• Journal of Sensor Science and Technology
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• v.23 no.6
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• pp.420-424
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• 2014

Aluminum-scandium nitride ($Al_{1-x}Sc_xN$) thin films with a TiN buffer layer have been fabricated on SUS430 substrate by RF reactive magnetron sputtering at room temperature under 50% $N_2$/Ar. The effect of Sc-doping on the structure and piezoelectric properties of AlN films has been investigated using SEM, XRD, surface profiler and pressure-voltage measurements. The as-deposited AlN films showed polycrystalline phase, and the Sc-doped AlN film, the peak of AlN (002) plane and the crystallinity became very strong. With Sc-doping, the crystal size of AlN film was grown from ~20 nm to ~100 nm. The output signal voltage of AlN sensor showed a linear behavior between 15~65 mV, and output signal voltage of Sc-doped AlN sensor was increased over 7 times. The pressure-sensing sensitivity of AlN film was calculated about 10.6mV/MPa, and $Al_{0.88}Sc_{0.12}N$ film was calculated about 76 mV/MPa.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.2
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• pp.67-74
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• 2002

The paper deals with a fully assumed strain soild element that can be used for modeling of thin sensors and actuators. To solve fully coupled field problems, the eledtric potential is regarded as a nodal degree of freedom in addition to three translations in an eighteen node assumed strain soild element. Therefore, the induced electric potential can be calculated for a prescribed load and the actuation displacement can be computed for an input voltage. Since the assumed strain solid element can alleviate locking. A finite element code is developed based on the formulation and typical numerical examples are solved for code validation. Using the code, we have conducted parametric study for THUNDER actuator. It is found that a particular combination of materials for layer curvature of THUNDER improves the actuation displacement.

• Journal of Sensor Science and Technology
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• v.26 no.2
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• pp.107-113
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• 2017

Energy source of a piezo-electric harvester is vibration. Sources of vibration are machineries operated with high frequencies, constructions and people operated with low frequencies and etc. In this study, we tried to figure out power generation properties over vibrations upon angles of a piezo-cantilever for applying them to movements of the construction and/or people, which are vibration sources at low frequencies. A uni-morph cantilever with a $59mm{\times}29mm{\times}0.2mm$ piezo-electric element attached on a $71mm{\times}46mm{\times}0.25mm$ copperplate was used. A spring was attached to the lower side of the cantilever and a mass was attached on the opposite side. Also, a structure with a specific angle which is an angle in between the ground and the cantilever was prepared and then, connected to a spring or the cantilever. Then, this structure was divided into the A-type and B-type and excited in the direction of z- axis. After that, the angle between the ground and the cantilever was changed and excited by 1 to 10 Hz upon the existence of a spring and/or a mass to compare power generation properties.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.458-465
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• 2009

In general, ultrasonic guided wave techniques that used for an evaluation of the internal defect have been applied without considering energy loss. It can be found out that the significant attenuation is observed in the signal of structure with defect by the scattering and absorption. Even in the signal acquired from defect-free structure, this attenuation can be also significant. Therefore, it is very essential to determine the Lamb wave propagation characteristics depending on modes because the dispersibility of Lamb wave can be easily influenced by the attenuation effect with frequency and thickness. For this reason, changing the propagation distance, attenuation coefficient of each Lamb wave mode needs to be investigated by the contact pitch-catch method with PZT(piezoelectric) sensors. In this paper, the experimental attenuation coefficient is measured by choosing the following three different variables; mode, thickness and plate materials. As a result, experimental attenuation coefficient is obtained as the function of variables.

• Journal of Sensor Science and Technology
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• v.28 no.6
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• pp.366-370
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• 2019

In this study, we have successfully fabricated a highly conductive transparent electrode using Ag nanowires, based on piezoelectric polyvinylidene difluoride (PVDF) film, that can be applied as transparent and flexible speakers. The structural morphology of the Ag nanowires was confirmed by a detailed scanning electron microscopy. Ultraviolet-visible spectroscopy demonstrated that the transparent electrode fabricated by the Ag nanowires exhibited a transmittance of above 70%. The transparent electrode also showed very low sheet resistance with high flexibility. We have further developed an anti-oxidation coating layer by using a tetraethyl orthosilicate-poly trimethyloxyphenylsilane (TEOS-PTMS) slurry technique. It was confirmed that the transmittance and sheet resistance of the antioxidant film depends critically on the humidity of the film surface. We believe such Ag nanowire electrodes are a very promising next-generation transparent electrode technology that can be used in future flexible and transparent devices.

• The Journal of the Acoustical Society of Korea
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• v.9 no.4
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• pp.18-32
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• 1990

Deeping on purpose, SAW device may have to function while immersed in a liquid. Those who are familiar with SAW devices would anticipate difficulty since the propagating surface waves will tend to radiate energy into the liquid and hence suffer attenuation. Thus, to design an immerable SAW device, more attention and full information about the wave properites is required to overcome the attenuation and get the highest SAW generation eficiency. Though numerical simulation, the optimal geometry of underwater SAW devices, such as optimal piezoelectric crystal cut, SAW propagation direction and nondimensional wave number(ka) is determined to get the maximum SAW excitation efficiency, the minimum attenuation in propagation and pure mode propagation for all the modes of surface wave propagation. The design technique can be appliedto an arbitrary combination of a piezoelectric layer, a substrate and a liquid medium. In this paper, PZT and PVDF layers and a steel substrate are use for the solid medium. The technique can be easily employed for the design of underwater sensors and actuators for the applications, such as sonar marine antifouling, industrial and medical uses.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.5
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• pp.553-567
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• 2011

During the last three years, the possibility of the time reversal Lamb waves has been paid attention to for structural health monitoring of a plate. This study proposes a numerical scheme which can simulate the spatial focusing of time reversal Lamb waves on a rectangular plate. In this scheme, a time reversal process is formulated in the frequency domain using active virtual sensors being equivalent to the mirror effects of an actual sensor due to wave reflection on the plate boundary. Forward and backward Lamb wave propagations are represented by scalar functions for simulating the spatial focusing of time reversal Lamb waves. The validity of the proposed scheme is demonstrated through the comparison to the results of finite element analysis in which the spatial focusing of time reversal Lamb waves is realized by wafer-type piezoelectric(PZT) transducers collocated on a rectangular plate.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.3 s.36
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• pp.267-274
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• 2005

This paper presents the fabrication of surface acoustic wave (SAW)-based pressure sensor for long-term stable mechanical compression force measurement. SAW pressure sensor has many attractive features for practical pressure measurement: no battery requirement, wireless pressure detection especially at hazardous environments, and easy other functionality integrations such as temperature, humidity, and RFID. A $41^{\circ}$ YX $LiNbO_3$ piezoelectric substrate was used because of its high SAW propagation velocity and large values of electromechanical coupling factors $K^2$. A silicon substrate with $\~200{\mu}m$ deep cavity was bonded to the diaphragm with epoxy, in which gold was covered all over the inner cavity in order to confine electromagnetic energy inside the sensor, and provide good isolation of the device from its environment. The reflection coefficient $S_{11}$ was measured using network analyzer. High S/N ratio, sharp reflected peaks, and clear separation between the peaks were observed. As a mechanical compression force was applied to the diaphragm from top with extremely sharp object, the diaphragm was bended, resulting in the phase shifts of the reflected peaks. The phase shifts were modulated depending on the amount of applied mechanical compression force. The measured $S_{11}$ results showed a good agreement with simulated results obtained from equivalent admittance circuit modeling.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.216-219
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• 2002

Conventional piezoelectric lead-zirconate-titanate (PZT) senor has high sensitivity, but it is very brittle. Recently polymer films such as polyvinylidene fluoride (PVDF) have been used use as a sensor. The advantages of PVDF are the flexibility and mechanical toughness. Simple process and possible several shapes are also additional advantages. PVDF sensor can be directly embedded and attached to a structure. In this study, PVDF sensor was embedded in single glass fiber/epoxy composites whereas PZT sensor with AE was attached to single fiber composites (SFC). Piezoelectric sensor responds to interfacial damage of SFC. The signals measured by PVDF sensor were compared to PZT sensor. PZT sensor detected the signals of fiber fracture, matrix crack, interfacial debonding and even sensor delamination, whereas PVDF sensor only detected fiber fracture signals so far, because PZT sensor is much more sensitive than current PVDF sensor. Wave voltage of fiber fracture measured by PVDF sensor was lower than that of PZT sensor, but the results of fast Fourier transform (FFT) analysis were same. Wave velocity using two PZT sensors was also studied to know the internal and surface damage effect of epoxy specimens.

• Journal of Sensor Science and Technology
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• v.4 no.2
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• pp.7-13
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• 1995

A new FET type semiconductor pressure sensor (PSFET : pressure sensitive field effect transistor) was fabricated and its operational characteristics were investigated. A ZnO thin film as a piezoelectric layer, $5000{\AA}$ thick, was deposited on a gate oxide of FET by RF magnetron sputtering. The deposition conditions to obtain a c-axis poling structure were substrate temperature of $300^{\circ}C$, RF power of 140watt, and working pressure of 5mtorr in Ar ambience. The fabricated PSFET device showed good linearity and stability in the applied pressure range($1{\times}10^{5}\;Pa{\sim}4{\times}10^{5}\;Pa$).