an equivalent to the spatial separation either side of a nominal median plane that is inherent in a bimorph is attained by structurally shaping the cross - section of a simple , single piezoelectric layer such that it has a multiplicity of piezoelectric portions arranged in two generally - planar groups one either side of a median plane , so that any dimension change undergone by a portion on one side of that plane will tend to bend the whole device in the opposite direction to the same sense dimension change undergone by a portion on the other side of that plane . the simple , single layer acts as though it were a bimorph if elongate and beam - like , bending along its length , one end moving up / down , or back / forth , relative to the other but with any need for an internal , electrode .