (OP) can fulfill this need with rational use of resources. OP was prepared by water-alcohol extraction method after freeze-thaw pretreatment (FTP)/sweeping frequency ultrasound pretreatment (SFUP), and used for corrosion inhibition of ANSI 304 stainless steel (304 SS) in 1 M hydrochloric acid (HCl). The molecular weight, hydrodynamic diameter and monosaccharide composition of OP were analyzed to determine the factors on the corrosion inhibition of 304 SS. During SFUP of okra, the time-domain variation of ultrasound field was monitored by piezoelectric film sensor, its frequency-domain variation was monitored by a hydrophone, and analyzed respectively by oscilloscope and spectrum analyzer. Static weight-loss method, electrochemical and microscopic analyses were used to evaluate the corrosion inhibition efficiency of OP at temperatures (25, 30, 40, 50 °C) and concentrations (0, 0.2, 0.5, 1, 2 g·L−1) to optimize corrosion inhibition performance. It was found that OP by FTP and SFUP had higher corrosion inhibition efficiency on metals in acidic environment. According to static weight-loss method, the corrosion inhibition efficiency of OP with concentration of 2 g·L−1 (25 °C) was improved to 90.27 % in the FTP group and 93.53 % in the SFUP group, which 5.14 % and 8.93 % higher than Control (without pretreatment). Meanwhile, the corrosion inhibition efficiency decreased gradually as the temperature increased. OP corrosion inhibition performance fit Langmuir adsorption isothermal model as a mixed adsorption based on physical adsorption. It was a mixed inhibitor to protect 304 SS from corrosion.

Resonance phenomena in dielectric media: A review and comparison of acoustic and electromagnetic modes

The theory and application of resonances and vibrational modes are part of the foundation of science. In this contribution, examples of acoustical resonators are highlighted, and compared to electromagnetic modes. As an example from architecture, we describe the phenomenon of whispering galleries; such modes are nowadays known in dielectric and optical resonators. A specimen of a semicircular whispering bench in Park Sanssouci in Potsdam is acoustically investigated and demonstrated to show low losses for sound propagation. A special acoustical bug is discussed which was used for the espionage of the U.S. ambassador in Moscow. The Sovyets could interrogate this passive device by radio waves. Its working principle was based on the electromagnetic resonance of the cavity that the sound-sensitive membrane was part of. The underlying relation between excitation and resonance is compared to the sound production in flue organ pipes. A stopped flue organ pipe was investigated using a piezoelectric film sensor inside the pipe body. The results show that even-numbered modes, which are usually suppressed in the radiated sound of a stopped pipe, are still present in the vibrations inside the resonator.

Highly sensitive, ultra-reliable flexible piezoelectret sensor for non-contact sitting motion tracking and physiological signal monitoring

Non-contact, cost-effective, multifunctional and robust monitoring platform without mechanical wearing burden is highly desired to enhance the immersive experience for users during the long-term health management. However, most reported intelligent electronics in human life need to be adhered conformably to key human body parts for accurate signal detection, giving rising to activity interference and wearing burden in the long-term usage. Herein, a highly sensitive flexible film pressure sensor with a folded structure configuration assembled from irradiation-cross linked polypropylene (IXPP) piezoelectret film featured with piezoelectric-like dynamic electrical output attributes are reported. Such simple folded structure incorporated specially into the device design endows the piezoelectric film sensor with merits such as enhanced sensitivity, high signal-to-noise ratio and excellent anti-interference capacity. Consequently, the sensor can achieve a linear pressure sensitivity of 92 pC/kPa over a wide pressure range of 0.6–62.4 kPa, a pressure resolution of 0.98%, and fast response/recovery time of 40 ms. The flexible piezoelectric film sensors are embedded into cushions and attached to the back of chairs for application demonstrations of non-contact sensing. Remarkably, low-frequency human motion and weak physiological signal detection are achieved in a non-contact mode by a highly sensitive piezoelectric sensing principle in an all-in-one configuration, simplifying the signal processing and monitoring system design. A vital sign monitoring system based on the intelligent cushion is further developed to unlock the health status of sedentary crowd. This is the first work that ever use commercially available irradiated cross-linked polypropylene (IXPP) film to design pressure sensor and such sensors are successfully connected to the commercial “C-life” smart home ecosystem, presenting strong practicability and application prospects of such films in smart households and remote healthcare beyond the laboratory.

Axial Load Measurement of Bolts with Different Clamping Lengths Based on High-Frequency Ultrasonic ZnO Film Sensor

The ultrasonic testing method has been widely used for measuring the axial load of bolts. However, systematic calibrations are prerequisite if specific bolts have different clamping length configurations, which leads to low efficiency and measurement errors. The focus of this work was to measure the axial load of bolts with different clamping lengths by proposing a method of clamping length correction based on piezoelectric films in order to avoid the complicated calibration steps. Firstly, the relationship between longitudinal wave time-of-flight (TOF) and axial load under different clamping lengths was studied to correct the difference between the effective stress length and the actual clamping length. Secondly, the high-frequency ZnO piezoelectric film sensor was fabricated on the bolts to improve the accuracy of longitudinal wave TOF measurement. The results showed that the center frequency of the fabricated ultrasonic sensor reached 25 MHz, which could realize the high precision measurement of TOF. The proposed correction model proved to be effective for decreasing the measurement error below 2.7% in this experiment. In conclusion, the proposed method simplified the calibration procedure for different application configurations of the same bolt and realized the efficient measurement of bolt axial load.

Study on Structure health monitoring method of space vehicle based on PVDF piezoelectric film

At present, health monitoring technology of large structures has been paid more and more attention, among which structure measurement system based on PVDF piezoelectric film sensor has been widely used in various fields. To solve the problem that large structural parts of aerospace are easy to be damaged, a load measurement system based on PVDF piezoelectric film sensor is built in this paper given the complex design structure of aerospace. A large cylinder of aerospace is taken as the test part, the stress state of structural parts is measured online, and the corresponding load value is obtained. With the load value, damage to the health state of the structural parts when they are overloaded by external force can be avoided.

Flexible piezoelectric PVDF nanofiber film sensor by blow spinning

Flexible piezoelectric PVDF nanofiber film sensor by blow spinning

Health Monitoring of Serial Structures Applying Piezoelectric Film Sensors and Modal Passport.

Health monitoring of critical structures, that form parts of serial operating objects, is a pressing task. The Operational Modal Analysis (OMA) techniques could be the optimal solution. An inexpensive measurement system, such as the OMA, uses a lot of sensors for structural response assessment. The health monitoring of serial structures has to also consider possible deviations between samples. A solution providing the OMA application includes the compact measurement system based on piezoelectric film sensors and modal passport (MP) techniques. For validation of the proposed approach, a series of five similar composite cylinders, with a network of piezoelectric film sensors, was used. Applying modal tests on the specimens, and using OMA with MP methods, the set of typical modal parameters was determined and analyzed. The results of the study confirmed the feasibility of the sensor network and its applicability for structural health monitoring of serial samples using OMA methods. The proven effectiveness of OMA/MP techniques, combined with a sensor network, provides a prototype of intelligent sensor technology, which can be used for health monitoring of structures, including those that are part of an operating facility.

Tire-road friction coefficient estimation method design for intelligent tires equipped with PVDF piezoelectric film sensors

Intelligent tires, as an emerging technology, have great potential in real-time monitoring of tire-road contact information and new automotive active safety design. In this paper, a tire-road friction coefficient estimation method is proposed based on intelligent tire technology. First, an intelligent tire finite element model with the use of five PVDF piezoelectric film sensors attached to the inner liner of the tire is built using ABAQUS software, and the validity of the finite element model is verified by a piezoelectric intelligent tire test platform. Then, through the finite element analysis method and control variable method, the influence of sideslip angle on the voltage signal of each piezoelectric film under the rolling state of tire is analyzed, and when the sideslip angle is 4°, the influence of load, tire pressure, vehicle speed and slip ratio on the voltage signal of each piezoelectric film under the rolling state of tire is analyzed. Finally, based on the signal response analysis of the piezoelectric film sensors, the response mechanism of the predicted object and the linear correlation analysis, the input eigenvalues of each prediction model are extracted. The longitudinal contact patch length estimation model based on the numerical method and the sideslip angle, vertical force, lateral force and aligning moment estimation model based on the neural network algorithm are built, and the predicted parameters are input into the brush tire model to solve the tire-road friction coefficient. The result shows that the estimation error percentage of the friction coefficient estimation method without genetic algorithm optimization is 16.98%, and the estimation error percentage of the friction coefficient estimation method with genetic algorithm optimization is 5.14%, indicating that the genetic algorithm optimization effect is ideal, and the friction coefficient estimation method is practical. ● Developing an intelligent tire finite element model equipped with PVDF sensors ● Real vehicle test verifies the validity of the intelligent tire finite element model ● Analyzing the signal response of PVDF sensors under different working conditions ● Estimating the tire-road friction coefficient using intelligent tire system and brush tire model

A novel ultra-thin and high toughness piezoelectric thin film sensor based on MEMS technology

A novel ultra-thin and high toughness piezoelectric thin film sensor based on MEMS technology