An injection device for injecting medication to a patient, comprising a surface having a through hole for passage of a needle, is characterised by further comprising a capacitive proximity sensor for detecting proximity or contact of human skin towith said surface. In an exemplary embodiment, the blades, partitions, and shafts of the waterwheel are composed of engineered plastics and composites for improved operation and longevity. Also disclosed as an air cleaning method and apparatus using the sterilizing method and apparatus. Thereby, the louver fin can be prevented from being curved in the longitudinal direction. The method includes: determining an optimal-selection subset containing some of the candidate vectors; selecting the motion vector from among the vectors of the optimal-selection subset; and inserting into the signal a piece of information designating the motion vector selected from among the vectors of the optimal-selection subset.