An inductive power transfer transmitter that includes an enclosure for accommodating devices to be energised. The enclosure has one or more side walls and one or more coils for generating an alternating magnetic field within the enclosure. The density of the one or more coils varies with distance from an end of the one or more sidewalls.There is also disclosed an inductive power transmitter that includes one or more magnetically permeable layers wherein the combined thickness or the permeability of the one or more magnetically permeable layers varies.