Because the components of a multiphase flow often exhibit different electrical properties, a variety of probes have been developed to study such flows by measuring impedance in the region of interest. Researchers are now using electric fields to reconstruct the impedance distribution within a measurement volume via Electrical Impedance Tomography (EIT). EIT systems employ voltage and current measurements on the boundary of a domain to create a representation of the impedance distribution within the domain. The development of the Sandia EIT system (S-EIT) is reviewed The construction of the projection acquisition system is discussed and two specific EIT inversion algorithms are detailed. The first reconstruction algorithm employs boundary element methods, and the second utilizes finite elements. The benefits and limitations of EIT systems are also discussed. Preliminary results are provided.
Sarkar K, Prosperetti A 1993, "Coherent and incoherent scattering from oceanic bubbles" The Journal of the Acoustical Society of America, 93(4_Supplement), 2379
In recent years, an effective medium theory has been applied to model the contribution of bubbles for low-frequency oceanic backscattering [Prosperetti et al. and Sarkar and Prosperetti, both submitted to J. Acoust. Soc. Am.] This approach differs from the more traditional one used to account for the effect of bubbles at higher frequencies, in which bubbles are treated as individual scatterers. Here, the relationship between these two apparently different approaches is clarified and a unified theory is presented. In this way, a better understanding of the rationale and limitations for the older theory is achieved. Applications to scattering and bubble counting are described.
Prosperetti A, Sarkar K 1992, "Enhanced backscattering from bubble cloud distributions on the ocean surface" The Journal of the Acoustical Society of America, 91(4_Supplement), 2315
It has been shown in earlier studies [Prosperetti, Lu, and Kim; Sarkar and Prosperetti, both submitted to J. Acoust. Soc. Am.] that bubble clouds produced by breaking waves at the ocean’s surface can explain the unexpectedly high backscattering levels observed experimentally by Chapman and Harris [J. Acoust. Soc. Am. 34, 1592 (1962)] and others at low grazing angles. Gas volume fractions of the order of 1%, linear dimensions of the order of 1 m, and surface coverage of the order of 1% (the latter of which agrees with the experimentally measured values for 10 m/s winds) are sufficient to give an excellent match of the data as a function of frequency in the range 0.1–2 kHz and wind speeds from 5 to 25 m/s. In the previous work the clouds were treated as independent scatterers. In the present work the previous results are refined to include lowest order multiple scattering effects along the lines of Foldy [Phys. Rev. 67, 107 (1945)] and Biot [J. Acoust. Soc. Am. 44, 1616 (1968)].
