• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.2
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• pp.90-98
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• 2021

Piezoelectric ceramic fiber composite (PCFC) was fabricated using a planar electrode printed piezoelectric ceramic fiber driven in transverse mode for small-scale wind energy harvester applications. The PCFC consisted of an epoxy matrix material and piezoelectric ceramic fibers sandwiched by interdigitated electrode (IDE) patterned polyimide films. The PCFC showed an excellent mechanical performance under a continuous stress. For the fabrication of PCB cantilever harvester, five -PCFCs were vertically attached onto a flexible printed circuit board (PCB) substrate, and then PCFCs were serially connected through a printed Cu circuit. The energy harvesting performance was evaluated applying an inverted structure, which imples its free leading edge located at an open end but the trailing edge at a clamped end, to enhance strain energy in a wind tunnel. The output voltage of the PCB cantilever harvester was increased as the wind speed increased. The maximum output power was 17.2 ㎼ at a resistance load of 200 ㏀ and wind speed of 9 m/s. It is considered that the PCB cantilever energy harvester reveals a potential use for wind energy harvester applications.

• Steel and Composite Structures
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• v.50 no.1
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• pp.63-75
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• 2024

In this paper, the modified couple stress theory (MCST) and first order shear deformation theory (FSDT) are employed to investigate the free vibration and bending analyses of a three-layered micro-shell sandwiched by piezoelectric layers subjected to an applied voltage and reinforced graphene nanoplatelets (GPLs) under external and internal pressure. The micro-shell is resting on an elastic foundation modeled as Pasternak model. The mixture's rule and Halpin-Tsai model are utilized to compute the effective mechanical properties. By applying Hamilton's principle, the motion equations and associated boundary conditions are derived. Static/ dynamic results are obtained using Navier's method. The results are validated with the previously published works. The numerical results are presented to study and discuss the influences of various parameters on the natural frequencies and deflection of the micro-shell, such as applied voltage, thickness of the piezoelectric layer to radius, length to radius ratio, volume fraction and various distribution pattern of the GPLs, thickness-to-length scale parameter, and foundation coefficients for the both external and internal pressure. The main novelty of this work is simultaneous effect of graphene nanoplatelets as reinforcement and piezoelectric layers on the bending and vibration characteristics of the sandwich micro shell.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.13-16
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• 2005

The mechanical properties of composite materials may degrade severely in the presence of damage. Especially, the high-velocity impact such as bird strike, a hailstorm, and a small piece of tire or stone during high taxing, can cause sever damage to the structures and sub-system in spite of a very small mass. However, it is not easy to detect the damage in composite plates using a single technique or any conventional methods. In this paper, the PYDF(polyvinylidene fluoride) film sensors and strain gages were used for monitoring impact damage initiation and propagation in composite laminates. The WT(wavelet transform) and STFT(short time Fourier transform) are used to decompose the sensor signals. A ultrasonic C-scan and a digital microscope are also used to examine the extent of the damage in each case. This research demonstrate how various sensing techniques, PVDF sensor in particular, can be used to characterize high-velocity impact damage in advanced composites.

• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.4 s.23
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• pp.130-135
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• 2005

This paper presents application possibility of Lightweight Piezoceramic Composite Actuator(LIPCA) to suppress vibration of dynamic structures as an actuator. LIPCA is composed of a piezoelectric layer, a carbon/epoxy layer and glass/epoxy layers. When compared to the bare piezoelectric ceramic(PZT), LIPCA has advantages such as high performance, durability and reliability. In this study, performances of LIPCA have been estimated in an active vibration control system. Experiments were performed on an aluminum beam with cantilever configuration. In this test, strain gages and single LIPCA are attached on the aluminum beam with epoxy resin. Digital ON-OFF control algorithm is applied into the system to exhibit performance of LIPCA as actuator in active vibration control system. First, we performed static actuation test of bare PZT and LIPCA in order to show the superiority of LIPCA. Secondly, we carried out beam vibration control test using LIPCA. The results showed LIPCA could suppress free vibration of the aluminum beam, which means that LIPCA can be applied as an actuator to control vibration of dynamic structures.

• Composites Research
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• v.12 no.2
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• pp.1-9
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• 1999

The piezoelectric material connected to external electric networks possesses frequency dependent stiffness and loss factor which are also affected by the shunting circuit. The external electric networks are generally specialized for two shunting circuits: one is the case of a resistor alone and the other is the combination of a resistor and an inductor. For resistive shunting, the material properties exhibit frequency dependency similar to viscoelastic materials, but are much stiffer and more independent of temperature. Shunting with a resistor and inductor introduces an electrical resonance, which can change the characteristics of structural resonance optimally in a manner analogous to a PMD (proof mass damper). Passive damping enhancement of composite beam using piezoelectric material connected to external electrical networks is achieved and presented in this paper.

• Steel and Composite Structures
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• v.31 no.4
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• pp.387-396
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• 2019

This paper deals with the effect of ply orientation and control gain on tip transverse displacement of functionally graded beam layer for both active constrained layer damping (ACLD) and passive constrained layer damping (PCLD) system. The functionally graded beam is taken as host beam with a bonded viscoelastic layer in ACLD beam system. Piezoelectric fiber reinforced composite (PFRC) laminate is a constraining layer which acts as actuator through the velocity feedback control system. A finite element model has been developed to study actuation of the smart beam system. Fractional order derivative constitutive model is used for the viscoelastic constitutive equation. The control voltage required for ACLD treatment for various symmetric ply stacking sequences is highest in case of longitudinal orientation of fibers of PFRC laminate over other ply stacking sequences. Performance of symmetric and anti-symmetric ply laminates on damping characteristics has been investigated for smart beam system using time and frequency response plots. Symmetric and anti-symmetric ply laminates significantly reduce the amplitude of the vibration over the longitudinal orientation of fibers of PFRC laminate. The analysis reveals that the PFRC laminate can be used effectively for developing very light weight smart structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.33-37
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• 2000

The 1-3 piezoelectric composite transducer with 75 volume percents PZT was fabricated by the dicing-filling method. The resonance modes of the 1-3 transducer have been studied with electric impedance measurement as a function of frequency. The fundamental frequencies of the planar and thickness mode were observed at 0.95MHz and 1.63MHz respectively, but the lateral mode was not observed. In the thickness mode, the electromechanical coupling coefficient of the 1-3 piezoelectric composite transducer, 0.54, was very closed to that of the single phase PZT(0.52). The pulse-echo response by exciting the 1-3 transducer with an electric pulse was observed from the water/reflector interface, and analyzed bandwidth by the spectrum of the impulse response. The quality factor Q for the 1-3 transducer was observed as 1.5 smaller than that of the single phase(80) and then the 1-3 transducer may be used to the broad band type transducer applications.

• Computers and Concrete
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• v.8 no.5
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• pp.563-581
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• 2011

The signal-based acoustic emission (AE) characterization of concrete fracture process utilizing home-programmed AE monitoring system was performed for three kinds of static loading tests (Cubic-splitting, Direct-shear and Pull-out). Each test was carried out to induce a distinct fracture mode of concrete. Apart from monitoring and recording the corresponding fracture process of concrete, various methods were utilized to distinguish the characteristics of detected AE waveform to interpret the information of fracture behavior of AE sources (i.e. micro-cracks of concrete). Further, more signal-based characters of AE in different stages were analyzed and compared in this study. This research focused on the relationship between AE signal characteristics and fracture processes of concrete. Thereafter, the mode of concrete fracture could be represented in terms of AE signal characteristics. By using cement-based piezoelectric composite sensors, the AE signals could be detected and collected with better sensitivity and minimized waveform distortion, which made the characterization of AE during concrete fracture process feasible. The continuous wavelet analysis technique was employed to analyze the wave-front of AE and figure out the frequency region of the P-wave & S-wave. Defined RA (rising amplitude), AF (average frequency) and P-wave & S-wave importance index were also introduced to study the characters of AE from concrete fracture. It was found that the characters of AE signals detected during monitoring could be used as an indication of the cracking behavior of concrete.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.5
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• pp.418-425
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• 2019

A piezoelectric ceramic fiber composite (PCFC) was successfully fabricated using $0.69Pb(Zr_{0.47}Ti_{0.53})O_3-0.31[Pb(Zn_{0.4}Ni_{0.6})_{1/3}Nb_{2/3}]O_3$ (PZT-PZNN) for use in small-scale wind energy harvesters. The PCFC was formed using an epoxy matrix material and an array of Ag/Pd-coated PZT-PZNN piezo-ceramic fibers sandwiched by Cu interdigitated electrode patterned polyethylene terephthalate film. The energy harvesting performance was evaluated in a custom-made wind tunnel while varying the wind speed and resistive load with two types of flutter wind energy harvesters. One had a five-PCFC array vertically clamped with a supporting acrylic rod while the other used the same structure but with a five-PCFC cantilever array. Stainless steel (thickness: $50{\mu}m$) was attached onto one side of the PCFC to form the PZT-PZNN cantilever. The output power, in general, increased with an increase in the wind speed from 2 m/s to 10 m/s for both energy harvesters. The highest output power of $15.1{\mu}W$ at $14k{\Omega}$ was obtained at a wind speed of 10 m/s for the flutter wind energy harvester with the PZT-PZNN cantilever array. The results presented here reveal the strong potential for wind energy harvester applications to supply sustainable power to various IoT micro-devices.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.11
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• pp.743-748
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• 2017

For diseases that are difficult to detect by conventional imaging techniques, the development of a diagnostic method that allows sensors to be inserted into the human body to aid the diagnosis of local spots of the target tissue, is highly desirable. In particular, it is extremely difficult to determine whether vulnerable plaque can later develop into atherosclerosis using only imaging techniques. However, vulnerable plaques are expected to have slightly different mechanical properties than healthy tissue. In this study, we aim to develop a piezoelectric cantilever-type sensor that can be inserted into the human body and can detect the local mechanical properties of the target tissue. A piezoelectric polymer composite based on $BaTiO_3$ nanoparticles was optimized for fabrication of a piezoelectric cantilever. Next, a micro-cone tip was fabricated at the end of the piezoelectric cantilever by thermal drawing. Finally, stiffness of biological tissue samples was measured with the piezoelectric cantilever sensor for verifying its functionality.