Surface charge induction micromotors with two aluminium rotors isolated by SiO2

The present work characterises electric induction micromotors with rotors made of aluminium covered by a SiO2-layer. A variety of differently shaped rotors was fabricated and operated in weak electrolytes. The motor characteristics were measured, calculated theoretically and compared with data from other micromotors from the literature. We obtained a rotational velocity of 15000 rpm and a torque of about 0.3 pNm at pulse-amplitudes of 110 V and driving frequencies of 4 kHz. In contrast to a synchronous motor these characteristics were rather independent of the particular rotor-geometry, an advantage that might be used to design a rotor for a specific application. Furthermore, it is demonstrated that even two rotors may be operated with one stator, consisting of only four planar electrodes. By selecting appropriate driving conditions the direction of rotation can be changed such that both rotors either run in one direction or opposite to each other. In this way the rotors act as element s of a liquid pump.