• Korean Journal of Materials Research
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• v.12 no.7
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• pp.522-527
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• 2002

To investigate the SAW properties of GaN films on c-plane sapphire substrates, we carried out both the experimental measuring and theoretical calculation. The experimental characterization of SAW propagation properties was performed with a linear array of interdigital transducer (IDT) structures, while SAW velocities were calculated by matrix methods. HVPSAW mode with the propagation velocity over 10,000m/s and PSAW mode as well as GSAW could be observed in experimental determination. These results were verified by matching with the theoretical calculation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.379-382
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• 2004

In this paper, it is investigated in advance about the PZT-based composition for piezoelectric vibration device. The specimens of piezoelectric ceramics are made of Columbite method. The piezoelectric vibration device by this composition is designed by ATILA(Magsoft) program used FEM(Finite Element Method). The vibration device used for mobile phone must be driven in the frequency of $130{\sim}200Hz$, so the resonant frequency of piezoelectricity must adjust driven frequency bandwidth. The result of analysis by ATILA is appeared dependant property of length, width, thickness and dummy weight about resonant frequency of the piezoelectric vibration device. The size of manufactured actuator is $28{\times}12{\times}0.3mm^3(length {\times}width{\times}thickness)$ and this is bimorph type. The test of manufactured piezoelectric vibration device measure displacement, acceleration and power dissipation. The piezoelectric vibration device has the advantage more than electro-magnetic motor, however the size of manufactured device is larger than electro-magnetic motor.

• Journal of the Korean institute of surface engineering
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• v.54 no.6
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• pp.324-330
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• 2021

As energy harvesting technology becomes important in relation to environmental issues, piezoelectric materials that convert mechanical energy into electrical energy are attracting attention. However, PZT, a representative material for piezoelectricity, is becoming difficult to use due to the problem that its components can cause environmental pollution. For this reason, recent research suggests a triboelectric nanogenerator (TENG) that generates energy through the combined effect of triboelectricity and electric induction for alternative piezoelectric devices. In TENG, electrical power is determined by the dielectric constant, thickness, and grain generation of the charged material. Therefore, in this study, a Rutile phase TiO₂ thin film with high dielectric constant was formed using the spin-coating process and the effect of annealing was investigated. For electrical analysis, a TENG device was fabricated using PTFE as a material with an opposite charge, and electrical output according to film thickness and grain formation was comparatively analyzed.

• Korean Journal of Materials Research
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• v.28 no.11
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• pp.671-679
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• 2018

Finite element analyses are carried out to understand the piezoelectric behaviors of ZnO nanowires. Three different types of ZnO nanowires, with aspect ratios of 1:2. 1:31, and 1:57, are analyzed for uniaxial compression, pure bending, and buckling. Under the uniaxial compression with a strain of $1.0{\times}10^{-4}$ as the reference state, it is predicted that all three types of nanowires develop the same magnitude of the piezoelectric fields, which suggests that longer nanowires exhibit higher piezoelectric potential. However, this prediction is not in agreement with the experimental results previously reported in the literature. Such discrepancy is understood when the piezoelectric behaviors under bending and buckling are considered. When only the strain field due to bending is present in bending or buckling, the antisymmetric nature of the through-thickness stain distribution indicates that two piezoelectric fields, the same in magnitude and opposite in sign, develop along the thickness direction, which cancels each other out, resulting in a zero net piezoelectric field. Once additional strain contribution due to axial deformation is superposed on the bending, such field cancelling is compensated for due to the axial component of the piezoelectric field. Such numerical predictions seem to explain the reported experimental results while providing a guideline for the design of nanowire-based piezoelectric devices.

• Korean Journal of Materials Research
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• v.31 no.1
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• pp.43-53
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• 2021

Dynamic behavior of piezoelectric ZnO nanowires is investigated using finite element analyses (FEA) on FE models constructed based on previous experimental observations in which nanowires having aspect ratios of 1:2. 1:31, and 1:57 are obtained during a hydrothermal process. Modal analyses predict that nanowires will vibrate in lateral bending, uniaxial elongation/contraction, and twisting (torsion), respectively, for the three ratios. The natural frequency for each vibration mode varies depending on the aspect ratio, while the frequencies are in a range of 7.233 MHz to 3.393 GHz. Subsequent transient response analysis predicts that the nanowires will behave quasi-statically within the load frequency range below 10 MHz, implying that the ZnO nanowires have application potentials as structural members of electromechanical systems including nano piezoelectric generators and piezoelectric dynamic strain sensors. When an electric pulse signal is simulated, it is predicted that the nanowires will deform in accordance with the electric signal. Once the electric signal is removed, the nanowires exhibit a specific resonance-like vibration, with the frequency synchronized to the signal frequency. These predictions indicate that the nanowires have additional application potential as piezoelectric actuators and resonators.

• Advances in nano research
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• v.15 no.2
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• pp.175-189
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• 2023

The under-evaluation structure includes a functionally graded porous (FGP) core which is confined by two piezoelectric carbon nanotubes reinforced composite (CNTRC) layers. The whole structure rests on the Pasternak foundation. Using quasi-3D hyperbolic shear deformation theory, governing equations of a sandwich plate are driven. Moreover, face sheets are subjected to the electric field and the whole model is under thermal loading. The properties of all layers alter continuously along with thickness direction due to the CNTs and pores distributions. By conducting the current study, the results emerged in detail to assess the effects of different parameters on buckling of structure. As instance, it is revealed that highest and lowest critical buckling load and consequently stiffness, is due to the V-A and A-V CNTs dispersion type, respectively. Furthermore, it is revealed that by porosity coefficient enhancement, critical buckling load and consequently, stiffness reduces dramatically. Current paper results can be used in various high-tech industries as aerospace factories.

• Korean Journal of Materials Research
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• v.34 no.4
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• pp.215-222
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• 2024

Because collagen is inherently piezoelectric, research is being actively conducted to utilize it to harvest energy. In this study, a collagen solution was prepared using edible low-molecular-weight peptide collagen powder, and collagen films were fabricated using a dip coating method. The collagen films prepared by dip coating showed a smooth surface without defects such as pinholes or cracks. Dehydrothermal treatment of the collagen films was performed to induce a stable molecular structure through cross-linking. The collagen film subjected to dehydrothermal treatment at 110 ℃ for 24 h showed a thickness reduction rate of 19 %. Analysis of the collagen films showed that the crystallinity of the collagen film improved by about 7.9 % after dehydrothermal treatment. A collagen film-based piezoelectric nanogenerator showed output characteristics of approximately 13.7 V and 1.4 ㎂ in a pressure test of 120 N. The generator showed a maximum power density of about 2.91 mW/m² and an output voltage of about 8~19 V during various human body movements such as finger tapping. The collagen film-based piezoelectric generator showed improved output performance with improved crystallinity and piezoelectricity after dehydrothermal treatment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.637-644
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• 2010

A vibration-powered piezoelectric energy harvester yields the maximum power output when its resonant frequency is made equal to the excitation frequency; however, the power output is dramatically decreased when the energy harvester is operated at off-resonance frequency. It has been observed that the resonant frequency of a piezoelectric energy harvester may change with time and that the excitation frequency often varies when the energy harvester is used in real applications. Hence, in this study, we propose a piezoelectric energy-harvesting module that is suitable for excitations in a certain frequency range. The frequency characteristics of the electrical output of the module are studied through analysis and experiment. A simple frequency tuning method is also suggested for the proposed energy-harvesting module; in this method, frequency tuning is achieved by changing the electrical connections between the constituent energy-harvesting units of the module.

• Smart Structures and Systems
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• v.19 no.2
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• pp.163-179
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• 2017

The axisymmetric buckling delamination of the Piezoelectric/Metal/Piezoelectric (PZT/Metal/PZT) sandwich circular plate with interface penny-shaped cracks is investigated. The case is considered where open-circuit conditions with respect to the electrical displacement on the upper and lower surfaces, and short-circuit conditions with respect to the electrical potential on the lateral surface of the face layers are satisfied. It is assumed that the edge surfaces of the cracks have an infinitesimal rotationally symmetric initial imperfection and the development of this imperfection with rotationally symmetric compressive forces acting on the lateral surface of the plate is studied by employing the exact geometrically non-linear field equations and relations of electro-elasticity for piezoelectric materials. The sought values are presented in the power series form with respect to the small parameter which characterizes the degree of the initial imperfection. The zeroth and first approximations are used for investigation of stability loss and buckling delamination problems. It is established that the equations and relations related to the first approximation coincide with the corresponding ones of the three-dimensional linearized theory of stability of electro-elasticity for piezoelectric materials. The quantities related to the zeroth approximation are determined analytically, however the quantities related to the first approximation are determined numerically by employing Finite Element Method (FEM). Numerical results on the critical radial stresses acting in the layers of the plate are presented and discussed. In particular, it is established that the piezoelectricity of the face layer material causes an increase (a decrease) in the values of the critical compressive stress acting in the face (core) layer.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.1
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• pp.13-23
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• 2015

The paper experimentally deals with the radial in-plane vibration characteristics of disk-shaped piezoelectric transducers. The radial in-plane motion, which is induced due to Poisson's ratio in the piezoelectric disk polarized in the thickness direction, was measured by using an in-plane laser vibrometer, and the natural frequencies were measured by using an impedance analyzer. The experimental results have been compared with theoretical predictions obtained by simplified theoretical and finite-element analyses. It appears that the fundamental mode of a piezoelectric disk transducer is a radial mode and its radial displacement distribution from the center to the perimeter is not monotonic but shows maximum slightly apart from the perimeter. The theoretically-calculated fundamental frequencies agree well with the finite-element results for small thickness-to-diameter ratio, and they are accurate within 7 % error for the ratio up to 0.4.