Application of Fourier transforms to periodic heat flow into the ground under a building

Abstract Fourier transforms are used to obtain expressions for the heat flux from a surface region at a given temperature into a 2 or 3 dim. semi-infinite solid, with all quantities assumed to be periodic in time. These expressions are evaluated explicitly in the 2-dim. case and are used to obtain approximate results in 3-dim. valid for a wide range of frequencies. An explicit exact expression for the 3-dim. steady-state heat flux from a rectangular surface region is also obtained.