Miniature electrical tomography - imaging sprays and micro-fluids
Most previous applications of electrical tomography have been on a scale from centimetres to metres. Some efforts have explored miniature electrical tomography   and these have been based on circular sensor geometries. York et al (2006) reported an electrical capacitance tomography system based on a custom silicon chip mounted on a ceramic PCB hosting a 1mm diameter “sensor” comprising 8 electrodes (Fig. 1). The system, originally targeted at fuel injection, obtained images of the doses from an inhaler (Fig 2), with a rate of 6000 measurement frames per second, over a period of 70 ms.
Efforts have now moved on to microfluidic systems in which the channels frequently have a rectangular cross-section . Micro-fluidics is the science and technology of manipulating and analyzing minute volumes of fluids and has the potential to change the way modern chemistry and biology is performed. Typical sizes of the cross-sectional dimensions of micro-fluidic channels are from about 5-100μm.
Figure 2. ECT images of the dose from an inhaler for 8-electrode
ECT sensor over 70 ms. (blue - air, red - ventolin.)
There are several suggested advantages of microfluidic systems including; reduced inventory of reagent and sample consumption, improved separation efficiency, reduced power consumption and portability.
A subsection of microfluidics is the emergence of droplet-based microfluidics with droplets as discrete fluidic volumes created by two
Droplets in small channels (Fig 3 & 4.) also allow fluid flows with no dispersion, which is a general problem with single-phase fluids. In addition, when such droplets are surrounded by an immiscible fluid it can prevent contact between the surface of the chip and the sample within the droplet, eliminating adverse effects due to the large surface to volume ratios.
Since identical droplets are produced with a very high rate in one
 York, T. A. Phua, T. N., Reichelt, L., Pawlowski, A., Kneer, R. (2006) Meas. Sci & Tech. 17, 8, 2119-2129
 Tapp, H. S. and Williams, R. A. (2000) Special Issue of Chem. Eng. J., 77, 1-2, 119-125.
 Quek, S., Mohr, S., Goddard, N., Fielden, P and York, T. (2010) “Miniature electrical tomography
for Micro-fluidic systems.” 6th World Congress on Industrial Process Tomography, Beijing, China.