## 141 Measuring electrical conductivity or resistivity

The electrical resistivity of a thick metal foam sheet can be measured using a four-point probe technique sketched in Figure 14.1. Two probes (P1 and P4) are used to introduce a current, I, into the sample while a pair of different probes (P2 and P3) are used to measure the potential drop, V, between them. If the plate is sufficiently thick, the electrical resistivity, 0, of the foam (commonly measured in units of cm) is given by:

and s1, s2 and s3, are the probe spacings shown in the figure.

The electrical conductivity, a (units, m_1), is the reciprocal of the resistivity. The resistance, R, of a piece of foam of length I and a cross-sectional area A normal to the direction of current flow is given by:

where

Figure 14.1 A four-point probe method for measuring the electrical conductivity of metal foams

Relative density (p/pg

Figure 14.2 The relative electrical resistivity and conductivity of open- and closed-cell aluminum foams of differing relative density. The lines are plots of equation (14.4) with a = 0.33 and a = 0.05

Relative density (p/pg

Figure 14.2 The relative electrical resistivity and conductivity of open- and closed-cell aluminum foams of differing relative density. The lines are plots of equation (14.4) with a = 0.33 and a = 0.05

0 0