Polyvinylidene Fluoride Transducer Research Articles

A multi-function integrated PVDF transducer for fault detection and speed measurement of cylindrical roller bearings

Monitoring the condition of bearings in rotating machinery is crucial to ensure reliability, safety, and efficiency. Recently, integrated sensors have become more popular than traditional accelerometers in bearing condition monitoring because of their compact design, cost-effectiveness, and improved efficiency in fault detection through a short transmission path. This study presents a new approach to bearing condition monitoring by developing a bearing with an integrated Polyvinylidene Fluoride transducer. This polymer-based transducer, known as PVDF, has a piezoelectric effect which generates electric charge in response to mechanical excitation. The PVDF transducer was selected for its high sensitivity, flexibility, and thin structure. The developed bearing with the integrated PVDF transducer can detect faults under constant and variable speeds, and the damage size can be estimated with an accuracy of 10%. It outperformed a commercial accelerometer in noisy environments with artificial impacts from an air motor, making it a highly reliable option for bearing condition monitoring in noisy industrial settings. The PVDF transducer can also be used as a low-cost speed sensor with an accuracy of 5.2%, offering a versatile solution for machine monitoring. By simultaneously recording rotational speed and vibration, the developed integrated transducer provides a comprehensive view of machine health and performance as a multi-function transducer, enabling more accurate and efficient maintenance scheduling.

A Focused Optically Transparent PVDF Transducer for Photoacoustic Microscopy

This papers reports the development of a novel focused optically-transparent ultrasound transducer with a wide bandwidth for photoacoustic microscopy (PAM). It consists of a 9- $\mu \text{m}$ -thick polyvinylidene fluoride (PVDF) film coated with Indium-tin oxide (ITO) and metal electrodes, which is laminated onto a concave glass lens. A new fabrication process was developed to ensure the formation of continuous ITO coatings on the curved transducer surface without fracturing. Both optical and acoustic experiments were conducted to characterize the performance of the transducer. The testing results show that the transducer has an optical transmittance of 60% (@ 532 nm), an acoustic center frequency of 24 MHz, and an acoustic bandwidth of 26 MHz. With an acoustic numerical aperture (NA) of 0.23, it provides a 0.13-mm acoustic focal spot and a 1.6-mm focal depth. For demonstration, a PAM setup was built for conducting PA imaging on different targets. In contrast to existing PAM systems, the use of the optically-transparent focused transducer allows a simpler and more compact configuration and easier alignment of the optical excitation and acoustic focal points. Such features are especially useful for the development of miniaturized PAM systems for handheld, wearable and even endoscopic applications.

Truncated Conical PVDF Film Transducer for Air Ultrasound

In this paper, a truncated conical polyvinylidene fluoride (PVDF) film transducer for air ultrasound is investigated. The transducer was designed and fabricated using two identical pieces of fan-shaped PVDF film that makes the curve direction as consistent as possible with the molecular orientation direction of the film. The transducer has a truncated conical geometry, which provides a wide bandwidth with wide vertical beam angle. Measurements of the frequency response of transmitter output, angular performance, and pulse response are presented. The results show that the radiation directivity pattern of the transducer is in the axial direction of the conical film and the beam width is 140° at −6dB level, which is more than that of the commercial 40-kHz ceramic transducers and cylindrical PVDF transducers. Therefore, this ultrasonic transducer is well-suited for three-dimensional (3D) ultrasonic positioning systems, and in particular for mounting at the conical head of electronic pens as an ultrasonic position transmitter.

Exploiting Acoustic Anisotropy to Detect Recrystallization in a Ni Single Crystal Using Ultrasonic Nondestructive Inspection

Ultrasonic inspection was used to detect regions of recrystallization (RX) within a single crystal of Ni. RX can produce polycrystalline regions within single-crystal (SX) materials. Because RX regions act as initiator sites for failure by fatigue-crack growth in otherwise SX Ni-based superalloys, RX is an issue of direct concern for the service life of high-performance turbine blades. Detection and discrimination of RX regions in single-crystal materials are significant challenges for current nondestructive inspection technologies. The present study leverages the elastic anisotropy of single crystals, which produces acoustic anisotropy, to ultrasonically detect and characterize RX regions produced within single-crystal specimens. Single crystals of pure Ni were processed to create controlled regions of RX. These specimens were ultrasonically examined in an immersion tank using a high-resolution, polyvinylidene fluoride transducer to detect acoustic impedance changes across the boundaries between different crystals (i.e., grains) within the RX region. Data from time-of-flight and absolute peak amplitude measurements were used to create acoustic images that were compared against electron microscope images of the RX regions. The ultrasonic inspection technique described here successfully detected not only the locations of RX regions, but also the approximate sizes and shapes of the RX regions.

Planar and out of Plane Configuration Based Flexible Sensor of PVDF Polymer

PVDF (Polyvinylidene fluoride) a piezo polymer has been a potential candidate for its functional properties and device applications like flexible sensors, energy harvesting and biomedical applications. [1] There are various methods to fabricate free standing PVDF thin films.[2] One of such is solution casting method. It is known from the literature that PVDF films synthesized from varying viscosities through solution casting method exhibits different behavioural pattern of ferroelectric polarization components.[3] The study indicated that films prepared from precursor viscosity of 2.9 Pa.s exhibits dominant out-of-Plane polarization whereas films prepared from precursor viscosity of 4.6 Pa.s exhibit dominant in-plane polarization The orientation of these polarization components has an impact on the piezoelectric coefficient. [4] Piezoelectric coefficient is one of the important factor in deciding the efficiency and materials utilization in real time devices. The piezoelectric coefficient, d33 for the unpoled pure PVDF samples exhibiting dominant out-of-plane was found to be in the range of 0.4-4.24pm/v whereas the PFM scan shows the dominance of in-plane/planar domains indicates a significant value of d31. In this work we have fabricated out-of-plane and planar electrode based sensors of PVDF and tested for vibration detection. Film for the planar sensor is fabricated from precursor viscosity of 4.6 Pa.s and out-of-plane sensor from precursor viscosity of 2.9 Pa.s. When the fabricated sensors were tested by finger taping, it is observed that planar configured sensor are more sensitive than out-of-plane sensor. In figure we could see the piezoresponse microscope images along with ferroelectric hysteresis loop which confirm the ferroelectric nature of PVDF films. Also response of the sensor for a given vibration caused due to finger tapping is shown from both the configuration. REFERENCES [1] A. Proto, B. Fida, I. Bernabucci, K. Vlach, V. Kasik, M. Penhaker, Wearable PVDF Transducer for Biomechanical Energy Harvesting and Gait Cycle Detection, IEEE EMBS Conference on Biomedical Engineering and Sciences (IECBES), Kuala Lumpur ,Malaysia, 2016, 62-66. [2] P. Martins, A.C. Lopes, S. Lanceros-Mendez, Electroactive phases of poly(vinylidene fluoride):Determination, processing and applications, Prog. Polym. Sci. 39, (2014) 683 - 706. [3] R. Ganguly, S. Bandyopadhyay, k. Mirilaya, V. Gunasekaran, S. Bhattacharya, A. Acharyya, R. Ramadurai, Tunable polarization components and electric field induced crystallization in polyvinylidenefluoride (PVDF); a piezopolymer, Polymer Crystallization ,(2018) . DOI:10.1002/pcr2.10027. [4] S. K. Mahadeva, J. Berring, K. Walus, B. Stoeber, Effect of poling time and grid voltage on phase transition and piezoelectricity of poly(vinyledene fluoride) thin films using corona poling, J. Phys. D:Appl. Phys, 46, (2013) 285305 Figure 1

Shock Wave Attenuation Characteristics of Aluminum Foam Sandwich Panels Subjected to Blast Loading

Comparative experiments were conducted with two different structures to study the mechanism of aluminum foam sandwich attenuating blast shock wave. The sandwich structure is composed of “steel–aluminum foam–steel,” and the mild steel structure is composed of “steel–steel.” In the experiment, the polyvinylidene fluoride transducers were used to directly test the load of stress wave between different interfaces of sandwich and mild steel structures. The strain of back sheet was simultaneously measured using high‐precision strain gauge. The accuracy of the test results was verified by Henrych’s formula. Experimental results show that the wave attenuation rate on the mild steel structure is only 11.3%, whereas the wave attenuation rate on the sandwich structure can exceed 90%. The interface effect is clearly a more crucial factor in the wave attenuation. The peak value of back sheet strain in the mild steel structure is much higher than the sandwich structure. The apparent overall “X” crushing band is produced in the aluminum foam core, and scanning electron microscope (SEM) observation clearly shows the collapse of the cell wall. Experiments on the sandwich structure with different aluminum foam densities indicate that increasing the relative density results in increased attenuation capability of the aluminum foam and decreased attenuation capability of the sandwich structure. Experiments on the sandwich structure with different aluminum foam thickness indicate that increasing the thickness results in increased attenuation capability of the aluminum foam and the sandwich structure.

Curved-Array-Based Multispectral Photoacoustic Imaging of Human Finger Joints.

In this study, we present the design, fabrication, and evaluation of a curved-array-based photoacoustic imaging system designed for imaging vasculatures inside human finger joints with multispectral strategy. The transducers were fabricated with polyvinylidene fluoride (PVDF) film with a size of 30 mm × 2.8 mm and a curvature radius of 82 mm. A detailed comparison between the PVDF transducer and commercial piezoelectric ceramic transducers was performed. In addition, phantom and in vivo mouse experiments were carried out to evaluate the system performance. Furthermore, we recruited healthy volunteers and did multispectral photoacoustic imaging of blood vessels in finger joints. The transducers have an average center frequency of 6.6 MHz and a mean bandwidth of 95%. The lateral and axial resolutions of the system are 110 and 800 μm, respectively, and the diameter of the active imaging is larger than 50 mm. We successfully captured the drug-induced cerebral bleeding spots in intact mouse brains, and recovered both morphology and oxygen saturation of the blood vessels in human finger joints. The PVDF transducer has a better performance in bandwidth compared with commercial transducers. The curved design of the transducer offers a better sensitivity and a higher axial resolution compared with the flat design. Based on the phantom, animal, and human experiments, the proposed system has the potential to be used in clinical diagnosis of early-stage arthritis.

A new solution of measuring thermal response of prestressed concrete bridge girders for structural health monitoring

This study develops a novel buckling-based mechanism to measure the thermal response of prestressed concrete bridge girders under continuous temperature changes for structural health monitoring. The measuring device consists of a bilaterally constrained beam and a piezoelectric polyvinylidene fluoride transducer that is attached to the beam. Under thermally induced displacement, the slender beam is buckled. The post-buckling events are deployed to convert the low-rate and low-frequency excitations into localized high-rate motions and, therefore, the attached piezoelectric transducer is triggered to generate electrical signals. Attaching the measuring device to concrete bridge girders, the electrical signals are used to detect the thermal response of concrete bridges. Finite element simulations are conducted to obtain the displacement of prestressed concrete girders under thermal loads. Using the thermal-induced displacement as input, experiments are carried out on a 3D printed measuring device to investigate the buckling response and corresponding electrical signals. A theoretical model is developed based on the nonlinear Euler–Bernoulli beam theory and large deformation assumptions to predict the buckling mode transitions of the beam. Based on the presented theoretical model, the geometry properties of the measuring device can be designed such that its buckling response is effectively controlled. Consequently, the thermally induced displacement can be designed as limit states to detect excessive thermal loads on concrete bridge girders. The proposed solution sufficiently measures the thermal response of concrete bridges.

Experimental study on stress attenuation in aluminum foam core sandwich panels in high-velocity impact

The present work examined the dynamic behaviors of sandwich panels with aluminum foam core and steel faceplates at an impact velocity of about 370m/s. The stress attenuation before and after the foam core during penetration process was measured by means of Polyvinylidene Fluoride transducers. It was found that the stress value was remarkably reduced, and the rise velocity of stress slowed down evidently as foam core was compressed. The profile of the damaged aluminum foam illustrated no obvious localized “X” failure patterns at the velocity tested presently.

Design, fabrication and characterization of composite piezoelectric ultrafine fibers for cochlear stimulation

Sensorineural hearing loss, primed by dysfunction or death of hair cells in the cochlea, is the main cause of severe or profound deafness. Piezoelectric materials work similarly to hair cells, namely, as mechano-electrical transducers. Polyvinylidene fluoride (PVDF) films have demonstrated potential to replace the hair cell function, but the obtained piezoresponse was insufficient to stimulate effectively the auditory neurons. In this study, we reported on piezoelectric nanocomposites based on ultrafine PVDF fibers and barium titanate nanoparticles (BTNPs), as a strategy to improve the PVDF performance for this application. BTNP/PVDF fiber meshes were produced via rotating-disk electrospinning, up to 20/80 weight composition. The BTNP/PVDF fibers showed diameters ranging in 0.160–1.325μm. Increasing collector velocity to 3000rpm improved fiber alignment. The piezoelectric β phase of PVDF was well expressed following fabrication and the piezoelectric coefficients increased according to the BTNP weight ratio. The BTNP/PVDF fibers were not cytotoxic towards cochlear epithelial cells. Neural-like cells adhered to the composite fibers and, upon mechanical stimulation, showed enhanced viability. Using BTNP filler for PVDF matrices, in the form of aligned ultrafine fibers, increased the piezoresponse of PVDF transducers and favored neural cell contact. Piezoelectric nanostructured composites might find application in next generation cochlear implants.

Development of Vibration-Based Piezoelectric Raindrop Energy Harvesting System

The trend of finding new means to harvest energy has triggered numerous researches to explore the potential of raindrop energy harvesting. This paper presents an investigation on raindrop energy harvesting which compares the performance of polyvinylidene fluoride (PVDF) cantilever and bridge structure transducers and the development of a raindrop energy harvesting system. The parameters which contribute to the output voltage such as droplet size, droplets released at specific heights and dimensions of PVDF transducers are analyzed. Based on the experimental results, the outcomes have shown that the bridge structure transducer generated a higher voltage than the cantilever. Several dimensions have been tested and it was found that the 30 mm × 4 mm × 25 μm bridge structure transducer generated a relatively high AC open-circuit voltage, which is 4.22 V. The power generated by the bridge transducer is 18 μW across a load of 330 kΩ. The transducer is able to drive up a standard alternative current (AC) to direct current (DC) converter (full-wave bridge rectifier). It generated a DC voltage, VDC of 8.7 mV and 229 pW across a 330 kΩ resistor per drop. It is also capable to generate 9.3 nJ in 20 s from an actual rain event.

Simulation and Measurement of Air-Coupled Semi-Circular and Conical PVDF Sensors

For airborne sound navigation and ranging (SONAR) applications, low frequency and broadband transducers are required for the detection of obstacles with high axial resolution. In this paper, electrical and mechanical characteristics of semi-circular sensors and a semi-conical polyvinylidene fluoride (PVDF) sensor are compared through simulations and experiments. First, the implementation of semi-circular transducers and semi-conical transducer is presented. The electrical pulse, sine responses, dielectric impedance spectroscopy, and beam pattern measurements of transducers are achieved and compared. The vibration analysis of produced sensors was performed by a finite-element method and compared with experimental results. Experiments and simulations show that the semi-conical PVDF transducer has a higher bandwidth than the semi-circular transducers and it is suitable for low-frequency airborne pulse-echo ultrasound applications using single pulse or frequency chirped wave transducer.

A new fiber-optic non-contact compact laser-ultrasound scanner for fast non-destructive testing and evaluation of aircraft composites.

Laser ultrasonic (LU) inspection represents an attractive, non-contact method to evaluate composite materials. Current non-contact systems, however, have relatively low sensitivity compared to contact piezoelectric detection. They are also difficult to adjust, very expensive, and strongly influenced by environmental noise. Here, we demonstrate that most of these drawbacks can be eliminated by combining a new generation of compact, inexpensive fiber lasers with new developments in fiber telecommunication optics and an optimally designed balanced probe scheme. In particular, a new type of a balanced fiber-optic Sagnac interferometer is presented as part of an all-optical LU pump-probe system for non-destructive testing and evaluation of aircraft composites. The performance of the LU system is demonstrated on a composite sample with known defects. Wide-band ultrasound probe signals are generated directly at the sample surface with a pulsed fiber laser delivering nanosecond laser pulses at a repetition rate up to 76 kHz rate with a pulse energy of 0.6 mJ. A balanced fiber-optic Sagnac interferometer is employed to detect pressure signals at the same point on the composite surface. A- and B-scans obtained with the Sagnac interferometer are compared to those made with a contact wide-band polyvinylidene fluoride transducer.

Experimental identification of smart material coupling effects in composite structures

Smart composite structures have an enormous potential for industrial applications, in terms of mass reduction, high material resistance and flexibility. The correct characterization of these complex structures is essential for active vibration control or structural health monitoring applications. The identification process generally calls for the determination of a generalized electromechanical coupling coefficient. As this process can in practice be difficult to implement, an original approach, presented in this paper, has been developed for the identification of the coupling effects of a smart material used in a composite curved beam. The accuracy of the proposed identification technique is tested by applying active modal control to the beam, using a reduced model based on this identification. The studied structure was as close to reality as possible, and made use of integrated transducers, low-cost sensors, clamped boundary conditions and substantial, complex excitation sources. PVDF (polyvinylidene fluoride) and MFC (macrofiber composite) transducers were integrated into the composite structure, to ensure their protection from environmental damage. The experimental identification described here was based on a curve fitting approach combined with the reduced model. It allowed a reliable, powerful modal control system to be built, controlling two modes of the structure. A linear quadratic Gaussian algorithm was used to determine the modal controller–observer gains. The selected modes were found to have an attenuation as strong as −13 dB in experiments, revealing the effectiveness of this method. In this study a generalized approach is proposed, which can be extended to most complex or composite industrial structures when they are subjected to vibration.

Variable-thickness multilayered polyvinylidene fluoride transducer with improved sensitivity and bandwidth for photoacoustic imaging

The performance of photoacoustic imaging (PAI) is critically dependent on the sensitivity and bandwidth of the transducer. Here, we report the design and fabrication of a polyvinylidene fluoride ultrasonic transducer with variable-thickness layers that demonstrates significantly improved sensitivity and bandwidth. We show that the multilayered transducer provides more than 2-fold increase in sensitivity and more than 65% improvement in bandwidth compared with the conventional single-layer transducer. Photoacoustic imaging of mouse brain with the intact skull and scalp is conducted to demonstrate the power of the multilayered transducer for resolving brain structure in an in vivo setting.

A Four-Quadrant PVDF Transducer for Surface Acoustic Wave Detection

In this paper, a polyvinylidene fluoride (PVDF) piezoelectric transducer was developed to detect laser-induced surface acoustic waves in a SiO2-thin film–Si-substrate structure. In order to solve the problems related to, firstly, the position of the probe, and secondly, the fact that signals at different points cannot be detected simultaneously during the detection process, a four-quadrant surface acoustic wave PVDF transducer was designed and constructed for the purpose of detecting surface acoustic waves excited by a pulse laser line source. The experimental results of the four-quadrant piezoelectric detection in comparison with the commercial nanoindentation technology were consistent, the relative error is 0.56%, and the system eliminates the piezoelectric surface wave detection direction deviation errors, improves the accuracy of the testing system by 1.30%, achieving the acquisition at the same time at different testing positions of the sample.

High-Resolution Ultrasound Imaging of Human Skin In Vivo by Using Three-Dimensional Ultrasound Microscopy

Observing the morphology of human skin is important in the diagnosis of skin cancer and inflammation and in the assessment of skin aging. High-frequency ultrasound imaging provides high spatial resolution of the deep layers of the skin, which cannot be visualized by optical methods. The objectives of the present study were to develop a three-dimensional (3-D) ultrasound microscope and to observe the morphology of normal human skin in vivo. A concave polyvinylidene fluoride transducer with a central frequency of 120 MHz was excited using an electric pulse generated by semiconductor switching. The transducer was scanned two-dimensionally by using two linear motors on the region-of-interest and the ultrasonic reflection was digitized with 2-GHz sampling. Consecutive B-mode images perpendicular to the skin surface were reconstructed to generate multiplanar reconstructed images and 3-D volume-rendering images clearly showing microstructures such as sebaceous glands and hair follicles. The 3-D ultrasound microscope could be used to successfully image the morphology of human skin noninvasively and may provide important information on skin structure.

Experimental and theoretical analysis of the dispersion of laser-induced surface acoustic wave due to surface roughness

In the process of producing materials, the surface roughness always exists. And it can change the velocity of surface acoustic wave (SAW) which propagates in the material. To assess the properties of materials by laser induced SAW, an inverse method based on the wide-band velocity dispersion characteristic of laser-induced SAW is most commonly used. To study whether the surface roughness can be one of the inversion characteristic parameters, an experimental apparatus is constructed in this article. In the apparatus, the SAW is induced in the surface roughness sample by laser, and it is received by a polyvinylidene fluoride transducer with wide frequency band. Using this apparatus, we study the influences of different surface roughnesses on SAW velocity. In the paper a physical model of laser-induced SAW propagating in roughness surface is established theoretically. The time domain characteristic of SAW is obtained by the finite element method, and then the velocity dispersion curve of SAW is achieved. It is concluded that the theoretical result and the experimental result are in good agreement with each other. The studies in this article form theoretical and experimental bases for assessing surface roughness by means of laser-induced SAW technique.

Development of a Piezoelectric Transducers System to Improve Mixing of Fluids

Abstract The growing interest in microfluidic devices lead to the necessity of handling fluids at micro-scales and improve reaction times, which is intrinsically related to a fast and efficient mixing process. The 96 well microplates used for biochemical analysis, usually require fluids mixing before analysis, which is commonly performed by mechanically stirring. In this work, it was developed an electric actuating system based on piezoelectric PZT (Lead Zirconate Titanate) and PVDF (Polyvinylidene fluoride) transducers, which are to be placed under the microplate, in order to generate and transmit acoustic waves to the wells. A fast and efficient mixing process was achieved and demonstrated thought a qualitative approach.

Evaluation of the enhanced cavitation impact energy using a PVDF transducer with an acrylic resin backing

A transducer using a PVDF (Polyvinylidene Fluoride) film as a pressure sensitive material has been developed and applied to evaluate the cavitation impact energy. However, enhanced cavitation impact used for peening destroys the PVDF film, which is directly exposed to the cavitation impact through a polyimide tape. In the present paper, a newly developed PVDF transducer is proposed, in which a PVDF film with an acrylic resin, which attenuates the burst signal, is put on the backside of a metallic base, where the front surface of the metallic base is exposed to the cavitation impact.