A piezoelectric actuator for use in a fuel injection system of an internal combustion engine, the actuator comprising a stack of ferroelectric layers; an encapsulation for protecting the stack from the ingress of liquid; and oxygenation means for providing oxygen to the ferroelectric layers, the means positioned between the encapsulation and stack. The oxygenation means is preferably impregnated in a fabric which forms a layer between the encapsulation and the stack.