Developments in Ceramic Materials Research

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226 R. Ramesh, H. Kara, Ron Stevens and C. R. Bowen Figure 10b shows the free-field voltage sensitivity in water for the dense PZT hydrophone obtained by analytical model, finite element model and experimental studies. Figure 10. Comparison of FEM results with analytical and experimental data (a) electrical impedance spectrum and (b) receiving voltage sensitivity of a dense piezoceramic disc hydrophone. In the analytical model, the effect of encapsulation and water loading are not considered. This could lead to a shift in the resonance frequencies as seen in the figure. The polyurethane rubber used for encapsulating the hydrophone has acoustic impedance close to that of water and hence is assumed to be acoustically transparent. It can be seen from the figure that the
Progress in Porous Piezoceramics 227 sensitivity curve is flat for frequencies below 50 kHz. The radial mode resonance appearing at around 50 kHz is not generally desirable for hydrophone applications, since it limits the operating frequency band. An ideal hydrophone has a constant receiving sensitivity over a wide frequency range [41]. The resonance peaks can be shifted beyond the operating range by carefully selecting the dimensions of the active elements. 4.2. Model of Porous PZT Discs The porous PZT has an intricate structure that can not be generated by rotating the structure about the symmetric axis and hence a 2-dimensional axisymmetric model is not useful. Therefore, a 3-dimensional model is required to characterise hydrophones made up of porous piezoceramics with finite dimensions. In modelling piezocomposites, it has been a general practice to model only an unit cell of the structure, assuming that it is representative of the entire piezocomposite structure [iv]. However in certain cases, the results of the unit cell model deviate from the actual values, especially in the determination of resonance frequencies [24]. The unit cell model can correctly predict the resonance frequencies corresponding to the thickness-mode vibrations, whereas it cannot predict the lateral-mode (radial-mode) resonance frequencies if the lateral dimensions of the transducers are finite and comparable to the thickness. Even, the application of periodic boundary conditions can only simulate the infinite extent of the lateral dimensions (x-y plane). Further, in the case of transducers with finite dimensions, the resonance frequency corresponding to the dimension in the z-direction depends also on the dimensions in the x- and y- directions [24]. It is therefore necessary to use a real- dimensional model. However, this involves large computer memory size and prolonged computational time. Figure 11. (a) Photograph of the porous PZT disc filled with polymer and (b) 1/4 th of the model used for FEM. The porous piezoceramic structure used in the finite element model of a 3-3 piezocomposite is shown in Figure 11. This is chosen to be as close to the practical structure
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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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54 T. T. Basiev, V. A. Demidenko, K
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62 I, % 100 80 60 40 20 0 T. T. Bas
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68 Fluorescence, a.u. 1 T. T. Basie
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70 Fluorescence, a.u. 1 0.1 0.01 0.
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78 k, cm -1 20 18 16 14 12 10 8 6 4
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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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3.2. Wall-in Positions The Use of C
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IACC ( τ ) = t2 ∫ The Use of Cer
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where σ res is the scattering cros
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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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Page 256 and 257: 242 Development of Display Technolo
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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
Page 270 and 271: 256 Li Chen Figure 9. Life time tes
Page 272 and 273: 258 Figure 11(a). Plasma generated
Page 274 and 275: 260 Li Chen [13] C.A. Spindt, K.R.
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276 S. Ardizzone, C. L. Bianchi, G.
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278 S. Ardizzone, C. L. Bianchi, G.
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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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efraction index, 61 refractive inde
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time, vii, ix, 1, 3, 7, 8, 11, 26,
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Developments in Ceramic Materials Research

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