A plasma generating apparatus suitable for treating a package substantially without a conductive layer, comprising: a first electrode; a second electrode structure located forward of the first electrode; an insulating layer interposed between the first electrode and the second electrode structure, wherein: the second electrode structure has a plurality of second electrode portions defining gap portions therebetween, the width of the gap portions being w, the second electrode portions each having a forward surface, the gap portions comprise dielectric material and each have a forward surface, the height difference between the forward surface of each second electrode portion and the forward surfaces of the adjacent gap portions is h, wherein h is at most 1 mm and the ratio w/h is at least 1, the first electrode is connected to a signal generation source for applying an AC voltage signal to the first electrode, the second electrode structure is connected or connectable to ground, the forward surfaces of the second electrode portions and the forward surfaces of the gap portions together form a package treatment surface, wherein when a package to be treated is placed against the package treatment surface, the apparatus is operable to generate plasma, wherein operation of the first electrode allows the generated electric field to leak out through the structural shape of the second electrode structure and into the space above the package treatment surface, characterised in that the package treatment surface is conformable to conform with the package in use in order to limit the size of gaps between the package treatment surface and the package, so that the plasma is substantially wholly located inside the package to be treated. a first electrode; a second electrode structure located forward of the first electrode; an insulating layer interposed between the first electrode and the second electrode structure, wherein: the second electrode structure has a plurality of second electrode portions defining gap portions therebetween, the width of the gap portions being w, the second electrode portions each having a forward surface, the gap portions comprise dielectric material and each have a forward surface, the height difference between the forward surface of each second electrode portion and the forward surfaces of the adjacent gap portions is h, wherein h is at most 1 mm and the ratio w/h is at least 1, the first electrode is connected to a signal generation source for applying an AC voltage signal to the first electrode, the second electrode structure is connected or connectable to ground, the forward surfaces of the second electrode portions and the forward surfaces of the gap portions together form a package treatment surface, wherein when a package to be treated is placed against the package treatment surface, the apparatus is operable to generate plasma, wherein operation of the first electrode allows the generated electric field to leak out through the structural shape of the second electrode structure and into the space above the package treatment surface, characterised in that the package treatment surface is conformable to conform with the package in use in order to limit the size of gaps between the package treatment surface and the package, so that the plasma is substantially wholly located inside the package to be treated. the second electrode structure has a plurality of second electrode portions defining gap portions therebetween, the width of the gap portions being w, the second electrode portions each having a forward surface, the gap portions comprise dielectric material and each have a forward surface, the height difference between the forward surface of each second electrode portion and the forward surfaces of the adjacent gap portions is h, wherein h is at most 1 mm and the ratio w/h is at least 1, the first electrode is connected to a signal generation source for applying an AC voltage signal to the first electrode, the second electrode structure is connected or connectable to ground, the forward surfaces of the second electrode portions and the forward surfaces of the gap portions together form a package treatment surface, wherein when a package to be treated is placed against the package treatment surface, the apparatus is operable to generate plasma, wherein operation of the first electrode allows the generated electric field to leak out through the structural shape of the second electrode structure and into the space above the package treatment surface, characterised in that the package treatment surface is conformable to conform with the package in use in order to limit the size of gaps between the package treatment surface and the package, so that the plasma is substantially wholly located inside the package to be treated.