In general, this disclosure describes techniques for changing a sampling frequency of a digital signal. The AC input receptacle is connected to an input of a single output power converter which converts the input AC voltage into an output DC voltage of a specified level. The curved portion includes a curved surface that is concave in a direction of rotation of the fan and forms a part of the positive pressure surface. A second insulating layer is formed on an upper portion of the wiring layer and in the first aperture. As the sequence progresses, sets of co-linear receive beams are formed along each of the respective scan lines at a predetermined rate both within a particular frame and between successive frames.