The analytical model developed in section 2 includes relations in which the main spring–
magnet motion parameters are involved. By setting the spring–mass system into smalloscillation
mode, digitally recording its motion, and measuring the damping λ of the
oscillations we could in principle obtain a value for the electrical conductivity σ of the
plate material using equation (21), provided the remaining relevant parameters are known,
e.g. the plate thickness. Alternatively, we could measure the thickness of a conductive nonferromagnetic
plate. These would be modest but valuable assets given the simplicity and
the low-cost of the set-up. As a sample application we measured the conductivity of a thick
stock-aluminium plate (Alclad 3003-O). The oscillation amplitudes data were taken from the
rightmost-line in figure 7 that corresponds to a 3.74 mm thick plate, 150 mm in diameter. The
tabulated conductivity of Alclad 3003-O aluminium alloy is 2.741 × 107 ( m)−1 [16], while
the value we obtained with our method was 2.69 × 107 ± 0.03 ( m)−1, which correspond
to an error of ∼2%.
5.