Polyvinylidene Fluoride Sensor Research Articles

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.

Design and performance evaluation of a multi-axis thin-film sensor for milling process measurement

A multi-axis sensor made of flexible, light, and sensitive PVDF (polyvinylidene fluoride) thin film is designed and fabricated for cutting force measurement in milling process. The single-layer PVDF thin film is constructed with six electrodes in a certain pattern, which has two electrodes in each pair to measure the signals due to bending moment as well as torque moment on the cutter in the process of milling. All the detected voltage signals will be calibrated by the digital signal processing unit and transmitted to the remote receiver via wireless communication. A cutting-force model is established in association with the measurement scheme that can compute the feed force, transverse force, and tangential force via the collected voltage signals from the electrodes. In experiment, the PVDF sensor is directly attached to the cutter, and the commercial dynamometer is implemented under the workpiece for synchronous measurement and comparison. As a result, the developed thin-film sensor associated with the sensing circuitry and wireless communication device as well as the cutting force model can effectively measure the important cutting force with satisfactory accuracy.

Equivalent capacitor of polyvinylidene fluoride sensor and its influence on impact load measurement

As one of the main components of the polyvinylidene fluoride (PVDF) piezoelectric sensor, the equivalent capacitor of PVDF will influence the electrical signal output when subjected to the impact load, thus influencing the accuracy of its measurement. However, in previous research, the equivalent capacitor of PVDF and its possible influence on measurement results have usually been ignored. In this paper, by changing the external resistance, the influence of the equivalent capacitor of PVDF on its electrical signal output characteristics when subjected to impact load is studied. The results show that at this time, the charge generated by the PVDF will be partially concentrated on the equivalent capacitor, and the amount of concentration is determined by the impact load characteristics, external resistance and equivalent capacitance. Therefore, in some cases, it is unreasonable to ignore the equivalent capacitor in previous research, and this may lead to some errors and even get completely wrong results. Considering the charge concentrated on the equivalent capacitor can effectively avoid the problems of conventional methods, and reflect the applied impact load more accurately. In addition, to improve the accuracy of the measurement, on the basis of quantitative evaluation of the influence of the equivalent capacitor on electrical signal output, this paper puts forward a design method of the test circuit; that is, for different types of impact load and measurement accuracy requirements, PVDF with appropriate capacitance and reasonable external resistance should be selected. The research in this paper is helpful for the impact load measurement of PVDF and will improve the accuracy of the measurement to a certain extent.

A High-Precision Low-Cost Analog Acceleration and Vibration Amplifier using PVDF Piezoelectric Sensors

This paper describes a high-resolution analog acceleration and vibration amplifier for use with piezoelectric polyvinylidene fluoride (PVDF) sensors. The purpose of this system is to monitor automated parts placement on integrated circuit boards. One of the problems facing production and inspection equipment is the occurrence of resonant and ambient vibrations. Even small errors can cause systems with micrometer and nanometer precision to exceed design tolerances. This work describes a method to monitor mechanical vibrations through a portable and inexpensive signal-processing unit. The system provides user-selectable gain and filtering modules that are compact and reliable. PVDF is currently used in sensing applications, and its material properties have proven very useful for sensing mechanical stress, strain, pressure, and temperature.

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.

Damage identification for a beam structure based on a PVDF piezoelectric film combined sensor

The structural strain curvature mode is widely used in structural health monitoring because of its high sensitivity to local changes and accurate damage localization capability. In this research, a combined polyvinylidene fluoride (PVDF) sensor was designed and manufactured based on measurement characteristics of the PVDF sensor. The designed sensor can directly measure the response signal of the strain difference in the structure. According to the central difference principle, the measured value is deduced and used to obtain the local strain curvature of the structure, and the strain curvature modal parameters of the structure are identified with the operating modal identification method. Taking the strain curvature mode shape difference as the damage index, the damage recognition results of the single-chip PVDF sensor and the combined PVDF sensor are compared by performing single damage, multiple damage and damage range experiments on a beam structure. The experimental results show that the combined PVDF sensor proposed in this study is more sensitive to local minor damage.

Experimental and Analytical Study of under Water Pressure Wave Induced by the Implosion of a Bubble Generated by Focused Laser.

In various domains of material processing, such as surface cleaning and surface treatment, cavitation phenomenon may become an alternative to traditional methods if this phenomenon is well understood. Due to experimental and mathematical difficulties in theoretical models, it is still a challenge to accurately measure the physical mechanism of the fluid/structure interactions. In this study, we verified the feasibility of using polyvinylidene fluoride (PVDF) sensors to quantitatively measure the under-water pressure wave generated by the collapse of a single cavitation bubble. The electrical signal obtained by PVDF can be converted into pressure information only by using the sensor material parameters provided by the supplier. During the conversion process, only the capacitance of the acquisition chain needs to be additionally measured. At the same time, a high-speed video recording system was used to visualize the evolution of the cavitation bubble. The Gilmore analytical model and an associated wave propagation model were used to simulate the pressure peak of the first collapse of the cavitation bubble. This theoretical pressure was compared with the experimental results. The result showed that, for bubbles with a normalized standoff distance larger than 5, the PVDF sensor had the ability to quantitatively measure the pressure wave generated by a single cavitation bubble.

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.

Research on the rotor/stator interaction noise through vane unsteady pressure test based on polyvinylidene fluoride sensor array

The rotor/stator interaction noise is the primary noise source of modern turbofan engines. Vane unsteady pressure test is essential to understand the generation mechanism and propagation characteristics of the noise, as well as examine the passive/active noise control technologies. However, limited by the Vane’s thickness as well as the requirement for high spatial and temporal resolutions of the sensor, traditional transducers still have considerable limitations and difficulties carrying out the measurement. In this paper, a polyvinylidene fluoride (PVDF) piezoelectric-film sensor array was developed for the vane unsteady pressure test. The dynamic characteristics of the sensor were obtained by the shock tube test. The calibration results further confirm the effectiveness of the self-developed PVDF sensor and also show the advantage in frequency response over traditional pressure transducer. Time histories of the vane fluctuating pressures were obtained by the PVDF sensor. The blade passing frequency (BPF) harmonic component and the broadband component of the unsteady pressure were analyzed individually by time-domain averaging and spectral analysis. The distributions of BPF content and broadband content on both sides of the vane at different fan tip speeds and operating conditions were investigated in detail. The results indicate that the operating conditions have little effect on both of them. The broadband component yielded by the rotor-wake turbulence seems to be quasi-isotropic. The average broadband level increases linearly with the fan tip speed. The developed PVDF sensor shows potential in noise evaluation and noise source diagnosis, which can properly guide further noise reduction technology development.

Laser Cavitation Peening and Its Application for Improving the Fatigue Strength of Welded Parts

During conventional submerged laser peening, the impact force induced by laser ablation is used to produce local plastic deformation pits to enhance metallic material properties, such as fatigue performance. However, a bubble, which behaves like a cavitation, is generated after laser ablation, known as “laser cavitation.” On the contrary, in conventional cavitation peening, cavitation is generated by injecting a high-speed water jet into the water, and the impacts of cavitation collapses are utilized for mechanical surface treatment. In the present paper, a mechanical surface treatment mechanism using laser cavitation impact, i.e., “laser cavitation peening”, was investigated, and an improvement in fatigue strength from laser cavitation peening was demonstrated. The impact forces induced by laser ablation and laser cavitation collapse were evaluated with a polyvinylidene fluoride (PVDF) sensor and a submerged shockwave sensor, and the diameter of the laser cavitation was measured by observing a high-speed video taken with a camera. It was revealed that the impact of laser cavitation collapse was larger than that of laser ablation, and the peening effect was closely related to the volume of laser cavitation. Laser cavitation peening improved the fatigue strength of stainless-steel welds.

Investigation of resonant and energy harvesting characteristics of piezoelectric fiber composite bimorphs

This study investigates the resonant and energy harvesting characteristics of a piezoelectric fiber composite bimorph by using theoretical and experimental techniques, including the full-field optical technique, for the purpose of getting a new perspective on the mechanical and electrical energy transformation ability of piezoelectric composites. A laser Doppler vibrometer, impedance analysis, fotonic sensor, and polyvinylidene fluoride sensor are used in the experiments. Furthermore, an full-field optical technique is also used to measure the resonant frequencies and mode shapes of in-plane and out-of-plane vibrations. Finally, the electrical voltage of the piezoelectric fiber composite bimorph with shaker excitation is measured and used for a light-emitting diode. The shaker input voltage, output voltage of the piezoelectric structure, and light intensity are all measured to find out the power generation capacity of piezoelectric composite. The relationship between the energy harvesting ability and excitation methods, the input voltage value, and frequency are obtained through analyses. From the experiment results, it is indicated that the most efficient modes are affected by the excitation method and the location of an excitation point of the shaker. This study helps in understanding the resonant characteristics as well as the energy harvesting capability of piezoelectric composite.

Monitoring the Structural Health of Glass Fibre-Reinforced Hybrid Laminates Using Novel Piezoceramic Film.

This work investigates a new generation structural health monitoring (SHM) system for fibre metal laminates (FML) based on an embedded thermoplastic film with compounded piezoceramics, termed piezo-active fibre metal laminate (PFML). The PFML is manufactured using near-series processes and its potential as a passive SHM system is being investigated. A commercial Polyvinylidene fluoride (PVDF) sensor film is used for comparative evaluation of the sensor signals. Furthermore, thermoset and thermoplastic-based FML are equipped with the sensor films and evaluated. For this purpose, static and dynamic three-point bending tests are carried out and the data are recorded. The data obtained from the sensors and the testing machine are compared with the type and time of damage by means of intelligent signal processing. By using a smart sensor system, further investigations are planned which the differentiation between various failure modes, e.g., delamination or fibre breakage.

Analysis of Methods for Long Vehicles Speed Estimation Using Anisotropic Magneto-Resistive (AMR) Sensors and Reference Piezoelectric Sensor.

With rapidly increasing traffic occupancy, intelligent transportation systems (ITSs) are a vital feature for urban areas. This paper analyses methods for estimating long (L > 10 m) vehicle speed and length using a self-developed system, equipped with two anisotropic magneto-resistive (AMR) sensors, and introduces a method for verifying the results. A well-known cross-correlation method of magnetic signatures is not appropriate for calculating the vehicle speed of long vehicles owing to limited resources and a long calculation time. Therefore, the adaptive signature cropping algorithm was developed and used with a difference quotient of a magnetic signature. An additional piezoelectric polyvinylidene fluoride (PVDF) sensor and video camera provide ground truth to evaluate the performances. The prototype system was installed on the urban road and tested under various traffic and weather conditions. The accuracy of results was evaluated by calculating the mean absolute percentage error (MAPE) for different methods and vehicle speed groups. The experimental result with a self-obtained data set of 600 unique entities shows that the average speed MAPE error of our proposed method is lower than 3% for vehicle speed in a range between 40 and 100 km/h.

Experimental Study of Sidewall Pressure Induced by Ferroparticles in Fluid under a Pulsating Magnetic Field

For several decades, magnetic nano- and microparticles have been used in various applications, as they can be attracted and controlled using external magnetic fields. Recently, carbonyl iron microparticles were used in a feasibility study of a new cardiac pacing application. The particles were inserted into a heart, attracted to its sidewall using a pulsating magnetic field, and applied pulsating pressure on its sidewall. The magnitude of the sidewall pressure is a critical parameter for the success and safety of the application, and it was evaluated analytically using a simplified model. In the present study, the behaviour of carbonyl iron microparticles in a water chamber was studied experimentally. Several masses of these particles were attracted to the sidewall of the chamber using an external pulsating magnetic field; the behaviours of the masses of particles, the particle–particle interaction, and the influence of fluid dynamics on them were examined during different periods of pulses. The sidewall pressure during their attraction was measured using an in-house piezoelectric polyvinylidene fluoride sensor. The relations between the measured sidewall pressure and the mass of the particles, their sizes, and the magnetic field exposure time were investigated. The obtained results suggest an asymptotic sidewall pressure value for the specified magnetic field. The measurements of the sidewall pressure are compared with evaluated results from the analytical model, showing that the model over-predicts the sidewall pressure.

Design of distributed piezoelectric modal sensor for a rotating beam with elastic boundary restraints

As an advanced sensing technique, modal sensors have been attracting a lot of research interest in modal filtering and active control fields. Most of the existing investigations are mainly focused on the static structure. In contrast, there is little effort made for its rotating counterpart, which is frequently encountered in various power machineries. Motivated by such limitation, a unified framework for the distributed piezoelectric modal sensor design of rotating beams with elastic boundary restraints is proposed using polyvinylidene fluoride piezoelectric integral equation and the second-order structural modal functions. A boundary smoothed Fourier series is used to obtain the modal information of rotating beams by solving the differential governing equation and elastic boundary conditions, simultaneously. Modal sensor shape of rotating beams can be determined for any boundary condition by simply setting the elastic restraining coefficients accordingly, instead of reformulating the equation or rewriting the codes like other approach usually does. Numerical examples are presented to demonstrate the correctness and effectiveness of the proposed framework. Modal sensitivity coefficient and charge output frequency response under external excitation are calculated to demonstrate the performance of the designed piezoelectric modal sensors. Influence of rotation speed and boundary restraining stiffness on the modal sensing accuracy of the shaped polyvinylidene fluoride sensor is analyzed and addressed. To our best knowledge, this work represents the first time that an analytical solution for the distributed piezoelectric modal sensor design of a rotating beam with general boundary conditions is derived, which can shed some new lights on further design and implementation of polyvinylidene fluoride modal sensing technique for rotating structures.

Impact and acoustic emission performance of polyvinylidene fluoride sensor embedded in glass fiber-reinforced polymer composite structure

Smart materials find vital applications in the aerospace industry due to their ability to adapt to surrounding conditions according to design requirements and applicability. Piezoelectric materials are commonly used under the category of smart materials for transducer applications. Among piezoelectric materials, piezo polymer polyvinylidene fluoride (PVDF) is widely used for structural health monitoring (SHM) applications of composite structures, acoustic emission (AE) sensor, accelerometer, strain gauge, pressure sensor, and so on because of its outstanding piezo stress constant ( g 33), piezo strain constant ( d 33), flexibility, and lightweight. In this article, glass fiber-reinforced polymer (GFRP) laminates have been prepared by embedding the PVDF sensor into GFRP for the first time. A detailed study has been done on the behavior and characterization of the PVDF sensor embedded in GFRP. The PVDF sensors embedded in laminates were subjected to impact test, where a constant weight of 5.5 kg was dropped from a height of 10–60 mm in the interval of 10 mm, and the voltage response of the PVDF sensor was recorded. Sensitivity analysis and AE test of the PVDF sensor in GFRP were also carried out. This is useful for various aerospace applications especially for SHM of aircraft.

Long Short-Term Memory Networks for Unconstrained Sleep Stage Classification Using Polyvinylidene Fluoride Film Sensor.

Sleep stage scoring is the first step towards quantitative analysis of sleep using polysomnography (PSG) recordings. However, although PSG is a gold standard method for assessing sleep, it is obtrusive and difficult to apply for long-term sleep monitoring. Further, because human experts manually classify sleep stages, it is time-consuming and exhibits inter-rater variability. Therefore, this article proposes a long short-term memory (LSTM) model for automatic sleep stage scoring using a polyvinylidene fluoride (PVDF) film sensor that can provide unconstrained long-term physiological monitoring. Signals were recorded using a PVDF sensor during PSG. From 60 recordings, 30 were used for training, 10 for validation, and 20 for testing. Sixteen parameters, including movement, respiration-related, and heart rate variability, were extracted from the recorded signals and then normalized. From the selected LSTM architecture, four sleep stage classification performances were evaluated for a test dataset and the results were compared with those of conventional machine learning methods. According to epoch-by-epoch (30 s) analysis, the classification performance for the four sleep stages had an average accuracy of 73.9% and a Cohen's kappa coefficient of 0.55. When compared with other machine learning methods, the proposed method achieved the highest classification performance. The use of LSTM networks with the PVDF film sensor has potential for facilitating automatic sleep scoring, and it can be applied for long-term sleep monitoring at home.

Respiration Signal Extraction From Pulse Wave Collected by PVDF Sensor

The respiratory signal is a critical index of cardiopulmonary function. In this paper, we implement the polyvinylidene fluoride (PVDF) sensor to collect the data of pulse waves and reference respiration signals. The correlations between the major feature values and breaths are investigated and presented. As a result, several feature values exhibit relatively good correlations with reference respiratory amplitude. The improvements of Kalman Filter for the respiratory signals extracted from feature value variances are also introduced. Moreover, we display the comparisons with low-pass filtering, Wavelet filtering, and ensemble empirical mode decomposition (EEMD) method. Using the method of identifying error breaths, the error rate of the new method is about 4.146%. The new method is feasible for real-time applications at quiet state.

Investigation of in-plane wave motion in a Fibre Metal Laminate using PVDF foil sensors

Structural Health Monitoring (SHM) via Guided Ultrasonic Waves (GUW) has been the subject of research for years and has already been described in detail for purely isotropic and purely anisotropic materials. Fibre Metal Laminates (FML) combine isotropic metal layers with anisotropic fibre composite layers to a laminate. They are mainly used in the aerospace industry to reduce mass while optimizing stiffness and strength properties. On the other hand, the combination of different materials leads to high differences in the acoustic impedance at the interfaces, which in turn leads to the question to what extent these materials can be monitored via GUW. This research investigates the applicability of polyvinylidene fluoride (PVDF) foil sensors for the detection of GUW in the interior of an Aluminium Glass Fibre laminate. Preliminary analytic investigations based on new adaptions of the partial-wave method gave insight into general GUW characteristics along fibre-metal interfaces and within an FML plate waveguide. Analytic and transient finite element simulation results were used to predict displacement fields. Composition and dimension of fabricated FML plates as well as excitation frequency were chosen based on these predictions, particularly maximizing dominance of the in-plane displacement components. For manufacturing the FML specimen with embedded PVDF sensors, a cold-curing epoxy resin was used to prevent the temperature-sensitive sensors from being destroyed or depolarized during production. After the design and application of a PZT actuator on the laminate, GUW were excited with particular attention to the frequencies in which a particularly dominating in-plane displacement field was assumed. Laser-Doppler Vibrometry (LDV) was used for measurements of the GUW's out-of-plane component.

Flexible electrospun PVDF-BaTiO3 hybrid structure pressure sensor with enhanced efficiency.

Ceramic doped-polymer structures as organic and inorganic hybrid structures constitute a new area of advanced materials for flexible and stretchable sensors and actuators. Here, uniform ceramic-polymer composites of tetragonal BaTiO3 and polyvinylidene fluoride (PVDF) were prepared using solution casting to improve the pressure sensitivity. By introducing Ba–TiO3 nanoparticles to PVDF nanofibers, piezoelectricity and pressure sensitivity of hybrid nanofiber mats were significantly improved. In addition, we proposed a novel flexible and stretchable multilayered pressure sensor composed of electrospun nanocomposite fibers with high electrical sensitivity up to 6 mV N−1 compared to 1.88 mV N−1 for the pure PVDF sensors upon the application of cyclic loads at 2.5 Hz frequency and a constant load of 0.5 N. Indeed, this work provides a composition-dependent approach for the fabrication of nanostructures for pressure sensors in a wide variety of wearable devices and technologies.