Magnetisation surviving the transit to the pickup

By the time the slug reaches the pickup coil, how much of its remanence is left?

The formula

M = Mr e^{- x / (v τ)}

LaTeX

M = Mr \cdot e^{-\,x / (v \cdot τ)}

Work it out

Mr Remanence leaving the drive

A/m

The medium's remanence — what it keeps once the drive field is gone.

τ Holding time

How long the particles keep their orientation in the carrier, from the relaxation calculation.

x Drive to pickup

The distance the slug travels between the two coils.

v Velocity

in/s

How fast the medium moves — the EPG #1 holding says 50 for slurry.

or see a worked example with typical numbers

Convert the velocity to metres per second and divide the distance by it: the transit time.
Divide the transit time by the holding time and take e to the minus of that — the fraction of the particles still pointing the way the drive left them.
Multiply the remanence by that fraction. That is the magnetisation the pickup coil sees arrive.

Exponential relaxation with a single time constant — the effective τ the relaxation calculation gives, which is already the shorter of the Brownian and Néel times. A real powder has a spread of sizes and therefore of τ, and the tail of large particles arrives better than this says.
No field between the coils. A second drive coil, or the stray field of the first, re-magnetises or demagnetises the slug on the way, and this line does not know about it; the studio's transport model does.
The slug moves at the mean velocity. In laminar flow the centre goes twice as fast and the wall not at all, so parts of it arrive early and parts late — the smearing calculation covers that; this one covers the forgetting.
Nothing here is Meyer's. The estate material specifies the speed and says nothing about what the medium keeps, or for how long.