Polyvinylidene Difluoride Film Research Articles

Micropatterning of Flexible and Free Standing Polyvinylidene Difluoride (PVDF) Films for Enhanced Pyroelectric Energy Transformation

In an effort to harvest thermal energy and exploit abundantly available waste heat the pyroelectric effect offers the opportunity to convert temperature fluctuations into useable electrical energy. Here, the micropatterning of the surface of a pyroelectric in order to enhance heat transfer and achieve faster and larger temperature fluctuations, which improve pyroelectric energy transformation, is reported. Methods for the fabrication of partially covered electrodes on polyvinylidene difluoride (PVDF) films are developed to investigate and quantify the benefits of such an electrode structure for pyroelectric energy harvesting. The micropattern consists of an array of holes that are etched into the upper aluminum electrodes of free standing ferroelectric PVDF films using a low cost photolithography and wet etching process. Under the application of infrared radiation heating, it is demonstrated that such microfeatures are able to significantly improve the open circuit voltage by 380% and the closed circuit current by 420% for an electrode area coverage of 45% when compared to a fully covered electrode design. Capacitance measurements show constant electric fields with microfeatures for electrode area coverages as low as 28%. A specific generator performance of 66.9 μJ cm−3 cycle−1 is presented at oscillation temperatures of 2.8 °C.

A layered sensor for simultaneous measurement of skin water content and softness

In this paper, a layered sensor was developed for simultaneous measurement of skin water content and softness. The sensor consisted of a thin stainless steel film on top of a polyvinylidene difluoride (PVDF) film. Electrostatic and piezoelectric effects generated voltages which were measured simultaneously in the stainless steel and PVDF films while the sensor was repeatedly in contact with/released from the skin. The voltages in the films depended on the skin water content and softness. The layered sensor measured the skin water content and softness at the same position using the voltage waveforms. The relationships between the voltages obtained using the layered sensor and results obtained with commercial moisture and softness sensors were evaluated. The potential of the proposed sensor for skin condition measurements was evaluated.

Safety of Ultrasonic Bone Curette in Ear Surgery by Measuring Skull Bone Vibrations

Mastoidectomy using an ultrasonic bone curette (UBC) is as safe for the inner ear as a mastoidectomy using a high-speed drill. Transcanal endoscopic ear surgery (TEES) is a minimally invasive, secure, and functional technique, which has been performed using high-speed drills. We have started to use a UBC instead of the high-speed drill because a UBC allows for simultaneous bone cutting, irrigation, and aspiration. These features of the UBC make it an excellent candidate for use in one-handed TEES, but the safety of the UBC still needs to be confirmed. We thus measured skull vibrations caused by the UBC to estimate the effects of UBC on the inner ear. Eight patients with cholesteatoma underwent mastoidectomy using a Sonopet UST-2001 UBC (Stryker, MI, USA) and 2 high-speed drills (drills A and B). Skull vibrations were measured using polyvinylidene difluoride film taped to the forehead as a piezoelectric vibration sensor. The recorded data were transformed to the power spectrum in the frequency domain by fast Fourier transform. The mean and peak values of vibrations were analyzed in four frequency bands: 200 to 500 Hz, 500 to 2,000 Hz, 2,000 to 8,000 Hz, and 8,000 Hz to 20 kHz. Both the mean values and the peak values of skull vibrations caused by the UBC were significantly smaller than those values obtained for drill B between 500 and 8,000 Hz, (p < 0.05). No significant differences were found among the 3 instruments below 500 Hz or above 8,000 Hz. Skull vibration levels generated by the UBC were found to be comparable or even lower than those levels associated with conventional high-speed drills. These findings indicated that the UBC can be safely applied to TEES without the risk of harmful effects on the inner ear.

Temperature Dependent Surface Resistivity Measures of Commercial, Multiwall Carbon Nanotubes (MWCNT), and Silver Nano-Particle Doped Polyvinyl Alcohol (PVA) Films

Pure and doped Polyvinylidene difluoride (PVDF) films, for the detection of infrared radiation, have been well documented using the mechanism of pyroelectricity. Alternatively, the electrical properties of films made from Polyvinyl Alcohol (PVA) have received considerable attention in recent years. The investigation of surface resistivities of both such films, to this point, has received far less consideration in comparison to pyroelectric effects. In this research, we report temperature dependent surface resistivity measurements of commercial, and of multiwall carbon nanotubes (MWCNT), or Ag-nanoparticle doped PVA films. Without any variation in the temperature range from 22°C to 40°C with controlled humidity, we found that the surface resistivity decreases initially, reaches a minimum, but rises steadily as the temperature continues to increase. This research was conducted with the combined instrumentation of the Keithley Model 6517 Electrometer and Keithley Model 8009 resistivity test fixture using both commercial and in-house produced organic thin films. With the objective to quantify the suitability of PVDF and PVA films as IR detector materials, when using the surface resistivity phenomenon, instead of or in addition to the pyroelectricity, surface resistivity measurements are reported when considering bolometry. We found that the surface resistivity measurements on PVA films were readily implemented.

Pyroelectric figures of merit and associated properties of LiTaO3/poly vinylidene difluoride nanocomposites for thermal/infrared sensing

Polymer–ceramic nanocomposites with good pyroelectric properties are proposed as promising materials for the detection and measurement of thermal waves, including infrared radiation. They possess simultaneously the advantages of high detection sensitivity of the ceramic as well as the flexibility and light weight of the polymer. Selection of the appropriate ceramic additive and the polymer matrix is the key to the success for the development of the best material for any application. The aim of this work is to develop highly sensitive, at the same time flexible, polymer-nanocomposites for pyroelectric detector applications by dispersing the well known pyroelectric material, lithium tantalate, LiTaO3, in nanocrystalline form, in an inherently pyroelectric host polymer matrix, polyvinylidene difluoride (PVDF). LiTaO3 nanoparticles are synthesised and dispersed in PVDF at varying volume fractions, and composite materials cast in the form of films for measurements. The β-phase of PVDF is confirmed from powder XRD, FT-IR and DSC measurements. The dielectric properties, shore D hardness and pyroelectric coefficients of the cast films are measured. The thermal conductivity and specific heat capacity of the films are measured following a photothermal technique. From these data the pyroelctric figures of merit of the composite films have been determined and values compared with that of pure PVDF film. It is found that, in general, the pyroelectric figure of merit increases with concentration of LiTaO3; however, it is at the expense of mechanical flexibility of the material. This paper aims at providing guidelines to strike the right balance between detection sensitivity and material flexibility (or mouldability), depending on the application.

A Proposal of New Multifunctional Pressure Sensor Based on PVDF Films

In this paper, a new multifunctional pressure sensor based on polyvinylidene difluoride (PVDF) films is proposed. The proposed sensor consists of a pair of PVDF films with urethane gel. The electrical voltage (capacitance) and ultrasonic propagation time are simultaneously measured by a pair of PVDF films. In addition, the voltages generated on the PVDF film by the vibration and temperature change are also measured due to the piezoelectric and pyroelectric effects. When the object is loaded onto the proposed sensor, the pressure is measured by the change of propagation time because the thickness of the urethane gel changes. In addition, information about the object, such as the electrical properties and vibration and temperature change, is obtained by the measured capacitance and voltages. Therefore, it is possible to measure the pressure, the electrical property, temperature change, and vibration of the object with the proposed sensor. In this experiment, the fundamental properties of the proposed sensor-pressure (weight), electrical property, vibration, and temperature-were presented. As results, electrical voltage and propagation time were measured with the relative standard deviations (RSDs) of the 21% and 2% between 0 and 50 kg weights. Two types of vibrations-sinusoidal wave of 1 Hz and pulse wave of 1.2 Hz-were detected with the RSDs of 2% and 1%, respectively. In addition, the peak voltage generated by temperature change between 14°C and 40°C was approximately measured with the RSD of 26%.

Photoflash thermal diffusivity measurement of carbon nanotube-filled PVDF composite at low temperature

The suitability of a simple photoflash technique was further examined in the measurement of thermal diffusivity of nanotube-filled polyvinylidene difluoride (PVDF) film composites at low temperature. The effect of temperature and carbon nanotube (CNT) composition in PVDF composite on its thermal diffusivity is presented as equivalent to the effect of changing thermal phonon mean free path. It is done by assuming no other thermal carrier effects other than from phonons detected during measurement by using photoflash technique. The results show that thermal diffusivity of CNT-filled PVDF film composites was found to have consistently increased with increasing the CNT concentration or decreasing temperature, as in the case of insulators with dominant phonon thermal carriers. At any particular temperature, a dramatic increase in thermal diffusivity was noticed at the beginning as the CNT concentration was systematically increased up to a 1% turning point, from which the thermal diffusivity increased further at a much smaller rate with the CNT addition up to 10%. The thermal diffusivity of the samples was in the range of about (10–35) × 10− 8 m2/s depending on the temperature and the CNT concentration of the composites.

A layered sensor for simultaneous, spatially coincident softness and moisture measurements

This paper proposes a layered sensor for the simultaneous measurement of the softness and surface moisture of an object, at the same position. In the proposed sensor, a thin stainless steel film is pasted on a polyvinylidene difluoride (PVDF) film. The voltages in the stainless steel and PVDF films are generated because of electrostatic and piezoelectric effects, and the resulting waveforms can be measured while the proposed sensor repeatedly contacts and releases the object. The voltages in the films depend on the softness and surface moisture conditions of the object. The proposed sensor therefore makes it possible to measure the softness and surface moisture of the object using the voltage waveforms. Here, we present the relationship between the measured voltages obtained using the proposed sensor and the volume of distilled water infiltrated into the filter paper on the surface of the object, and the relationship between the voltages and the softness of the object. In addition, the potential of the proposed sensor for applications is discussed.

J164016 ロール型触刺激計測システムの開発([J164-01]医療・健康・福祉のためのセンシングおよびロボティクス(1))

This paper describes development of a roll type contact stimulus evaluation system. In this study, contact force applied on skin with diaper and diaper friction are measured as the contact stimulus. First, in order to measure the contact stimulus, contact stimulus sensor is fabricated. The sensor comprises a polyvinylidene difluoride (PVDF) film and strain gauge. Next, roll type contact stimulus evaluation system is designed. In the system, roundish body part of infants such as hip is simplified into cylindrical shape. The relative motion of the hip joint is simplified into rotational motion of the cylinder. Based on the features of sensor outputs, some parameters are proposed in order to evaluate the contact stimulus. Then, three kinds of commercial disposable diaper are used as measuring objects. Sensory test about contact stimulus of the diapers are carried out on adults. And using the developed roll-type system, measurement of the diapers are conducted. By comparing the sensory evaluation value with the evaluation parameters calculated from sensor output, it is found that some evaluation parameters for the diaper obtaining the strongest "prickly sensation" and "irritated sensation" are bigger than others. From the results, it is confirmed that the developed system is useful for estimation of contact stimulus.

All Polymer Piezoelectric Film for Low Resonance Frequency Vibration Driven Energy Harvesting Application

We developed all polymer piezoelectric film which consists of polyethylene terephthalate (PET) film substrate, conductive polymer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) electrodes, and polyvinylidene difluoride (PVDF) piezoelectric film in order to achieve the low resonance frequency of energy harvesting device. Existing piezoelectric films have been deposited on rigid silicon or inorganic materials which lead to high resonance frequency and low efficiency of energy generating under low frequency of human or animal motions. Therefore, we developed all polymeric piezoelectric films on very soft PET films. To deposit PVDF film on PEDOT:PSS coated PET, low temperature coating process using low boiling temperature solvent (methyl ethyl ketone) and annealing method (under 150°C) was developed. Developed film achieved low frequency of 81 Hz.

Encapsulation of Semiconductor Gas Sensors with Gas Barrier Films for USN Application

Sensor nodes in ubiquitous sensor networks require autonomous replacement of deteriorated gas sensors with reserved sensors, which has led us to develop an encapsulation technique to avoid poisoning the reserved sensors and an autonomous activation technique to replace a deteriorated sensor with a reserved sensor. Encapsulations of In2O3 nanoparticles with poly(ethylene-co-vinyl alcohol) (EVOH) or polyvinylidene difluoride (PVDF) as gas barrier layers are reported. The EVOH or PVDF films are used for an encapsulation of In2O3 as a sensing material and are effective in blocking In2O3 from contacting formaldehyde (HCHO) gas. The activation process of In2O3 by removing the EVOH through heating is effective. However, the thermal decomposition of the PVDF affects the property of the In2O3 in terms of the gas reactivity. The response of the sensor to HCHO gas after removing the EVOH is 26%, which is not significantly different with the response of 28% in a reference sample that was not treated at all. We believe that the selection of gas barrier materials for the encapsulation and activation of In2O3 should be considered because of the ill effect the byproduct of thermal decomposition has on the sensing materials and other thermal properties of the barrier materials.

A Locally Amplified Strain Sensor Based on a Piezoelectric Polymer and Organic Field-Effect Transistors

Piezoelectric sensors are useful for a range of applications, but passive arrays suffer from crosstalk and signal attenuation, which have complicated the development of array-based polyvinylidene difluoride (PVDF) sensors. We have used organic field-effect transistors, which are compatible with the low Curie temperature of a flexible piezoelectric polymer, i.e., PVDF, to monolithically fabricate transimpedance amplifiers directly on the sensor surface and convert the piezoelectric charge signal into a current signal, which can be detected even in the presence of parasitic capacitance. The device couples the voltage generated by the PVDF film under strain into the gate of organic thin-film transistors using an arrangement that allows the full piezoelectric voltage to couple to the channel while also increasing charge-retention time. A bipolar detector is created using ultraviolet-ozone treatment to shift the threshold voltage and increase the current of the transistor under both compressive and tensile strain. An array of devices that maps the strain field on a PVDF film surface is demonstrated.

Impact force of low velocity liquid droplets measured using piezoelectric PVDF film

When a liquid droplet impacts on a solid surface, a transient impact force is developed at the interface between the liquid and the solid surface. Impact velocity, surface tension and density of the liquid are the important parameters that influence the impact force. In the present study, impact forces of two different oils’ droplet (hydraulic oil ISO VG 68 and lubrication oil SAE 30) are compared with the impact force of water droplet. The impact velocity is varied from about 1.38 to 2.96 m/s. The impact force is determined experimentally using polyvinylidene difluoride (PVDF) piezoelectric film attached on the solid surface. The dynamic response of the PVDF piezoelectric film is acquired using data acquisition system with personal computer. The film is dynamically calibrated using bead drop impact method. A linear relationship between voltage output of the PVDF piezoelectric film and impact force is established. The droplet impact force is determined by measuring the voltage output delivered by the PVDF piezoelectric film and converted it into the impact force. Impact forces developed by both the oils’ droplets are lesser than the impact force of water droplet. The impact duration observed is about 600 μs.

Minipressure sensor using AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors (HEMTs) with a polarized polyvinylidene difluoride (PVDF) film coated on the gate area exhibited significant changes in channel conductance upon exposure to different ambient pressures. The PVDF thin film was deposited on the gate region with an ink-jet plotter. Next, the PDVF film was polarized with an electrode located 2 mm above the PVDF film at a bias voltage of 10 kV and 70 °C. Variations in ambient pressure induced changes in the charge in the polarized PVDF, leading to a change in surface charges on the gate region of the HEMT. Changes in the gate charge were amplified through the modulation of the drain current in the HEMT. By reversing the polarity of the polarized PVDF film, the drain current dependence on the pressure could be reversed. Our results indicate that HEMTs have potential for use as pressure sensors.

Pressure Sensing with PVDF Gated AlGaN/GaN High Electron Mobility Transistor

AbstractAlGaN/GaN high electron mobility transistors (HEMTs) with a polarized Polyvinylidene difluoride (PVDF) film coated on the gate area exhibited significant changes in channel conductance upon exposure to different ambient pressures. The PVDF thin film was deposited on the gate region with an inkjet plotter. Next, the PDVF film was polarized with an electrode located 2 mm above the PVDF film at a bias voltage of 10 kV and 70 °C. Variations in ambient pressure induced changes in the charge in the polarized PVDF, leading to a change of surface charges on the gate region of the HEMT. Changes in the gate charge were amplified through the modulation of the drain current in the HEMT. By reversing the polarity of the polarized PVDF film, the drain current dependence on the pressure could be reversed. Our results indicate that HEMTs have potential for use as pressure sensors.

Application of square optical heating pulse model in measuring thermal diffusivity of SiC/B4C composites by using photoflash technique

This paper examines the application of a square pulse approximation to the camera flash temporal profile as a heating source in the photoflash technique. The technique was used in measuring SiC/B4C composites whereby thin-film polyvinylidene difluoride film was the detector. The analytical model derived for the square pulsed heating source was tested against the data obtained from SiC/B4C composites of different B4C composition. The suitability of the model is also compared with the model for Dirac-δ function approximation to the camera flash. The square pulse model was found to fit reasonably well to the experimental data obtained from all the composites. The thermal diffusivity measured at room temperature was in the range of (10–35) × 10− 6 m2 s− 1.

Asymmetric reflectivity from surfaces with distributed dipoles and IR experiments on poled polyvinylidene difluoride films

It is widely accepted that as a monochromatic unpolarized light beam impinges on a flat surface at an angle, the reflection occurs symmetrically with a calculable amount of power in accordance with the Fresnel equations. Furthermore, reversing the light path offers no difference owing to the inherent symmetry. However, this picture changes when the interface is a distributed double layer responsive to the incident light. Theoretical elaboration and then IR experiments on poled polyvinylidene difluoride films were conducted to verify the emergence of asymmetric reflections at varying incident angles, as well as the inverse dependence of reflectivity on the impinging light intensity.

Development of a high sensitive MEMS hydrophone using PVDF

The design and experimental evaluation of a PVDF-based MEMS hydrophone is presented in this paper. The basic structure of the hydrophone was fabricated on a silicon wafer using standard NMOS process technology. A MOSFET with extended gate electrode was designed as the interface circuit to the sensing material, which is a piezoelectric polymer, polyvinylidene difluoride (PVDF). Acoustic impedance possessed by this piezoelectric material provides a reasonable match to water, which makes it very attractive for underwater applications. The electrical signal generated by the PVDF film was directly coupled to the gate of the MOSFET. To minimize the parasitic capacitance underneath the PVDF film and hence improve the device sensitivity, a thick photoresist was first employed as the dielectric layer under the extended gate electrode. For underwater operation, a waterproof Rho-C rubber encapsulated the hydrophone. A silicon nitride layer passivated the active device, which is a good barrier material to most mobile ions and solvents. The device after passivation also shows a lower noise level. The theoretical model developed to predict the sensitivity of the hydrophone shows a reasonable agreement between the theory and the experiment.

Determination of thermal parameters of PVDF using a photoacoustictechnique

An application of the photoacoustic technique is developed fordetermining the thermal diffusivity and thermal conductivity of thermallythick samples by rear excitation. In the present work, thermal parametersmeasurements of polyvinylidene difluoride films over the temperature rangefrom 100 K to 300 K are reported. Results regarding thermal parameters at roomtemperature are in very good agreement with results from the literature. Inorder to obtain these results we have determined the thermal parameters ofquartz. To date, there do not exist in the literature data on the thermalparameter variation of polyvinylidene difluoride over the temperature range.

Absolute measurements of ultrasonic pressure by using high magnetic fields

A hydrophone is introduced that exploits the emf signal generated in a conductor when sonicated in the presence of a uniform static magnetic field. The method uses a small metal coil or metal membrane as a hydrophone receiver. Acoustic signals at 748 kHz are introduced in 1.5 T and 4.7 T fields and recorded both through direct electrical contact with the hydrophone and via RF pick-up coils, allowing wireless placement of the hydrophone. Linear response Is confirmed over four orders of magnitude in the pressure amplitude. Waveforms determined from the detected voltage are shown to be in excellent agreement with those obtained using a calibrated polyvinylidene difluoride film, and absolute values correlate within 20%. The methods are conceptually suitable for use in the presence of the high and uniform field of commercial MR scanners. The hydrophone may appear particularly useful as a quality assurance device in therapeutic and diagnostic acoustic techniques that use MRI.