Thermal emissive apparatus

A thermally emissive apparatus (2) having an electro-thermal heating element (6) comprising a layer (8) of a first material having a first resistivity and a plurality of discrete regions (10) of a second material having a second resistivity substantially lower than that of the first material in electrical contact with the first material. The plurality of regions (10) of second material are arranged spatially so as to impart a predetermined effective sheet resistivity to the first layer (8). A plurality of heating elements may be used having a common first layer (30) of first material, wherein the spatial arrangement of the regions (10) of second material within a first heating element are optionally different to that within a second heating element. In this configuration the first and second heating elements may emit infrared radiation (14) having different intensities. The apparatus (2) finds applications as a thermal target and as an electro-thermal ice protection device.