Developments in Ceramic Materials Research

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230 R. Ramesh, H. Kara, Ron Stevens and C. R. Bowen Figure 13. Comparison of FEM results with experimental data (a) electrical impedance spectrum and (b) receiving voltage sensitivity of a porous piezoceramic disc hydrophone.
Progress in Porous Piezoceramics 231 5. EVALUATION OF POROUS PIEZOCERAMIC HYDROPHONES As seen in the previous sections, the 3-3 piezocomposites made up of porous piezoceramics are useful materials for transducer applications, especially as hydrophones. The lossy nature of the composite materials leads to wide-band response, which is an important property of a hydrophone. Several commercially available hydrophones have flat frequency response over a large band below the first resonance [41]. However, such a hydrophone made up of dense piezoceramic material requires very careful selection of dimensions of various components used in the device and meets conflicting design challenges. Such a design gets greatly simplified if the piezoelectric component is wideband in nature, like the piezocomposites. This section presents the construction and underwater evaluation of hydrophones made up of 3-3 piezocomoposites and a comparison with hydrophones made up of dense piezoceramic material of the same size [10]. 5.1. Construction of Hydrophones 5.1.1. Sample Preparation Samples required for constructing the hydrophones are prepared using Foam-replication technique described in detail in Section 2. The foam replication method is well known for making reticulated ceramics [43, 44, 45] and involves dipping a polyethylene foam (Foam Engineers Ltd, UK, 10 ppi and 20 ppi) into a ceramic slurry. Since the hydrophones are for passive mode only, the ceramic chosen for this study is PZT-5H (Morgan Electroceramics, UK), a soft piezoelectric for sensor applications due to its high d33 piezoelectric coefficient. The ceramic-coated foam is then heat treated to remove the polyethylene foam structure at 600 °C for 1 hour. The remaining ceramic skeleton is then sintered at 1200 °C for 2 hours. Variation of the ceramic volume fraction, by changing the foam pore size or degree of coating, can be used to tailor the piezoelectric charge coefficients (d33, d31), permittivity ( T 33 ε ) and acoustic impedance. The dH of the material reaches a maximum at approximately 50% ceramic volume fraction, while the gH is a maximum at approximately 10-20% ceramic volume fraction [46]. Since gH is related to the electric field per unit hydrostatic stress, hydrophone materials with high gH are produced for this work with 11% and 22% PZT ceramic volume fractions by using 10 ppi and 20 ppi polyethylene foams, respectively. After heat treating and sintering, the discs (11% PZT and 22% PZT) are ground by SiC abrasive paper to dimensions of 40 mm diameter and 4±0.1 mm thickness. The 4 mm thickness is larger than the pore size of the material and ensures sufficient ceramic material is connected through the ceramic thickness. A dense PZT ceramic with same dimensions and tolerance is also prepared from the same ceramic powder for direct comparison. Due to the low strength of the 11% PZT disk, it is impregnated with epoxy (Specifix 40, Struers, Germany) to improve its mechanical strength. It acts as a 3-3 piezocomposite. Silver electrodes (~100 mm thick) are applied by brushing on silver conductive paint (RS Products, UK, Product 186-3593) to the two faces. The discs are subsequently poled in the thickness direction using a custom made corona poling using a 30 kV DC power supply (Glassman Europe Ltd., Product FC30P4) at an electric field equivalent to 2 kVmm -1 .
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DEVELOPMENTS IN CERAMIC MATERIALS R
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Copyright © 2007 by Nova Science P
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PREFACE Ceramics are refractory, in
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Preface ix crystals is discussed. A
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Preface xi spectra and the directio
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2 Leslie G. Cecil comprehensive dat
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4 Leslie G. Cecil Ringle et al. (19
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6 Leslie G. Cecil The main architec
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8 Leslie G. Cecil can study “the
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10 Leslie G. Cecil Middleton et al.
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12 Leslie G. Cecil The laser ablate
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14 Leslie G. Cecil There are two ge
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16 Leslie G. Cecil distinct recipes
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18 Leslie G. Cecil second group (Fi
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20 Leslie G. Cecil The Vitzil-Orang
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22 Leslie G. Cecil Table 3. Mahalan
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24 Leslie G. Cecil Ixlú and Ch’i
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26 Leslie G. Cecil structures (D. R
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28 Leslie G. Cecil paste and Macanc
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30 Leslie G. Cecil Bieber, A. M. Jr
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32 Leslie G. Cecil Kepecs, S. M., a
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34 Leslie G. Cecil Schele, L., Grub
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36 Z. C. Li, Z. J. Pei and C. Tread
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62 I, % 100 80 60 40 20 0 T. T. Bas
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70 Fluorescence, a.u. 1 0.1 0.01 0.
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82 Photon counts 300 250 200 150 10
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84 Fluorescence, a.u. I transfer ,
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86 ln(I transfer (t)) -4.2 -4.4 -4.
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88 Fluorescence, a.u. I transfer ,
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In: Developments in Ceramic Materia
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Synthesis, Spectroscopic and Magnet
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a c Synthesis, Spectroscopic and Ma
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Transmission Transmission Transmiss
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Sm (J/Kmol) Sm (J/Kmol) 15 10 5 Syn
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Intensity (a.u.) Intensity (a.u.) 8
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The Use of Ceramic Pots in Old Wors
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IACC ( τ ) = t2 ∫ The Use of Cer
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D50 0.8 0.7 0.6 0.5 0.4 0.3 The Use
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Definition (D50) 1 0.95 0.9 0.85 0.
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Modeling of Thermal Transport in Ce
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Modeling of Thermal Transport in Ce
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Page 256 and 257: 242 Development of Display Technolo
Page 258 and 259: 244 Li Chen technology moved to the
Page 260 and 261: 246 Li Chen The continuing evolutio
Page 262 and 263: 248 Li Chen the back contact cathod
Page 264 and 265: 250 Li Chen Figure 3. Vertical side
Page 266 and 267: 252 Li Chen Figure 6. Molybdenum mi
Page 268 and 269: 254 Li Chen Figure 8(a). I-V curve
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Page 272 and 273: 258 Figure 11(a). Plasma generated
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A absorption spectra, 66, 67, 77, 7
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correlation function, 156 corrosion
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group membership, 13, 20, 21, 22, 2
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microstructure(s), x, xi, 73, 74, 2
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Developments in Ceramic Materials Research

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