Polyvinylidene Fluoride Piezoelectric Sensor Research Articles

Self-poled PVDF/recycled cellulose composite fibers utilizing cellulose nanocrystals to induce PVDF β-phase formation through wet-spinning as a flexible fabric piezoelectric sensor

In general, PVDF (Polyvinylidene fluoride) needs polarization treatment to exhibit its piezoelectric properties. Introducing nanofillers or applying stretching during the processing can promote the β-phase transformation in PVDF, achieving self-polarization. Herein, by incorporation of cellulose nanocrystals (CNCs), continuous β-phase enriched PVDF/cellulose composite fibers are prepared via wet spinning and drawing, in which the cellulose is recycled from waste cotton textiles to improve the wet spinnability of PVDF and reduce the cost. The obtained composite fibers are woven into fabrics and subsequently assembled into a flexible sensor, exhibiting excellent piezoelectric performance (d33 = 26.2 pC/N) without requiring additional polarization treatment. It generates an open-circuit voltage of 12 V and a short-circuit current of 100nA, much higher than those of the previously reported piezoelectric PVDF sensors with high-voltage polarization. This fabric-based flexible sensor also exhibits notable characteristics, including stable output signals and heightened sensitivity, thereby fulfilling the demands for monitoring both minute and extensive human movements. Furthermore, it shows great potential for widespread use in sound sensing for human-machine interfaces. The self-poled PVDF composite fibers offer the advantage of being easily woven together with other fiber materials, which contributes towards the development of self-powered flexible piezoelectric fabric sensors.

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.

PVDF‐Based Flexible Piezoelectric Tactile Sensors: Review

AbstractWith 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.

Polyvinylidene fluoride piezoelectric yarn for real-time damage monitoring of advanced 3D textile composites

Real-time online damage monitoring is essential and critical to the safe service of the advanced fibers reinforced composites. This paper firstly reports a piezoelectric yarn sensor based on electrospinning and 2D braiding technology, to monitor advanced 3D textile composites, which can generate a voltage of about 1 V and sustain long-term cycles at high frequency of 4 Hz. The polyvinylidene fluoride (PVDF) piezoelectric yarn is embedded into 3D orthogonal composites to realize the online health monitoring of advanced 3D textile composites through the three-point bending test. Following the bending fatigue and modal tests, the PVDF piezoelectric yarn sensor proposed in this work enables long-term, low-frequency, high-frequency, and stable monitoring, thus showing good potential and wide application in damage monitoring as a piezoelectric sensor in composites.

On-line monitoring of steel ball stamping by mechatronics cold heading equipment based on PVDF polymer sensing material

Abstract In order to explore the influence of cold heading equipment based on polyvinylidene fluoride (PVDF) polymer sensing material on steel ball stamping, a new method was proposed to reflect the defects of cold heading forming of steel ball by load signal. PVDF piezoelectric film is used as the sensor design of force and support structure of steel ball cold heading electromechanical sensor model. PVDF piezoelectric thin film force sensor is used for the structural optimization and simulation. The structural parameters affecting the natural frequency are numerically analyzed by MATLAB software. The mapping relationship between the external load and the output load of the sensor is obtained by using ANSYS software, and the simulation curve of the natural frequency of the sensor is compared with the theoretical curve to verify the factors affecting the natural frequency. The results show that the nonlinear error of sensors refers to the measured curve and the maximum deviation between the fitting line and the percentage of full-scale output.

Formation Mechanism and Weights Analysis of Residual Stress Holes in E690 High-Strength Steel by Laser Shock Peening

To investigate the surface residual stress hole formation mechanism induced by laser shock peening (LSP) in an E690 high-strength steel sheet and to assign weights to the relevant causes; E690 steel samples were loaded using four laser beams with different power densities. The dynamic strain in thin plate samples was measured using a polyvinylidene fluoride piezoelectric sensor during LSP and the residual stress distributions on thin- and thick-plate samples were studied using an X-ray stress analyzer. The residual stress distribution of the simulated laser shock E690 high-strength steel sheet was consistent with that of the measured residual stress field, and the propagation pattern induced by a pulsed laser shock wave obtained via simulation shows good consistency with the surface dynamic strain test results. A shock wave propagation model was established for E690 high-strength steel sheets. At laser power densities of 1.98 and 2.77 GW/cm2, the residual stress fields obtained through simulations and experiments show the residual stress hole phenomenon. The combined effect of the shock wave, which is reflected back and forth, and the rarefaction waves that converge toward the center produced the residual stress hole phenomenon, and shock wave reflection has a slightly greater impact than surface rarefaction wave convergence on the residual stress holes on the material’s surface. When the laser power density is 4.07 GW/cm2, the maximum residual principal stress is distributed uniformly.

A Flow Velocity Measurement Method Based on Turbulent Pressure Fluctuation Characteristics

In order to perform flow velocity measurements without interfering in the flow field itself, a flow velocity measurement method based on the characteristics (the rule by which the power spectrum varies with the flow velocity) of turbulent pressure fluctuations is proposed. This method is based on the characteristics of turbulent pressure fluctuations in the turbulent boundary layer (TBL) and uses a polyvinylidene fluoride (PVDF) sensor to convert pressure fluctuations into voltage outputs. First, TBL pressure fluctuation characteristics are studied. Second, the piezoelectric characteristics of PVDF piezoelectric sensors are studied and a sensor array signal processing method that can improve the signal-to-noise ratio is provided. Then, numerical simulations are performed to verify the characteristics of turbulent pressure fluctuations in the TBL. Finally, a PVDF sensor is made and flow velocity measurement experiments are performed. The results show that the power spectrum of the PVDF sensor response to excitation by turbulent pressure fluctuations is proportional to the fourth power of the flow velocity. It is feasible to use this characteristic to measure the flow velocity.

Metal structures embedded with piezoelectric PVDF sensors using ultrasonic additive manufacturing

Traditional manufacturing approaches to embed active materials, such as piezoelectrics, into metals can be problematic due to their high process temperatures or long curing times of the adhesives utilized to bond the active component to the metal. This paper presents the development and characterization of aluminum embedded with a piezoelectric polyvinylidene fluoride (PVDF) sensor using a low-temperature, solid-state metal joining process called ultrasonic additive manufacturing (UAM). The embedded sensor is subjected to a pre-compression that is empirically optimized by varying the depth of the pocket and tape foils welded above the sensor, thus eliminating reliance on a bonding medium to mechanically couple the metal and the sensor. The technology presented in this study could enable rapid fabrication of functionalized metal structures that can be used in non-destructive testing, energy harvesting, and load monitoring applications.

Assessment of flow aggressiveness and erosion damage topography for different gap widths in ultrasonic cavitation testing

Incubation time and erosion rate of C15 steel (SAE 1016) are measured in a cavitation test-rig utilizing an ultrasonic horn. The gap width (separation distance) between horn tip and stationary sample is varied and effects on material damage are studied. Cavitation erosion shows a local maximum for a gap width of 0.5 mm at the stationary specimen, while it continuously rises on the horn tip with rising gap width. A characteristic erosion pattern develops at horn tip and stationary specimen. By a-posteriori surface erosion topography measurements, radial erosion depth profiles are evaluated. Together with scanning electron microscopy investigations, they provide information on the spatial distribution of the flow aggressiveness and on wear mechanisms. By means of computational fluid dynamics (CFD) results, the local surface erosion topography is associated to harmonic and subharmonic collapse events within the gap. Pressure measurements have been performed by piezoelectric polyvinylidene fluoride (PVDF) sensors, mounted in central as well as eccentric position on the specimen surface. A local mean of the erosion depth profile is evaluated on the surface portion that corresponds to the PVDF sensor locations. By temporally high-resolved pressure data, a cumulative force load is evaluated. For larger gap width, a good correlation of cumulative force load with the inverse incubation time, erosion rate, as well as mean erosion depth is obtained, while for the smallest gap width of 0.3 mm, the correlation deteriorates.

Measurement Method for Fluid Pressure Fluctuation in Fluid-Conveying Pipe Using PVDF Piezoelectric Film Sensor

As a representative fluid-transporting system, fluid-conveying pipes play an essential role in many fields. For a fluid-conveying pipe system in operation, fluid pulsation in pipes contains much information about fluid flow parameters (flow velocity, fluid pressure, etc.). Therefore, the measurement of fluid pulsation is important for understanding the internal fluid flow. To use polyvinylidene fluoride (PVDF) piezoelectric film sensors to indirectly measure the pressure fluctuation of the internal fluid, we simulated a fluid-conveying pipe with PVDF piezoelectric film sensors attached to the outer pipe wall. The simulation results showed that the variation of voltage signal of PVDF, circumferential stress and strain of the pipe wall, and the pressure fluctuation of internal fluid were highly positively correlated, which proved that the PVDF piezoelectric film sensor can be applied to indirectly measure the pressure fluctuation of internal fluid. We also studied the influences of flow velocity pulsation and mechanical vibration caused by the pipeline pump during operation. It is found that the flow velocity pulsation had little influence on the measurements of the variation of circumferential stress and strain of the pipe wall and the internal fluid pressure fluctuation. When both ends of the pipe were fixed by hoops, mechanical vibration had little influence on the measurement of the variation of circumferential stress and strain of the pipe wall as well as the fluid pressure fluctuation. Finally, simulation results were verified by experiments.

Improvement of vehicle axle load test method based on portable WIM

An improved portable weigh-in-motion test method was proposed based on the polyvinylidene fluoride piezoelectric sensor. Four different kinds of installation method were compared and the optimal installation method was confirmed. The influence of vehicle speed on the accuracy of axle load was studied and result showed that the maximum relative error was less than 14% under the same pavement temperature with constant automatic adjustment factor. At the same vehicle speed, the integral value of axle load increased linearly with the increase of temperature and an improved axle load calculation method was proposed to reduce the influence of temperature. The self-developed portable WIM system was compared with a portable WIM product in the real road test. Result showed that the deviation of the two systems was less than 13% and most of the deviations were under 8%, which showed the self-developed system can meet the requirement of the real road test.

Enhancement of PVDF Sensing Characteristics by Retooling the Near-Field Direct-Write Electrospinning System.

This research aimed to develop a direct-write near-field electrospinning system (DW-NFES) with three-axis positioning of controllable speed, torque and position to produce sizable and high-quality piezoelectric fibers for sensing purposes. Sensor devices with high electrical response signals were developed and tested. To achieve DW-NFES purpose, a servo motor controller was designed to develop a high response rate, accurate positioning, and stable mobile device through the calculation of bandwidth and system time delay. With this retooled system of DW-NFES, controllable and uniform size fibers in terms of diameters, stretching force, and interspaces can be obtained. Sensor devices can be made selectively without a complicated lithography process. The characteristics of this DW-NFES platform were featured by high response rate, accurate positioning, and stable movement to make fibers with high piezoelectric property. In this study, polyvinylidene fluoride (PVDF) was used to explore and enhance their sensing quality through the platform. The parametric study of the process factors on piezoelectric sensing signals mainly included the concentration of electrospinning PVDF solution, high voltage electric field, and collection speed. Finally, the surface morphology and piezoelectric properties of the as-electrospun PVDF fibers were examined by scanning electron microscopy (SEM) and characterized by electrical response measurement techniques. The results showed that the fiber spinning speed of the DW-NFES system could be increased to ~125 from ~20 mm/s and the accuracy precision was improved to ~1 from ~50 μm, compared to conventional step motor system. The fiber diameter reached ~10 μm, and the electrospinning pitch reached to as small as ~10 μm. The piezoelectric output voltage of the electrospun fibers was increased ~28.6% from ~97.2 to ~125 mV; the current was increased ~27.6% from ~163 to ~208 nA, suggesting that the piezoelectric signals can be enhanced significantly by using this retooled system. Finally, an external control module (Arduino-MAGE) was introduced to control the PVDF piezoelectric fiber sensors integrated as a sensing array. The behavior of long-term sedentary patients can be successfully detected by this module system to prevent the patients from the bedsores.

Use of Flat Ribbon like Electrode Geometry to Pole PVDF Piezoelectrics in Solution Processing

We study how ribbons of fluids subjected to electric fields can serve applications in energy harvesting. In particular the emphasis is on how the geometry (i.e. 2-D ribbons) can influence functionality. For applications related to energy harvesting, we consider the use of polymer Piezo-electric Polyvinylidene Fluoride (PVDF). Corona poling, photo-induced, photo-thermal and electron beam poling are the different conventional techniques used for PVDF poling. The parallel plate capacitor structure made for poling the PVDF material while the PVDF is being cured. One key advantage of preparing PVDF is the ability of solution processing. Normally, the liquid is then spin coated on a substrate and left to dry. Either during the process of spin coating, or after drying - the film of PVDF is poled so as to align the dipoles and make a piezoelectric. We propose the use of a metal-insulator ribbon like electrode geometry to combine the process of fabrication and poling thereby making the process more efficient. On the application of a voltage across the electrodes, the voltage of Vs is developed across the fluid. This result in a field of Vs/d across the PVDF fills aiding the process of poling while the film is in liquid phase. Therefore the ribbon like geometry aids the use of PVDF piezo-electrics in two ways. Firstly, it makes the fabrication process efficient by combining the poling with the structure development. Secondly, the control of width (w) and length (l) aids the setup of the PVDF piezoelectric resonant frequency for a given thickness (d). This helps match the resonant frequency of the ribbon with the incoming low frequency vibration to improve the energy harvesting levels. Piezo-electrics can be used in submerged applications, large area PVDF energy scavengers, mechanical filters and sensors, rural electrification, and charging circuits for hand-held devices.

Experimental study on dynamic behavior of woven carbon fabric laminates using in-house piezoelectric sensors

Piezoelectric Polyvinylidene fluoride (PVDF) nanofibers are produced through the electrospinning process and then characterized to examine their morphology, crystal structures, and thermal behavior for usage as an in-house strain sensor. Characterization results confirm that electrospinning of PVDF fibers promotes the formation of β-phase which is an electro-active phase for piezoelectricity. Load controlled dynamic flexural tests are performed on woven carbon fabric composites with embedded and surface mounted PVDF sensors to study the capability of these sensors for monitoring the fatigue life of composite materials. The correlation factor for PVDF sensors is obtained through comparing the output voltage of PVDF sensor and strain measurement by video extensometer. It is shown that the PVDF based sensor is able to monitor the strain history and damage progression in woven carbon fabric laminates under fatigue loading condition. Moreover, the strain field acquired by the surface mounted PVDF sensor can clearly capture the three distinct stages of overall fatigue life of woven carbon fabric laminated composite material. This result is validated by the strain measurement with the video extensometer during tests. It is important to emphasize that surface mounted PVDF sensors do not show any sign of detachment from the surface of the specimen or malfunctioning during the test. SEM analysis of fractured surfaces of composite specimens show vivid delamination and fiber pullouts through the thickness, thus indicating gradual growth of damage in laminates.

A Flow Velocity Measurement Method Based on a PVDF Piezoelectric Sensor.

To measure the flow velocity of a fluid without affecting its motion state, a method was proposed based on a polyvinylidene fluoride (PVDF) piezoelectric film sensor. A self-made PVDF piezoelectric sensor placed parallel with the flow direction was used to measure the flow velocity. First, the piezoelectric characteristics of PVDF were obtained theoretically. Next, the relationship between flow velocity and sound pressure was verified numerically. Finally, the relationship between flow velocity and the electrical output of the PVDF piezoelectric film was obtained experimentally. In conclusion, the proposed method was shown to be reliable and effective.

Space debris positioning based on two-dimensional PVDF piezoelectric film sensor

In order to determine the positions of debris collision spacecraft accurately, the experiments have been performed to impact orthogonal stacking two-dimensional Polyvinylidene fluoride (PVDF) piezoelectric film at different collision speeds based on the piezoelectric effects of the PVDF film by using two-stage light gas gun loading system and the self-constructed positioning system. The debris source was positioned accurately by PVDF strips sensor and testing system, which has been established to extract piezoelectric signals of the PVDF film during the process of impacting. The visualization of the position for debris impacting spacecraft was achieved through the LABview language programme and signal processing acquired by the signal acquisition system in the experiments. The experimental results show that the positions of the debris impacting source can be realized accurately by the piezoelectric effects of the orthogonal stacking two-dimensional PVDF film, the flight velocity and the incidence angle of the debris can be determined by installing the double-set PVDF film as the targets with a certain spacing.

Design of PVDF sensor array for determining airflow direction and velocity

An airflow sensor comprised of an array of piezoelectric polyvinylidene fluoride (PVDF) cantilever sensors mounted on a sensor ring is fabricated. A fluid-solid-electric coupling model based on the finite element method is presented to obtain the mathematical relationship between the normal airflow velocity and the response voltage. According to the response voltages from all pieces of PVDF cantilevers in the array, the values of the airflow direction and the velocity can be calculated. Furthermore, to find a suitable algorithm for error calculations and to achieve high accuracy, a method of reducing the flow angle error ( ) and flow velocity error ( ) by extracting Um of the effective cantilevers can be established. The experimental results show that the maximum value of is 1.2° (at 270° with 11.1 m/s) and the minimum value of is 0.3° (at 135° with 11.1 m/s) based on the PVDF sensor array with eight cantilevers. Meanwhile, the maximum value of is 3% (at 315° with 11.1 m/s), and the minimum value of is 1.5% (at 360° with 11.1 m/s). In addition, under 20 random airflow angles at 8 m/s, the error range in airflow velocity is from 1.27% to 2.67%, the error range in airflow angle is from 0.34° to 1.24°, and the response time is 20 ms. Therefore, the proposed design for an airflow sensory ring array can be used to determine the airflow direction and velocity, and the airflow sensor can be miniaturized as a bionic antennae, which is mounted on the skin of a piezoelectric autonomous mobile robot for sensing and escaping from an attack of the natural enemy.

A PVDF-Based Sensor for Internal Stress Monitoring of a Concrete-Filled Steel Tubular (CFST) Column Subject to Impact Loads.

Impact loads can have major adverse effects on the safety of civil engineering structures, such as concrete-filled steel tubular (CFST) columns. The study of mechanical behavior and stress analysis of CFST columns under impact loads is very important to ensure their safety against such loads. At present, the internal stress monitoring of the concrete cores CFST columns under impact loads is still a very challenging subject. In this paper, a PVDF (Polyvinylidene Fluoride) piezoelectric smart sensor was developed and successfully applied to the monitoring of the internal stress of the concrete core of a CFST column under impact loads. The smart sensor consists of a PVDF piezoelectric film sandwiched between two thin steel plates through epoxy. The protection not only prevents the PVDF film from impact damages but also ensures insulation and waterproofing. The smart sensors were embedded into the circular concrete-filled steel tube specimen during concrete pouring. The specimen was tested against impact loads, and testing data were collected. The time history of the stress obtained from the PVDF smart sensor revealed the evolution of core concrete internal stress under impact loads when compared with the impact force–time curve of the hammer. Nonlinear finite element simulations of the impact process were also carried out. The results of FEM simulations had good agreement with the test results. The results showed that the proposed PVDF piezoelectric smart sensors can effectively monitor the internal stress of concrete-filled steel tubular columns under impact loads.

Effect of electrode material on piezoelectric output of PVDF sensor with electrospun nanofiber web

The electrospun PVDF (Polyvinylidene Fluoride) nanofiber web is commonly agreed on a kind of new sensitive materials for the sensor testing the dynamic pressure and energy harvesting, and has the characteristics of fast response and high sensitivity of pressure. As a result of the nanofiber web, it must be packaged to collect piezoelectric charge and bear strong mechanical behavior before industrial practice. The packaging of PVDF nanofiber web is usually sandwiched by incorporating a pair of flexible electrode. However, the effects of the surface and mechanical properties of electrodes such as morphology, roughness and compressibility have not been well investigated yet. This work will introduce three common types of packaging electrode materials (adhesive copper foil tape, indium tin oxide (ITO) thin film, adhesive conductive cloth.) in previously published literatures, compares the piezoelectric output of their sensor prototypes under a periodic impact, and discusses the effect of surface morphology, electrical resistance, and compressibility. The results showed that it has higher output of PVDF piezoelectric sensor packaged by electrode materials with the smooth surface and low mechanical compressibility. This result provides a guideline for designing the textile electrode material for the PVDF nanofiber web.

Integrated 3D printing and corona poling process of PVDF piezoelectric films for pressure sensor application

This paper presents a novel process to fabricate piezoelectric films from polyvinylidene fluoride (PVDF) polymer using integrated fused deposition modeling (FDM) 3D printing and corona poling technique. Corona poling is one of many effective poling processes that has received attention to activate PVDF as a piezoelectric responsive material. The corona poling process occurs when a PVDF polymer is exposed to a high electric field created and controlled through an electrically charged needle and a grid electrode under heating environment. FDM 3D printing has seen extensive progress in fabricating thermoplastic materials and structures, including PVDF. However, post processing techniques such as poling is needed to align the dipoles in order to gain piezoelectric properties. To further simplify the piezoelectric sensors and structures fabrication process, this paper proposes an integrated 3D printing process with corona poling to fabricate piezoelectric PVDF sensors without post poling process. This proposed process, named ‘Integrated 3D Printing and Corona poling process’ (IPC), uses the 3D printer’s nozzle and heating bed as anode and cathode, respectively, to create poling electric fields in a controlled heating environment. The nozzle travels along the programmed path with fixed distance between nozzle tip and sample’s top surface. Simultaneously, the electric field between the nozzle and bottom heating pad promotes the alignment of dipole moment of PVDF molecular chains. The crystalline phase transformation and output current generated by printed samples under different electric fields in this process were characterized by a Fourier transform infrared spectroscopy and through fatigue load frame. It is demonstrated that piezoelectric PVDF films with enhanced β-phase percentage can be fabricated using the IPC process. In addition, mechanical properties of printed PVDF was investigated by tensile testing. It is expected to expand the use of additive manufacturing to fabricate piezoelectric PVDF-based devices for applications such as sensing and energy harvesting.