nLab geometric origin of inhomogeneous media

The geometric origin of inhomogeneous media


Just as geometry is encoded in the metric tensor and manifests itself via the Hodge star operator, so too do the electromagnetic constitutive equations?. For example, in linear media we have the simple constitutive relations

E=1ϵDandB=μH. E = \frac{1}{\epsilon} D \quad\text{and}\quad B = \mu H.

between the electric field EE and the magnetic field BB.

In 4d, we have

F=B+Edt F = B + E\wedge d t

The 4d constitutive relation is

G=F, G = \star F \,,

which under assumptions of linearity gives

F=η(DHdt), \star F = -\eta(D-H\wedge d t) \,,

where η=μϵ\eta = \sqrt{\frac{\mu}{\epsilon}}. This may be written in a form that more closely mimics the tradition relations via

(vdtE)=1ϵDandB=μHvdt, \star(v d t\wedge E) = \frac{1}{\epsilon} D\quad\text{and}\quad\star B = \mu H\wedge v d t \,,

where v=1μϵv = \frac{1}{\sqrt{\mu\epsilon}} (Note: v=cv = c in vacuum).

What this means is the the electromagnetic properties of matter can be interpreted geometrically and are encoded in the Hodge star operator. Conversely, it means that geometrical properties of matter can be interpreted electromagnetically.


For more details see page 111 of Eric Forgy's dissertation.

Last revised on October 27, 2011 at 05:14:33. See the history of this page for a list of all contributions to it.