Conductivity gradient

Chen, C.H., Lin, H., Lele, S.K., Santiago, J.G., Electrokinetic microflow instability with conductivity gradients. Micro Total Analysis Systems 2000, Proceedings pTAS 2000 Symposium, Enschede, Netherlands, May 14-18, 2000, 983-987. 

Fig. 8. Impedance spectrum calculated for a cubic sample (size L = 1 cm) with a linear, one-dimensional conductivity gradient Ubuik = 10 6 S cm-1 + (1 — x/L) 2 1CT5 S cm-1. Ohmic/ reversible electrodes are assumed.

From Eqs. (31) and (32) it can be calculated that 75% of the total resistance between a hemispherical microelectrode and a counter-electrode comes from a hemisphere with a radius of only 2dme and a semi-ellipsoid of a similar size can be defined for a circular microelectrode [49]. For that reason, the measured resistance reflects the electrical properties of a very small sample region. Microelectrodes can therefore serve as local conductivity probes on inhomogeneous solids as long as conductivity gradients occur on a much larger length scale than dme (Va/a dm J)> the conductivity in the 75% hemisphere is almost constant and the local conductivity obtained with circular microelectrodes reads... 

Interesting radioelectric properties have been discovered with this class of materials either from the point of view of level of radioelectric properties (typical values can attain 15-30 at 4 GHz) or under the form of absorption properties, since these films can be assembled by co-vulcanisation (especially in the case of polychoropene based films). In that case, they lead to flexible absorbing sheets which present levels of attenuation of [10] dB between 5 and 18 GHz by covulcanisation of different layers in order to produce a conductivity gradient [180]. 

For instance, the various methods employed to impregnate textiles with polypyrrole [90,93,94,187-189] were applied to polyaniline to fabricate absorbing surfaces (based on a conductivity gradient) operating between 3 GHz and 20 GHz. 

Surfaces with a conductivity gradient modify the phase/ amplitude of the impedance of the incident wave upon... 

Chen, C.H., et ah. Convective and absolute electrokinetic instabihty with conductivity gradients. 

Lin, H., et al.. Instability of electrokinetic microchannel flows with conductivity gradients. Phys. Fluids, 2004, 16 1922-1935. 

Since the conductivity of a buffer is temperature-dependent, a conductivity gradient is established in the channel due to the temperature difference. The relationship between the conductivity and the temperature can be written as... 

Markx, G.H., Dyda, P.A., Pethig, R., 1996. Dielectrophoretic separation of bacteria using a conductivity gradient. J. Biotechnol. 51, 175—180. 

The boundary conditions for the above equation are specified potentials at the reservoirs, 4>i = < f appiied> nd zero potential gradient at solid channel walls, n.Vcj) = 0. It should be pointed out that if there is no spatial conductivity gradient (1 is a constant), Eq. 14 takes a simpler format ... 

---