Industrial Process Tomography - Platform II grant funded by EPSRC

FACULTY OF ENGINEERING

 

Colloid Vibration Potential Imaging

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 [1] [2] 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 [3]. 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 1. Ultrasonically drilled hole


1b
Figure 3. Schematic of electrode arrangement
in microfluidic channel
1b

Figure 4. Reconstructed images of objects
in the channel

 
X ray diffraction
Figure 2. ECT images of the dose from an inhaler for 8-electrode
ECT sensor over 70 ms. (blue - air, red - ventolin.)



A vast majority of microfluidic devices are simple planar microchips fabricated by photolithography on substrates such as glass, silicon or polymers. Current commercial interest is in plastic fabrication for single-use disposable microfludic devices.

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
immiscible phases. Droplets can be seen as micro-reactors that can be transported, sorted, mixed and individually analyzed.

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
experiment, parallel processing is achievable to produce large data sets. These advantages offer the potential of higher throughput and the possibility to create new products.

     

 

Author Information: Prof. Trevor York , University of Manchester. Email: t.york@manchester.ac.uk

References:

[1] York, T. A. Phua, T. N., Reichelt, L., Pawlowski, A., Kneer, R. (2006) Meas. Sci & Tech. 17, 8, 2119-2129
[2] Tapp, H. S. and Williams, R. A. (2000) Special Issue of Chem. Eng. J., 77, 1-2, 119-125.
[3] 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.