• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.509-510
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• 2009

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.8
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• pp.620-623
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• 2013

The carbon nanotube / poly-vinylidene fluoride (CNT/PVDF) composite films for the nano-generator devices were fabricated by spray coating method using the CNT/PVDF solution, which was prepared by adding PVDF pellets into the CNT dispersed N-Methyl-2-pyrroli-done (NMP) solution. The flexible CNT/PVDF composite films were investigated by the scanning electron microscopy, which revealed that the CNTs were uniformly dispersed in the PVDF matrix and thickness of the films was approximately $20{\mu}m$. Fourier transform infra-red spectra were used to investigate crystal structure of the as-spray-coated CNT/PVDF films, and we found that they revealed extremely large portion of the ${\beta}$ phase PVDF. The capacitance of the CNT/PVDF films increased by adding CNTs into the PVDF matrix, and finally saturated. However, the resistance didn't show any saturation effect in the CNT concentration range of 0~4 wt%. Finally, the resulting nano-generator devices revealed reasonable current output after given mechanical stress.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.8
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• pp.1115-1119
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• 2013

The carbon nanotube/poly-vinylidene fluoride (CNT/PVDF) composite films for the use of electronic devices were fabricated by spray coating method using the CNT/PVDF solution, which was prepared by adding PVDF pellets into the CNT dispersed N-Methyl-2-pyrroli-done (NMP) solution. The CNT/PVDF composite films were peeled off from the glass substrate and were investigated by the scanning electron microscopy, which revealed that the CNTs were uniformly dispersed in the PVDF films and thickness of the films were approximately $20{\mu}m$. The capacitance of the CNT/PVDF films increased dramatically by adding CNTs into the PVDF matrix, and finally saturated approximately 1880 pF. However, the I-V curves didn't show any saturation effect in the CNT concentration range of 0 ~ 0.04 wt%. Therefore we can control the performance of the devices from the CNT/PVDF composite film by adjusting the current level resulted from the CNT concentration with the uniform capacitance value.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.118-121
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• 2002

Polyvinylidene di-fluoride (PVDF) film sensor appeared to be practically useful for the structural health monitoring of composite materials and structures. PVDF film sensors were either attached to or embedded in the graphite/epoxy composite (CFRP) samples to detect the fatigue damage at the bondline of single-lap joints or the tensile failure of unidirectional laminates. PVDF sensors were sensitive enough to detect and determine the crack front in linear location since composites usually produce very energetic acoustic emission (AE). PVDF sensors are extremely cost-effective, as flexible as other plastic films, in low profile as thin as a few tens of microns, and have relatively wide-band response, all of which characteristics are readily utilized for the structural health monitoring of composite structures. Signals due to fatigue damage showed a characteristics of mode II (shear) type failure whereas those from fiber breakage at DEN notches showed that of mode I (tensile) type fracture.

• Journal of Sensor Science and Technology
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• v.14 no.4
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• pp.225-230
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• 2005

This paper describes a novel tip position sensor made of a triangularly shaped piezoelectric PVDF (polyvinylidene fluoride) film for a cantilever beam. Due to the boundary condition of the cantilever beam and the spatial sensitivity function of the sensor, the charge output of the sensor is proportional to the tip position of the beam. Experimental results with the PVDF sensor were compared with those using two commercially available position sensors: an inductive sensor and an accelerometer. The resonance frequencies of the test beam, measured using the PVDF sensor, matched well with those measured with the two commercial sensors and the PVDF sensor also showed good coherence over wide frequency range, whereas the inductive sensor became poor above a certain frequency.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.571-572
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• 2010

• Smart Structures and Systems
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• v.12 no.1
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• pp.55-71
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• 2013

Structural health monitoring (SHM) is vital for detecting the onset of damage and for preventing catastrophic failure of civil infrastructure systems. In particular, piezoelectric transducers have the ability to excite and actively interrogate structures (e.g., using surface waves) while measuring their response for sensing and damage detection. In fact, piezoelectric transducers such as lead zirconate titanate (PZT) and poly(vinylidene fluoride) (PVDF) have been used for various laboratory/field tests and possess significant advantages as compared to visual inspection and vibration-based methods, to name a few. However, PZTs are inherently brittle, and PVDF films do not possess high piezoelectricity, thereby limiting each of these devices to certain specific applications. The objective of this study is to design, characterize, and validate piezoelectric nanocomposites consisting of zinc oxide (ZnO) nanoparticles assembled in a PVDF copolymer matrix for sensing and SHM applications. These films provide greater mechanical flexibility as compared to PZTs, yet possess enhanced piezoelectricity as compared to pristine PVDF copolymers. This study started with spin coating dispersed ZnO- and PVDF-TrFE-based solutions to fabricate the piezoelectric nanocomposites. The concentration of ZnO nanoparticles was varied from 0 to 20 wt.% (in 5 % increments) to determine their influence on bulk film piezoelectricity. Second, their electric polarization responses were obtained for quantifying thin film remnant polarization, which is directly correlated to piezoelectricity. Based on these results, the films were poled (at 50 $MV-m^{-1}$) to permanently align their electrical domains and to enhance their bulk film piezoelectricity. Then, a series of hammer impact tests were conducted, and the voltage generated by poled ZnO-based thin films was compared to commercially poled PVDF copolymer thin films. The hammer impact tests showed comparable results between the prototype and commercial samples, and increasing ZnO content provided enhanced piezoelectric performance. Lastly, the films were further validated for sensing using different energy levels of hammer impact, different distances between the impact locations and the film electrodes, and cantilever free vibration testing for dynamic strain sensing.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.10
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• pp.966-970
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• 2006

We reported on characteristics of the piezoelectric ceramic-polymer composite for the application of the thick-film speaker. The PVDF-PZT composites were fabricated to incorporate the advantages of both ceramic and polymer with various mixing ratios by 3-roll mill mixer. The composite solutions were coated by the conventional screen-printing method on ITO electrode coated PET (Polyethylene terephthalate) polymer film. After depositing the top-electrode of silver-paste, 4 kV/mm of DC field was applied at $120^{\circ}C$ for 30 min to poling the composite films. The value of $d_{33}$ (piezoelectric charge constant) was increased when the PZT weight percent was increased. The maximum value of the $d_{33}$ was 24 pC/N at 70 wt% PZT. But the $g{33}$ (piezoelectric voltage constant) showed the maximum value of $32mV{\cdot}m/N$ at 65 wt% of PZT powder. The SPL (sound pressure level) of the speaker fabricated with the 65:35 composite film was about 68 dB at 1 kHz.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.1
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• pp.212-218
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• 2002

This research is the development of a distributed tactile sensor using PVDF film far the detection of the contact state. The prototype of the tactile sensor with 8$\times$8 taxels was fabricated using PVDF film and flexible circuitry. In the fabrication procedure, the electrode and the common electrode patterns are attached to the both side of the 28${\mu}m$ thickness PVDF film. The sensor is covered with polyester film for insulation. The signals of a contact pressure to the tactile sensor are sensed and processed in the DSP system in which the signals are digitalized and filtered. And the signals are integrated for taking the force profile. The processed signals of the output of the sensor are visualized to take the shape and force distribution of the contact object in personal computer. The usefulness of the sensor system is verified through the sensing examples.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.130-131
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• 2007

In this study, polyvinylidene fluoride/trifluoroethylene (PVDF-TrFE) was investigated. For a metal-ferroelectic-metal (MFM) structure, We obtained that the 70 nm-thick film showed the maximum polarization of $8.24\;{\mu}C/cm^2$, 2Pr of $6\;{\mu}C/cm^2$ and the coercive voltage of ${\pm}3.1\;V$ at 12 V. The 140 nm-thick film showed higher performance. However, the thicker film required a higher voltage. The current density was $10^{-6}{\sim}10^{-7}\;A/cm^2$ under 15 V. We can expect from these results that the electrical properties of the devices particularly ferroelectric thin film transistor using PVDF-TrFE copolymer, be able to be on the trade-off relationship between the remanent polarization and the leakage current.