• Smart Structures and Systems
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• v.24 no.4
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• pp.435-446
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• 2019

The existing piezoelectric spherical transducers with fixed prescribed dynamic characteristics limit their application in scenarios with multi-frequency or frequency variation requirement. To address this issue, this work proposes an improved design of piezoelectric spherical transducers using the resistance tuning method. Two piezoceramic shells are the functional elements with one for actuation and the other for tuning through the variation of load resistance. The theoretical model of the proposed design is given based on our previous work. The effects of the resistance, the middle surface radius and the thickness of the epoxy adhesive layer on the dynamic characteristics of the transducer are explored by numerical analysis. The numerical results show that the multi-frequency characteristics of the transducer can be obtained by tuning the resistance, and its electromechanical coupling coefficient can be optimized by a matching resistance. The proposed design and derived theoretical solution are validated by comparing with the literature given special examples as well as an experimental study. The present study demonstrates the feasibility of using the proposed design to realize the multi-frequency characteristics, which is helpful to improve the performance of piezoelectric spherical transducers used in underwater acoustic detection, hydrophones, and the spherical smart aggregate (SSA) used in civil structural health monitoring, enhancing their operation at the multiple working frequencies to meet different application requirements.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.6
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• pp.455-459
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• 2001

In this paper, the dielectric and pizoelectric properties of 0.05Pb(M $n_{04}$ $W_{0.2}$N $b_{0.4}$) $O_3$-0.95(PbZ $r_{x}$ $Ti_{1-x}$ ) $O_3$+yN $b_2$ $O_{5}$ , are investigated as a function of the mole ratio of Zr and the amount of N $b_2$ $O_{5}$ . Also, the phase is analyzed by XRD. When the mole ratio of Zr is 0.51, the electromechanical coupling coefficient( $k_{p}$ ), relative dielectric constant ($\varepsilon$$^{T}$ $_{33}$ /$\varepsilon$$_{0}$ ), piezoelectric stain constrain ( $d_{33}$ and dielectric loss tangent show maximum, while the mechanical quality factor shows minimum value ; $k_{p}$ =56.5%, $d_{33}$ =258pC/N, $\varepsilon$$^{T}$ $_{33}$ /$\varepsilon$$_{0}$ =1170, $Q_{m}$ =1150, tan$\delta$=0.51%. At that composition, MPB which rhombohedral and tetragonal phase coexist in this ternary system is shown by the results of XRD analysis. Also, when the amount of N $b_2$ $O_{5}$ is 0.3wt%, the mechanical quality factor is increased to about 2000. The phase transition temperature of the ternary piezoelectric ceramic system showed about 35$0^{\circ}C$.TEX>.>.>.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.728-732
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• 2011

In this study, piezoelectric and dielectric properties of Lead-free $0.97[(K_{0.5}Na_{0.5})(Nb_{0.97}Sb_{0.03})O_3]+0.03[(Bi_{0.5}K_{0.5})TiO_3]$ (abbreviated as 0.97NKNS-0.03BKT)ceramics synthesized by conventional solid-state reaction process were investigated as a function of $K_{5.4}Cu_{1.3}Ta_{10}O_{29}$ addition. The results indicated that the $K_{5.4}Cu_{1.3}Ta_{10}O_{29}$ addition significantly improved the sinterability, grain growth and piezoelctric properties of 0.97NKNS-0.03BKT ceramics. The optimum values as planar piezoelectric coupling coefficient ($k_p$= 0.355), piezoelectric constant ($d_{33}$= 207 pC/N) and mechanical quality factor ($Q_m$= 128) were obtained when 0.009KCT was added. The electromechanical coupling factor($k_p$) was slightly decreased according to the increasing temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.112-112
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• 2009

In this study, the effect of a long post-deposition thermal annealing(600 and 1000 $^{\circ}C$) on the surface acoustic wave (SAW) properties of polycrystalline (poly) aluminum-nitride (AlN) thin films grown on a 3C-SiC buffer layer was investigates. The poly-AlN thin films with a (0002) preferred orientation were deposited on the substrates by using a pulsed reactive magnetron sputtering system. Experimental results show that the texture degree of AlN thin film was reduced along the increase in annealing temperature, which caused the decrease in the electromechanical coupling coefficient ($k^2$). The SAW velocity also was decreased slightly by the increase in root mean square (RMS) roughness over annealing temperature. However, the residual stress in films almost was not affect by thermal annealing process due to small lattice mismatch different and similar coefficient temperature expansion (CTE) between AlN and 3C-SiC. After the AlN film annealed at 1000 $^{\circ}C$, the insertion loss of an $IDT/AlN/3C-SiC/SiO_2/Si$ structure (-16.44 dB) was reduced by 8.79 dB in comparison with that of the as-deposited film (-25.23 dB). The improvement in the insertion loss of the film was fined according to the decrease in the grain size. The characteristics of AlN thin films were also evaluated using Fourier transform-infrared spectroscopy (FT-IR) spectra and X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) images.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.235-235
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• 2009

This paper describes the influence of a polycrystalline (poly) 3C-SiC buffer layer on the surface acoustic wave (SAW) properties of poly aluminum nitride (AlN) thin films by comparing the center frequency, insertion loss, the electromechanical coupling coefficient ($k^2$), andthetemperaturecoefficientoffrequency(TCF) of an IDT/AlN/3C-SiC structure with those of an IDT/AlN/Si structure, The poly-AlN thin films with an (0002)-preferred orientation were deposited on a silicon (Si) substrate using a pulsed reactive magnetron sputtering system. Results show that the insertion loss (21.92 dB) and TCF (-18 ppm/$^{\circ}C$) of the IDT/AlN/3C-SiC structure were improved by a closely matched coefficient of thermal expansion (CTE) and small lattice mismatch (1 %) between the AlN and 3C-SiC. However, a drawback is that the $k^2(0.79%)$ and SAW velocity(5020m/s) of the AlN/3C-SiC SAW device were reduced by appearing in some non-(0002)AlN planes such as the (10 $\bar{1}$ 2) and (10 $\bar{1}$ 3) AlN planes in the AlN/SiC film. Although disadvantages were shown to exist, the use of the AlN/3C-SiC structure for SAW applications at high temperatures is possible. The characteristics of the AlN thin films were also evaluated using FT-IR spectra, XRD, and AFM images.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.980-986
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• 2001

Bragg reflector type FBAR was fabricated on the Si(100) substrate. We measured a frequency response of the resonator at 5.2 GHz and analyzed it by numerical calculation considering actual acoustic losses of each layer in the structure. We fabricated nine layer Bragg reflector of W-SiO$_2$pairs using r.f. sputtering method and fabricated AlN piezoelectric and Al electrodes using pulsed dc sputtering. The return loss(S$_{11}$) of the fabricated Bragg reflector type FBAR was 12 dB at 5.38 GHz and the series resonance frequency(f$_{s}$) was 5.376 GHz and the parallel resonance frequency(f$_{p}$) was 5.3865 GHz. Effective electro-mechanical coupling constant (K$_{eff{^2}}$) and Quality factors(Q$_{s}$), the Figures of Merit of the resonator, were about 0.48% and 411, respectively. We extracted acoustic parameters of AlN piezoelectric and reflection coefficient of the Bragg reflector by numerical calculation. We could know that material acoustic impedance and wave velocity of AlN piezoelectric decreased for intrinsic value and the electromechanical coupling constant(K$_2$) value was very low owing to the poor quality of the AlN piezoelectric. Reflection coefficient of Bragg reflector was 0.99966 and reflection band was very wide from 2.5 to 9.5 GHz.

• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.11
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• pp.688-692
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• 2017

$Pb(Zr,\;Ti)O_3$ (PZT) is a piezoelectric material applied in a typical actuator and has been actively studied. However, in order to overcome the limitations of PZT, piezoelectric ceramics comprising mixed solid solutions of PZT with various relaxer electric materials have been studied. The $Pb(Zn_{1/3}Nb_{2/3})-Pb(Ni_{1/3}Nb_{2/3})-Pb(Zr,\;Ti)O_3$ (PZN-PNN-PZT) piezoelectric ceramic, known to have high piezoelectric constant and electromechanical coupling coefficient, was studied herein. The piezoelectric characteristics with various Zr contents (Zr/Ti ratios), PZN molar ratios, and sintering temperatures were compared. The piezoelectric properties of $d_{33}=580pC/N$ and $k_P=0.68$ were obtained with the $0.1PZN-0.2PNN-0.7PbZr_{0.46}Ti_{0.54}O_3$ composition sintered at $1,290^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.5
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• pp.292-296
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• 2014

We investigated the effect of Ta doping on the dielectric and piezoelectric properties of lead-free $(K_{0.5}Na_{0.5})NbO_3$ ceramics prepared using a conventional ceramic processing. X-ray diffraction analysis revealed that Ta was perfectly substituted into Nb-sites in the range of 0 to 20 at%. As Ta content in the KNN increased, the sinterability of KNN ceramics was significantly degraded while the Ta doping enhanced the piezoelectric constant $d_{33}$, planar mode piezoelectric coupling coefficient ($k_p$), and electromechanical quality factor ($Q_m$). The highest values for $d_{33}$, $k_p$, and $Q_m$ was found to be 156 pC/N, 0.37, and 155, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.1
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• pp.390-395
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• 2011

In order to develope piezoelectric transformer for the ballast of fluorescent lamp, the composition of piezoelectric ceramics was 0.95Pb($Zr_xTi_{1-x}$)O3+yPb($Mn_{1/3}Nb_{2/3}$)$O_3$+(0.05-y)Pb($Sb_{1/2}Nb_{1/2}$)$O_3$. PMN compound was selected to improve mechanical quality factor and PSN to prevent the decrease of dielectric constant and electromechanical coupling coefficient. Dielectric and piezoelectric characteristics in the region of MPB of 0.95Pb($Zr_xTi_{1-x}$)$O_3$+yPb($Mn_{1/3}Nb_{2/3}$)$O_3$+(0.05-y)Pb($Sb_{1/2}Nb_{1/2}$)$O_3$ ceramics was discussed both quantatively and qualitatively.