血泵具有微型电机（10），其定子包括磁性护套（18）。 护罩由一个连续的无缝隙金属合金护套组成，其中含有铁素体铁和高达30％的铬，最好是铝和氧化钇。 通过氧化铝，电导率降低。 类似的功能是氧化钇。 电导率降低很大程度上抑制了涡流。 护罩（18）在低壁厚处具有高导磁率，从而电动机以小直径增加。

The invention relates to a micromotor (10), the stator of which contains a back iron jacket (18). Said back iron jacket consists of a continuous unslotted sleeve consisting of a metal alloy that contains ferritic iron as the main constituent, up to 30% chromium and preferably aluminium and yttrium oxide. Electric conductivity is reduced by the oxidation of the aluminium. The yttrium oxide performs the same function. The reduced electric conductivity suppresses eddy currents to a great extent. The back iron jacket (18) has a high magnetic conductivity with a small wall thickness, thus increasing the electrical output for a motor with a small diameter.