Browsing by Author "Ahn, Cheol-Woo"

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    Design and characterization of broadband magnetoelectric sensor
    Park, Chee-Sung; Ahn, Cheol-Woo; Ryu, Jungho; Yoon, Woon-Ha; Park, Dong-Soo; Kim, Hyoun-Ee; Priya, Shashank (American Institute of Physics, 2009-05-01)
    In this study, we present a broadband magnetoelectric (ME) sensor design comprising of Metglas and piezoelectric ceramic laminate composite. A systematic study was conducted to elucidate the role of various composite variables toward the ME response [longitudinal-transverse (LT) mode] over the applied range of magnetic dc bias. The broadband behavior was characterized by flat ME responses over a wide range of magnetic dc bias at frequency of 1 kHz. The variation in ME coefficient as a function of magnetic dc bias was found to be significantly dependent on the size and shape of the laminate composites, the number of Metglas layers, and composite structure of sandwich versus unimorph. By adjusting these variables, we were able to achieve near-flat ME response over a magnetic bias range of 90-220 Oe. ME coefficient was also measured as a function of frequency, and at electromechanical resonance the peak value was found to be almost independent of applied magnetic bias in the range of 90-220 Oe. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3117484]
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    Dimensionally gradient magnetoelectric bimorph structure exhibiting wide frequency and magnetic dc bias operating range
    Park, Chee-Sung; Ahn, Cheol-Woo; Yang, Su-Chul; Priya, Shashank (American Institute of Physics, 2009-12-01)
    We report results on a dimensionally gradient magnetoelectric (ME) sensor that demonstrates high performance over a wide frequency range and a magnetic dc bias operating in the longitudinal-transversal mode. The design of the sensor is based on a piezoelectric bimorph structure and utilizes a laminate configuration with Pb(Zn1/3Nb2/3)(0.2)(Zr0.5Ti0.5)(0.8)O-3 and Metglas as material layers. The wide-band behavior was characterized by a flat ME response over a wide range of magnetic dc biases corresponding to 60-215 Oe and frequencies corresponding to 7-22 kHz. By using tip mass, the wide-band frequency response was shifted to a lower frequency range of 5-14 kHz. The results show that the operating frequency range of the sensor can be easily shifted by changing the tip mass at the end of the composite.
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    A generalized rule for large piezoelectric response in perovskite oxide ceramics and its application for design of lead-free compositions
    Ahn, Cheol-Woo; Maurya, Deepam; Park, Chee-Sung; Nahm, Sahn; Priya, Shashank (American Institute of Physics, 2009-06-01)
    We present a general rule for the perovskite oxide ceramics: "A large piezoelectric constant in ABO(3) perovskite ceramics can be obtained by tuning the weight ratio of A and B sites, WA/WB or WB/WA, to 3. Piezoelectric constant decreases significantly when WA/WB or WB/WA is in the range of 0.5-2.0, termed as forbidden zone." A comparative analysis was conducted for broad range of materials demonstrating the applicability of proposed rule. Further based on this rule optimized compositions in BaTiO3 and alkali niobate based systems were developed. Polycrystalline ceramics in modified BaTiO3 system were found to exhibit longitudinal piezoelectric coefficient (d(33)) of 330 pC/N, while alkali niobate ceramics showed d(33) of 294 pC/N. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3142442]
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    Stress-controlled Pb(Zr0.52Ti0.48)O-3 thick films by thermal expansion mismatch between substrate and Pb(Zr0.52Ti0.48)O-3 film
    Han, Guifang; Ryu, Jungho; Yoon, Woon-Ha; Choi, Jong-Jin; Hahn, Byung-Dong; Kim, Jong-Woo; Park, Dong-Soo; Ahn, Cheol-Woo; Priya, Shashank; Jeong, Dae-Yong (American Institute of Physics, 2011-12-15)
    Polycrystalline Pb(Zr0.52Ti0.48)O-3 (PZT) thick films (thickness similar to 10 mu m) were successfully fabricated by using a novel aerosol deposition technique on Si wafer, sapphire, and single crystal yitria stabilized zirconia (YSZ) wafer substrates with Pt electrodes and their dielectric, ferroelectric, and piezoelectric properties, and in-plane stresses were investigated. The films with different stress conditions were simply controlled by the coefficient of thermal expansion (CTE) misfit of PZT films and substrates. The results showed that the films bearing in-plane compressive stress deposited on the YSZ and sapphire substrates have superior dielectric, ferroelectric (similar to 90%), and piezoelectric (>200%) properties over that of the Si wafer. Among these three substrates, YSZ shows superior properties of the PZT films. However, films on Si wafer with tensile stress present lower properties. We believed that in-plane compressive stresses within the films are benefited, the formation of c-domain parallel to the thickness direction resulting in the higher piezoelectric properties. These results suggest that the properties of polycrystalline PZT thick films can be adjusted by simply choosing the substrates with different CTEs. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3669384]