Polyvinylidene Fluoride Sheet Research Articles

A versatile acoustically active surface based on piezoelectric microstructures

We demonstrate a versatile acoustically active surface consisting of an ensemble of piezoelectric microstructures that are capable of radiating and sensing acoustic waves. A freestanding microstructure array embossed in a single step on a flexible piezoelectric sheet of polyvinylidene fluoride (PVDF) leads to high-quality acoustic performance, which can be tuned by the design of the embossed microstructures. The high sensitivity and large bandwidth for sound generation demonstrated by this acoustically active surface outperform previously reported thin-film loudspeakers using PVDF, PVDF copolymers, or voided charged polymers without microstructures. We further explore the directivity of this device and its use on a curved surface. In addition, high-fidelity sound perception is demonstrated by the surface, enabling its microphonic application for voice recording and speaker recognition. The versatility, high-quality acoustic performance, minimal form factor, and scalability of future production of this acoustically active surface can lead to broad industrial and commercial adoption for this technology.

Mechanical and electrical properties of electrospun CNT/PVDF nanofiber for micro-actuator applications

Electrospun polyvinylidene fluoride (PVDF)-containing carbon nanotubes (CNT) were prepared for use in fabricating actuator materials. Actuating displacement was measured in an electrochemical environment. The electrospun nanofibers were arranged using a drum-type collector, and morphology was investigated using a field emission-scanning electron microscope. The uniformity of dispersion of CNT in the PVDF nanofibers was monitored by electron probe X-ray micro-analysis. Tensile strength and electrical resistivity results were used as an indication of the state of alignment. The electrospun CNT/PVDF nanofiber sheets exhibited better mechanical and electrical properties in the arranged direction. The efficiency and electrical capacities of electrospun CNT/PVDF nanofiber sheet were compared with those of cast PVDF sheets for use in actuator applications in electrochemical environments. The electrospun CNT/PVDF nanofiber sheets exhibited much better actuator performance than PVDF sheets, which are attributed to their superior electrical properties.Highlights(1) The interfacial durability of CNT/PVDF nanofibers was enhanced to increase contact area by reinforcing CNT.(2) The efficiency of CNT/PVDF actuators was improved due to interfacial properties.(3) Thin thickness drum-type collector was made to enhance nanofiber alignment.(4) The arranged CNT/PVDF nanofibers exhibited better mechanical and actuating displacements.

Finger-Mounted Tactile Sensor for Evaluating Surfaces

This paper presents a finger-mounted tactile sensor for extracting information on fine surface properties of objects such as textile fabrics. The prototype sensor has a thin structure composed of a sheet of PVDF (polyvinylidene fluoride) film sensor and some metal parts for converting compressive forces into area expansion of the PVDF film. By using a signal processing program based on the FFT (fast Fourier transform), voltage signal sequences from nine different fabrics were distinguished, even in the presence of variations in the pressing force and the speed of rubbing motion induced by the fluctuations in the user’s hand motion. In addition, the signal sequences from abraded fabrics were sorted by their levels of abrasion by extracting a signal component correlated with the abrasion level.11. This paper is the full translation from the transactions of JSME, Series C, Vol.77, No.784, 2011.

Localized Ligand Induced Electroless Plating (LIEP) Process for the Fabrication of Copper Patterns Onto Flexible Polymer Substrates

AbstractThe “ligand induced electroless plating (LIEP) process” is a simple process to obtain localized metal plating onto flexible polymers such as poly(ethylene terephtalate) and polyvinylidene fluoride sheets. This generic and cost‐effective process, efficient on any common polymer surface, is based on the covalent grafting by the GraftFast process of a thin chelating polymer film, such as poly(acrylic acid), which can complex copper ions. The entrapped copper ions are then chemically reduced in situ and the resulting Cu0 species act as a seed layer for the electroless copper growth which, thus, starts inside the host polymer. The present work focuses on the application of the LIEP process to the patterning of localized metallic tracks via two simple lithographic methods. The first is based on a standard photolithography process using a positive photoresist masking to prevent the covalent grafting of PAA in designated areas of the polymer substrate. In the second, the patterning is performed by direct printing of the mask with a commercial laser printer. In both cases, the mask was lifted off before the copper electroless plating step, which provides ecological benefits, since only the amount of copper necessary for the metallic patterning is used.

Finger-Mounted Tactile Sensor for Evaluating Surfaces

This paper presents a finger-mounted tactile sensor for extracting information on fine surface properties of objects such as textile fabrics. The prototype sensor has a thin structure composed of a sheet of PVDF (Polyvinylidene Fluoride) film sensor and some metal parts for converting compressive forces into area expansion of the PVDF film. By using a signal processing program based on FFT (fast Fourier transform), voltage signal sequences from nine different fabrics were distinguished, in spite of the variation in the pressing force and the speed of rubbing motion induced by the fluctuation of the user's hand motion. In addition, the signal sequences from abraded fabrics were sorted in the order of the level of abrasion, by extracting a signal component correlated with the abrasion level.

Nonlinear and time-dependent electromechanical behavior of polyvinylidene fluoride

This paper describes the results from electromechanical tests conducted on polyvinylidenefluoride (PVDF) sheets showing its nonlinear and time-dependent electromechanicalbehavior. Mechanical and electromechanical tests were carried out for both uniaxiallystretched and biaxially stretched PVDF sheets. The tests show nonlinearity in both thestress–strain response and the time-dependent response. Electromechanical dynamic testswere conducted at various superimposed pre-stress conditions. From the dynamicalelectromechanical tests, it is found that both biaxially stretched and uniaxially stretchedPVDF sheets exhibit pre-stress dependence of their electromechanical coefficients. Inaddition, an attempt has been made to model the mechanical and the electromechanicalbehavior using a simple three-parameter viscoelastic solid model. The model captures thetrends observed in the experiments and is recommended as a useful tool for designs usingthese materials.

High-frequency backscattering enhancements by thick finite cylindrical shells in water at oblique incidence: Experiments, interpretation, and calculations

Impulse response backscattering measurements are presented and interpreted for the scattering of obliquely incident plane waves by air-filled finite cylindrical shells immersed in water. The measurements were carried out to determine the conditions for significant enhancements of the backscattering by thick shells at large tilt angles. The shells investigated are made of stainless steel and are slender and have thickness to radius ratios of 7.6% and 16.3%. A broadband PVDF (polyvinylidene fluoride) sheet source is used to obtain the backscattering spectral magnitude as a function of the tilt angle (measured from broadside incidence) of the cylinder. Results are plotted as a function of frequency and angle. These plots reveal large backscattering enhancements associated with elastic excitations at high tilt angles, which extend to end-on incidence in the coincidence frequency region. Similar features are present in approximate calculations for finite cylindrical shells based on full elasticity theory and the Kirchhoff diffraction integral. One feature is identified as resulting from the axial (meridional ray) propagation of the supersonic a0 leaky Lamb wave. A simple approximation is used to describe circumferential coupling loci in frequency-angle space for several surface waves. The resulting loci are used to identify enhancements due to the helical propagation of the subsonic a0− Lamb wave.

A planar array for the generation of evanescent waves

Wavenumber-frequency calibration of underwater, planar, receiving arrays requires the ability to generate single-wavenumber pressure fields over the surface of the array. When the wavenumber-frequency region of interest is evanescent, transmitting arrays previously constructed have been found to generate fields contaminated with harmonics, acoustic wavenumbers, and nonacoustic wavenumbers from the excitation of antisymmetric Lamb waves. An array that greatly reduces contamination has recently been constructed using a sheet of polyvinylidene fluoride (PVDF) with independent rectangular electrode stripes. The array operates in the frequency range of 500 Hz to 2 kHz and generates evanescent waves with phase speeds between 30 and 150 m/s. Contamination due to the excitation of antisymmetric Lamb waves is eliminated by shifting the phase speed of the Lamb wave out of the region of interest. This is accomplished by bonding the thin sheet of PVDF directly to a thick plate of LEXAN. Contamination from harmonics and acoustic wavenumbers is eliminated by driving the electrode stripes with suitably chosen shading coefficients generated by a simple-source numerical algorithm. Measured pressure fields and phase velocities compare favorably with numerical calculations.

Primary and secondary pyroelectricity in highly oriented polyvinylidene fluoride

AbstractMeasurements of the pyroelectric response in both free and constrained conditions are presented for low‐draw ratio, high‐draw ratio and voided form I polyvinylidene fluoride sheets. The results are used together with related data for the piezoelectric response and for the thermal expansion behavior to estimate the primary and secondary components of the total macroscopic pyroelectricity. For the high‐draw ratio and voided sheets the primary response was approximately 90% of the total pyroelectricity compared with 40% for the low‐draw ratio nonvoided sheet. It is proposed that the role of reversible temperature‐dependent crystallinity is more pronounced in the high‐draw samples. Previous NMR studies provide support for this conclusion.

The ion plating of polyvinylidene fluoride surfaces for transducer elements

The unique piezoelectric and pyroelectric properties of polyvinylidene fluoride (PVDF) combined with its ease of manufacture have resulted in many new applications involving sensor and transducer elements. The adhesion and vacuum sealing of metal films to PVDF sheet samples were investigated using r.f. ion plating. Gold is favourable for vacuum-sealing applications but unfavourable for adhesion. The highest values for adhesion were obtained with reactive metals on surfaces that had been pretreated with acetone and in an r.f. oxygen discharge. The physical processes governing adhesive performance of the bond are complex, but it seems reasonable that adhesion between coating and substrate may be influenced by oxygen atom adsorption with the formation of ionic or covalent bonds with the deposited metal.

Polymeric ultrasonic probe

A small piezoelectric polymer hydrophone has been made and tested. It can be used over a broad range of frequencies to probe the temporal and spatial variations of the sound field produced by transducers such as those used in medical ultrasonics. The hydrophone is bilaminar. Each layer consists of a poled central area having a 2‐mm diameter defined by evaporated aluminum electrodes on each side of a 25‐μm‐thick sheet of polyvinylidene fluoride about 7 cm in diameter. The combined sheets are held taut in a metal hoop. Well‐separated leads of evaporated aluminum to the outside of the hoop were applied after poling so that the polymer under the leads is inert. The response does not vary by more than a few decibels from 0.5 to 10 MHz. At about 1 MHz, the change in the received signal when the hydrophone is inserted between a source and receiver is less than 0.2 dB. The broadband response of the hydrophone makes it useful for determining the output pattern of diagnostic transducers which typically use pulses. ...